Band 29, Heft 1

Compared with large size foam, pressure microfoam has the characteristics of a good pipeline transportation stability, good jet orientation, strong impact force, and strong ability to capture fine dust, which is more suitable for dust removal. The traditional foam preparation device has the disadvantages of high-pressure loss, poor foaming effect, and foam uniformity. To overcome the above shortcomings, the annular air supply vertical foam preparation device was proposed in the article. The foaming cylinder of the device adopts a vertical design to avoid the influence of uneven distribution of foam caused by gravity; the spiral nozzle is used to evenly spray the foaming liquid on the foaming mesh to increase the contact area between foam and airflow. The stainless steel wire mesh and cotton wire mesh are adopted to improve the reliability and durability of concave foaming mesh. The performance of the new device was obtained by the self-built experimental system. Finally, the field test shows that the conditions of the heading face could fully meet the requirements of the device for pressure water and compressed air, and the produced pressure microfoam can effectively control dust.

The effect of hydrothermal aging on the impact resistance of foam core sandwich panels is studied in this study. The sandwich panels with glass fiber-reinforced skins and polyurethane foam core were fabricated and then were treated with different hydrothermal aging conditions. The moisture absorption characteristic of the composite skins was evaluated. A modified Fickian formulation was proposed to predict the moisture absorption behavior of composite skins. The low-velocity impact resistance of the aged sandwich panels was determined at three different impact energies. The impact responses including contact force, deflection, and dissipated energy of the sandwich panels with and without hydrothermal aging were analyzed. The macroscopic and microscopic damage morphologies were observed by visual inspection and scanning electron microscope methods, respectively. The damage mechanism of the aged panels was revealed. Results indicate that the impact resistance of aged sandwich panels is degraded, and the performance degradation is larger with increasing aging temperature. Compared to the panel without hydrothermal aging, the reduction of the contact force is 35.69%, and the increase of the deflection is 71.43% for the aged panel at 70°C aging temperature. The fiber/matrix interfacial cohesive performance is degraded resulting from the hydrothermal aging.

Expanded polystyrene (EPS) concrete is a low-carbon green building material, which has the properties of thermal insulation, but its strength is not high at present. To improve the strength of EPS concrete, EPS particles were wrapped on the surface by magnesium phosphate cement, ultra-high performance concrete, and waterborne polyurethane, they were used to make concrete after aging, and then the strength and microproperties of concrete were tested. The test results show that the wrapping material form a shell structure on the surface of EPS particles; the hydrophilic property of the wrapped EPS particles and the uniformity of the concrete have been significantly improved; the contact between the wrapped EPS particles and the cement base has become more closer; the cube compressive strength of concrete is increased by 80–110%, the flexural strength of concrete is increased by 40–90%. The research results of this study are of great significance for EPS concrete used as structural material and fabricated lightweight wallboard.

In the present study, the resistance characteristics of Shanghai clayey soil-expanded polystyrene (EPS) mixture have been explored, using unconfined compressive and consolidation and rebound tests. EPS beads were mixed homogenously with clay soil in accordance with different mass ratios of beads to soil, that is, 0, 0.02, and 0.03%. Four particle sizes of EPS were used in the mixtures, that is, 0.5, 1, 3, and 7 mm, to reconstruct the samples. The experimental results indicated that (1) under the condition of unconfined compressive test, with the increase of EPS particle size, the compressive strength of reinforced soil increases significantly, but the compressive strength of reinforced soil decreases compared with the control sample, and it also decreases with high content compared to low EPS content; (2) under the consolidation and rebound test, compression index and rebound index of reinforced soil increased obviously compared with the control sample, but the compression modulus of reinforced soil decreases significantly; (3) in addition, the ductility of reinforced soil decreases with the increase of EPS particle size but increases compared with the control sample. At the same time, the stiffness of reinforced soil is much decreased compared with the control sample. Finally, the cause of deformation characteristics of reinforced soil was explained based on the feature of EPS material and the interaction between soil particles and particles of EPS beads.

In this article, a new technology of surface wrapping and strengthening of expandable polystyrene (EPS) beads is proposed. Three wrapping materials including magnesium phosphate cement (MPC), ultra-high performance concrete (UHPC), and water-borne polyurethane (WPU) were evaluated. Four groups of uniaxial compression tests of EPS concrete specimens were conducted: the failure process and the characteristics of the specimens were analyzed; and the complete stress–strain equation is proposed based on these analyses. The research shows that the EPS beads were strengthened by wrapping, and the axial compressive strength of concrete is increased by 50–75%; the concrete with EPS beads wrapped by MPC and WPU has obvious brittleness; the concrete with EPS beads wrapped by UHPC has axial compressive strength close to that of EPS concrete wrapped with MPC and WPU but has a larger ductility coefficient (150%), a larger toughness coefficient (50–90% larger), a higher energy dissipation coefficient (40% larger), and larger residual stress. The proposed stress–strain model is in good agreement with the experimental results, which can accurately describe the stress and deformation characteristics of EPS concrete under uniaxial compression and has good applicability. The discovery of this study provides background knowledge for the structural analysis and design of this kind of concrete; it provides a basis for selecting EPS concrete as structural materials.

A novel superabsorbent copolymer (SAP) was developed by grafting acrylic acid onto the pretreated soybean straw (PSBS) using gamma-ray irradiation. The structure of soybean straw, treated soybean straw, and SAP were characterized through Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TG), and scanning electron microscopy (SEM). The effect of irradiation dose, the dosage of cross-link agent, and the monomer ratio of the graft copolymer on the water absorbency of the SAP was investigated. The highest water absorbency of 1,489 g/g in distilled water and 56 g/g in 0.9 wt% NaCl solution was obtained, when the ratio of acrylic acid (AA) to PSBS was 6:1. This irradiation technique is superior to traditional methods with advantages such as less heavy pollution, low-energy consumption, and high-water retention performance. The outcome is deemed to open up new pathways to synthesize environmentally safe superabsorbents with applications in the food, pharmaceutical, and medical industries.

The line laser scanning thermography was applied for the defect detection and evaluation of composite material in this work, which was carried out by the following procedures. First, a novel contrast enhancement method by homomorphic technology was proposed and validated by a case study. Then, a specimen containing 12 prefabricated defects was detected using line laser scanning thermography and the obtained thermal image sequence and changeable temperature were analyzed. Finally, the defect area was obtained via such thermal image processing as contrast enhancement based on the proposed method, threshold segmentation and quantitative evaluation. The obtained results show that the composite material defects with a depth of less than 4 mm can be detected using line laser scanning thermography but that with a depth of less than 3 mm can be evaluated quantitatively with a small error less than 10%.

Cemented sand and gravel (CSG) is a new type of dam-building material. Aiming at the cumbersome process and long calculation time of traditional methods to invert the meso-parameters, a mesophase parameter inversion method based on Box-Behnken Design response surface was proposed. By constructing a response surface simulation test scheme with different inversion parameters (elastic modulus of aggregates, mortars and interfaces, and interfacial tensile strength), the stochastic aggregate model is used to complete the numerical simulation of the damage process, and different results are obtained. The equation between the response variable (stress at different loading times) and the independent variable (inversion parameter) was verified, and the rationality of the response model was verified; the action mechanism of mesophase parameters at different stages on the mechanical properties of the specimen was analysed. The test results are brought into the response surface model, and the meso-parameters are obtained by inverse analysis. The stress–strain curve obtained by numerical simulation with this parameter has an error of 1.1% at the peak stress and 3.27% at the peak strain. The accuracy is high, the number of test groups is much smaller than other conventional inversion methods, and has feasibility of application in CSG.

Through hot compression experiments at temperatures ranging from 603 to 723 K and strain rates ranging from 0.01 to 10 s −1 , the hot deformation behavior of a 0.5 wt% graphene nanoplatelet-reinforced aluminum (0.5 wt% GNP/Al) composite prepared by the powder metallurgy method was studied. The constitutive equations obtained by mathematical models and a neural network were evaluated. The deformation property of the composite can be better described by the Johnson–Cook (JC) constitutive model optimized by establishing a relationship between the coefficient and variables obtained in the hot compression test, with a correlation coefficient ( R ) reaching 99.97% with the average relative error of 0.37% (98.1 and 4.17%, respectively, before optimization). Compared with the JC model, the neural network has perfect calculation accuracy and whole-process effectiveness, providing expanded and more accurate constitutive equations for subsequent simulations and for building the dynamic recrystallization model of the composite. The dynamic recrystallization model, hot processing map, and EBSD results are in agreement with each other and indicate that the optimal strain rate and temperature range of the composite are 0.01–0.1 s −1 and 693–723 K, respectively.

In the existing composite four-rail electromagnetic launcher (CFREL), the armature and rail contact surface produces significant heat and bears considerable wear, thereby reducing the potential amount of electromagnetic thrust to be generated. To eliminate the damage caused by the thermal effect of the rail contact surface and to meet the electromagnetic thrust demand of the load, a CFREL is proposed. The proposed CFREL model is constructed, and the launcher’s electromagnetic characteristics are simulated and compared using the finite element method. The current density, distribution of magnetic flux density, and electromagnetic thrust characteristics are analysed. The results showed that the proposed CFREL reduced the maximum current density of the contact surface and effectively eliminated the current concentration of the armature and rail contact surfaces. Effective magnetic field shielding is realised with a larger range, which can better meet the requirements of the intelligent load’s magnetic field environment and provide stronger electromagnetic thrust for the load, hence solving the problem of insufficient thrust.

A graphene hybridizing polyurethane/polyethyl methacrylate (GR-PU/PEMA) damping composite was synthesized using the sequential interpenetration method. The effects of the graphene content and the microphase separation structure on the damping properties, thermal stability, and mechanical properties have been studied in detail. The dynamic mechanical analysis indicated that graphene could improve the damping peak value of PU/PEMA, and the microphase separation structure could be beneficial for broadening the damping temperature range. The damping peak (tan  σ max ) of PU/PEMA hybridizing with 0.5 wt% graphene reached 0.82, and the temperature range of the loss factor (tan  σ ≥ 0.3) was expanded to 88.3°C. Analysis of scanning electron microscopy, transmission electron microscopy, and small-angle X-ray scattering reveals that graphene is uniformly dispersed in the polymer matrix, and the composite with interpenetrating polymer network (IPN) shows more microphase separation structures. Fourier transform infrared analysis indicated that there is strong interaction between graphene and IPN matrix. Furthermore, the addition of graphene improved the mechanical properties and thermal stability of composites.

Based on the thick-wall cylinder theory and composite material mechanics, the stress distribution model of the CFRP shaft tube and metal shaft head has been established, and the relationship between the layup parameters and the value of interference on the maximum assembly force and failure torque in the interference fit joints of the CFRP shaft tube and the metal shaft head is deduced. Combining the three-dimensional finite element analysis model with experimental data, the result shows that the layup angles of the CFRP shaft tube have a greater influence on the joint connection performance than the layup sequence, and the larger the layup angle, the better the joint assembly performance while keeping the value of interference constant. The maximum assembly force and failure torque of the interference fit joints increase linearly while the value of the interference amount increases when the layup parameters are constant.

In this article, the pipeline design is introduced. The new pipe structure is made of new fiber metal laminates with the unidirectional composite and sheet metal (Ti–Ni alloy). Many pipe structures are in the heating environment such as in or around the engine, which will also cause the heating-up structure. If the shape memory alloy (SMA) fiber is added to the composite lamination, it can be seen that with the increase of temperature, the stiffness of the structure is increased and so is its frequency. The changed frequency of the structure can avoid the excitation frequency in this way, which effectively inhibits the resonance. In dynamic analysis, it can also show that the pipeline with the SMA fiber has good performance for vibration reduction and noise attenuation. Additionally, the convergence of the meshing model and the effect of the thickness of the SMA material on vibration and noise reduction are also discussed.

Composite sections are found to be a novel technique in modern day scenario of construction. This stands tall than the ordinary and conventional type of constructions. Columns as a structural element play a vital role in structural frame. This research comments on the behavior of composite columns. The main objective of this study is to analyze the behavior of steel-encased concrete composite columns as experimentally under axial compression and the mode of failure under ultimate failure and yield point. The steel-concrete composite system combines the formability and rigidity of reinforced concrete with the ductility and strength of structural steel to meet the demand for earthquake-resistant constructions. Three specimens were chosen for this study: one was a composite column, the other two were ordinary RC columns and structural steel columns. The raw materials' natural properties are assessed. As a result, material testing for cement, fine aggregate, and coarse aggregate was completed, as well as a concrete mix design. A comparative analysis of the local and post-local buckling behavior of different composite sections has been studied and the column sections have been designed according to Eurocode 4 (ENV 1994) to determine the plastic resistance of the section. These three specimens underwent compression test and the results are tabulated and compared. The corrosion resistance and fireproof nature (resistance to fire at higher temperatures) that are transmitted into the member are related to the steel being encased within the concrete. These are the two major drawbacks of any steel construction combined with an earthquake-resistant structure. Rather than a traditional steel construction, earthquake structures benefit from this type of load handling capabilities. The portion can be used before it completely collapses if proper design factors are taken into account.

This article used the strip element method to study the dynamics problems of the functionally graded plate with variable gradient parameters under the harmonic loads. The dynamic model of the functionally graded plate is established by using the strip element method, the rationality and accuracy of the theoretical results are verified by finite element method, and the displacement response under different gradient parameters is also calculated. The results show that under the different gradient parameters, the displacement varies harmonically with time, and with the increase of gradient parameters, the fluctuation period of displacement with time increases continuously, and the displacement peak also gradually increases. The displacement along the thickness direction also shows the harmonic form. Through comparison, it is found that the gradient parameters have a greater impact on the dynamic response for the functionally graded plate; with the increase in the gradient parameters, the displacement response also increases, but the displacement response trend slows down.

A novel separating device, Inertial particle separator (IPS), has been developed recently to separate solid particles and to protect the turbine engine from particle erosion damage. Herein first, an advanced model based on IPS was proposed to investigate the deformational behavior of deformable particle separator, and to meet the higher requirements of sand discharge and pneumatic demand, which are operated under hostile working conditions or environments and severe climate conditions. We established a three-dimensional (3D) nonlinear finite element analysis (FEA) model of bump consequently, which was the core of centerbody. The essential material parameters of the FEA model were obtained via experimental data (tensile testing). By comparing the influence of these factors (pressure and laying angle), the deformational behavior of the centerbody was discussed. Finally, based on the simulation results with the experimental data (Schlieren testing), the model was found to perform with high reliability and accuracy, demonstrating the great capability in precisely predicting the deformational characteristics of the bump under practical working environments.

The effect of carbon fiber Z-pin on carbon fiber composite under moisture condition with and without flexural load was investigated in this work. Moisture absorption property and crack propagation of carbon fiber reinforced epoxy matrix composite and Z-pinned composite were evaluated under moisture only and moisture-coupled load conditions. The moisture property was evaluated by moisture content and microscopic morphology obtained using X-ray micro-computed tomography (X-ray μCT). The microstructures inside composites and Z-pinned composites after moisture conditions and three-point flexural test were detected using X-ray μCT and optical microscope. It illustrates that the moisture content of Z-pinned composites is higher due to the rich-resin pocket brought by the implantation of Z-pin. The cracks are obvious inside Z-pinned composites after moisture-coupled load conditions. It is attributed to the implantation of each pin which is the weak point for stress concentration and crack formation. Failure morphologies on the surface of composites and Z-pinned composites are different under different moisture conditions. Less macro-interlayer cracks are detected on the surface of Z-pinned composites, and plenty of microcracks initiating from pins are observed.

The water-lubricated bearing is mainly installed at the stern of the ship to support the rotation of the main shaft of the ship, which is an important component of the ship’s power plant. The rubber stave of the water-lubricated bearing acts as an elastic body, which can effectively suppress the rotational vibration of the rotating shaft and improve the shaft alignment effect. To monitor the operational status of the water-lubricated bearing at the stern of a ship, a design method of smart rubber stave for water-lubricated bearings is proposed in this article. According to the structure of the rubber stave, the packaging and protection form of the optical fiber, the forming process of the rubber stave, and the mechanical analysis were carried out to determine the distribution design principle of the fiber Bragg grating (FBG) in the rubber stave. Then, FBGs were packaged, protected, and implanted with an uneven distribution into the rubber stave to achieve force sensing in the bearing. With reference to the force state of the water-lubricated bearing during shipbuilding and ship operation, various types of condition monitoring tests were conducted on the smart rubber stave using an elastomer testing machine, which were to analyze the effects of load sizes, frequencies, and ambient temperatures. The tests showed that the FBGs in the rubber stave could monitor the static and dynamic loads of the bearing under the seawater environment or inland water environment below 30°C. This method can be used for the smart designing and online load condition monitoring of water-lubricated bearings.

Modern materials science has faced the problem of reducing the cost of raw materials and labor costs while obtaining basic construction materials (cement concrete) with increased performance properties. The article aims to substantiate the use of carbon nanotubes of fly ash as a cement concrete modifier to be reasonable for solving the above problem. Experimental studies are carried out using standard and special methods. The technological properties of cement concrete mixtures are determined in accordance with the European and American standards. The study investigates the impact of carbon nanotubes of fly ash on the structure and properties of the mineral Portland cement binder. The article provides the examination of structural and rheological characteristics of nano-modified cement concrete mixtures. The effect of a carbon nano-modifier on the strength, deformation, and performance properties of cement concrete mixtures is defined. As a result, the optimal composition of nano-modified cement concrete mixture has been developed that meets the criteria of concrete compressive strength and flowability. Positive research results allow determining the areas of application of the obtained compositions in civil engineering.

This article was designed with a plurality of impact tests of three-dimensional four-directional braided composites, and the impact response of specimen impacted by a circular punch was studied. Ultrasonic C-scanning was used to detect the internal damage area to study the damage propagation process under multiple impact loads. The finite-element software ABAQUS was used to model the meso-structure of three-dimensional four-directional braided composites. Based on material characteristics, the three-dimensional Hashin damage criterion was used for the fiber bundle, and the maximum stress criterion was used for the matrix to judge the material damage. Combined with test and simulation results, the failure mode and damage evolution process of the specimen under multiple impact loads were studied. The results showed that the impact resistance of the three-dimensional woven composite material is affected by the braided angle. The larger the braided angle of the specimen, the better the impact resistance. The damaged area of the large braided angle material expanded to the periphery, and the damaged area of the small braided angle material was primarily developed in the longitudinal direction. The failure modes of the specimen during the impact process were primarily a longitudinal tensile failure of fiber bundles, transverse tensile failure and transverse compression failure of fiber bundles and matrix.

Honeycomb materials are widely used across engineering fields. The use of honeycomb sandwich structures as energy dissipation and impact protection materials for reinforced concrete components in the field of civil engineering is a novel concept. Therefore, it is of great significance to study the energy absorption characteristics, dynamic response theoretical model, and collapse energy dissipation theory for the use of honeycomb sandwich structures as protective materials. Based on the large-scale low-speed pendulum impact test and the corresponding finite element model, this study establishes an ideal model for the honeycomb sandwich panel under the impact of a square flat head and gives the corresponding theoretical derivation. At the same time, it puts forward a method to estimate the energy consumption and dynamic crushing distance based on the energy consumption theory angle of the covering layer.

To comprehend the fatigue failure mechanism at the fiber discontinuity in fiber-reinforced composites, it is necessary to evaluate the local mechanical behaviors. The fatigue strength depends on the stress distribution at the fiber inclusion corner. An improved advanced finite element method (IAFEM) is proposed for the stress intensity factor (SIF) analysis at the fiber inclusion corner. In the IAFEM, the element stiffness matrix of singular inclusion corner element (SICE) is obtained, and the singular elastic field at the tip of the fiber inclusion is determined. The effects of load direction, fiber distribution, fiber geometry, and material properties on SIFs are analyzed numerically using the IAFEM. The difference in stress field distribution between two-dimensional and three-dimensional fiber inclusions is discussed. The IAFEIM and calculation results can provide reference for fatigue strength analysis and preparation of composite materials.

This article describes work concerning the compressive properties in hygrothermal environment of three-dimensional (3D) five-directional braided composites. Hygrothermal aging tests at temperatures of 40, 60, and 80°C and compression tests were carried out on the specimens with three braiding angles of 15, 25, and 35°. The surface morphologies of the samples taken using scanning electron microscope before and after the hygrothermal aging test were used to analyze the influence of the hygrothermal environment on the internal structure of braided composites. The experimental results indicate that the hygrothermal environment has a more influence on the specimens with a braiding angle of 15°, and the greater the moisture absorption percentage, the lower the retention ratios of compressive strength and modulus. Compared with room temperature, the compressive strength and modulus of specimens with a braiding angle of 15° reduced by 72.2 and 82.7% as the water bath temperature increased from 40 to 80°C. Moreover, the failure mechanisms of 3D five-directional braided composites in the hygrothermal environment were analyzed.

In this work, we studied the failure mechanism of steel–polypropylene hybrid fiber reinforced concrete (HFRC) at the mesolevel. The uniaxial tensile test of HFRC was simulated using ABAQUS finite element analysis software. Then, the relationship between the mesoscale failure process and the mechanical properties was analyzed based on the simulation results. The results showed that the cracks first appeared in the interfacial transition zone and then gradually propagated into the mortar elements and intersected with adjacent cracks, forming major macroscopic cracks. According to the crack evolution process, the incorporation of steel fibers and polypropylene fibers changed the concrete crack expansion paths and served to inhibit crack expansion. Furthermore, the increase in the hybrid fiber volume had a positive effect on the mechanical properties, and the steel fibers dominated in providing reinforcement compared to the polypropylene fibers.

The uniformity of the monofilament diameter plays a key role in the performance of continuous filament yarns and their subsequent products. However, traditional methods for measuring fiber or filament diameters focus on estimating the arithmetic mean data, and only part of the diameter data can be obtained. Additionally, most of these traditional methods require complex sample preparations, such as by making cross-sectional slice samples. This study intends to present a simple method for measuring almost all of the monofilament diameters in a single yarn. It is not necessary to make slice samples. After the yarn sample or fabric sample is taken and prepared, synthetic laser images can be obtained directly by scanning the cross section of the sample with a 3D laser scanning confocal microscope. According to the results of many experiments, more than 90% of the monofilament diameters of a single yarn can be measured. The result also shows that the difference in the diameter data between the traditional method and the synthetic laser imaging method is less than 2%. This method presents the differences between the majority of monofilament diameters, and the yarn clustering property can be evaluated by the sum of the monofilament diameters and the yarn cross-sectional area.

This article focuses on an experimental study of the flexural response of a polymer composite laminate (CL) reinforced with a plain weave carbon fiber fabric. The aim of this research is to investigate the effect of the span length-to-specimen thickness ratio on the flexural properties of the selected CL. The laminate specimens were tested in the three-point flexure configuration for span length-to-specimen thickness ratios of 16, 20, 32, 40 and 60. The investigations were carried out to identify on-axis and 45° off-axis flexural responses of the CL. For this reason, two types of rectangular flat specimens were prepared, differing in reinforcement orientation relative to the support span. Using the special code, the lay-up of the specimens was designated as [(0/90)F] 8 and [±45 F] 8 , respectively. It was found that the flexural modulus and flexural strength of the specimens depend on the span length-to-specimen thickness ratio. Despite testing the same CL, the response of the specimens to the change in the span length is different. In addition, it was concluded that the span length also has a significant influence on the final failure of the laminate specimens.

In this article, aiming at the problems of low mechanical properties and the unstable structure of the binder in inorganic artificial stone, performance improvements were studied. The effects of 12 materials of blast-furnace slag (BFS), fly ash (FA), and kaolin on the properties and microstructure of inorganic binders were systematically studied and analyzed. As a result, the compressive strength of BFS-2, FA-1, and FA-2 binder was increased by 10.0, 6.0, and 1.5%, and the flexural strength was increased by 44.8, 79.2, and 1.3%, respectively. It was worth noting that BFS and FA could effectively promote hydration reactions due to active materials and boost the growth of C–S–H and CH, leading to the inorganic binder forming a stable structure. Thus, this work systematically designs and prepares inorganic binders with high compressive strength and excellent flexural strength. This reveals how inorganic materials affect the properties of inorganic binders on the microstructure and offer a new idea for the development of this field.

Carbon/silica composite (C/SiO 2 ) aerogels were synthesized by using tetraethyl orthosilicate, 3-aminopropyltriethoxysilane, trimethylchlorosilane, resorcinol as the silicon and carbon sources, and ethanol as solvent, via the sol–gel process followed by supercritical ethanol drying and thermal treatment. The influence of thermal treatment process on the structure of C/SiO 2 composite aerogels was analyzed mainly and measured by Fourier transform infrared spectrometer, X-ray diffraction and nitrogen adsorption–desorption analysis. The results showed that the optimum thermal treatment temperature of C/SiO 2 composite aerogels was 1,300°C. With the increase in the thermal treatment time, the linear shrinkage of the composite aerogels increased gradually, and the pore volume, average pore diameter and specific surface area of the composite aerogels increased first and then decreased.

To improve the mechanical properties and corrosion resistance of the hydraulic column in the mine, a semiconductor fiber-coupled laser was used to laser-clad iron-based alloy powder on a 27SiMn steel substrate (SUB). The microstructure, mechanical properties, and corrosion resistance of the obtained cladding layer (CL) were studied based on experiments. Results show that equiaxed grains at the top of the CL are fine and tightly arranged. Compared with the SUB, the CL average microhardness is increased by 0.3 times, the average friction coefficient is decreased by 0.12, and the wear amount is significantly reduced. The bonding strength between the CL and the SUB is good, and the tensile strength is increased by 10.82%. Compared with the SUB, the mechanical properties and corrosion resistance of the CL are better. The research has an important guiding significance for the practice of hydraulic column repair and strengthening engineering.

In order to evaluate the effect of rare earth Y 2 O 3 on the wear and corrosion properties of WC–Ni composite coatings, X-ray diffraction, scanning electron microscopy(SEM), electrochemical polarization curve, electrochemical impedance spectroscopy (EIS), and friction and wear tests were used to analyze the metallographic structure, corrosion characteristics in simulated seawater and friction and wear principle of the composite coatings. Results of SEM revealed that the microstructure of the Y 2 O 3 added coatings was refined with the grains changing smaller and the impurity disappearing. The EIS results proved that the addition of Y 2 O 3 brought a positive influence on the corrosion resistance by reducing the capacitance and increasing the R f and R c . The hardness of the coatings with Y 2 O 3 addition tends to be smooth without wild fluctuation, and the coating with 0.5 wt% Y 2 O 3 owned the hardness values reaching 850 HV. With the addition of rare earth elements, the coefficient of fiction values decreased, reaching the lowest (0.3418) at the content of Y 2 O 3 of 0.5 wt%. The surface of the coating without Y 2 O 3 appears grooved due to the abrasive wear; the coatings with Y 2 O 3 did not suffer serious wear and tear. The coating with 0.5 wt% Y 2 O 3 exhibited the best corrosion resistance and wear resistance properties in all the specimens.

The low-velocity impact and compression after the impact of the composite stiffened panels were carried out after damp-heat aging. The experimental results show that reinforcing the ribs can enhance the impact resistance of test pieces after damp-heat aging. After impacting, the specimens were tested in an axial compression. The results show that the ultimate bearing capacity of the specimen is also affected by different located positions of the impact and different aging times. Compared with the intact specimen, the ultimate load-bearing capacity was reduced to 16.83, 12.10, and 17.10% with the specimen aging for 0, 45, and 90 days, respectively, while the impact position located at the intersection of longitudinal and transverse bars has the greatest influence on the damp-heat aging of specimens.

SiC fiber-reinforced SiC matrix composites (SiC f /SiC) with 2D woven fabric as preform were tested under compression with in-situ X-ray computed tomography. The microstructure and damage evolution of the material under continuous loading levels were accurately revealed by image reconstruction of CT data. There were inhomogeneous pores in SiC f /SiC composite because of the un-uniform fiber distribution in the preform. The result also showed that 2D woven SiC f /SiC composite had obvious non-linear characteristics by its compressive load–displacement curve, and the damage modes included transverse matrix cracking, interlayer cracking, longitudinal matrix cracking, and fiber bundle fracture. Matrix cracking tended to occur near the pores or holes of the material, and the number of longitudinal cracks was relatively high compared to the number of transverse cracks.

Glass Fiber Reinforced Polymer (GFRP) is widely used as aerospace material requiring high specific strength, specific stiffness, and excellent mechanical and chemical properties. To apply the already approved composite materials to other processes, an equivalency test that compares the mechanical properties of the composite materials based on the database is required. For the successful completion of the equivalency test, it is important to control the factors affecting the mechanical properties. The resin content and density of the specimens are manufactured differently according to the process. The effect of these factors on the change of mechanical properties required for equivalency qualification has not been sufficiently reported. In this study, an equivalency test was performed on the GFRP applied to the aircraft radome based on the procedure of the equivalency test and acceptance test proposed by the National Center for Advanced Materials Performance. The causes of problems occurring between equivalency tests were analyzed. It was confirmed that the resin content, density, and voids of the specimen affect the mechanical properties. As the resin content decreases, the density and voids were controlled, and it was confirmed that the average strength and modulus increase by 13.12 and 6.78%, respectively. The equivalency qualification was completed by applying an improved process in which these factors were controlled.

The study aims to optimize the composition of the main composite, the components of which, in their joint presence, make it possible to obtain the most significant positive synergistic effect. The authors of this article used the fibers of fly ash from thermal power plants as a finely dispersed component added to the crushed stone sand mixture. The result of the study was a high-strength corrosion-resistant material consisting of a crushed stone sand mixture (CSSM) with the addition of the fibers of fly ash. The authors applied the thermogravimetric and standard methods to study and determine the performance and strength characteristics of the obtained material. The combined effect of a complex organic-mineral modifying additive and the cement with the fibers of fly ash provided a compacted and reinforced structure of cement stone. An optimal binder composition was developed, consisting of cement and fiber of fly ash. The authors of this article examined the physical-mechanical and structural-mechanical properties of a CSSM of fine-grained concrete reinforced with a complex additive of cement, fibers of fly ash, and a superplasticizer. The study also provided technological solutions for manufacturing a functional mixture of fine-grained concrete based on the developed complex organic-mineral additive.

This article investigates the sliding wear behavior of ZTA (zirconia toughened alumina) particle (ZTAp)- and NbC (niobium carbide) particle (NbCp)-reinforced Fe60 matrix composites (ZTAp–NbCp/Fe60). ZTAp–NbCp/Fe60 was produced through vacuum sintering and tested on an M-2000 wear-testing machine. As revealed by the results, the wear loss increased with the increase in rotation speed and load. Abrasive wear occurred in the mild wear region; adhesive wear and serious abrasive occurred in the moderate wear region; and fatigue wear and ZTAp broken occurred in the severe wear region. According to the aforementioned conclusions, a more clean and intuitive wear mechanism diagram was established. In the process of wear, ZTAp was well combined with the matrix, and there was no crack at the interface. Meanwhile, in the wear process, ZTAp could block furrow, weaken the wear of the micro-convex ring, and improve the sliding wear performance of the composite material.

The characteristic of interphase has a significant influence on the macroscopic performance of carbon fiber-reinforced plastics (CFRP). To investigate the effect of interphase on composite elastic modulus, a representative volume element (RVE) of unidirectional CFRP with inhomogeneous interphase was established. Based on the bridging model, a theoretical calculation method of composite elastic modulus was given. The elastic modulus of T300/BSL914C composites was obtained by the theoretical method. Results are in good agreement with the finite element method and experimental data. Four types of interphase models were given including inhomogeneous transversely isotropic, inhomogeneous isotropic, homogeneous transversely isotropic, and homogeneous isotropic. The results demonstrate that interphase type has an influence on the prediction of CFRP composites’ elastic modulus. With the increase of thickness, the prediction error of elastic modulus caused by interphase type increases rapidly. Furthermore, the relationship between composite elastic modulus and interphase thickness and stiffness is analyzed. With the increase in thickness, the changes in shear modulus G 12 and Poisson’s ratio ν 23 are more evident than in other elastic properties, and with the enhancement of interphase stiffness, the increase of G 12 is the most significant.

The aim of this article is to investigate the failure and enhancement mechanism of bolt-strengthening glass fiber-reinforced polymer (GFRP) T-joints under quasi-static tension. One-step molding technology based on the vacuum-assisted resin infusion process is carried out to fabricate the GFRP T-joints structures. Then, a special fixture and constraint condition are set up to take the quasi-static tensile test with high reliability. Moreover, it is demonstrated that the T-joints structures may decrease their bearing capacity, resulting in interlaminar delamination at the corner region. Further, to strengthen the T-joints, the bolts are employed to effectively prevent the initiation and propagation of interlaminar delamination in the tensile loading. At the same time, as their enhancement and failure mechanisms are revealed deeply, the strengthening method is optimized as well.

Objective To prove that calcium alginate beads can be used as scaffolds during in vitro culture. Methods Mouse preosteoblastic cells (MC3T3-E1) were encapsulated in calcium alginate hydrogel beads. The Cell Counting Kit-8 (CCK-8) assay was used to assess cell viability at 2, 5, 8, 11, 14, and 21 days. Calcein-AM and propidium iodide (PI) were employed for live/dead staining. Results MC3T3-E1 cells were alive on day 21 and had the highest viability on day 14. Conclusion MC3T3-E1 cells could be encapsulated in calcium alginate hydrogel beads and cultured. Calcium alginate hydrogel beads can be used as scaffolds for three-dimensional in vitro culture.

A ceramic–steel composite structure which consists of Si 3 N 4 ceramic bars and twinning-induced plasticity (TWIP) steel matrix was prepared using lost foam casting method. Microstructural analysis indicated that the ceramic bars and TWIP steel matrix can form favorable and tight interface. A comparison of mechanical properties between the composite structure and TWIP steel matrix was made. Results show that the bending strength increased from 388 to 805 MPa compared with TWIP steel matrix. The influence of annealing heat treatment on the bending strength of this new type of composite structure was also discussed.

A theoretical framework that underlies an accelerated testing method for unidirectional (UD) composites is proposed in this article, based on the continuum damage mechanics and time–temperature superposition. By the way of demonstration, it has been applied to problems involving constant strain rates and fatigue loading conditions. The damage evolution law for the matrix of composites was constructed using the Weibull distribution of defects, which will develop into cracks as a result of deformation. In conjunction with the Wiechert model, the theoretical framework formulated here is capable of capturing the mechanical behaviour of UD composites. Demonstration and initial verification of this acceleration method were carried out through experiments. This work can provide theoretical and technical support for the durability verification and the evaluation of the high cycle fatigue performance of composite structures.

Graphite flakes/Al composites are promising thermal management materials due to high thermal conductivity (TC) in basal plane orientation, matched coefficient of thermal expansion, and good machinability. In this article, the acoustic mismatch model and the effective medium approach are applied to predict the influence of different interfacial coatings on the interfacial thermal conductance (ITC) and the TC of graphite flakes/Al composites, respectively. With the increase in the thickness of interfacial coatings, the ITC and the TC of graphite flakes/Al composites decrease. For the composites with Ni, Cr/Cr 7 C 3 /Cr 3 C 2 , Si/SiC, Ti/TiC, WC, and Mo/Mo 2 C coatings, the ITC is sensitive to coating thickness. In order to obtain ideal TC of graphite flakes/Al composites, the thickness of the coatings should be controlled below 1 μm. It is reasonable that the TC of the graphite flakes/Al composites increases as the volume fraction of graphite flakes increases. The TC of the graphite flakes/Al composites increases with the ITC and changes slowly when the ITC increases to a certain extent. Si/SiC and WC coatings are proposed to be the most promising candidates to improve the thermal performance of graphite flakes/Al composites.

Needle-punched (NP) carbon/carbon composites (CCCs) are widely used in structures re-entering the atmosphere of aerospace, thanks to their excellent mechanical properties. They are easily oxidized at high temperatures with atmospheric oxygen. The oxidation behavior is influenced by the process of heat conduction. In this study, longitudinal and transverse heat conduction in micro- and mesoscale models of CCCs was investigated. It was established that the heat transfer interface of a fiber bundle demonstrated peak-like morphology, while the punching structures of composites slowed down the process of heat conduction. Oxidation behavior of NP CCCs was predicted with a fractional Brownian motion strategy. It was found that the oxidized fiber bundles formed “bamboo shoots” morphology due to different oxidation rates of the matrix and fibers. Stochastic oxidation behavior was successfully described with this fractal strategy.

The low-velocity impact finite element model of the carbon fiber-reinforced composite grid sandwich structure was established by ABAQUS. Its panels and grid are both carbon fiber-reinforced composite laminates. The constitutive relation of composite laminates is written into the VUMAT user subroutine using the Fortran language. Simulation of intralaminar failure behavior of composite laminates using the three-dimensional Hashin failure criterion. The quadratic stress criterion and the B-K energy criterion were used to simulate the interlaminar failure behavior, and the delamination damage of the composite panel and the interface debonding damage were simulated. The finite element models of four different types of composite grid sandwich structures, including quadrilateral configuration, triangular configuration, mixed configuration, and diamond configuration, were established. The influence of the single grid width and the height of the grid on the impact resistance of each composite grid configuration was studied. Compared with other geometric configurations, triangular grid sandwich structure provides the best energy absorption characteristics, and T-6-10 has the highest fracture absorption energy (15816.46 mJ). The damage propagation law of carbon fiber-reinforced composite grid sandwich structure under impact load is analyzed.

Compo-casting method is one of the popular techniques to produce metal-based matrix composites. But one of the main challenges in this process is un-uniform spreading of reinforced subdivisions (particles) inside the metallic matrix and the lack of desirable mechanical properties of the final produced composites due to the low bonding strength among the metal matrix and reinforcement particles. To remove these difficulties and to promote the mechanical properties of these kind of composites, the accumulative press bonding (WAPB) technique as a supplementary technique to heighten the mechanical and microstructural evolution of the casted Al/TiO 2 composite bars was utilized as a novelty in this study. The microstructure evolution and mechanical properties of these composites have been compared with various WAPB steps using tensile test, average Vickers micro hardness test, wear test and scanning electron microscopy (SEM). The SEM results revealed that during the higher APB steps, big titanium dioxide (TiO 2 ) clusters are broken and the TiO 2 particles are distributed uniformly. It was shown that cumulating the forming steps improved the mechanical properties of the composites. In general, combined compo-casting and APB process would consent making Al/TiO 2 composites with high consistency and good microstructural and mechanical properties.

Melanin comes from a wide range of sources. It can be isolated and characterized from some plants, animals and microorganisms, and can also be simply polymerized by dopamine. It has many biological properties such as antioxidant, ultraviolet shielding and bacteriostasis. Based on the above characteristics, the addition of melanin to film-forming materials can improve the relevant physical properties and functional properties of the film. In this article, the structure and properties of melanin were briefly introduced, and then the advantages and related research progress of melanin as a functional filler in the field of composite film were summarized.

As an environmentally friendly, green, and low-carbon construction material, cemented sand and gravel (CSG) dam is widely used in civil engineering and water conservation projects in China. This study describes the progress of research on CSG dams (materials) in recent years, including the progress of engineering related to cemented gravel dams, the static, dynamic, and thermodynamic properties and intrinsic structure models of dam building materials, the static, dynamic, and temperature field analysis of dam structures, and the design of dam profiles; and on this basis, it proposes the direction of further research and development of cemented gravel structures, which will provide research for new cemented gravel structures in China. Structure design, old and diseased engineering structure removal and reinforcement, and safety assessment to provide research status and new ideas.

In order to enhance the service life of special complex shaped workpieces under severe working conditions, a new coating preparation process, namely, easy-coating and sintering technology, has been proposed. In this study, the feasibility of preparing Co-based coatings on 38CrMoAl substrates using the easy-coating and sintering process was investigated, and the microstructure and properties of the Co-based coatings were studied. By optimizing the parameters of the sintering process, the prepared coating is dense, and the coating forms a good metallurgical bond with the substrate with few pores, but no other defects. As the process has good applicability to the surface of complex-shaped parts, the inner wall of small serpentine tubes and large thicknesses, and is low-cost and easy to operate, the easy-coating-sintering process has great application prospects.

The aim of this study is to investigate an approach to the electricity conductivity of nano-graphite in concrete by experiments, and different doses of nano-graphite have a different influence on the electrical conductivity of the whole structure. In this research project, the compression test was carried out on a 50 mm × 100 mm cylinder using a Baldwin machine and a digital multimeter to measure the conductivity. To find out the patterns of how different nano-graphites influence the properties of concrete structures, multifarious percentages of nano-graphite’s content are employed for testing both the electrical resistivity and compressive strength. These results are important to predict and prevent structural failure and fill the gap in nano-graphene concrete research, thereby saving human lives and significantly reducing the structures’ cost of maintenance and repair.