Volume 22, Issue 6

This study investigated the effect of four different types of reinforcements on the mechanical properties of an epoxy system. The epoxy resin used was diglycidyl ether of bisphenol A (DGEBA) cured by cycloaliphatic polyamine. These four mechanisms use a multi-wall carbon nanotube (MWCNT) as a nanofiber, clay as a nanolayer, SiO 2 as a particulate nanofiller and high impact polystyrene (HIPS) for polymeric alloying. The properties that were studied are tensile, compression and flexural resistance. We used solvent mechanism to prepare homogeneous mixture samples. The test results were compared between different weight percent loading of each reinforcement and also between different mechanisms. Also, the morphological properties of DGEBA/CNT, DGEBA/clay, DGEBA/SiO 2 and DGEBA/HIPS were studied using scanning electron microscopy. Generally, the comparison between the results led the authors to conclude that among the mentioned mechanisms, using silica nanofillers is the most effective way to enhance the mechanical properties of an epoxy resin.

Composites of low melting polyamide-6 (LPA6)/glass beads/styrene, and maleic anhydride copolymer (SMA) were prepared by melt extrusion in a co-rotating twin screw extruder. This is a completely new method for the preparation of LPA6, compared with traditional copolymerization, ultra-fine grinding, and solution grafting. The effect of the SMA concentration on the structures and properties of the composites was systematically investigated. This work deals with the combination of both components, which are the effects of the complex reaction on the structures and properties of LPA6, as well as the enhanced mechanical behavior in an analogous reactively compatibilized ternary system. The results show that the complexation reaction has an important effect on the crystallization behavior of nylon6, and the presence of SMA could significantly improve the interfacial compatibility of the glass beads and PA6 matrix. Moreover, the Vicat softening temperature, notched impact strength, tensile strength, and flexural strength of the blends are significantly increased. A slight decrease of the crystallinity and crystallization temperature of the mixture was observed.

The purpose of this paper was to investigate the surface modification of zeolite with polyethylene glycol (PEG) and the modified zeolite as a reinforcing filler partly replacing carbon black (CB) into rubber to prepare the rubber composites. The surface characteristics of zeolite modified by PEG and the unmodified zeolite were characterized by infrared (IR) spectroscopy and scanning electron microscopy (SEM). Moreover, the evaluations of the zeolite/rubber composite were carried out on characteristics such as tensile property, abrasion loss, and hysteresis heat generation with different amounts of zeolite and PEG. The results showed that the tensile strength and elongation at break of the composites were improved, and the abrasion and lag heat generation were reduced when 5–8 phr zeolite modified by 3 wt% PEG was filled into rubber. These results indicated that the modified zeolite has a good compatibility and dispersion in rubber.

In this paper, the effects of microstructural parameters on the initial yield surface of non-isothermal composites were investigated. The fiber phase was assumed to be a linear elastic material, and the matrix was assumed to be a non-linear material. Incorporating the Bodner-Partom viscoplastic constitutive model into a high-fidelity generalized method of cells allowed the initial yield surfaces of non-isothermal composites with different microscopic arrays and fiber cross-section shapes to be studied. Moreover, working temperature effects on initial yield surface are also discussed. The results show that the initial yield stress in the σ xx –σ yy plane of unidirectional fiber-reinforced composites tends to decrease with increasing working temperature. Furthermore, the effects of fiber arrays and fiber off-axis angles on initial yield stress show similar variation at different working temperature conditions.

In this study, the relationships between geotechnical index properties and the pore-size distribution of compacted natural silt and artificial soil mixtures, namely, silt with two different clays and three different clay percentages (10%, 20%, and 40%), were examined and compared. Atterberg’s limit tests, standard compaction tests, mercury intrusion porosimetry, X-ray diffraction, scanning electron microscopy (SEM) analysis, and Brunauer-Emmett-Teller specific surface analysis were conducted. The results show that the liquid limit, the cumulative pore volume, and specific surface area of artificially mixed soils increase with an increase in the percentage of clay. The cumulative pore volume and specific surface area with geotechnical index properties were compared. High correlation coefficients were observed between the specific areas and both the liquid limit and the plasticity index, as well as between the cumulative pore volume and both the clay percentage and the S coefficient. In addition, qualitative SEM analyses were conducted.

Thermoplastic resins used as a matrix of fiber reinforced thermoplastics (FRTPs) are composed of high polymers that remain highly viscous even at a higher temperature than their melting points. As a result, they need an even higher temperature, a higher pressure and a longer processing time to allow them to bond with fibers that require large and specialized equipment. In contrast, fiber-reinforced thermoset plastics (FRPs) can be easily molded owing to the use of lower viscosity liquid resin as the matrix using simpler devices. In this paper, a new fabrication method of FRTPs using in situ polymerizable ε caprolactam as the matrix is presented. This method uses vacuum-assisted resin transfer molding without the need for large and specialized equipment. The ε-caprolactam molecules were converted from their monomer form into a polyamide 6 resin, with ring-opening polymerization of ε-caprolactam during the molding process at a lower temperature than its melting temperature. The two kinds of FRTPs obtained using ε-caprolactam as the matrix had neither voids nor unfilled parts because ε-caprolactam had a very low viscosity before the polymerization. These FRTPs not only exhibit superior bending properties but also are suitable for high-speed molding, namely, within a few minutes of process time.

An inorganic-organic hybrid (IOH) of silica particulates and polyethylene (PE) was investigated, where silica was employed as an analogue to lunar soil. The objective was to search for the optimum materials design strategy for “lunar cements” – infrastructural materials based on locally harvestable resources on the Moon. If the silica particulate size was uniform, the flexure strength of the IOH decreased quite linearly with the PE content. With a two-step size gradation of silica particulates, the flexure strength of the silica-PE IOH could be much improved, higher than that of Portland cements with only 4 wt% of PE. A threshold PE content around 6 wt% existed. Above the threshold, the PE content has only a secondary effect on the IOH flexure strength; below the threshold, the IOH flexure strength decreases abruptly. In order to further enhance the IOH strength and to reduce the binder content, this threshold value must be minimized.

This paper investigates the degradation of basalt fiber reinforced polymer (BFRP) bars used for concrete construction in an alkaline environment. The relationships between tensile strength, elastic modulus, shear strength and moisture absorption rate over time are analyzed using a tension test, short-beam test and moisture absorption weighting. The tensile strength degradation of BFRP bars was further compared with that of Glass FRP (GFRP) bars in the literature. The results indicated that BFRP bars exhibit relatively good resistance to alkaline corrosion, maintaining more than 60% of their original strength after 9 weeks at 55°C in an alkaline solution. The moisture absorption of BFRP bars conforms to Fick’s law, which shows that the degradation mechanism is controlled by matrix and related interface degradation. This finding is supported by comparison with the shear strength degradation trend. Compared to GFRP bars under similar alkaline conditions, BFRP bars exhibit a similar degradation rate during the initial phase, but maintain higher tensile strength and strength retention over time.

The microstructure of iron-based alloy (FeCrC) cladding layers on the surface of Q235B mild steel was analyzed by means of SEM, XRD, and EPMA tests. The results indicated that structure morphology of FeCrC alloy cladding layers by TIG welding is mainly hexagonal and elongated in shape. These structures were composed of some hard phases, such as Cr 23 C 6 , Cr 3 C 2, and Cr 7 C 3 . When element B was added, the structure morphology of iron-based alloy cladding layers could be changed into an irregular clumpy and cracking shape, which appears as a Fe 23 (C, B) 6 hard phase. When element V was added, the surface morphology was changed into a small clumpy shape, which was composed of (Fe, Cr) C and (Fe, Cr, V) C phase.

The Cu-7vol.%ZrB 2 alloy examined in this study was consolidated via powder metallurgy (PM) processing by combining mechanical alloying and hot pressing. Powder mixture with composition: 94.78 wt.% copper, 4.1 wt.% zirconium, and 1.12 wt.% boron was used as a starting material. Mechanical alloying of powder mixture was performed at various times: 5, 10, 15, 20, 25, and 30 h. Structural changes that occur in the samples of copper alloy with 7vol.%ZrB 2 after milling and during hot pressing process were studied with the use of X-ray diffraction. Scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometry (EDS) was applied to examine the morphological properties and elemental analysis of the hot-pressed samples as a function of milling times. Also, hardness of the Cu-7vol.%ZrB 2 alloy was investigated, and the results showed that hardness of the samples increased as the milling time increased. The compressive properties at room temperature are correlated to the corresponding hardness results. Distribution of ZrB 2 particles and presence of agglomerates in the Cu matrix directly depend on the milling time and show strong influence on compressive properties and fracture of Cu-7vol.%ZrB 2 alloy.

The aim of this paper was to investigate the effect of vacuum hot pressing sintering temperature, sintering time and pressure on the properties of SiCp/2024Al composites. The microstructures and mechanical properties were tested by scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and a mechanical testing machine. The results indicated that increasing hot pressing temperature decreased the number of pores and increased the density and interfacial bonding strength, and improved the mechanical properties of the composites. The composite fabricated at 580°C exhibited the optimum tensile strength, excessive hot pressing temperature easily produced micro-cracks, and the liquid aluminum extrusion and the reduction of Al 2 Cu phase. Prolonged sintering times had an adverse effect on the strength of the composite. A hot vacuum pressure needed to be higher than 60 MPa to achieve densification of composites above 99%. Solution treatment plus aging of the composites resulted in a significant improvement in strength and hardness. The higher the sintering temperature, the shorter the time taken to achieve the hardness peak.

Ti-6Al-4V alloys are difficult-machine materials. These alloys are extensively used in medicine, chemical units, marine and food industries, and particularly in the aerospace industry. Machinability of Ti-6Al-4V in wire electric discharge machining (WEDM) has been empirically investigated. WEDM performance tests were conducted on TiN coated Ti-6Al-4V alloy with physical vapor deposition (PVD) method, which is harder and has higher wear resistance. The performance of machinability of Ti-6Al-4V and Ti-6Al-4V/TiN materials was analyzed. The most important performance characteristics of WEDM cutting are surface roughness, machining gap, and cutting speed. The tests were conducted under cutting parameters including varying pulse durations (300, 500, 700 μs), tension (50, 100 V) and wire feed rate (5, 8 m/min). Based on tension, pulse duration, and wire feed rate of heat-treated uncoated samples when compared to untreated samples and coated samples, feed rates were found to be at the highest value.

Natural frequency analysis of anisotropic functionally graded material (FGM) annular sector plates on Winkler elastic foundations based on three-dimensional theory of elasticity was investigated. The three-dimensional graded finite element formulation was derived based on the principle of minimum potential energy and the Rayleigh-Ritz method. For an orthotropic FGM, the material properties were assumed to have in-plane polar orthotropy and transverse heterogeneity according to an exponential law, whereas the mass density was assumed to be constant. For an isotropic FGM, material properties varied continuously through the thickness direction according to a power-law distribution, whereas Poisson’s ratio was set to be constant. The effects of material gradient exponents, different sector angles, different thickness ratio, Winkler parameter and two different boundary conditions on the natural frequencies and mode shapes of FGM annular sector plates have been investigated. Numerical solution was compared with the result of an FGM annular circular plate, which showed good agreement.

Numerical investigations were performed on a series of laminated composites when subjected to dynamic loadings, in order to determine their energy absorption rate and dissipating energy during impact. The details of numerical modeling, contact analysis, material parameters, and failure criteria were explained and discussed. We aimed to determine the energy absorption rate of various quasi-isotropic lay-ups when subjected to the dynamic loadings, and found that energy dissipation rate varied depending on stacking sequence. In this investigation, we studied how the energy absorption rate and the peak impact load change as a result of changing stacking sequence, with all stacking sequences being quasi-isotropic. Using a constant impacting mass and varied impacting speeds, we found that stacking sequence can significantly control the energy transfer rate or energy absorption rate under dynamic load condition.