Volume 24, Issue 5

The work presented in this paper addresses various techniques for automated preforming of profiles for structural components made from fiber-reinforced polymer composites. After reviewing the existing preforming techniques, a quantitative comparison with respect to two different application scenarios is presented. The technology comparison is conducted individually for the two application scenarios by means of a weighted decision matrix approach incorporating a list of technical and economic criteria. The preforming costs are derived by means of a bottom-up cost estimation model and are incorporated in the technology comparison.

In the present work, functionalized copper nanoparticles (FCuNPs) were grafted onto flax fibers, and the effects on the tensile properties, bonding strength to an epoxy resin, as well as the properties of the flax fiber-epoxy model composites were investigated. The copper nanoparticles were synthesized at ambient temperature by a chemical reduction method. The reduction of solution of copper chloride salt in the polyvinylalcohol medium was done by using sodium borohydrate. Ultraviolet-visible spectroscopy, transmission electron microscopy, and X-ray diffraction studies were used to characterize the size of the synthesized particles. The synthesized copper nanoparticles were applied to saturate the unidirectional flax natural fibers, whose surfaces were previously tailored with the cationic agent triethylammonium chloride. A remarkable improvement in the tensile strength by 75% and modulus by 50% for FCuNPs grafted flax fibers was found. Thermo-mechanical properties of the flax fiber reinforced epoxy composites were studied using DMTA. Finally, the anti-microbial analysis for composites was also conducted against Aspergillus niger spores, and enhanced anti-microbial performance was observed for treated fiber-based composites.

Polyethylene (PE) membrane has been extensively used in microtransport areas due to its high porosity, chemical stability, and easy processability. However, pure PE membrane shows poor thermomechanical properties. In this paper, silicon dioxide (SiO 2 ) was used to composite PE membrane in nanogel format. The morphology of the combination and surface layer was demonstrated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SiO 2 gel on membrane was analyzed by Fourier transform infrared (FTIR), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The effect of the SiO 2 gel on the thermomechanical properties of PE membrane was investigated in terms of thermal shrinkage, thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). The results showed that the SiO 2 gel effectively reduced the thermal shrinkage of PE membrane by 47.25% without increased crystallinity, and the coating layer slowed down the decomposed speed of PE membrane at melting point. Comparison tests showed that SiO 2 gel enlarged the storage modulus and Young’s modulus of PE membrane. Tensile test revealed that the maximum load on pure PE and PE composite membranes at the yield point were both decreased with the increased temperature.

Ternary blends based on polyamide 6 (PA6)/acrylonitrile-butadiene rubber (NBR)/polycarbonate (PC) were prepared by melt compounding via extrusion process. The effect of organoclay (OC), compatibilizer, and blend ratio was investigated on structural and mechanical properties of the blend. The effect of OC and compatibilizer studied on crystallization temperature, melting temperature, and crystallinity of PA6/NBR/PC ternary blends was studied by differential scanning calorimetry. Improvement in the crystal structure of compatibilized blend compared to unfilled blend was observed by polarized optical microscope. Dispersion of OC into PA6/NBR/PC ternary blends was done by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy (SEM)/energy-dispersive X-ray. The results confirmed the exfoliation of OC particles into the polymer matrix. The improvement in yield stress and tensile modulus of the ternary blend was observed in the presence of OC. The impact strength showed an increase using NBR-glycidyl methacrylate-grafted (g-GMA) to prepare compatibilized PA6/NBR/PC ternary blend.

Silicone rubber (SiR) is extensively used in outdoor insulation and other applications. However, like other polymers, SiR also degrades and lessens its performance in the exposition of environmental stresses. Nanofillers improve the aging behavior of polymeric insulating materials. To investigate the effect of nanosilica on the aging behavior of SiR, we fabricated nanocomposites of SiR with 2.5 wt.% nanosilica (SNC-2.5) and 5 wt.% nanosilica (SNC-5) by mechanical mixing and ultrasonication method. The prepared samples were subjected to uniform ultraviolet (UV) radiation, heat, humidity, salt fog, and acid rain along with neat SiR in cyclic manner at 2.5 kV for 5000 h in a specially fabricated weathering chamber. Neat SiR and both nanocomposites showed gradual decrease in transparency. Random loss and recovery in hydrophobicity and increase and decrease in leakage current (LC) were recorded for all samples, in which SNC-5 showed the best hydrophobic behavior and least LC. For SNC-5, Fourier transform infrared (FTIR) results showed negligible reduction in absorption peaks at important wave-numbers and increase and intactness were observed at absorption peaks related to the hydrophobic methyl group. Scanning electron microscopy (SEM) results also concurred with FTIR, LC measurements, and hydrophobicity analysis.

In this study, the dynamic-mechanical properties and thermal behavior of the nanocomposites of a photocurable epoxy-acrylate resin and CuO nanohybrid were determined. In order to improve the dispersion of CuO nanoparticles and prevention of nanoparticle migration to the surface coating, the surface of commercial nanoparticles was modified by triethoxymethylsilane (TEMS) and vinyltrimethoxysilane (VTMS) as silane-coupling agents. Dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) tests were then performed on CuO-filled epoxy-acrylate resins to identify the loading effect on the properties of material. The thermal stability of nanocomposites was affected slightly after incorporation of CuO nanoparticles. DMA studies revealed that filling the CuO nanoparticles into epoxy-acrylate resin can produce a significant enhancement in storage modulus, as well as a shift in the glass transition temperature. The films reinforced with the modified CuO exhibit the most significant enhancements in properties.

In the present work, we investigated the effects of the addition of α-hydroxylethyl ferrocene, polymerization initiator and pre-polymer on preparation temperature, microstructure and optical properties of PMMA/PS compound light scattering material. It was found that the haze of the compound material increases significantly from 64% to 84% after introducing styrene (St) pre-polymer. The addition of α-hydroxylethyl ferrocene also leads to several notable properties change of the composite materials including the in situ polymerization temperature decrease to 300 K. The optical property change after the addition of small amount of α-hydroxylethyl ferrocene and prepolymer (St) demonstrates the soft matter characteristic of PMMA.

The SiC/Al-Mg-Cu-Si-Sn composites with different quantities of SiC particles by volume were fabricated using hot-pressing sintering. The effects of SiC volume fraction on the microstructure, Vickers hardness, and corrosion behavior of the composites were studied using the optical microscope, scanning electron microscope, Vickers hardness test, and corrosion testing. The results show that adding SiC particles shortened the time required to reach the peak-aged state of the composites and increased the hardness. Corrosion potentials of the composites did not vary greatly or show any definite trends in relation to the amounts of the SiC contents.

Ti-3Al-2V alloy is an important aviation material but shows poor resistance to slid wear. Laser cladding of the Fe 3 Al-B 4 C pre-placed powders on a Ti-3Al-2V substrate can form the TiC-TiB 2 reinforced composites, which improved the wear resistance of the substrate. In this study, it was noted that the addition of the Al 2 O 3 and 7 wt.% yttria partially stabilized zirconia (YPSZ) was able to further increase the wear resistance of such composites. Al 2 O 3 increased the dilution rate of the substrate to the laser molten pool to a certain extent; moreover, Al 2 O 3 improved the hardness, elastic modulus and the mechanical properties of such laser clad composites. The YPSZ addition led t-ZrO 2 -ZrSiO 4 to be produced in such composites.

In this article, poly(lactic- co -glycolic acid) (PLGA) microspheres containing the drug OIC-A006 were prepared by ice bath extraction and poly(lactic- co -glycolic acid)/ β-tricalcium phosphate (PLGA/β-TCP) scaffolds were prepared by freeze-drying. Three kinds of scaffold were prepared by adding no drug, direct loading the drug, and loading with drug microspheres. The mechanical strength, degradation, and microstructure of the scaffolds were analyzed. The drug delivery properties of the scaffolds were determined using high-performance liquid chromatography (HPLC). It was found that PLGA/β-TCP scaffolds with PLGA microspheres that contained the drug OIC-A006 exhibited a biphasic drug release pattern. Sustained release of the drug OIC-A006 was beneficial to cell adhesion and proliferation. Experiments on rats showed that composite PLGA/β-TCP scaffolds with PLGA microspheres containing the drug OIC-A006 produced good bone formation and bone induction.

The aim of this research was to study the feasibility of using wheat straw fiber with epoxy resin for developing natural fiber-polymer composites. For this purpose, the epoxy resin was reinforced with 5, 10, 15, 20, and 25 wt.% of the wheat straw fiber with the help of the hand lay-up technique. Further, in order to improve the composite characteristic, wheat straw fibers were treated with three different concentrations of alkali (1%, 3%, and 5%). The mechanical and water absorption properties of the treated fiber composites were characterized and compared with those of untreated fiber-filled epoxy composites. It was observed that the mechanical properties and water resistance were reduced with the increase in wheat straw fiber loading from 5 to 25 wt.%. Among the three levels of alkali treatment, the composite made with 3% alkali-treated fiber exhibited superior mechanical properties than the other untreated and treated fiber composites, which pointed to an efficient fiber-matrix adhesion. The scanning electron microscope was used to observe the surface features of the wheat straw fiber.

TiC particulates-reinforced Fe-based nanocomposites were fabricated using ferrotitanium and carbon black powders by mechanical alloying (MA). The raw materials were milled in a planetary ball mill and sampled in different times. The phase type, crystallite size, and mean strain of milled samples were estimated by X-ray diffraction (XRD) instrument. The scanning electron microscopy (SEM) images of milled powders showed that titanium carbide was synthesized gradually after 90 min of milling and its formation was completed after 5 h and the crystallite size of the produced carbide was in nanometer scale. Increasing milling times gave rise to the reduction of crystallite size as well as the augmentation of the mean strain. Microstructural studies confirmed the accuracy of crystallite size calculations by XRD patterns.

Functionally graded biomaterials (FGBMs) have received significant attention in the recent years as potential candidates for the next generation of dental implant improvement. This happened due to their unique advantages and their ability to satisfy the requirements of both biomechanical and biocompatibility properties simultaneously. This study was aimed to analyze the effects of two radial and axial FGBM dental implants on the stress distribution near the dental implant-bone interface under a static load using finite element method (FEM). The model was restrained on a base supporting bone and vertically loaded with a force of 100 N on the top of the abutment. In the FGBM models, the implants are made of a combination of bioceramic and biometal composition, with properties that change gradually and continuously in the radial and axial directions. The numerical results indicated that the use of both radial and axial FGBM dental implants reduced the maximum von Mises stress in the cortical and the cancellous bones in comparison with the common titanium one, which leads to faster bone regeneration and early stabilization of dental implant system. The findings of the present study may have implications not only for understanding the stresses and deformations around the implant-bone interface but also for improving the performance as well as application of FGBMs in dental implant materials.

Solid-state sintering is the most used process to produce composites. In this paper, the effect of inert inclusions on densification during sintering was evaluated for Cu-WC and Cu-W composites, which have several industrial applications. Dilatometry tests were performed to follow the densification of composites. The effects of the quantity, size, and interphase bonding on densification of the matrix were studied. Distribution of the inert particles inside of the matrix was observed by scanning electronic microscopy. The results show that densification is decreased as the volume fraction of inclusions increases. Two different behaviors are detected when two different sizes of inclusions are used. For <20% vol. of inclusions, smaller tungsten particles have a minor effect on the densification than those of tungsten carbide. On the contrary, higher volume fractions of smaller tungsten particles drastically decrease the densification. The microhardness of the copper matrix is improved up to 15% vol. of inclusions, being higher for tungsten carbide particles. It was found that 15% vol. of inclusions is the maximal quantity of inclusions that can be used, as higher quantities inhibit densification and reduce the mechanical properties of the composite.

A study of the micromechanical behavior to predict the overall response of short fiber-reinforced composites under cyclic mechanical and thermal loading is presented. The instantaneous average over a “representative volume” of the material is considered. The influence of the short fiber’s aspect ratio, volume fraction, and spatial orientation has been investigated. The linear combined hardening model is used to describe the cyclic hardening effects in the case of metal matrix. A numerical procedure is used to predict the response of composites under mechanical and thermal conditions. The results of the numerical procedure have been compared to the results of three different models and to published experimental data.

The study investigates the effects of the alkaline solution/binder ratio and the curing condition on the mechanical properties of alkali-activated fly ash (AAFA) mortars. Class F fly ash was used as the raw material, and sodium hydroxide and liquid sodium silicate were used for the preparation of alkaline activators. Three alkaline solution-to-binder ratios (0.35, 0.5, and 0.65) and four different initial curing conditions (curing in air at ambient temperature for 24 h, 30°C for 24 h, 65°C for 12 h, and 85°C for 6 h) were considered. Test results show that AAFA mortars with alkaline solution-to-binder ratio of 0.35 had higher compressive strength, lower drying shrinkage, lower water absorption, and lower initial surface absorption rate than the other mortars. Furthermore, the curing condition influenced the compressive strength development and drying shrinkage of AAFA mortars at early ages. AAFA mortars cured at 65°C for 12 h appeared to have superior mechanical properties. XRD demonstrates that the hydration products of AAFA mortars are mainly amorphous alkaline aluminosilicate gel, which attributed to the compressive strength. Consequently, the alkaline solution-to-binder ratio significantly affects more the mechanical properties than the curing condition based on the presented results.

Z-pinning technology is applied to composite T-joints in this paper to explore the strengthening mechanisms. The structural properties of T-joints with skin thickness values at 2 and 4 mm were determined under stiffener tensile load. The results revealed that the initial failure strength and failure modes of T-joints were affected by the thickness of skin. Under stiffener tensile load, the actual stress situation of Z-pin tends to be complicated with the deflection of skin. As a result, a mixed mode I/II stress condition exists at the delamination crack tip during tensile loading, and an enhanced frictional zone is located near the delamination surface. When the deflection of skin is indispensable, the snubbing effect acts as a significant factor to strengthening. As the pullout process of pins from the flange is limited by snubbing, pins could fail by split. This paper discusses the strengthening mechanism of Z-pinning and elaborates a potential enhancing effect of Z-pins resulting from the complicated loading condition due to different structure dimensions.

In this paper, we introduce an embedded method of carbon nanotube threads (CNTs) in three-dimensional (3-D) braided composite material preform. We investigate the strain sensing properties of CNTs embedded into 3-D braided composites using three-point bend test under different loads. The resistance change rate properties of CNTs in composites under tensile and compressive loading are analyzed in detail. Experimental results show that in the three-point bending process, the resistance of CNTs exponentially increases with the increase of strain until the specimen loading to fracture. Moreover, the residual resistance of CNTs has been observed after unloading. Our experiments have shown that structure health status of 3-D braided composites can be sensed and monitored in real-time using CNTs sensor under bending load. This study provides an experimental basis to lay the foundation for the structural health monitoring system construction of 3-D braided composites.