Volume 25, Issue 4

This paper presents a research review on fabrication processes and mechanical characterization of aluminum matrix composites (AMCs), which have found application in structural, electrical, thermal, tribological, and environmental fields. A comprehensive literature review is carried out on various types of fabrication processes, the effects of individual reinforcement and multiple reinforcements, its percentage, size, temperature, processing time, wettability, and heat treatment on the mechanical characterization of AMCs including different product applications. Various models and techniques proposed to express the mechanical characteristics of AMCs are stated here. The concluding remarks addresses the future work needed on AMCs.

Sandwich panels made of fibre-reinforced plastic (FRP) skins and a honeycomb core can be effectively damped through the choice of the skin and especially of the core materials. Because the core is often highly damped, a lateral deflection that causes more shearing of the core than bending of the skin increases sandwich damping. Aside from the skin and the core material properties, the shearing/bending ratio depends on a number of other, often interacting, factors, including the sandwich planar as well as transverse dimensions, the particular modal pattern in which the panel vibrates and its relationship to the type of skin layup, as well as the panel end conditions. In the present work, using a simple, first-order shear deformation theory, damping results have been produced for simple modes of vibration of a sandwich panel comprising composite skins and a damped honeycomb core, demonstrating the mechanisms by which the above factors affect the FRP skin/honeycomb core sandwich damping.

Numerous experimental studies have proven the efficiency of externally bonded fiber-reinforced polymer (FRP) systems on structural concrete elements, such as reinforced concrete (RC) beams. The current paper presents an analytical formulation of mechanical constants based on the results of experimental data, which were acquired from fatigue testing of intact and CFRP-retrofitted RC beams. A total of six scaled RC beams were prepared for the test, three of which were strengthened with carbon fiber-reinforced polymers (CFRPs). A specific finite element model coupled with experimental results from the proposed RC beams made it possible to compare the theoretical and experimental fatigue behavior of RC beams with and without composite reinforcement. The developed numerical model was then extended to evaluate a higher number of fatigue load cycles, as recommended by bridge codes. This was carried out to monitor the performance of CFRP-retrofitted RC beams in terms of flexural stiffness deterioration and damage propagation. The relationships presented in this paper were calibrated to the tested specimens. Moreover, they were useful for the design of RC and CFRP-retrofitted RC beams and for predicting fatigue performance, including the damage behavior of constituent materials.

Fracture toughness of particle-filled polymer composite beams with different particle content for varying of crack inclination angles was investigated in mode I and mode III loading conditions. The beams were tested using three-point bending test with crack inclination angles of 30°, 45°, 75°, and 90°. Sewage sludge ash (SSA), fly ash (FA), and silicon carbide (SiC) microparticles were used as toughening fillers with 5, 10, 15, and 20 wt% contents of the total weight of the polymer composites. The scanning electron microscope (SEM) micrographs showed that a good indication was observed for dispersion of FA, SSA, and SiC particles within the polymer matrix. The critical crack tip stress intensity factors K Ic (crack angle 90°) and K IIIc , and the critical strain energy release rates G Ic and G IIIc were calculated and their results were compared. The mode I and mode III fracture toughness of the particulate polyester composite were improved by addition of particulate fillers. The maximum values of fracture toughness mode I ( K Ic and G Ic ) and mode III ( K IIIc and G IIIc ) were recorded at particle content of 5 wt% polymer composites.

An offset representative unit cell (ORUC) is introduced to predict elastic properties of three-dimensional (3D) eight-harness satin weave composites both analytically and numerically. A curved beam model is presented based on minimum complementary energy principle, which establishes an analytical solution for elastic modulus and Poisson’s ratio calculation. Finite element method is developed to predict engineering constants of composites. Modified periodic boundary conditions and load method for ORUC are also presented. Experiments of simulated material are performed under tensile test. Close correlation is obtained between experimental data and predictions. Sensitivity study is conducted and manifests that within a large variation of constitutive material properties, the curved beam model derives close predictions comparing to finite element model, which indicates the stability of the curved beam model. Parametric study is also conducted to discuss the effect of weave type and geometric dimensions on elastic properties. It is argued that the curved beam model could manifest fine predictions accurately and stably, and is recommended for the prediction of elastic properties of satin weave composite.

Double-layer absorbing cement-based composites with the thickness of 10 mm were prepared, including different replacement levels of fly ash (FA) in the absorbing layer as well as the matching layer for impedance matching. Waste polyethylene terephthalate bottle fragment was introduced as electromagnetic transparent reinforcement aggregate. Carbon black was used to be original absorbent in the absorbing layer. The microstructure and electromagnetic parameters of FA were closely looked at through scanning electron microscope, X-ray diffraction, and analyzer of vector network. The absorption and mechanical properties of cement-based composites were tested. It turned out that when the optimal replacement ratio of FA in the absorbing layer and matching layer gets to 50%:30%, the minimum value of reflection loss achieves −22.3 dB at 13.2 GHz; also, the value of absorption bandwidth that is effective (<−8 dB) is 6.4 GHz. Ni-Zn ferrite proves to be a feasible absorbent that is additional for the matching layer compared to what is added to the absorbing layer. The compressive strength of all the mixtures decreased, while the flexural strength decreased first and then increased with the rise of the FA replacement level.

In this study conductive composites of low-density polyethylene (LDPE)/ethylene-vinyl acetate (EVA) filled with carbon black (CB) and carbon fiber (CF) were prepared by melt-mixing method. The morphological, rheological, and electrical properties of CB filled composites were compared with CF filled composites by digital multimeter, scanning electron microscope, rotational rheometer, etc. The composites filled with different fillers have same percolation threshold but the EVA concentration has different effect on the two systems. For CB filled composites the increase in EVA concentration decreased resistivity first and reached lowest point when the LDPE:EVA ratio was 70:30; then the resistivity increased, but for CF filled composites the resistivity continued to decrease. The differences were caused by the diverse morphological and filler distribution of two different composite systems. The rheological behaviors of two types of composites also had significant difference; the value of complex viscosity of CB filled composites was about two orders of magnitude more than CF filled composites in low frequency region. It was because CB particles was nano-scale and had large surface area, so it had great influence on the value of complex viscosity of composites.

Epoxy resin is a thermoset polymer and is one of the main candidates for radiation shielding application. In this investigation, carbon, hydrogen, and nitrogen analysis showed that the presence of the light element of nitrogen in cured epoxy could lead to more effective neutron shielding ability compared with physical curing. The effect of neutron irradiation of amine-cured epoxy was studied by infrared spectroscopy. Neat epoxy samples were irradiated at the core of the Tehran Research Reactor in the same neutron flux in the order of 10 13 (neutron/cm 2 ×s) at several radiation times (up to 12 h). The results indicated that neutron irradiation caused moderate changes in peak absorption locations of epoxy spectra. This result indicates that, in this neutron flux and irradiation time, the molecular structure of epoxy remains stable.

A polymer-bonded explosive, also called PBX or plastic-bonded explosive, is an explosive material in which explosive powder is bound together in a matrix using small quantities (typically 5%–10% by weight) of a synthetic polymer. A PBX substitute material was made from sugar granules and polymer binder. Its compressive creep properties were investigated at room temperature. The creep deformation was found to depend strongly on the applied stress amplitude. Under an applied stress near the strength, creep deformation developed and reached the final rupture very quickly. A power law relationship, ε˙=4.14×10−8σ2.5,$\dot \varepsilon = 4.14 \times {10^{ - 8}}{\sigma ^{2.5}},$ was established between steady creep rate and applied stress. Microscopic observations show that the damage mechanism processes include mainly the intergranular and transgranular fractures, binder fracture, and peeling. Both porosity and granule size decrease almost linearly with increasing applied stress.

Ag/Cr 2 O 3 -AgCrO 2 nanocomposite powders were chemically synthesized using a chemical precipitation method. The synthesis method stages included precipitation and calcination. The initial precipitates contained Cr(OH) 3 ·3H 2 O and Ag 2 CO 3 compounds. Calcination of the initial precipitates led to thermal decomposition of the precipitates and evaporation of volatile compounds such as H 2 O and CO 2 . The calcined precipitates contained silver, chromium oxide, and silver-chromia. The crystallite size of Ag 2 CO 3 and Ag were determined as 18.9 and 45 nm, respectively. The scanning electron microscopy investigations showed that the particle size of the initial precipitates was lower than 100 nm. The calcined powders were sintered at 550°C in air atmosphere. The sintered samples were cold-repressed under 300 and 550 MPa. It was found that by increasing the repressing compaction magnitudes, the density and hardness of the sintered samples were increased. The scanning electron microscopy evaluation of the densified samples showed nearly dense microstructure.

The influence of calcium carbonate (CaCO 3 ) with different polymorphs (calcite and aragonite) and morphologies (granular and rod-like) on mechanical and crystallization properties of polypropylene (PP) was investigated. Meanwhile, these CaCO 3 fillers coated with oleic acid were added in different contents to PP. The results indicate that the tensile strength, flexural strength, modulus, and crystallization property of the filler-treated samples are improved, but the impact strength decreased. The crystallinity of the composites is higher than that of neat PP. Moreover, in the rod shape filler-treated sample, in both whisker species, the mechanical properties of composites are superior to the particles filled. Differential scanning calorimetry, X-ray diffraction, and mechanical tests display that calcite whisker-reinforced composite has higher crystallization enthalpy, melting enthalpy, degree of crystallinity, and mechanical properties than aragonite whiskers and calcite particles filled composites.

For improved performance of epoxy, its composites were studied for high-voltage insulation. Epoxy composites may offer several advantages over neat epoxy and ceramic materials. We fabricated nano- and microepoxy/silica composites with 5 wt% nanosilica and 20 wt% microsilica, respectively. The composites and neat epoxy were studied for thermal, mechanical, and electrical properties. A thermogravimetric analyzer was used for analyzing wt% loss with temperature. Tensile and hardness tests were performed according to DIN 53504/ASTM D412 and DIN 53505/ASTM D2240 standards, respectively. Electrical properties such as dielectric strength and resistivity were tested according to IEC-60243-1 and ASTM D257/IEC 60093 standards, respectively. Neat epoxy, microcomposite, and nanocomposite showed 50% weight loss at 392°C, 410°C, and 421°C, respectively. At 550°C, nanocomposite remained at 20% of its initial weight whereas neat epoxy and microcomposite remained at 10% of their initial weights. Microcomposite and nanocomposite showed tensile strengths of 65.7 Mpa and 69.3 Mpa, respectively. Enhancements of 8% and 19% in dielectric strength were recorded for microcomposites and nanocomposites, respectively. Nanosilica greatly improved surface and volume resistivity whereas microsilica showed negligible effect on resistivity.

The aim of this work is to investigate the adhesive dry sliding wear and friction performance of biodegradable cashew nut shell (CNS)-filler-reinforced epoxy composite. The composites are prepared with 5, 10, 15, 20, 25, 30, 35, and 40 weight content of CNS filler. Experiments were conducted to perform the required measurements. The results show that the specific wear rates and frictional coefficients are found lower at 30% untreated and treated CNS-containing composites. The NaOH-treated CNS filler composites showed low wear and frictional performance compared to raw CNS. The back film formation was associated with the predominant wear mechanics with the formation of fine debris on the worn surface and counterface.

Using low-cost materials, carbon, and alum, a new solid composite electrolyte system was fabricated and characterized using various techniques. Complex impedance spectroscopy was used to measure its ionic conductivity. A maximum conductivity of 3.4×10 −5 S/cm was obtained when alum was doped with 40% carbon. An Arrhenius behavior was reported when the temperature dependence of conductivity was analyzed. Scanning electron microscopy was used to study the surface morphology of the synthesized electrolyte. Fourier transform infrared and X-ray diffraction results confirmed the formation of composite material. The synthesized solid composite electrolyte exhibited excellent humidity sensing behavior in the relative humidity range of 15%–65%. Various humidity characteristics of the sample were measured such as hysteresis loop, recovery, and response time of the sensor. An expert system was modeled using artificial intelligence techniques and failure of the sensor was predicted with 97.2% accuracy using artificial neural networks.

This paper investigates the three-body wear resistance rates of five restorative dental composite materials at different mastication cycles and compares the results with that of an amalgam material. Five specimens of each material were exposed three-body wear tests using a computer-controlled chewing simulator with steatite balls as the antagonist (1.6 Hz, 49 N load; 120,000, 240,000 and 480,000 mechanical cycles; and thermal cycling between 5 and 55°C at 5 min/cycle and 3000 cycles) immersed in a poppy seed slurry (three-body wear environment). Initially, the microhardness values of the composite materials in the Vicker’s hardness (HV) scale were determined. The mean volume loss of the worn surfaces was measured with a three-dimensional profilometer. Means and standard deviations were calculated, and statistical analysis was performed using one-way ANOVA (α=0.05). Additionally, scanning electron microscopy analysis was performed to examine the wear tracks on the surface. The interactions between the composite resin and mean volume loss were found to be significant. The three-body wear rates for the composites Durafil and Kalore composite were significantly higher than those of the other composites and the amalgam irrespective of the number of mastication cycles. Filtek Z250 and Filtek Supreme composite resins had good three-body wear resistance similar to that of the amalgam. However, this study suggests that the correlation between Vicker’s hardness and three-body wear resistance is not significant.

Closed-cell aluminum foams with different percentages of zinc content were successfully prepared and investigated. The foamable precursors were prepared in a pit furnace by adding calcium as thickening agent, calcium carbonate as blowing agent and different percentages (0 wt.%, 0.5 wt.% and 1 wt.%) of zinc particles at 650–750°C. The distribution of Zn elements and quassi-static behavior of the foams at room temperature were investigated. The experimental results show that Zn element is uniformly distributed in cell wall matrix. The distribution of Zn elements had a significant effect on the quasi-static compressive behavior of aluminum foams; from the results, it is obvious that zinc-containing foams possessed higher compressive strength and energy absorption capacities than pure aluminum foams. Hence, it can be concluded that increase in percentage of Zn particles helps to increase the compressive strength, plateau region and energy absorption, in addition to providing better and uniform pores.

Honeycomb sandwich panels entice continuously enhanced attention due to its excellent mechanical properties and multi-functional applications. However, the principal problem of sandwich panels is failure by face/core debond. Novel lightweight sandwich panels with hybrid core made of honeycomb, foam and through-thickness pin was developed. Reinforcing polyester pins between faces and core is an effectual way to strengthen the core and enhance the interfacial strength between the face/core to improve the structural performance of sandwich panels. To provide feasibility for pin reinforcement, honeycomb core was pre-filled with foam. Mechanical properties enhancement due to polyester pinning were investigated experimentally under flatwise compression, edgewise compression and flexural test. The experimental investigations were carried out for both “foam filled honeycomb sandwich panels” (FHS) and “polyester pin-reinforced foam filled honeycomb sandwich panels” (PFHS). The results show that polyester pin reinforcement in foam filled honeycomb sandwich panel enhanced the flatwise, edgewise compression and flexural properties considerably. Moreover, increasing the pin diameter has a larger effect on the flexural rigidity of PFHS panels. PFHS panels have inconsequential increase in weight but appreciably improved their structural performance.

The present study deals with the effects of fiber loading and alkali treatment (AT) on thermal behavior of a hair fiber (HF)-reinforced high-density polyethylene (HDPE) composite. The HF/HDPE-reinforced polymer composite has been prepared through a compression molding technique, which provided optimum thermal stability at 15 wt% of the fiber in the reinforced composite. The thermal stability of the composite has been investigated using a thermal analyzer [thermogravimetric analysis (TGA), derivative thermogravimetric analysis (DTG) and differential scanning calorimetry (DSC)]. The ATs of HF-reinforced composites have affected the thermal stability of the material, in which the observed optimum thermal stability is 0.25 N AT 15% HF/HDPE-reinforced composites. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and tensile test played an important role in the study of the thermal stability of the material. FTIR analysis was used to investigate the chemical groups between the fiber and matrix. The morphology of the fiber is beneficial for the study of the surface treatment effect on the HF. The tensile test examined the optimum strength at 0.25 N AT 15% HF/HDPE composite, and a good relationship between the thermal and mechanical properties was also observed.

Sol-gel method was used to prepare a novel In-Sm co-doped TiO 2 photocatalyst. The materials were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared/far infrared, UV-Vis diffuse reflectance, and N 2 adsorption-desorption analyses. Anatase phase TiO 2 is formed in the pure and doped TiO 2 samples. Anatase TiO 2 crystal formation and growing are disturbed by the dopants. The substitution of smaller Ti 4+ ions by the larger Sm 3+ and In 3+ ions causes the expansion of TiO 2 cell. The doping of indium and samarium ions has no noticeable influence on the bonding characters of TiO 2 . A continuous red shift of the absorption edge of x In-0.05%Sm-TiO 2 occurs at increasing indium doping content. Brunauer-Emmett-Teller surface area, average pore size, and total pore volume are enhanced after doping of samarium and indium. The adsorption of methyl orange on the surface of x In-0.05%Sm-TiO 2 increases with rising indium content. The 5%In-0.05%Sm-TiO 2 has the maximum photocatalytic activity. About 97.7% of the initial methyl orange is decolorized on 5%In-0.05%Sm-TiO 2 after 45 min of irradiation.

In this work, the influence of fiber/matrix meso-structure on the strain concentration of three-dimensional (3D) reinforced carbon-carbon composites with a drilling hole is discussed by experimental and numerical ways. The full-field digital image correlation (DIC) method is adopted to obtain the strain field of the experimental specimens, and the meso-FEM model with the consistent meso-structure of the experimental specimens is established to reveal the main deformation and damage mechanism. The results show that the strain concentration appeared off the location of ±90° hole tips, which is different with homogeneous material. Furthermore, the shear bands are observed and located on the region between the cut fiber yarn and the adjacent uncut one. The peculiarities are found connecting with the meso-structure. Moreover, the damage locations obtained from the meso-model show good agreements with the experimental fracture path, thereby, the analyses are verified.