Multi-factorial strength evolution of CFRP composites: Integrating macroscopic thermo-mechanical rate-dependency and microstructural 3D fiber network topology

Carbon fiber-reinforced polymer (CFRP) composites are essential for high-performance applications, yet their mechanical reliability depends on complex multi-factorial interactions and microstructural morphology. In this study, the tensile properties of CFRP composites were first systematically investigated, focusing on the effects of temperature (20–80 °C), strain rate (1.04 × 10⁻⁴–1.04 × 10⁻¹ s⁻¹), and fiber loading (0–9.80 wt%). By leveraging macroscopic thermo-mechanical rate-dependency via time–temperature equivalence treatment, strength master curves were established to characterize strength evolution over extended strain rate and temperature ranges. Subsequently, the fiber strength utilization efficiency was quantified (0.05–0.2), which decreases with rising temperature and fiber loading, but is enhanced at higher strain rates. Fiber breakage during processing, resulting in a limited average fiber length, was identified as the major contributor to the low strength utilization efficiency. Furthermore, to identify the structural origin of these macroscopic trends, micro-computed tomography (Micro-CT) characterization was employed to capture the processing-induced 3D fiber network topology. The analysis demonstrates that while the fiber length exhibits a marginal reduction at higher fractions, the fiber orientation degree declines significantly. This disorientation, triggered by intensified fiber-fiber collisions during processing, acts as the predominant mechanism constraining reinforcement efficiency as fiber fraction increases. Overall, this study clarifies how loading conditions and processing-induced microstructures influence the strength of CFRP, providing a systematic understanding of the mechanical strength evolution of CFRP composites.