## 4 Conclusions  
In this study, the tendency according to the aspect ratio of UHMWPE fibers was comparatively analyzed to develop a composite material in which these fibers were used as reinforcing materials with a PP-based matrix. The composite materials were analyzed using finite element analysis and micromechanical models. Finite element analysis was performed sequentially from an aspect ratio of 0.2 to 30. In the finite element analysis, an aspect ratio of 30 or more was modeled in the form of continuous fibers. Therefore, the limit of convergence occurred, and a finite element analysis was performed up to an aspect ratio of 30. Theoretical numerical analysis was performed using the Halpin-Tsai model to analyze and compare aspect ratios from 0.2 to 100. In the finite element analysis, the basic model included PP used as a matrix, and UHMWPE fibers oriented in the x-axis direction. The volume fractions of the UHMWPE fiber and matrix were set to 5% and 95%, respectively. An analysis model was constructed using the homogenization method. An ANSYS Material Designer was used to construct this composite material analysis model using the homogenization method. According to a comparative analysis of E\({}_{11}\), which is the modulus of elasticity in the longitudinal direction of the fiber, when the aspect ratio of the UHMWPE fiber was 0.2 and 30, the modulus of elasticity was calculated to be 1518 MPa and 2365 MPa, respectively. Theoretical numerical analysis indicated that the modulus of elasticity was 2415 MPa when the aspect ratio was 100. The higher the aspect ratio of the UHMWPE fibers, the higher the elastic modulus (E\({}_{11}\)) is in the longitudinal direction. Figure 7: Shear modulus (G\({}_{12}\)) according to the UHMWPE aspect ratio. Analyzing the tendency of the elastic modulus to increase together with the theoretical analysis results confirmed that the rate of increase in elastic properties decreased above UHMWPE aspect ratios of 40 and converged to 2400 MPa. Based on these characteristics, an aspect ratio above 40 can be interpreted as a continuous fiber. In addition, a comparative analysis of the elastic modulus in the E\({}_{22}\) direction indicated that, in the low aspect ratio range, the anisotropy property of the existing anisotropic material in the x-axis direction was reversed to the y-axis longitudinal direction. This was owing to the reversal of the aspect ratio, such that the elastic modulus of E\({}_{22}\) was increased. Therefore, the E\({}_{22}\) elastic modulus with an aspect ratio of 0.2 was the highest at 1620 MPa. Furthermore, the elastic modulus of E\({}_{22}\) converged to a constant value because it was related to the cross-sectional shape of the UHMWPE. A comparative analysis of the shear modulus (G\({}_{12}\)) confirmed that the larger the aspect ratio, the greater the convergence to 510 MPa. The shear modulus (G\({}_{12}\)) is related to the fiber cross-section of the UHMWPE because it is a shear modulus that occurs in the cross-section in which the fibers of the composite material are oriented. The UHMWPE modeled in this study had a circular cross-section, and the number of fibers added was limited according to the volume fraction, resulting in a convergent outcome. If the volume fraction is 50% or more, a curved graph will be obtained rather than one that converges to a constant value. When developing a PP/UHMWPE composite material based on these research results, the expected elastic properties can be calculated for UHMWPE short-fiber reinforcement to secure injection moldability. The expected elastic behavior can be predicted when developing long and continuous-fiber composite materials to secure elastic properties. This can be used to develop various materials and components based on the characteristics of the PP/UMHWPE composite material derived in this study. Since the PP/UHMWPE composite material is lightweight and high-strength, it can be used for developing parts in the automobile field and can be used for various lightweight components.