Mechanical and Dynamic Responses of Carbon–Innegra Hybrid Composites: Insights into Viscoelasticity and Failure Mechanisms

Carbon–Innegra (CI) hybrid composites combine the high stiffness and strength of carbon fibers with the high deformation and energy dissipation capabilities of Innegra fibers, offering potential for lightweight structures subjected to complex mechanical and dynamic loading. This study investigates the mechanical, viscoelastic, and dynamic behavior of a woven CI hybrid composite through an integrated experimental approach. Tensile tests were performed on specimens cut along three different directions (0°, 90°, and 45°), revealing a pronounced orientation dependence of the tensile response. The average tensile strength was 239.53 MPa in the longitudinal direction, 186.84 MPa in the transverse direction, and 53.52 MPa in the diagonal direction, while the 45° specimens exhibited strains at failure of approximately 15–17.5%. Dynamic mechanical analysis (DMA) showed strong orientation dependence of the viscoelastic response. At 30 °C, the storage modulus ranged from approximately 8.7–9.9 GPa in the transverse direction and 6.1–7.6 GPa in the diagonal direction, while the maximum tan δ values were approximately 0.656–0.699, depending on specimen orientation. Free-vibration tests conducted on cantilever specimens demonstrated a clear anisotropic dynamic response. For a free length of 200 mm, the natural frequencies were 60.00 Hz, 51.28 Hz, and 32.87 Hz for the transverse, longitudinal, and diagonal orientations, respectively, while the highest damping ratio reached 0.0240 in the diagonal direction. Optical microscopy was used to examine the post-failure morphology and identify the main damage mechanisms, including yarn reorientation, delamination, reinforcement damage, and resin degradation. The combined tensile, DMA, vibration, and microscopic results demonstrate that the woven CI architecture strongly influences the mechanical, viscoelastic, and dynamic responses of the composite.