Journal of Composite Materials

A maximal product of stiffness and viscoelastic damping (E tan δ), a figure of merit for damping layers, is desirable for structural damping applications. Particulate-reinforced metal–matrix composites were prepared by ultrasonic agitation of the melt and composed of the zinc–aluminum (ZnAl) alloy Zn₈₀Al₂₀ (in wt%) as the lossy matrix and SiC or BaTiO₃ as the particulate reinforcements. ZnAl–SiC composites were stiffer and exhibited higher damping at acoustic frequencies in comparison to the base alloy. ZnAl–SiC composites were superior to Sn–SiC composites and possessed an E tan δ in excess of 0.6 GPa, the maximum figure of merit provided by commercial polymer damping layers. Furthermore, ZnAl–SiC composites displayed a high figure of merit over a broad temperature range. ZnAl–BaTiO₃ composites exhibited anomalies in modulus and damping associated with partial restraint of the phase transformation; one specimen was much stiffer than diamond over a narrow temperature range.

In this study, strength behavior and crack-formation mechanism of E-glass fiber exposed to sulfuric acid environment for different immersion times were investigated. In order to study the strength degradation, E-glass fibers were immersed in sulfuric acid. Strength reduction, stiffness, and fracture strain of fibers vs. immersion times were studied. The corrosion mechanism of E-glass fiber exposed to acid, were examined by quantitative X-ray fluorescence method. The results showed that corrosion of E-glass fiber was accompanied by removal of Al, Ca, and Fe ions from the fibers. Moreover, intact and degraded fibers were examined by scanning electron microscope and energy dispersive X-ray (EDX) microanalysis methods to show the relation between the reaction of E-glass fiber elements and acid environment. The ion-depletion-depth model was used to study the fracture process. The results showed that by increasing the immersion time in acid, spiral stress induced due to the shrinkage of E-glass fiber surface caused axial cracks in fibers. Different points of fibers, in which cracks were generated, were examined by EDX method. The results were used to explain the role of Al, Ca, and Fe ions in creation of surface cracks on E-glass fibers subjected to sulfuric acid for different immersion times.

Polyhedral oligomeric silsesquioxane (POSS)–siloxane-modified polyimide (PI) hybrid nanocomposites were prepared by the reaction of siloxane-modified polyamic acid (PAA) with octaaminophenylsilsesquioxane (OAPS). PAA was prepared by the reaction of 4,4-diaminodiphenylsulfone with pyromellitic dianhydride in N-methylpyrrolidone (NMP), followed by the reaction of PAA with bis(3-aminopropyl) polydimethylsiloxane to obtain siloxane-modified. The siloxane-modified PI was further blended with varying weight percentages of OAPS using NMP solution. The reactions occurred during the formation of hybrid nanocomposites were confirmed by Fourier transform infrared spectra. The siloxane-modified PI OAPS nanocomposites were characterized for their thermal properties using differential scanning calorimeter and by thermogravimetric analysis. Morphological studies of the nanocomposites indicate that the incorporation of siloxane moieties creates heterogeneous morphology. Data from thermal studies indicate that the incorporation of POSS appreciably enhanced the glass transition temperature, thermal stability, and char yield of hybrid nanocomposites compared to neat PI.

This article presents a simulation method to analyze process-induced stresses of a meso-level unit cell of a pin-reinforced sandwich structure (carbon fiber-reinforced plastics/foam). During the manufacturing process, different mechanisms lead to process-induced deformations and stresses. These mechanisms depend on thermal expansion, shrinkage, nonlinear viscoelastic properties of the material, and variation in local temperatures. In critical cases, these residual stresses can lead to initial degradation and up to failure of the material. This article demonstrates a method to perform a sequential coupled thermo-mechanical analysis of the manufacturing process with focus on the correct determination of stresses and description of the viscoelastic relaxation effect. A novel approach to take into account anisotropy of characteristic relaxation times dependent on the cure process is presented.

In this study, creep/recovery behavior of wood flour/polypropylene (PP) composite was compared with solid wood and PP. Wood flour–PP composite samples (strips with 10 mm thickness and 70 mm width) were made using a laboratory twin-screw extruder. Short-term flexural creep tests at 30% of ultimate bending load were performed using flexural creep equipment. Total time to complete every test was 120 min (60 min creep and 60 min recovery). Creep parameters (relative creep, fractional deflection, creep rate, etc.) were measured for all creep test samples. The result showed that the relative creep in wood–plastic composite (WPCs, with or without coupling agent) is significantly higher than solid wood and lower than PP. Also, it was observed that the creep rate in WPC (with or without coupling agent) is significantly lower than plastic, but is approximately equal to solid wood. The use of coupling agent decreased relative creep and fractional deflection in wood flour–PP composite panels. Findley creep model predicted creep strain with a high acceptable accuracy for studied materials.

Carbon fiber-reinforced composite materials are finding increased application in many areas. Machining of these composites cannot be avoided to avail a near-net shape. The study and development of prediction model for cutting force, cutting power, and specific cutting force have been an important area for researchers. Interest toward this subject is increasing due to the factors which restricts from carrying out the experimental studies like the number of machining parameters to be controlled and time taken for machining to determine cutting forces. This study attempts to develop a fuzzy model to predict the cutting force thereby cutting power and specific cutting force. The developed models offer satisfactory performance on comparison with the experimental results and hence these models can be effectively used to predict cutting forces in machining of carbon fiber-reinforced plastic composites.

The effect of carbon nanofibers on the crystallization of polyethylene using differential scanning calorimetry operating in dynamical mode at various cooling rates (2, 4, 8, 15, and 30°C/min) is reported. Experimental data were analyzed using the Avrami, Ozawa, and the combined Avrami–Ozawa methods. It is concluded that the addition of carbon nanofibers modifies the crystallization process of polyethylene (changing the value of the Avrami exponent), and that the combined Avrami–Ozawa approach describes more accurately the crystallization of carbon nanofiber reinforced polyethylene composites. The analysis of the experimental data indicates that the dispersion of carbon nanofibers within polyethylene leads to complex changes in the crystallization process such as increased crystallization temperature, longer times to reach 50% crystallization, higher crystallization rates, and lower degrees of crystallinity of the polymeric component.

The main aim of this article is to introduce a bending fatigue testing apparatus and a new fatigue testing method, which can be used to characterize the bending fatigue behavior of flexible materials by setting the following parameters: pre-tension, bending angle, and bending frequency. The Kevlar 49, poly(p-phenylene benzobisoxazole), Nomex, and high-performance polyethylene fibers are chosen to analyze the bending fatigue properties by the new apparatus. The cyclic stress data, number of cycle bending and bending fatigue photos are recorded during the process of the bending fatigue. The curve of the cyclic stress shows that the stress changes in periods during the cyclic bending process. The curve of the cyclic stress is theoretically analyzed. The S–N and the θ−lnN curves indicate that the pre-tension and the bending angle have significant effects on the bending fatigue life. The morphologies obtained from the digital optical apparatus can be used to explain the bending failure mechanisms of high-performance fibers. It is evident that the new bending fatigue testing apparatus is feasible and accurate in measuring and characterizing bending fatigue properties of fibers. The apparatus could effectively describe the bending fatigue lifetime and bending failure mechanisms of high-performance fibers.

Phase contrast microscopy (PCM) was used to study the relation of the phase structure and morphology of isotactic polypropylene/poly(ethylene-co-octene) (iPP/PEOc) blends and the composition and the shear rate. The digital image analysis containing the analysis both in real space and wave-number space was introduced to deal with the PCM micrographs. The average characteristic length, L_m, in real space and the mean square radius of gyration, R g 2 ¯ , in wave-number space were defined and calculated to discuss the phase structure and morphology of iPP/PEOc blends. In addition, the fractal dimension, D_c, was introduced to describe spatial distribution uniformity of the dispersed phase. The results showed that these parameters were effective to study the size and its distribution of the dispersed phase particles.

In this study, the wear behaviors of aluminum matrix composites with an A360 matrix reinforced with silicon carbide (SiC) and boron carbide (B₄C) ceramic particles using Taguchi method were investigated. Wear tests of unreinforced aluminum alloy and Al17%SiC and Al17%B₄C particles reinforced aluminum composites (Al/17%SiC and Al/17%B₄C, respectively) versus AISI316L stainless steel disc were carried out for a dry sliding condition in a so-called a pin-on-disc arrangement. The wear tests were realized at the sliding speeds of 0.5, 1.0, and 1.5 m s⁻¹ and under the loads of 10, 20, and 30 N. The obtained average specific wear rates for Al/17%B₄C and Al/17%SiC composites are lower than unreinforced aluminum specific wear rate under the same test conditions. The experimental results are transformed into a signal-to-noise (S/N) ratio of using Taguchi method. Type of the material, applied load, and sliding speed exert a great effect on the specific wear rate, at 48.13%, 31.83%, and 8.77%, respectively. The estimated S/N ratio using the optimal testing parameters for specific wear rate were calculated and a good agreement was observed between the predicted and actual specific wear rate for a confidence level of 99.5%.

In this manuscript, we generally study the role of functionalized MWCNT in improving mechanical properties of epoxy resins. Also we use ‘central composite design’ model as a statistical experimental design in order to qualitatively investigate the role of various parameters on experiment results. Statistical results show non-linear behavior of effective parameters on experiment results. Also the results of experiments show that, existence of Nano-filler has positive effects on mechanical properties of the Nanocomposites. The results also represent that functionalized Nano-filler with acid and amino agent improve the mechanical properties. Attention to results shows that MWCNT with amino agent is more effective than acid agent in improving the properties.

In this study, an approach based on grey relational analysis and the Taguchi method is used to optimize machining parameters with multiple performance characteristics in drilling hybrid Al 356/SiC-mica composites. Experiments were conducted on a vertical machining centre, and Taguchi’s Quality Concept, a L₉, 3-level orthogonal array was chosen for the experiments. The drilling parameters, namely spindle speed, feed rate, drill and wt% of SiC, were optimized based on multiple performance characteristics including thrust force, surface roughness, and torque. The grey relational analysis with multiple performance characteristics indicates that the feed rate and the type of drill are the most significant factors which affect performance. Experimental results have shown that drilling process performance can be improved effectively by using this approach.