<![CDATA[This work evaluates the impact of manufacturing method and fiber orientation on the mechanical properties of carbon fiber-reinforced polymer (CFRP) for automotive applications. CFRP composites were fabricated using vacuum bagging (VB), vacuum-assisted resin infusion (VARI), and hand lay-up (HLU) processes. Composites in each method were manufactured with 0° and 90° fiber orientations for compressive and tensile tests, and ±45° for in-plane shear response by tensile test. Short beam and V-notched beam tests were performed to determine the interlaminar shear and shear properties. Microstructural characterization was performed on the manufactured composites and the fracture specimens after testing. Unlike previous studies that mainly focused on selected mechanical properties or a single manufacturing route, this study provides a comprehensive comparative assessment of HLU, VB, and VARI unidirectional CFRP laminates by integrating mechanical characterization, CT-scan defect analysis, SEM observations, and finite element validation. The findings reveal that superior laminate compactness and tensile-related properties achieved by VARI do not necessarily translate into higher interlaminar shear strength, providing new insight into the role of manufacturing-induced laminate architecture on composite performance. The study results showed that composites manufactured with vacuum infusion using 0° and ±45° fiber direction had higher tensile strength and stiffness than those fabricated with vacuum bagging and hand lay-up. The ultimate tensile strengths of the 0° CFRP composites for HLU, VB, and VARI specimens are 507.72 ± 52.14 MPa, 685.69 ± 62.65 MPa, and 774.31 ± 58.18 MPa, respectively. Meanwhile, for the 45° CFRP composite specimens, the tensile strength values were measured as 20.85 ± 0.82 MPa for HLU, 21.20 ± 0.45 MPa for VB, and 22.18 ± 0.81 MPa for VARI. However, at 90° fiber direction, the manufacturing method did not significantly affect the tensile strength, although the tensile modulus was still affected by the method used. The compressive strength results of the 0° composites showed that hand lay-up specimens (124.8 ± 13.1 MPa) had the highest values, while vacuum infusion specimens had the highest compressive strength at 90° fiber direction (44.60 ± 0.82 MPa). The vacuum infusion composites had lower shear (15.31 ± 1.01 MPa) and interlaminar shear strength (13.68 ± 0.85 MPa), indicating that the high fiber volume fraction did not significantly affect this behavior. However, it has a significant effect on composite stiffness, where the tensile (39.31 ± 4.58 GPa) and shear (1.50 ± 0.15 GPa) modulus values of these composites are the highest. Microstructural evaluation showed that the improvement of resin distribution and fiber/matrix bonding in vacuum infusion composites contributed to the improvement in mechanical properties.]]>
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