چكيده به لاتين
Mechanical properties of woven fabric composites are influenced by fabric geometry, harness, strain rate, and the addition of nanofiber reinforcement. In the present research, the mechanical properties of woven fabric composites were studied in three stages. Stage 1: Composites made of ML 506 epoxy resin and E-glass woven fabrics with three different fabric geometries (harnesses of 2, 5, and 8) were studied experimentally. The new concepts of warp and fill fiber volume fractions were introduced. Based on these new concepts, a new micromechanical model for predicting the stiffness and strength of composites made of woven fabrics was presented. The results obtained by the new micromechanical model have been compared with experimental results and very good correlations were obtained. Stage 2: Harness and weave style are the most important properties of woven fabrics. Most of the previous studies utilized woven fabrics with specific harnesses to explore the effects of nano-reinforcements on woven composites. Therefore, an experimental study was initially conducted to examine the impact of three weave patterns, namely plain, 5-harness satin, and 8-harness satin, on the mechanical properties of woven composites under tensile and shear loads. Subsequently, the effect of applying carbon nanofibers (CNFs) to woven glass/epoxy composites with various harnesses was studied. The experimental results were then evaluated statistically, indicating that using CNFs as reinforcement differently affects various fabric harnesses. The addition of 0.5 wt.% CNFs to the woven composites with varied harnesses (2, 5, and 8) enhanced the ultimate tensile strength (UTS) and tensile failure strain. However, the elastic tensile modulus of the woven composites was not increased. A further increase in the weight fraction from 0.5 wt.% did not improve the tensile properties. Moreover, the addition of 1.5 wt.% and 1.0 wt.% CNFs increased the shear strength and shear modulus, respectively. The experimental results showed that the addition of CNFs more significantly affected the shear properties than the tensile properties. It was also revealed that employing an optimal weight fraction of CNFs and a proper fabric harness significantly improves the mechanical properties of woven composites. Based on experimental results, an empirical model was developed to predict the strength and elastic modulus of woven composites with different harnesses and CNF weight fractions. Stage 3: The mechanical property such as ultimate strength, ultimate strain, and elastic modulus in tensile and shear of woven composite with three different harnesses were studied under dynamic loading. The new hydro-pneumatic testing machine was designed and manufactured for this special subject. Then, each harness was loaded in tension and shear with 5 different strain rates of 10-5 s-1, 5 s-1, 7 s-1, 42 s-1, and 70 s-1. The experimental results showed that the mechanical properties of the woven composite with the harnesses of 2, 5, and 8 were affected by the loading rate. According to the experiment results, by increasing the strain rate from 10-5 s-1to 70 s-1, the tensile strength of the composite with fibers woven with harnesses 2, 5, and 8 increased by 60.5%, 60.1%, and 60.3%, respectively. Also, the elastic modulus of glass/epoxy woven composite with harnesses 2, 5, and 8 increased by 0%, 24.11%, and 25.19%, respectively. At these strain rates, the tensile failure strain of the composite with fibers woven with harnesses 2, 5, and 8 also increases by 27.18%, 24.28%, and 28.18%, respectively. The mechanical properties also increased in shear loading. by increasing the strain rate from 10-5 s-1 to 70 s-1, the shear strength of the woven composite with harnesses 2, 5, and 8 increased by 53.2%, 54.5%, and 55.6%, respectively. Also, the shear modulus of glass/epoxy woven composite with harnesses 2, 5, and 8 increased by 22.25%, 24.65%, and 22.97%, respectively. At these strain rates, the shear failure strain of the composite with fibers woven with harnesses 2, 5, and 8 also increases by 12.19%, 13.97%, and 13.63%, respectively. The experimental result obtained for the mechanical behavior of the glass/epoxy composite with woven fibers under dynamic loading (up to a strain rate of 70 s-1) shows that the changes in the woven fiber geometry and the increase in their harness do not affect the mechanical properties of the composite. Based on experimental results, a dynamic empirical model was developed to predict the shear and tensile mechanical properties of woven composites with different harnesses and different strain rates.
