Volume 61, Issue 1

The main aim of the article is to analyze the state of the art in short steel fiber-reinforced geopolymers, taking into consideration also waste fibers. Steel fibers are currently the most widely applied additive to composites in the building industry. The work is dedicated to the usage of short steel fibers and the mechanical properties of geopolymer composites. Research methods applied in the article are a critical analysis of the literature sources, including a comparison of the new material with other, traditional concrete materials used in similar applications, especially in the construction industry. The results of the research are discussed in a comparative context. They indicate that the addition of fibers is an efficient method not only for improving compressive and flexural strength, but also mechanical properties such as fracture toughness. The potential applications in the construction industry as well barriers and challenges for the effective application of geopolymer materials reinforced with steel fibers are presented. Further research directions are discussed.

In the construction industry, fibers have been added to concrete to improve the mechanical properties of concrete for decades. Steel fiber has been widely used as an additive fiber owing to the unique properties; it provides reinforced concrete. However, the large-scale production of steel fibers generates a large amount of CO 2 and aggravates the depletion of natural resources. In response to the requirements of green environmental protection, some scholars have focused their attention on replacing industrial steel fibers with recycled steel fibers from waste tires (WTSF). It is found that WTSF can be used to reinforce the mechanical properties of concrete and even replace industrial steel fiber (ISF) in some engineering applications. The existing research results are summarized and discussed, with emphasis on the process of recycling WTSFs. This review not only has a great impact on the environment but also has fiber characteristics as well as the mechanical properties (compressive strength, tensile strength, and flexural strength) and durability of the concrete with WTSF. The purpose of this article is to review the existing literature with a critical attitude and summarize the existing related literature, which determines the research gap for those who are committed to this direction.

The sun’s energy, though free and virtually limitless, is a largely unexploited resource, as its conversion into a storable form presents several technological challenges. A promising way of capturing and storing solar energy is in the form of “solar fuels,” in a process termed artificial photosynthesis. In a photoelectrochemical (PEC) system, the reduction of CO 2 to carbon-based fuels is driven on the surface of an illuminated semiconductor electrode. Through the decades, many different classes of semiconducting materials have been studied for this purpose, to varying successes. Because of their cheap and abundant nature, semiconducting transition metal oxides are good candidates to realize this technology in an economic scale and have thus attracted considerable research attention. In this review article, the progress achieved with a specific class of metal oxides, namely, the copper ternary oxides such as copper iron oxide and copper bismuth oxide, for PEC CO 2 reduction is examined. Although there have been significant advances in terms of strategies to improve the efficiency and stability of these materials, further studies are warranted to address the many challenges to PEC CO 2 reduction and solar fuel production.

Rice husk is considered as a waste product of farming. However, rice husk ash (RHA) has a good pozzolanic activity, which can be used in cement-based materials as a supplementary cementitious material (SCM), and it is also suitable for self-compacting concrete (SCC). This study reviews the physical and chemical properties of RHA and the properties of RHA–SCC mixtures such as fresh properties (crucial factors and evaluation methods of workability for fresh SCC), mechanical properties (compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity), and durability (water absorption and sorptivity, acid resistance, chloride penetration resistance, electrical resistivity, and alkali silica reaction). It was observed that the workability of SCC decreases with an increase in the incorporation rate of RHA. An incorporation rate of RHA in the range of approximately 15–20% enhances the mechanical properties and durability of SCC. The incorporation of RHA into SCC can reduce the environmental burden of rice husk treatment, and promote sustainable development of cement industries and reduce the cost of SCC.

Rubber material is widely used in railway vehicles due to its superior damping performance. The testing methods, fatigue, and aging theories of rubber materials are of great significance to improve the design, manufacture, and application of rubber components for railway vehicles. This work systematically introduces the constitutive theory, mechanical testing standards, and testing methods of rubber materials. Then, the aging mechanism is described and the research progress of rubber fatigue properties is reviewed from the perspectives of fatigue crack initiation and fatigue crack propagation. Moreover, the reinforcement methods of rubber materials are presented. Finally, according to the working conditions of rubber components in railway vehicle, the technical difficulties and future research trends of fatigue characteristics analysis of rubber materials and components are pointed out.

Marine concrete is a kind of construction material which is seeking its growing application in marine engineering. However, the marine concrete structures are exposed to aggressive environment and harmful ions. Therefore, it is crucial to improve the durability of marine concrete. The concrete structure located in the tidal zone is subjected to the dry–wet cycles caused by tidal action, chloride ion (Cl − ) erosion in seawater, and CO 2 erosion in air. When these factors work together, they cause great damage to the marine concrete structure. In view of the three environmental factors, namely, Cl − erosion, carbonation, and dry–wet cycles, taking fly ash, fibers, and nanomaterials as examples, this article expounds the research status of durability of marine concrete, introduces the latest research progress, the addition of fibers, fly ash, and nanomaterials can improve the Cl − corrosion resistance and dry–wet cycles resistance of marine concrete, while the addition of fly ash is unfavorable for carbonation resistance. And the future development trend of marine concrete is prospected.

Today, the growth of the cosmetic industry and dramatic technological advances have led to the creation of functional cosmetical products that enhance beauty and health. Such products can be defined as topical cosmetic drugs to improve health and beauty functions or benefits. Implementing nanotechnology and advanced engineering in these products has enabled innovative product formulations and solutions. The search included organic molecules used as cosmeceuticals and nanoparticles (NPs) used in that field. As a result, this document analyses the use of organic and inorganic particles, metals, metal-oxides, and carbon-based particles. Additionally, this document includes lipid and nanoparticles solid lipid systems. In conclusion, using NPs as vehicles of active substances is a potential tool for transporting active ingredients. Finally, this review includes the nanoparticles used in cosmeceuticals while presenting the progress made and highlighting the hidden challenges associated with nanocosmeceuticals.

After tin–lead solders are banned, the widely used electronic packaging interconnect materials are tin–silver, tin–copper, and other alloy solders. With the application of high-power devices, traditional solders can no longer meet the new requirements. Nano-silver (Ag) paste, as a new solder substitute, exhibits excellent properties, such as excellent thermal and electrical conductivity, sintering at lower temperatures, and service at high temperatures. However, many organic devices still cannot withstand this temperature, and are often not suitable for the connection of nano-Ag paste packaging materials, therefore, it is very urgent to further reduce the sintering temperature of nano-silver paste. Based on the transient liquid phase sintering technology, by doping the nano-Ag paste with the nano-tin paste with a lower melting point to make the two uniformly mix, pressureless sintering at low temperature can be realized, and a sintered joint with a connection strength greater than 20 MPa can be formed. Considering that tin is easy to be oxidized, and the core–shell material can prevent the oxidation of tin, and at the same time ensure the uniform distribution of tin in silver, the doping scheme of the core–shell structure is determined. Heterogeneous flocculation method refers to the particles with different properties of charges which attract each other and agglomerate. It is a continuous reduction method for preparing core–shell materials. This method has the advantages of mild reaction conditions and less equipment investment, so the heterogeneous flocculation method is selected to prepare Sn@Ag core–shell nano paste. And research its sintering performance and strengthening mechanism.

Nonoxide ceramics excel among the reinforcements used for aluminum matrix composites due to their variety of morphologies and mechanical properties. Among these reinforcements are carbides (SiC, B 4 C, and WC); carbon materials (graphite, carbon fibers, carbon nanotubes, and graphene); nitrides (silicon nitride [Si 3 N 4 ] and BN); and hollow Fe spheres. Although the effect of adding different percentages of reinforcements has been widely studied for Al matrices, matrix–reinforcement interactions need more attention. The consequences of these interactions can include interface formation, loss of alloying elements, reinforcement deterioration, modifications in the matrix microstructure, different precipitation sequences and kinetics, and interfacial diffusion of elements. These interactions may be significantly modified by the alloying elements, needing more in-depth analyses for a correct selection of the matrix–reinforcement system. Al matrices with Si, Cu, and Mg outstand, and the focus of the present work is their reciprocal interactions with nonoxide reinforcements. The novelty of this review consists of the analysis and discussion of these interactions, emphasizing the modifications originated by each one of these alloying elements, and the conditions needed to increase or avoid their effects on the composite. Besides, an analysis of the crystallography of the generated interfaces is presented, including their impact on mechanical properties. This could be helpful for a better understanding and selection of the matrix–reinforcement system, also serving as a benchmark study. Graphical abstract

For the plate or multicabin structure of ships, the vibration transmission characteristics have a great correlation with the structural mode. When the excitation force frequency get close to the natural frequency of the structure, strong vibration and sound radiation will occur. Therefore, it is very important and meaningful to study the vibration characteristics and protection methods of ship structures. Based on the classic finite element method, this article studies the influence of structural forms and parameters on the vibration characteristics of typical ship structures. Taking the multicabin structure as a benchmark structure model, the influence of the structural form on vibration mode and transmission characteristics of the target deck and other cabin decks in the multicabin structure was analyzed. Then, without changing the original structural layout, the effects of different structural parameters on the vibration mode and transmission characteristics were analyzed. Finally, the vibration protection process of the ship structure was formed. The results of this study can provide methodological basis and data reference for relevant research in future. Graphical abstract

In this study, the comprehensive performance and material properties of recycled aggregate concrete (RAC) under the coupled effect of salt-frost cycles were investigated to simulate the effect of complex environmental effects on the durability and deterioration of RAC. The tests on mass loss, relative dynamic modulus of elasticity (RDME), and compressive strength of RAC were conducted after 0, 25, 50, 75, and 100 standard salt-frost cycles. The results show that the mass loss, RDME, and compressive strength of RAC develop in a bad direction with the increase of the number of salt-frost cycles and the amount of recycled aggregate admixture. The concrete damage is particularly severe at more than 40% recycled aggregate admixture. This phenomenon is explained by the changes in the microscopic morphology, distribution of the pore structure, and functional groups of RAC.

In this study, super-amphiphobic nano-silica nanoparticles (SA-NPs) were used to enhance the shale stabilization performance of water-based drilling fluids (WBDFs) by altering the surface wettability, preventing the capillary self-priming effect, and plugging the nano-micro pores of shale. The results of transmission electron microscopy, particle size distribution, and scanning electron microscopy characterization revealed that SA-NPs exhibited a nanoscale “coalesce” structure, which is composed of spherical particles joined together, and could form a nano-papillary structure on the shale surface. Due to the presence of nano-micro scale rough structures and ultra-low surface energy components, the shale treated by SA-NPS exhibited super-amphiphobic surface property in the contact angle test. Contact angles of water and hexadecane on the shale surface reached up to 154.13° and 151.34° after being treated with SA-NPs, respectively. Furthermore, the addition of 1% SA-NPs in WBDFs could reduce the linear swelling rate from 40.5 to 6.0%, increase the shale cuttings recovery percentages from 82.5 to 95.6%, increase the plugging rate of low permeability shale core from 81.25 to 94.00%, and raise the high-temperature and high-pressure uniaxial compressive strength from 3.45 to 4.87 MPa. Compared with the polyether amine and fumed nano-silica, the addition of SA-NPs produced the best performance. Based on the excellent shale stabilization performance of SA-NPs, a high-performance WBDF was developed and applied in Dagang Oilfield. During the drilling operation， no wellbore instability, sticking, and other complex situations occurred. The results indicate that SA-NPs could better address the issue of wellbore instability in shale formations and have a great application prospect in shale well drilling.

With the increasing scale, complexity and diversity of supporting equipment of offshore platform, the low-frequency vibration of equipment such as dynamic positioning system and the main engine is difficult to attenuate in the propagation process of the platform structure, which causes a local resonance of platform, aggravates the fatigue damage of structure and causes discomfort to the human body. Dynamic vibration absorption is widely used in the low-frequency vibration control of offshore platforms; however, there is little research about the multiline spectrum vibration control method in the local resonance region of platforms. In the current research, we first take the stiffened plate under multipoint excitation as the research object, and the effectiveness of the optimal homology design method of dynamic vibration absorption is verified. Subsequently, the low-frequency multiline spectrum vibration control method about the local resonance region of the offshore platform is proposed. Finally, a large offshore platform is chosen as the research object and the measured load of the main engine is taken as the input to calculate the vibration response of the platform. The effect of distributed dynamic vibration absorption of the resonance area verifies the effectiveness of the vibration control method presented in the article and provides a basis for the engineering application. Graphical abstract

A convex-like one-dimensional holey phononic crystal (PnC) strip with multiple wide band gaps but simple construction is investigated. By dint of the unique folding topology constituted by deformable L-shaped connectors and rigid lumps, the wide band gaps can exist with a compact spatial size. Moreover, the geometrical parameters are tunable in a large range. A maximum band gap of up to 63% is achievable. These salient merits outweigh the already published counterparts, enabling the proposed PnC strip to be a more promising candidate for engineering applications. Therefore, we are convinced that such a folding strategy of unit cells provides a practicable direction for the further structural design of PnC devices.

Traditional methods for the optimization design of the air spring are based on the deterministic assumption that the parameters are fixed. However, uncertainties widely exist during the manufacturing stage of the air spring. To model the uncertainties in air springs, evidence theory is introduced. For the response analysis of the air spring system under evidence theory, an evidence theory-based polynomial chaos method, called the sparse grid quadrature-based arbitrary orthogonal polynomial (SGQ-AOP) method, is proposed. In the SGQ-AOP method, the response of the air spring is approximated by AOP expansion, and the sparse grid quadrature is introduced to calculate the expansion coefficient. For optimization of the air spring, a reliability-based optimization model is established under evidence theory. To improve the efficiency of optimization, the SGQ-AOP method is used to establish the surrogate model for the response of the air spring. The proposed response analysis and the optimization method were employed to optimize an air spring with epistemic uncertainties, and its effectiveness has been demonstrated by comparing it with the traditional evidence theory-based AOP method.

The process of calcium silicate hydrate (C–S–H) generation in graphene oxide (GO) nanoslits was investigated via molecular dynamics simulations using the structural polymerization reaction of silica chains in the synthesis of silica gels. The structural evolution of C–S–H, radial distribution functions, chemical components, and distribution of Q n units in the system were analyzed to investigate the influence of GO on the early growth mechanism of C–S–H and compare the structural differences of C–S–H in the presence and absence of GO. The results showed that the proportion of silicon atoms bonded to bridge-site oxygen atoms in the C–S–H structure increased in the presence of oxygen-containing graphene groups. Ion adsorption in the GO surface layer led to an increase in the degree of polymerization of C–S–H. The nucleation and templating effects of GO were confirmed, revealing the intrinsic mechanism for the formation of GO-modified reinforced cementitious materials.

Monolithic thin-wall components of 2219 Al–Cu alloy are widely used in aerospace and military fields, and usually treated with solution and quenching to improve their comprehensive performance. However, a high magnitude residual stress is introduced into the components during the quenching process, which is unfavorable to the subsequent manufacturing process and service performance. Therefore, residual stress relief is essential to enhance the performance of the components. A conventional effective method is thermal stress relief (TSR). However, the underlying mechanisms of TSR still remain unclear and lack a quantitative interpretation. In the present work, the evolution and distribution laws of the residual stresses, tensile properties, Vickers hardness, dislocations, precipitated phases, and metallography during TSR were investigated. Based on the experimental results, dislocation theory and strengthening mechanisms were applied to reveal the underlying mechanisms of the residual stress relief by TSR. The results showed that the circumferential and axial residual stress relief rates can reach 86.37 and 85.77% after TSR, respectively. The residual stress relief after TSR is attributed to the dynamic evolution of dislocation configuration and density. The improvement in the mechanical properties mainly depends on the precipitated phases and is also affected by the stress orientation effect caused by the residual stress.

A novel method is developed for reusing the waste glass fiber-reinforced polymer (GFRP) powder as a precursor in geopolymer production. Several activation parameters that affect the workability and strength gain of GFRP powder-based geopolymers are investigated. The results of an experimental study reveal that the early strength of GFRP powder-based geopolymer pastes develops slowly at ambient temperature. The highest compressive strength of GFRP powder-based geopolymer pastes is 7.13 MPa at an age of 28 days. The ratio of compressive strength to flexural strength of GFRP powder-based-geopolymers is lower than that of fly ash and ground granulated blast furnace slag (GGBS)-based geopolymers, indicating that the incorporation of GFRP powder can improve the geopolymer brittleness. GGBS is incorporated into geopolymer blends to accelerate the early activity of GFRP powder. The binary geopolymer pastes exhibit shorter setting times and higher mechanical strength values than those of single GFRP powder geopolymer pastes. The GGBS geopolymer concrete mixture with 30 wt% GFRP powder displayed the highest compressive strength and flexural strength values and was less brittle. The developed binary GFRP powder/GGBS-based geopolymers reduce the disadvantages of single GFRP powder or GGBS geopolymers, and thus, offer high potential as a building construction material. Graphical abstract

Adsorbent is an important waste water-based drilling fluid treatment agent, which can adsorb and settle heavy metal ions, high polymer organics, and other soluble harmful substances in the waste drilling fluid. Traditional adsorbents such as polyaluminum chloride and polyacrylamide will produce other metal ions or toxic monomers after hydrolysis, which cannot fully meet the requirements of safety and environmental protection. Therefore, a new environmentally friendly waste water-based drilling fluid adsorbent, named RH-β-CD, was prepared by the Wilson etherification reaction, which was initiated by epichlorohydrin and ceric ammonium nitrate, and successfully grafted rhamnolipid and amine strong adsorption groups onto β-cyclodextrin. The adsorption effect and environmental protection performance of RH-β-CD on the organic matter and chromium ion in waste sulfonated water-based drilling fluid were evaluated and compared with commonly used adsorbents such as activated carbon, PAM, and polyaluminum chloride. The results show that RH-β-CD can effectively adsorb the organic matter in the filtrate of waste water-based drilling fluids, reduce its chemical oxygen consumption, and reduce the concentration of heavy metal ions in the filtrate. The effect is better than PAM, activated carbon, and polyaluminum chloride, with the BOD 5 /COD cr >20% and EC 50 >1,000,000 mg·L −1 , which is environmentally friendly.

The purpose of the experiment was to determine the distribution of shear stresses in the measurement area of a natural and modified wood sample. Previous wood shear tests conducted on a typical Iosipescu specimen have shown that a complex stress state exists at the bottom of the notch. With transverse loading of the samples, flexure occurs and normal stresses arise from the bending moment and thus fibers are deformed. For the investigations oriented on shear, shear with stretching, and shear with compression, a special specimen was prepared which differed by notch geometry from a typical Iosipescu specimen. A new test machine is described in the article, which is equipped with special specimen holders to perform investigations in complex stress conditions. Crack patterns recorded for natural and modified wood are presented. For all tests, numerical finite element model simulations were performed to obtain stress distributions inside the specimens. The calculated stress distributions were visualized as contour line projections for natural and modified wood. Transverse shear strength values for the modified Iosipescu sample were found to exceed the magnitude of previously published ASTM D1037-87 test results. The test results proved that the strength properties of anisotropic materials in a complex state of stress can be assessed with great accuracy. This is very important in engineering applications.

As a green and environmental protection method, the self-repairing technology has great expectations to be met. In this study, the influence of ettringite on the crack self-repairing of cement-based materials in a hydraulic environment was systematically analyzed. First, the composition and pore characteristics of the self-repairing carrier was studied by XRD, XRF, and the mercury injection method. The composition was basically consistent with cement-based materials, and the structure of the self-repairing carrier was relatively dense. Second, the products were analyzed by SEM and EDS, and it was found that the distribution range of crystal size was from 1 to 20 µm, the cube and flocculent accumulation was calcite, while the rod and flake crystals were ettringite. Finally, the repair effect on the surface and inside of the crack was demonstrated by the crack area repair rate and water permeability resistance. Compared with single microbial mineralization, the synergistic repair effect of microbial mineralization and ettringite formation was better in water permeability resistance. With the further increase of water pressure, its advantages would be more obvious.

Safety evaluation of key support components remains a challenge for freight trains because of the difficulties in direct and precise monitoring. In this work, the longitudinal stop on well-hole freight train, which prevents the cargo from sliding in anterior-posterior direction, is investigated. Load identification approach is proposed via strain perception at multiple locations, which are selected from the optimal positions sensitive to longitudinal and lateral loading in Finite Element Analysis (FEA). Validation is performed in random loading simulations. The identified loads deviate from the random sets within 4.07%. Longitudinal and lateral forces are recognized in an attempt to calculate the signed von Mises (SVM) stress of the longitudinal stop structure for fatigue evaluation. In application, the reconstructed structural stress climbs up to 107.1 MPa for the right weld base. Employing the rain-flow counting and Miner’s damage rule, the recommendation for load spectra grade in convergence is 64 groups. The equivalent fatigue damage is 0.854 and it drops to 30% in the statistical annual maximum mileage equivalency. Research outcome reveals that the proposed method enables the real-time monitoring of service loads and structural stress in railway freight transport, which provides scientific evidence for its maintenance planning and structural optimization. Graphical abstract

Aiming at the current situation that the existing acidizing corrosion inhibitors are difficult to apply in high temperature, high concentration acid, and other complex conditions, this article uses nano-SiO 2 as the core and preferably functional monomers to synthesize nano-SiO 2 @octadecylbisimidazoline quaternary ammonium salt (nano-SiO 2 @OBQA). Analytical methods such as nuclear magnetic resonance, infrared, and scanning electron microscopy were used for characterization. The corrosion inhibition performance of the N80 steel sheet by nano-SiO 2 @OBQA in 20% concentrated hydrochloric acid was studied using the high-temperature corrosion testing machine and adsorption isotherm model combined with quantum chemistry calculations to explore its mechanism of action. The results show that nano-SiO 2 @OBQA has good high-temperature resistance. When the temperature is 180℃ and the dosage of nano-SiO 2 @OBQA is 4%, the corrosion inhibition rate is 61.42 g·m −2 ·h −1 . Studies have shown that the adsorption of nano-SiO 2 @OBQA on the surface of the N80 steel sheet follows the Langmuir isotherm adsorption model, which is spontaneous chemical adsorption.

One key obstacle restricting the application of fiber-reinforced polymer (FRP) bars from being used as reinforcement in structural concrete is the significantly reduced ductility because FRP under tension is linear elastic up to brittle rupture at small strain. Recently, a new structural concept, compression yielding (CY), has been proposed as a way to overcome the insufficient ductility of concrete structures reinforced with FRP bars or other non-ductile materials. In the CY structural system, the compression-zone of normal concrete is replaced by a ductile material within the plastic hinge. This enables the flexural deformation to be achieved by the compressive deformation of CY material rather than a tensile deformation of longitudinal reinforcing bars. To this end, an ideal CY material requires strength to be maintained during the extraordinarily large deformation process. This study tries to identify methods for developing this kind of CY material by designing and optimizing perforations inside a mild steel block. The effects of key parameters, including ratio, diameter, and arrangement of perforations on the stiffness, strength, and ductility of CY materials were experimentally investigated. In addition, a finite element (FE) model was developed to predict the behavior of the proposed CY material.

The interfacial transition zone (ITZ) between the fiber and the matrix significantly influences the strengthening and toughening effect of the fiber for the matrix. The ITZ between the fiber and mortar is a weak link in strain hardening cementitious composites (SHCC), the loose structure is easily damaged, and it is the main channel of ion attack. The oil reduces the hydrophilicity of fiber and the bonding strength of fiber and mortar, which decreases flexural and compressive strengths, but increases the tensile ductility. The compressive strength increased with the increase in the microhardness of ITZ. Both freeze-thawing cycle and sulfate attack reduce the flexural and compressive strengths, and ductility of SHCC. The failure of ITZ is responsible for the performance decrease. The strength of the samples containing oiled fiber after the freeze-thawing cycle and sulfate attack decreases more significantly. Graphical abstract

On one hand, the nature of linear elastic up to brittle rupture hinders the application of fiber-reinforced polymer (FRP) bars as reinforcement in the concrete member due to the displacement ductility demand of structures. On the other hand, FRP bars are equipped with many irreplaceable advantages as reinforcement in concrete structures. To resolve this contradiction, a possible solution is to use the so-called compression yield (CY) structural system and the ductility of a concrete beam incorporating a CY system comes from the compressive side rather than the tensile side. Thus, the development of material in the compressive side (CY material) with well-designed mechanical properties (strength, stiffness, and ductility) is a key challenge. In this study, the CY material is developed by perforating the mild steel block and then substantiated by the test results. Then, experimentally calibrated finite element models are used to conduct systematic parametric studies, based on which parametric equations are proposed to predict the stiffness and ultimate strength of the CY material. Finally, theoretical constitutive models are developed to predict the stress–strain response of perforated steel block under compression and a reasonably acceptable agreement is reached between the model predictions and the test results.

Nonwater reacted polyurethane grouting materials are new materials developed to make up for the shortcomings of water-reactive materials in emergency rescue. However, its viscoelastic properties and constitutive model under dynamic loads have not been systematically studied. Based on dynamic thermal mechanical analysis (DMA), the dynamic viscoelastic indexes such as storage modulus, loss modulus, and loss factor of nonwater reacted polymer grouting material were obtained, and the frequency spectrum of polymer with different densities were analyzed. In addition, comparing and analyzing the classical viscoelastic constitutive models such as Maxewell model, Kelvin model, and Fractional model, the fourth-order generalized Maxwell model (GMM) was selected to construct the viscoelastic constitutive model of polyurethane grounding materials. Then, the parameters of the viscoelastic constitutive model of polyurethane grounding materials were obtained by using multi-objective shared parameter fitting method, and dynamic viscoelastic constitutive model of nonwater reacted polyurethane grouting materials was established. Furthermore, the viscoelastic constitutive model with different densities was verified by the DMA test. The results show that the dynamic viscoelastic constitutive model of nonwater reacted polyurethane grouting materials in the article can accurately and efficiently describe the dynamic viscoelastic properties of polyurethane grounding materials, which lays a foundation for the dynamic response analysis of polymer structures.

Two novel nonpneumatic tires named Tweel-2, designed based on the commercial Tweel model, and Saddle with hyperbolic paraboloid spokes are proposed in this study. Four nonpneumatic tire samples were successfully prepared with the 3D printing technology to measure and analyze and compare their properties. The results of quasi-static compression experiments showed that with the same relative density, the vertical bearing capacity of Tweel-2 tire was 1.4 times that of Tweel tire, while the vertical bearing capacity of the saddle tire was 4 times and 2.4 times that of Tweel and honeycomb tires, respectively. The finite element simulation method was used to explore the mechanism of improvement in vertical bearing capacity and energy absorption of the Tweel-2 and saddle design. The so-called circumferential unit in Tweel-2 and honeycomb tires enhances the deformation coordination between the spokes of Tweel-2 and increases the critical bearing capacity of the spokes by shortening the length of the deformation zone, so that more external work can be consumed under the same vertical deformation. The spatial configuration of the hyperbolic paraboloid can optimize the spatial stress distribution of the saddle tire and makes sure that a bigger amount of material deforms and participates in energy absorption, thus improving the overall strain energy level of the spokes.

Al–Mn–Fe alloy was prepared by traditional casting, injection casting, and melt spinning. The effect of cooling rate on the microstructure of alloy was studied. Results show that the phases in the alloy are the same for the three methods, including quasicrystal icosahedral phase (I-phase), Al 6 Mn phase, and Al phase. With the increase in cooling rate, the morphology of the I-phase changed from long strips to short rods and gradually to a daisy shape, and the content of the I-phase increased from 28 to 70%. Meanwhile, the morphology of the Al 6 Mn phase in the alloy changed from long bars to short rods, and the content decreased from 45 to 20%. Meanwhile, the thermal expansion coefficient of the alloy in the injection casting state is significantly reduced by about 15% at all temperature stages compared with that in as-cast state, and the results show that an appropriate cooling rate can improve the microstructure and properties of the alloy.

2219 aluminum alloy rings are important part of liquid cryogenic rocket fuel tanks. Residual stress is inevitably introduced in the forming process of the rings due to the nonlinear thermomechanical coupling conditions, which will affect its mechanical properties, fatigue properties, corrosion resistance, and dimensional stability. Thermal vibratory stress relief (TVSR) has great potential in reducing residual stress, and process optimization of TVSR is necessary to further improve its application, but it is rarely reported. In this study, process optimization of roll formed 2219 aluminum alloy rings is conducted. The influence of vibration amplitude, vibration time, vibration frequency, heating time, holding time, and cooling time on TVSR treatment are investigated. Results show that the maximum equivalent residual stress of 2219 aluminum alloy rings can be reduced by 93.6% after optimized TVSR treatment. With the increase in vibration time, heating time, holding time, and cooling time, the maximum equivalent stress decreases. However, the increase in the vibration amplitude results in an increase in the maximum equivalent stress. Further, a genetically optimized artificial neural network intelligent optimization algorithm is applied to quickly predict the TVSR effect of 2219 aluminum alloy rings.

Steel pipes are widely used in offshore structures and buried seafloor pipelines. Buried single-wall pipelines or piles of fixed offshore platforms crossing the earthquake fault can experience very large displacement, which could cause considerable damages or failures to the pipes. The elevated strains induced in pipelines from welding connection between the pipes also can drastically reduce the pipe’s performance. Therefore, to prevent these types of damages and failures, this research used an enhanced strain-based design method along with finite element analysis, developed bonded and unbonded double-wall composite pipes, which were in replacement of the single-wall ones, and studied the effects of welding on the double-wall composite pipeline in terms of wrinkles, ovalization, stresses, and strain. Here, the double-wall annulus of the pipelines was grouted with polymer. Extensive experiments were performed with displacement loads being applied to the pipelines in clay and in air and the results were analyzed. It was found that using an enhanced strain-based design method, failures in the pipelines could be significantly reduced or possibly even eliminated. This work would also potentially lead to a new area of research in the oil and gas industries since the elevated strains induced in pipelines due to weld could lead to several modes of failure. In addition, this research found some significant impacts in terms of safety due to the bond between steel and polymer and weld imperfection in the pipelines.

In this article, the deterioration law of concrete under the coupling action of freeze–thaw cycles and salt solution erosion is studied through the comprehensive thermal analysis, the field emission electron microscope, and the nuclear magnetic resonance, and the influence of salt solution type and salt solution concentration is considered. The results show that the freeze–thaw damage of concrete in the salt solution is the combined effect of the expansion pressure of the freeze–thaw erosion product, the crystallization pressure of the salt solution, and the frost heave pressure of the fresh water; the damage degree increases with the increase of freezing and thawing cycles; the damage degree of concrete in the chloride solution is greater than that in the sulfate solution and fresh water before 150 freezing and thawing cycles; the damage degree of concrete in the sulfate solution is greater than that in the chloride solution after 150 freezing and thawing cycles; the pores size of concrete in the salt solution is larger than that in fresh water, the main peak of the difference of pore size proportion shifts to the harmful pore area, and the secondary peak and third peak appear in the seriously harmful pore area; the pore diameters of the main peak, the secondary peak and the third peak of concrete in different salt solution, and the limiting pore diameters are 0.0662, 1.145, and 10.116 μm, respectively; the safe service life of concrete in salt solution environment after freezing and thawing cycles is predicted by the Weibull distributed life evaluation model. The maximum life after the freeze–thaw cycle is 33 years, which is at least 42% lower than that in the fresh water environment after freezing and thawing cycles.

In the present research work, the 2.25Cr1Mo0.25V steel plates with a thickness of 112 mm were welded using the multi-pass submerged automatic arc welding process. The creep specimens were prepared from the base metal (BM) and weld metal (WM) in the welded joint after heat treatment process. The uniaxial creep tests were performed to investigate the creep deformation and rupture behaviors at 550°C under different applied stress levels. The microstructure and fracture surface morphology of crept BM and WM samples were also characterized using the scanning electron microscope with energy-dispersive X-ray spectroscopy. The results showed that typical three-stage creep deformation curves are observed in both BM and WM specimens, and the BM exhibits a faster deformation rate than the WM. Both the creep rupture time and uniaxial creep ductility are found to be increased with a decrease in applied stress. Furthermore, the relationship between the minimum creep rate and time to rupture of both BM and WM samples was obtained, and it can be described using a unified Monkman–Grant equation. In addition, it is found that the creep fractures of the BM and WM are a transgranular ductile failure. The creep damages of both materials are mainly associated with the microstructural degradations, that is, the initiation and coalescence of creep cavities at second phase particles such as carbide and inclusion particles along the loading direction.

Two-component foaming polymer (TFPU) grouting material is increasingly used in civil engineering. Its compressive strength is key to achieving the desired enhancing effect. The constitutive model of TFPU grouting material is a theoretical basis to evaluate the strength performance, which, however, is not fully understood. Here the uniaxial compression experiment of TFPU samples of different densities (0.11–0.53 g·cm −3 ) was conducted. Based on the stress–strain curves, the damage evolution equation of each sample was obtained by function fitting, followed by the establishment of statistical damage constitutive model. The model was simplified to a universal function with density as the argument. Results show that the stress–strain curves contain the initial compression stage, linear elastic stage, yield stage, yield plateau stage, and strain hardening stage regardless of the varied density. The variation laws of the damage with strain conform to the form of first-order decay exponential function. The theoretical stress–strain curves are in good agreement with the experimental ones, indicating that the statistical damage constitutive model can well reflect the mechanical behavior of TFPU grouting material. With this constitutive model, the mechanical properties of TFPU grouting material can be obtained according to the density alone, which is more convenient for practical engineering applications.

In this study, nano-structural and nano-constraints behavior of two silica aggregate mortars are investigated. The first silica aggregate (A) is almost pure silica and the second one (B) contains silica, calcite and dolomite phases. The relationship between the durability and nano-structural changes is evidenced using Transmission Electron Microscope, X-ray diffraction (XRD) and TGA/DTA. The nano-structural results show that the macroscopic properties of mortars greatly depend on physico-chemical properties of aggregates. Higher the water absorption, higher the consumption of the Portlandite; the consumption of Portlandite, after 28 days of curing, is more in Bm sample than in Am sample. A relationship between the Portlandite content and the water absorption is evidenced. The relationship between reactivity and nano-constraints deduced from XRD modeling is highlighted.

This article presents the experimental results of the compressive strength, the splitting tensile strength, the macro destruction mode, and the microstructure of recycled clay brick aggregate concrete (RBC) with different recycled clay brick aggregate (RBA) replacement rates. The results show that the compressive strength and the splitting tensile strength of RBC are lower than those of natural aggregate concrete (NAC), but the effect of RBA on the splitting tensile strength of concrete is not significant. The effect of the water–cement ratio (w/c) on the splitting tensile strength of RBC is smaller than that on the splitting tensile strength of NAC. The compressive strength of concrete shows a trend of first decreasing and then increasing with the increase in RBA replacement rates. The effect of RBA replacement rates on the compressive strength gradually decreases with the increase in the w/c. The AFt in NAC is thicker than that in RBC, and the C–S–H of RBC is in the form of agglomerated networks with large and uniform pores and less filler. Graphical abstract

In recent years, it has been widely recognized that the incorporation of Mg–Al–LDH into cement-based materials can improve the salt corrosion resistance of cement-based materials. The reason for the improvement comes from the anion adsorption capacity of Mg–Al–LDH. It was confirmed that the addition of Mg–Al–LDH would accelerate the setting and hardening of cement paste. With the increase in the Mg–Al-LDH content, the initial setting time of cement slurry with different gypsum contents will decrease by 10–50% and the viscosity of the cement slurry will increase by 100–200%. Depending on different gypsum contents, the degree of cement hydration varied. This article also found that the gypsum in the cement has a negative effect on the resistance to salt erosion, which was brought about by the Mg–Al-LDH adsorption capacity.

Six different types of polyamic acids were synthesized by reacting 1,2,4,5-cyclohexanetetracarboxylic dianhydride with the diamine monomers 3,4-oxydianiline, 1,3-bis(3-aminopheno- xy )benzene, 1,4-bis(4-amino-phenoxy)benzene, m -bis[4-(3-aminophenoxy)phenyl]sulfone, p -bis[4-(4-aminophenoxy)-phenyl]sulfone, and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane. Thereafter, polyimide (PI) films were prepared via various heat treatment processes. The diamine monomers used in this study for the synthesis of colorless and transparent PI (CPI) were characterized by a bent meta-structure or a para-linear chain containing ether (–O–) bonds. In addition, some monomers included fluorine (–CF 3 ) substituents and sulfone (–SO 2 –) groups. Furthermore, the thermal and mechanical properties, optical transparency, and solubility of the CPI films with six different diamine monomer structures were investigated. The correlation between CPI film properties and related monomer structures was specifically emphasized.

At present, the cylindrical shell was regarded as the dominating structure in underwater vehicles, which raised the crucial significance to research underwater vehicles’ vibration and acoustic radiation features. In this study, the analytical expression of vibration–acoustic theory had been given according to the derivation with the vibration–acoustic theory of ribless cylindrical shell structure. Meanwhile, the effects of key parameters on vibration–acoustic characteristics are investigated including modulus, density, thickness, loss factor, etc. The research shows that the stiffness and damping of the shell directly affected the vibration of the structure. Furthermore, the performance of vibration attenuation and noise reduction of the shell had been enhanced by increasing the modulus, thickness, and loss factor in materials.

Recycled steel fiber (RSF)-reinforced concrete is not only an innovative research trend in the field of civil engineering materials, but also a new type of civil engineering composites under the trend of low-carbon development. This article deals with the experimental study of applying waste steel fibers to form recycled steel fiber concrete (RSFC). The main materials in this study are RSF, coarse and fine aggregate, fly ash, silica fume, and water reducer agent formed by machining surplus materials as the main materials. Three types of concrete were prepared. They were normal concrete, primary steel fiber concrete (PSFC), and RSFC with six different volume contents. The slump and air content of the three types of concrete are compared and analyzed. Then, the effects of the volume content of RSF on the cube compressive strength, splitting tensile strength, flexural strength, and axial compressive strength of RSFC are studied. Finally, the toughness of RSFC is discussed. The test results show that with the increase in the volume content of RSF, the slump of RSFC is significantly reduced, the compressive strength, tensile strength, and flexural strength are enhanced, the increase in tensile strength and flexural strength is significantly higher than the cube compressive strength, and the RSF has an obvious inhibitory effect on the development of concrete cracks which can obviously enhance the ductility and toughness of the concrete.

As a hot content of research in recent years, acoustic black holes have bright application prospects in the field of vibration and noise reduction. In this article, based on the acoustic black hole theory, we carry out a study on the dynamic characteristics of a typical raft structure. The manuscript gives the simplified method of the acoustic black hole model, verifies the validity of the method by the structure natural frequency and vibration response, and discusses the influence of the main parameters such as acoustic black hole tip cutoff ratio and damping thickness ratio on the vibration characteristics of the raft frame structure. The better values of the parameters were applied to the raft structure on this basis, and the results showed that the peak value of some frequency points decreased by about 10 dB after the acoustic black hole was laid in the raft structure, which improved the vibration isolation performance of the raft. Graphical abstract

In this paper, the unified Jacobi–Ritz method (JRM) is utilized to analyze the dynamic response of rectangular plates with general boundary conditions. First, the structural energy functional is established in the framework of the first-order shear deformation theory, and the rectangular plate is divided into several equal parts according to the domain decomposition method. Then, the artificial springs are introduced to ensure the continuity of segments and diversified boundary conditions. The Jacobi orthogonal polynomials are expanded to represent the displacement field in one direction. Finally, the free and forced vibration characteristics of the rectangular plate can be obtained by utilizing the Rayleigh–Ritz method, where the Newmark-β integration method is adopted to realize the time-domain solutions for transient vibration response. The results for different structural scale parameters and various boundary conditions are presented, and the validity and accuracy of the presented method are verified by comparing the results from published literature and FEM. The results of the study can provide technical support for vibration control of the plate structure.

How to more effectively and comprehensively utilize recycled aggregate resources to prepare a richer new low-carbon concrete material system is the key path to achieve low-carbon development in China’s construction field. Based on the material properties of graphite tailings (GT), this article explores the organic combination of GT to replace sand and recycled aggregates (RA) to replace natural stones, in order to propose an efficient recycling path for multiple solid wastes and a new and cost-effective recycled aggregate concrete (RAC). This article focuses on investigating the influences of GT (0–40%) and RA (0–40%) on the workability, water absorption, and mechanical properties of GT reinforced recycled aggregate concrete (GTRAC). Simultaneously, the hydration products, microstructure morphology, key chemical bonds, and pore structure characteristics were analyzed by a combination of microscopic tests such as X-ray diffraction, scanning electron microscope, Fourier transform infrared and mercury intrusion porosimetry to propose the key factors affecting the macroscopic performance of GTRAC. The results show that incorporating 10–30% GT has significant positive effects on water absorption, surface water content, compressive strength, and elastic modulus of RAC. RAC’s micro-crack density, hydration, and pore structure distribution can be maximally improved by appropriate GT (20%). However, the high content of GT will lead to the degradation of its mechanical properties. Therefore, 20% GT and 30% recycled aggregate are the optimum combinations of the concrete material system. However, it might be changed when the ratio of water to binder varies. Finally, this article also comprehensively analyzes and evaluates the performance and price of different types of RACs, which provides theoretical support for evaluating and predicting the practical engineering application value of GTRAC. In summary, the research results in this study provide theoretical guidance for understanding the mechanism of GT on the enhancement of mechanical properties of RAC and exploring new ways of practical engineering application of it.

Gradient porous structures are extensively studied in impact-resistant structures due to their light weight and high energy absorption. Different from existing studies, this article focuses on novel Voronoi structures with gradient perpendicular to impact direction, and compares their dynamic response with the uniform structure through numerical simulation. It shows that the novel gradient design comprehensively improves the impact resistance of Voronoi structures. Furthermore, density gradient is introduced into the one-dimensional shock model, and the theoretical solution of the plateau stresses at the impact end are compared with the simulation results, which verifies the correctness of the model in this article.

Nano-modified multimodal and conventional Cr 3 C 2 –NiCr coatings were fabricated by high-velocity oxygen-fuel spraying deposited on CuCrZr substrates. Results showed that individual nano-modified multimodal Cr 3 C 2 –NiCr particles were composed of nano (25−180 nm), submicron (200 nm to 0.5 μm), and micron (2–4.5 μm) Cr 3 C 2 grains, NiCr binder phases, and a tiny amount of rare earth oxide additives. The nano-modified multimodal Cr 3 C 2 –NiCr coatings maintained a unique structure: submicron Cr 3 C 2 grains embedded in the voids formed by micron Cr 3 C 2 grains, NiCr binder phases and nano Cr 3 C 2 grains imbedded in the voids formed by submicron and micron Cr 3 C 2 grains, and nano Cr 3 C 2 grains are dispersed in NiCr metal binder phases. A few discontinuous elongated amorphous and nanocrystalline phases existed in them. The mechanical interlocking was the dominant bonding mechanism accompanied by local metallurgical bonds. Compared to the conventional coating, the multimodal coating was uniform and dense (porosity was 0.3 ± 0.12%) as well as not obvious lamellar structures, the adhesive strength was 75.32 ± 1.21 MPa, exhibiting a 65 pct increase, and the microhardness was increased by about 18%. The lower porosity and higher strength of nano-modified multimodal structure coating were mainly related to dispersion distribution and synergistic coupling effects of Cr 3 C 2 hard grains with different scales.

Aiming at the present situation that the effect of excitation type on typical ship grillage structure vibration is not fully revealed, different excitations are applied on typical ship grillage structure to study the effect of different excitation. Finite element method (FEM) is introduced to solve grillage vibration and sound radiation, and a test model is used to verify the effectiveness of the simulation method by comparing test results and simulation results. Mean square vibration velocity and acoustic power are compared to explore the effect of excitation type on grillage vibration. The research shows that the simulation method (FEM) is effective in grillage vibration and sound radiation; the peak frequency of acoustic power and mean square velocity of grillage structure under different excitation are basically the same; uniform distribution excitation is a better way to reduce structure vibration and noise. Graphical abstract

Graphene oxide (GO) has been widely used to enhance the tensile/compressive strength of cement-based materials, whereas its shear reinforcing effect is still unknown. To verify the feasibility of GO as a shear reinforcement material, the shear reinforcing effect of GO on cement was experimentally investigated. The nanoscale Young’s modulus ( E ) of the GO-enhanced cement was measured with the peak force quantitative nanomechanical mapping method to clarify the enhancing mechanism. Results show that the addition of 0.02 and 0.04 wt% GO in cement could improve the shear strength by about 12 and 40%, respectively, which is mainly due to the enhanced cohesion, and at the nanoscale, the average E of the low-density hydration product increased by 1.6 and 13.2%, whereas that of high-density hydration product remains almost unchanged. There exist fewer nanoholes/cracks and unhydrated cement grains but more the high-density hydration product in GO-enhanced cement, implying a denser microstructure and higher hydration degree. GO can enhance the shear strength of cement because of its enhancing effects on the microstructure, nanoscale Young’s modulus of hydration products, as well as the hydration degree.

Recycled rubber particles can be produced by using waste tires. Adding recycled rubber particles to concrete can form rubber concrete (RC). RC can not only reduce the amount of natural sand and reduce the cost of concrete but also improve the static compressive toughness of concrete. Adding steel fiber into RC can improve the strength of concrete. In order to study the compressive toughness of steel fiber rubber concrete (SFRC), rubber particles washed with NaOH are added to steel fiber reinforced concrete. This can enhance the bonding performance between the recycled rubber particles and concrete. The volume ratio of recycled rubber is 5, 10, and 15%. Prismatic and cubic test blocks were prepared and their compressive tests were carried out. The results show that the stress interaction between the rubber particles and steel fiber in concrete significantly improves the compressive strength, elastic modulus, and stress–strain relationship of concrete. The compressive toughness and ductility of concrete are improved. When the content of rubber particles is 15–20%, the compressive toughness of SFRC is improved most obviously. Through experiments, the toughness index and specific toughness of rubber steel fiber reinforced concrete are calculated, which explores a new way and method for studying the compressive toughness of similar recycled material concrete.

The holes and defects in rock materials have a great impact on the mechanical properties and failure mechanism of rock, cracks often appear in the form of flat ellipses in natural rock mass, and the current research is still insufficient. For this purpose, based on the Particle Flow Code (PFC) of discrete element particle flow program, the numerical prefabricated fractured rock samples with the ratios of the long and short axes of the elliptical fractures being 5, 7.5, 10, 12.5, and 15 were simulated in order to obtain the strength and failure characteristics, stress concentration characteristics at tips of numerical rock samples in uniaxial compression test. The results of the numerical test simulation show that: (1) When the rock models with prefabricated elliptical crack were damaged, the initial cracks occurred at the end of the short axis of the elliptical crack, and penetrated up and down from the surface of the elliptical crack, the wing cracks occurred at both ends of the long axis, gradually formed a macro-crack, and the secondary cracks extended near the wing crack. (2) With the increase of the ratios a : b of long and short axes of the elliptical fracture, the strength and elastic modulus of the numerical rock samples gradually decreased, Poisson’s ratio gradually increased, and the total number of micro-cracks in the rock models decreased. (3) The numerical solutions of stress concentration factor k obtained by numerical simulations at the tip of the elliptical crack increased with the increase in the ratio of a : b ; it was highly consistent with the variation law of the analytical solution of the stress concentration factor calculated by the theory of flat ellipse. The stress concentration is an important reason for failure of rock with elliptical cracks. Study on the crack tip will be very useful and significant.

The durability of concrete structures is often reduced owing to the corrosion of reinforcement in an aggressive environment. Ordinary reinforcement methods, such as wrapping section steel or steel plate, are also vulnerable to corrosion. Using 6061-T6 aluminium alloy as near-surface reinforcement of the concrete structure is a feasible method. In this study, the corrosion resistance of 6061-T6 aluminium alloy bars was studied by simulating the coastal environment, atmospheric environment, and concrete internal environment with chloride solution, simulated acid rain solution, and saturated Ca(OH) 2 solution. The corrosion rate of the 6061-T6 aluminium alloy in the above environments was tested using a weight loss method, and its corrosion resistance was evaluated using the metal corrosion resistance classification standard. Based on the electrochemical reaction mechanism, the polarisation properties and AC impedance spectra of steel and 6061-T6 aluminium alloy were compared, and the corrosion resistance mechanisms of steel and the 6061-T6 aluminium alloy in the above corrosive environments were obtained. The results show that the 6061-T6 aluminium alloy has better corrosion resistance than steel bars in chloride and atmospheric environments, with corrosion currents of 0.012 and 0.037 µA·cm −2 , and 8-day corrosion rates of 0.051 and 0.031 mm·a −1 , respectively. However, owing to the activity of the aluminium alloy, its corrosion resistance in an alkaline environment inside concrete is poor; the corrosion current is 0.22 µA·cm −2 and the 8-day corrosion rate is 16.166 mm·a −1 . The research results can provide a reference for applying aluminium alloy bars as external prestressed concrete bars and near-surface steel bars.

In the present work, manganese cobaltite (MnCo 2 O 4 ) spinel (MCO) was synthetized by Pechini and hydrothermal method, characterized and photocatalytically evaluated toward H 2 production through water splitting under visible-light irradiation. Characterization consisted in Thermogravimetry analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy, scattering transmission electronic microscopy, BET surface area, UV-Vis spectroscopy, cyclic voltammetry, Hall effect, and photoluminescence. The MCO were evaluated as photocatalyst using an artificial visible light lamp and monitored by gas chromatography. XRD analysis found a pure spinel phase MCO. The surface area was ∼5 m 2 ·g −1 for the MCO synthetized by Pechini and increased to 155 m 2 ·g −1 with the hydrothermal method with acetates as precursors. The Pechini MCO showed higher carrier mobility but the fastest recombination. Photocatalytic evaluation of the MCOs showed that the highest photocatalytic activity generated was 12 μmol H 2 /g cat at 8 h with the MCO obtained by hydrothermal method with the acetates.

The failure of rock mass is mainly due to the failure of the structural plane, which is an important factor to reduce the mechanical properties and stability of rock mass. The shear strength of rock mass is one of the parameters for the stability calculation of large-scale rock mass engineering. The shear strength of a rock structural plane is strongly influenced by surface morphology. Considerable research has been conducted regarding the correlation between two-dimensional structural plane morphology and shear strength. However, quantitative research on three-dimensional (3D) morphology is relatively limited. In this study, 3D printing technology was used to create molds. Using cement and sand as the main materials, additives such as early strength and water-reducing agents were added, and test samples of irregular surface topography were created. The 3D roughness was quantified by formula calculation. Using a ZScanner ® 800 hand-held 3D laser scanner to perform scanning on the structural surface, the parameter curve was analysed by generating 3D coordinate information and a 3D image of the fracture surface, and the quantitative parameter M p 3 D {M}_{\text{p}}^{3\text{D}} describing the 3D morphology of the structural surface was constructed. The change rule of R p 3 D {R}_{\text{p}}^{3\text{D}} and joint roughness coefficient (JRC) were analysed under different scanning resolutions, Δ( r ), the scanning precision was suggested, and the functional relationship between JRC and M p 3 D {M}_{\text{p}}^{3\text{D}} was established. Finally, a formula for shear strength parameters considering the 3D characteristics of a structural plane surface was established. The model validation results show that the experimental data were within the 95% confidence band of the model curve, the average error of the shear strength was 10.4%, the errors of friction angle and cohesion, C , were 3.4 and 9.4%, and the reliability was fine.

Aluminum alloy AA2020 has a greater demand for the high strength-to-weight ratio used in applications like aerospace, naval, and automotive applications because heat treatment produces high strength. Friction stir welding (FSW) is widely employed in forming butt joints of AA2020-T4 using a square profile tool. In this work, the wear characteristics and the corrosion behavior with and without age-hardened treatment are studied and compared. In this work, the wear characteristics and the corrosion behavior with and without age-hardened treatment (after a 1-hour solution treatment of AA2020 alloy at 505°C, quenched in water at ambient temperature) are studied and compared. Age-hardened models with a high aging duration (16–20 h) at 177°C showed a reduction in wear resistance for low spindle speed in contrast to the as-FSWed joints. In the corrosion medium, long aging time heat-treated FSWed joints showed high passivity in a 3.5 wt% NaCl solution. Intergranular and pitting types of corroded surfaces in as-FSWed joints were spotted. 20 h of age-hardened FSWed joints achieved the minimal corrosion rate (CR) and is suggested for moderate wear resistance and good CR. The speed appears to have a greater impact on wear rate than the weld speed and applied load. It is also worth noting that the CR increases by 5% with the increasing spindle speed and falls by 4% with the increasing weld speed.

The flexspline (FS) of the harmonic drive (HD) is subjected to thermal load and force load during operation, leading to the deformation difference between the inner and outer surfaces of the FS. As a result, the transmission performance of the HD assembly decreases. To overcome this problem, the thermal–mechanical coupling deformation mechanism of the FS is analyzed, and then the influence of the deformation difference on the transmission accuracy of the HD is studied in this article. On this basis, the structural parameters of the wave generator are optimized to eliminate actual backlash and to improve the actual transmission accuracy. Finally, the effectiveness of the calculation method proposed in this article was proved by the prototype test.

Freeze–thaw damage and the lack of aggregate resources have become two major problems facing the construction industry. The use of recycled aggregate to produce recycled concrete has good social and economic value. In this study, the author used recycled coarse aggregate as a substitute for stone to mix recycled concrete. In order to enhance the performance of concrete, a microwave heating modification process was introduced and 0.10% volume fraction of polypropylene fiber (PPF) was added. The effect of microwave heating modification on the frost resistance of fiber-reinforced self-compacting recycled concrete was studied. The results show that with the increase in the number of freeze–thaw cycles, the degree of denudation and deterioration of the three groups of concrete surfaces becomes more and more serious, the number of surface cracks gradually increases after the concrete is damaged, and the plastic deformation becomes more and more serious, W n gradually increases, E n gradually increases, D n gradually increases, σ 0 gradually decreases, ε 0 gradually increases, ε u gradually increases, E c gradually decreases, and μ gradually decreases. Under the same number of freeze–thaw cycles, the frost resistance of the three groups of concrete is A > C > B. Microwave heating modification improved the frost resistance of group C concrete compared to that of group B concrete. Due to the incorporation of PPF into the concrete, the load did not drop sharply when the load acting on the concrete reached the failure load. The prediction results of the established constitutive model are in good agreement with the experimental results.

A series of titanium dioxide (TiO 2 ) modified with 3-aminopropyltriethoxysilane (APTES) was prepared by high-temperature calcination in an argon atmosphere in the temperature range from 800 to 1,000°C. The properties of the obtained samples were compared with those of pure TiO 2 annealed under the same conditions. Examining electron paramagnetic resonance (EPR) parameters at room temperature for APTES–TiO 2 showed an intense resonance line from defects related to conducting electrons with g eff from 2.0028 to 2.0026 and 1.9052 for temperatures 800, 900, and 1,000°C, respectively, while for pure calcined TiO 2 , these ERP lines were not observed. With the increase in the calcination temperature to 900°C for APTES–TiO 2 samples, the EPR increases linearly. This has been combined with a relatively high anatase content and small crystallites. The EPR line intensity at RT calculated for 1 g of sample showed an almost linear relationship with the photoactivity in removing ORANGE II dyes from water.

This study first tried to fabricate AA1060/Al 2 O 3 composites via the stir casting and accumulative roll bonding process. Then, the effect of nano Al 2 O 3 Vol% on mechanical, wear, and microstructural properties of these kinds of composites have been investigated. An excellent particle distribution through the aluminum matrix has been achieved after the fourth cycle. Then, mechanical properties, wear resistance, and microstructural properties have been investigated. The results showed that the strength of these composites was enhanced and the elongation of samples decreased by higher alumina Vol% contents. Also, there is a significant increase in wear resistance by increasing alumina content in the Al matrix through the stir casting process.

Numerous researches have been directed toward enzyme-free biosensors to alleviate the shortcomings encountered with enzymatic biosensors, in particular the intricate enzyme immobilization procedure. Herein, Co 3 O 4 /electrospun carbon nanofiber (ECNF) nanocomposites are successfully prepared to be employed as enzyme-free biosensors for diagnosis of glucose. Two parameters including the carbonization time and the amount of Cobalt( ii ) acetate tetrahydrate precursor are optimized, which are 5 h and 0.5 g, respectively. The 0.5 Co 3 O 4 /ECNF-5 h nanocomposite delivers superior sensitivity (475.72 μA·mM −1 ·cm −2 ), broad linear range (2–10 mM), and detection limit (LOD) less than 1 mM (0.82 Mm). In addition, the electrode shows excellent selectivity. The chronoamperometric analysis of 0.5 Co 3 O 4 /ECNF-5 h nanocomposite is performed by adding successively glucose analyte and interfering agents to the 0.1 M sodium hydroxide solution. No significant amperometric signal to the interfering agents including uric acid, ascorbic acid, and dopamine is delivered by this electrode, testifying the great selectivity of the electrode toward the diagnosis of target analyte (glucose) in spite of the existence of interfering species. Taking the aforementioned explanations into account, it can be concluded that the Co 3 O 4 /ECNF nanocomposite can be an appropriate free-stand electrode for high-performance enzyme-free glucose biosensor.

In the course of the construction of deep foundation pits during the winter in seasonally frozen areas, the pit wall soil is often unstable due to frost heave and thawing settlement, which leads to hidden safety hazards in engineering construction. Based on the analysis of the deformation data of a pile-anchor supporting a deep foundation pit in Harbin obtained from monitoring during the winter, the influence of freezing and thawing cycles was investigated. The results show that the horizontal displacement in the middle of the shallow layer of the foundation pit is significantly larger than that on both sides during the freeze–thaw cycles, and the spatial effect becomes noticeable. The stress concentration at the external corner of the foundation pit, coupled with the effects of atmospheric precipitation and freeze–thaw cycles, led to the maximum growth rate of horizontal displacement up to 1.40 mm·day −1 . The external corner effect is evident from 1 m in the shallow layer of the pit to the depth H/2 of the foundation pit. The support scheme is generally feasible, and we can appropriately enhance the support of the shallow layer of the foundation pit during the freeze–thaw cycles. For similar projects experiencing freeze–thaw cycles, the safety reserve can be appropriately enhanced when carrying out support design.

Elastic modulus plays a key role in the application of porous metallic materials. However, to the best of our knowledge, few attempts have been made to model the simultaneous dependence of elastic modulus on temperature and porosity for metallic materials. The present article contributes to a rational temperature-porosity-dependent elastic modulus model for metallic materials with all parameters having definite physical significance. The model can well predict the elastic moduli of porous metallic materials, from extremely low temperature to ultrahigh temperature, and from dense material to about 0.9 porosity, with reference to an easy-to-access elastic modulus. In a special case, when intrinsic elastic modulus [ M ] = 2 and critical porosity P C = 1, a phenomenological parameter-free predictive model can be obtained. The model can be applied when the matrix Poisson ratio is 0.1 < v < 0.4 for Young’s modulus and 0.17 < v < 0.27 for shear modulus, which covers most metallic porous materials.

In order to understand the diffusion behavior of polyurethane (PU) in asphalt and the adhesion between modified asphalt and aggregate, the diffusion system of PU-modified asphalt was studied by molecular dynamics simulation software. Asphalt molecular model, PU molecular model, and PU-modified asphalt molecular model were established, respectively, and were geometrically optimized. The interface model between original asphalt molecule and aggregate, modified asphalt molecule and aggregate, PU molecule and asphalt molecule are established. The diffusion coefficient is calculated from the mean square displacement curve of asphalt and PU, so as to characterize the diffusion ability of asphalt and PU. The adhesion between modified asphalt and aggregate is characterized the interface energy between modified asphalt and aggregate. The results show that the molecular movement of the two substances is relatively active, and the micro-holes in the system structure can be filled in a short time. The interface energy between PU-modified asphalt and aggregate is more significant than that between original asphalt and aggregate. PU-modified asphalt has good diffusion ability and better adhesion with aggregate.

To achieve better mechanical properties and higher scour resistance of yellow mud in Qiang Village, this study investigated how to improve yellow mud by single factors of straw, starch, cement, and epoxy resin. First, the effect of each material on the shear strength of yellow mud was analyzed through the direct shear test, and the effect of the respective material on the scour resistance of yellow mud was examined using a self-made spray device. Subsequently, combined with the results of the two experiments, the improvement effect of the material was comprehensively studied, and the optimal dosage of the respective material was determined. Lastly, an electron microscope was used to observe the microscopic morphology of the samples, and the improvement mechanism of each material was discussed from qualitative and quantitative perspectives. As revealed by the results, straw, starch, cement, and epoxy resin improved the shear strength and scour resistance of yellow mud. Peaks of straw, starch, and epoxy resin were found in their corresponding properties-dosage curves, corresponding to the optimal dosage in the experimental range. The corresponding performance curve of cement showed a unidirectional change, which was found with a significant improvement effect.

The large-scale application of phenolic aerogel is limited by its complex and lengthy production process as well as its expensive cost. Herein a simultaneous drying-curing method for phenolic aerogels was designed based on the sol–gel process, and a series of phenolic aerogels with different hexamethylenetetramine (HMTA) contents were prepared. The material parameters such as microstructure, pore structure, mechanical properties, shrinkage, and density of the aerogel were characterized. The results show that compared with the conventional full-sealing method, the simultaneous drying-curing method shortens the preparation time of aerogels by nearly half and improves the safety of the preparation process. The prepared phenolic aerogels still maintain the nanoporous microscopic morphology. When the HMTA content is 1/6 of the phenolic mass, the linear shrinkage rates of the aerogels prepared by this method and the conventional full-sealing method are 9.8 and 9.4%, respectively. The densities are 0.25 and 0.22 g·cm −3 , and the BET specific surface areas are 54.42 and 54.31 m 2 ·g −1 , and the compressive yield strengths are 1.76 and 1.16 MPa. At the same time, the thermal conductivity of the phenolic aerogels prepared by the simultaneous drying-curing method is less than 0.06 W·(m·K) –1 at room temperature. These results indicate that the properties of the aerogels prepared by the simultaneous drying-curing method are close to those prepared by the conventional method, which proves that this method has guiding significance for the large-scale, low-cost, and rapid production of nanoporous phenolic aerogels.

Sublimation growth of cubic silicon carbide (3C–SiC) with diameters of 50 and 100 mm was performed on freestanding homoepitaxial grown seeds. For both seeds and sublimation grown crystals, two different relaxation axes with varying curvature could be observed with the higher bent axis aligned perpendicular to the original wafer flat. A general reduction in the wafer bow independent of the starting curvature and size of the seeds could be observed. Using the X-ray imaging, we could observe in situ that the bow reduction is linked to the growth of new material and cannot be initiated by heat up or cool down processes alone. Raman spectroscopy of the grown crystals revealed that the observed flattening goes along with a tensing of the seeding layers while the surface of the crystals remains free of a stress gradient. A slight concave bending of lattice planes along the main relaxation axis could be observed by high-resolution XRD rocking curve measurements while for the lower bent axis, no lattice plane bending occurred. Full width half maximum values of the (002) reflection showed values as low as 67 arcseconds proofing the possibility to grow large-area, high-quality 3C–SiC using sublimation growth.

Fused deposition modelling is known for its ability to customise materials at peak performance for instant use but lacks in terms of interfacial adhesion of layup sequences. Hence, the mechanism of acquiring excellent interfacial adhesion, mainly via dried-up printed sample, has been discovered, resulting in the proper bonding formation upon layers. Result reveals that the flexural strength increased by 23% under 70°C drying conditions (5 h) and the impact strength increased by 240% compared to pure polyamide. This mechanism resists the deformation growth between the layers and enhances the mechanical strength at the highest level.

This work presents the design and application of a low-cycle reciprocating loading test on 23 recycled aggregate concrete-filled steel tube columns and 3 ordinary concrete-filled steel tube columns. Additionally, a systematic study on the influence of various parameters (e.g., slenderness ratio, axial compression ratio, etc.) was conducted on the seismic performance of the specimens. The results show that all the specimens have good hysteresis performance and a similar development trend of skeleton curve. The influence of slenderness ratio on the seismic index of the specimens is more significant than that of the axial compression ratio and the steel pipe wall thickness. Furthermore, artificial intelligence was applied to estimate the influence of parameter variation on the seismic performance of concrete columns. Specifically, Random Forest with hyperparameters tuned by Firefly Algorithm was chosen. The high correlation coefficients ( R ) and low root mean square error values from the prediction results showed acceptable accuracy. In addition, sensitivity analysis was applied to rank the influence of the aforementioned input variables on the seismic performance of the specimens. The research results can provide experimental reference for the application of steel tube recycled concrete in earthquake areas.

This research focuses on the addition of low-cost rare earth metals (REMs) to improve the comprehensive properties of hyper duplex stainless steels (DSSs). The effects of REM on the microstructure, mechanical properties, and pitting corrosion of hyper DSSs were analyzed by optical/scanning electron microscope metallographic examination, X-ray diffraction analysis, tensile test, impact test, and potentiodynamic polarization test. With the addition of REM, micro/nanoscale REM inclusions were formed, and the microstructure of the alloy was refined. With the increasing content of REM, the average diameter and area of inclusions in the alloy decreased at first and then increased. While the mechanical properties showed a trend of first increasing and then decreasing. An appropriate amount of stable REM inclusions could reduce the susceptibility of pitting corrosion and improve the pitting corrosion resistance of the alloy. The hyper DSSs with REM content in the range of 0.018–0.031 wt% have excellent mechanical properties and pitting resistance.

Acoustic black holes have good application prospects in the field of vibration and noise reduction. Based on engineering practice, this study proposes a systematic process method for the application of acoustic black hole structure in raft structure, which provides new ideas and references for improving the vibration isolation performance of floating raft system and reducing the level of ship vibration and noise. The influence law of each parameter on structural vibration and the recommended value range of each parameter are given, which provides support for the systematic method and process of the application of acoustic black holes in the raft structure. Then, the acoustic black hole process is applied to a floating raft system. According to the characteristics of the raft structure, an application scheme of the acoustic black hole in the raft structure is formed, and the vibration level drop of the floating raft vibration isolation system before and after the acoustic black hole is embedded, calculated, and analyzed. The changes further improve the vibration reduction and isolation performance of the raft system and effectively reduced the mechanical noise level of the ship’s cabin. Graphical abstract

In this study, different input parameters for electric discharge machining (EDM) are examined in order to revise the distinctiveness of EDM for machining aluminum-based hybrid metal matrix composites (MMCs). The versatility of hybrid aluminum MMCs makes them very popular and sought after in the automotive, aerospace, marine, and space industries. In this article, an optimized process parameter setting for hybrid MCCs machining with an EDM machine is determined that have silicon carbide (SiC p ) and graphite (Gr p ) particles added as reinforcement materials in varying amounts (Al–0.7Fe–0.6Si–0.375Cr–0.25Zn/10 wt%SiC/3 wt%Gr–MMC, Al–0.7Fe–0.6Si–0.375Cr–0.25Zn/15 wt%SiC/5 wt%Gr–MMC, and Al–0.7Fe–0.6Si–0.373Cr–0.25Zn/20 wt%SiC/8 wt%Gr–MMC). The stir casting method was used to prepare these hybrid aluminum MMCs (3 samples). A study of surface roughness (SR) and material removal rate (MRR) was conducted to examine the effects of dominant parameters. An experiment is planned using a central composite rotatable design (CCRD) of response surface methodology (RSM). It is possible to predict MRR and SR with 95% degree of accuracy by utilizing the quadratic model. Non-dominating Sorting Genetic Algorithm-II was employed to solve “mathematical models” for multi-objective optimization of output response characteristics. The scanning electron microscope (SEM) images of the tool and workpiece materials show that the recast layer has been formed on the tool face and the surface of the machined work-piece. Based on the results, it was determined that an optimal value of MRR (2.97 g·min −1 ) was obtained at 90 µs, 30 µs, 7.0 V, and 14 A as P on , P off , gap voltage, and peak current, respectively. As a result of the findings, the SR is reciprocally proportional to P on , and the SR is commensurate with P off . It was determined that the optimal value of SR (2.41 µm) could be attained at 30 µs, 52 µs, 6.0 V, and 12 A as the P on , P off , gap voltage, and peak current, respectively. For an optimal set of response variables, P on can be specified as 30 µs, P off as 30 µs, gap voltage as 6 V, and peak current as 14 A as process parameters for MRR and SR. The SEM images of the tool material and the workpiece material clearly demonstrate a recast layer formed on the tool face and the machined surface of the workpiece. The optical microscopy analysis reveals a uniform distribution of SiC p and Gr p particles in the Al–0.7Fe–0.6Si–0.375Cr–0.25Zn matrix. In addition to recast layers and machined surfaces, EDS analysis reveals the deposition of tool material on the surface of the workpiece. The composites fabricated may replace materials in many of these applications where “friction” is a significant factor.

Glass fiber-reinforced polymer (GFRP) composite materials are widely used in many manufacturing industries due to their low density and high strength properties, and consequently, the need for precision machining of such composites has significantly increased. Since composite materials have an anisotropic and heterogeneous structure, the machinability of composite materials is quite different from conventional materials. In the machining of GFRP composite pipes, tool wear, cracks or delamination, a rough surface, etc., many unwanted problems may occur. Therefore, GFRP composite pipes are difficult to process. To prevent such problems, it is very crucial to select suitable process parameters, thereby achieving the maximum performance for the desired dimensional integrity. In this study, through turning of GFRP composites with different orientation angles (30°, 60°, and 90°), the effects of cutting speed (50, 100, and 150 m·min −1 ), feed rate (0.1, 0.2, and 03 mm·rev −1 ), and depth of cut (1, 2, and 3 mm) on cutting force and surface roughness were determined. Then, with the use of these machining parameters, a model of the system for determining cutting force and surface roughness was established with artificial neural networks (ANNs). The ANN was trained using Levenberg–Marquardt backpropagation algorithm. It has been observed that the results obtained with the ANN model are very close to the data found in experimental studies. In both experimental and model-based analysis, minimum cutting force (44 N) and surface roughness (2.22 µm) were achieved at low fiber orientation angle (30°), low feed rate (0.1 mm·rev −1 ), and depth of cut (1 mm) at high cutting speeds (150 m·min −1 ).

This study examines the cyclic pullout behavior of two types of cold-drawn NiTi shape memory alloy fibers, such as paddled and crimped fibers. For this, two diameters of 1.0 and 0.7 mm are considered. The experimental cyclic pullout results show that the deep crimped fibers produce a higher maximum pullout resistance than the shallow crimped fibers. When heated, the shallow crimped fiber increases the diameter more significantly than the deep crimped fiber, whereas the fiber wave depth decreases more than the deep crimped fiber. Thus, the maximum pullout resistance increases for the heated shallow crimped fiber and decreases for the heated deep crimped fiber. The displacement recovery ratio (DRR) reduction with an increasing slip is significant for the fiber with a low anchoring bond. The high anchoring bond fiber also introduces a higher average DRR than the fiber with a relatively low anchoring bond. Under heating treatment, the average DRR increases due to the prestressing in the fiber due to the shape memory effect. However, the anchoring bond of the fiber is enough to produce prestressing in the fiber. The anchoring bond of the fiber and the prestressing also influence the energy dissipation (ED). The higher anchoring bond results in a higher ED value, and the prestressing in the fiber contributes more to the increased ED values.