## 3 Results and Discussion
The shear moduli of Plain-G\({}_{23}\) and Plain-G\({}_{31}\) were estimated to be 1.4 GPa when the UHMWPE volume fraction was 45% and 3.8 GPa when the UHMWPE volume fraction was 75%. When the twill-woven UHMWPE fibers  
Figure 3: Comparison of the predicted values of elastic modulus. were used as reinforcements in the composites, the shear moduli of Twill-G\({}_{12}\), Twill-G\({}_{23}\), and Twill-G\({}_{31}\) were equivalent at approximately 1.6 GPa when the UHMWPE volume fraction was 45%. Even at a UHMWPE volume fraction of 75%, similar shear moduli were observed at 4.2 and 4.3 GPa. This trend appears to be the same as for isotropic materials, but it is not. The shear modulus is a measure of the elastic shear stiffness of a material and is defined as the shear stress-to-shear strain ratio [43; 44; 45]. Therefore, it is assumed that the shear stress applied to each shaft surface is identical in the shear elasticity section of the composites prepared with twill-woven UHMWPE fibers as reinforcements. This characteristic is applicable only in the elastic range of a material. If the plastic deformation of a real composite material is analyzed using the graph of the change in the breaking point of the material obtained by the shear test, it may appear as an anisotropic material depending on the orientation and characteristics of the fiber textiles. Therefore, additional tests are required to evaluate the isotropic and anisotropic properties of the material. Several investigations have demonstrated that locations with significant warp-welt intersections in fiber textiles induce stress concentration, which leads to cracks, and thus they serve as crack initiation points [46; 47; 48]. Consequently, there may be differences between the plain and twill-woven textiles. Thus, it is thought that the tensile and shear strengths of plain-woven textiles with multiple warp-welt intersections will be low. Figure 5 shows the Poisson's ratio results estimated by FEA for the composites prepared with UHMWPE textiles. Poisson's ratio is one of the fundamental properties of any engineering material and represents key mechanical characteristics for woven textiles in many applications, including in engineering systems that incorporate textiles as structural elements. The magnitudes of Poisson's ratios can reach unexpected values for woven textiles, which are significantly different from those for conventional engineering materials, leading to unusual stress-strain behavior [49; 50]. The Poisson's effect in a woven textile originates from the interaction between the warp and weft yarns and can be expressed in terms of the structural and mechanical properties of the system. This characteristic is exclusive to textiles and different from a typical continuum, although their mechanical characteristics are relatively similar. The Poisson's ratio calculation result for the composites based on FEA revealed that when the UHMWPE volume fraction increases, the effect of UHMWPE in the composite increases and the Poisson's ratio decreases. Furthermore, a  
Figure 4: Comparison of the predicted values of shear modulus. difference in the Poisson's ratio between the twill weave and plain weave was observed, and the Poisson's ratio of the twill weave was higher. The Poisson's ratio of Plain-v12 was estimated to be 0.22 at 45% UHMWPE volume fraction and decreased to 0.20 when the UHMWPE volume fraction increased. As the UHMWPE volume fraction increased, the Poisson's ratio of the Plain-v13 composite decreased from 0.31 to 0.23. Similarly, the Poisson's ratio of Twill-v12 decreased from 0.21 to 0.19 as the UHMWPE volume fraction increased, while that of Twill-v13 decreased from 0.34 to 0.24. These characteristics may be analyzed owing to the difference in the number of orthogonal points of UHMWPE fibers depending on the weaving conditions. In the plain weave, orthogonal fiber points are constantly generated, but in the twill weave, fewer orthogonal fiber points are formed than in the plain weave.