Abstract: This study investigates the mechanical behavior of pultruded carbon fiber-reinforced thermosetting resin matrix composites(pultruded CFRP) under complex loading conditions. Through a series of mechanical tests combined with digital image correlation(DIC) and scanning electron microscopy(SEM), the failure mechanisms were elucidated. A three-dimensional solid element model incorporating the 3D Hashin failure criterion was employed to predict the strain field and mechanical response of pultruded CFRP under open-hole tension. The results indicate that the material exhibits significant anisotropic failure behavior under different loading directions. Both longitudinal tensile and compressive properties are markedly superior to their transverse counterparts, primarily due to the direction-dependent failure modes in pultruded composites. Under longitudinal tension, failure is dominated by fiber-matrix interfacial debonding, triggering stress redistribution and subsequent fiber brittle fracture, whereas transverse tension failure is governed by matrix-dominated fracture accompanied by interfacial debonding. Under compressive loading, longitudinal failure originates from fiber micro-buckling, while transverse failure is characterized by matrix shear yielding-induced interfacial debonding and localized fiber yielding. Since the fracture and yielding loads of fibers are substantially higher than those of the matrix, the longitudinal mechanical properties significantly outperform the transverse properties. In shear failure mode, the composite exhibits multiple crack propagation features, initiated by horizontal matrix cracks near the notch, which develop into multiple parallel matrix cracks along the fiber direction, ultimately leading to global failure. Additionally, the open-hole tensile strength reaches 1 246.83 MPa, demonstrating a typical fiber-matrix interfacial longitudinal splitting failure induced by hole-edge stress concentration. Numerical simulation of open-hole tension predicted the material’s failure mechanism with a deviation of 11.06%. Finally, a comparative analysis between DIC and conventional strain gauge measurements revealed discrepancies of less than 4% at all stress levels, validating the reliability of the DIC-derived full-field strain maps and stress-strain curves. This study systematically analyzes the failure mechanismsof pultruded CFRP through multiple fundamental mechanical tests, providing a theoretical basis for structural design and failure assessment under complex loading conditions.

Key words: carbon fiber reinforced polymer, pultrusion, mechanical property, finite element simulation, non-contact digital image correlation method