Abstract: Due to the coupling effects between stresses in different directions, the mechanical behavior of an advanced composite material under multiaxial loading is extremely complex. In this study, the influence of through-thickness compressive stress on the interlaminar shear performance of a carbon fiber-reinforced composite was experimentally investigated. Hollow cylindrical unidirectional laminate specimens were fabricated to conduct combined compression-shear tests, and the fracture morphologies of the specimens were characterized to reveal their failure behavior. The results indicate that a moderate compression load significantly enhanced the shear properties of the laminate by inhibiting crack propagation and improving the friction effect. The shear strength and modulus of a laminate specimen subjected to combined stresses improved up to a maximum of 76% and 231%, respectively, over those of an equivalent specimen subjected to pure shear. However, as the applied through-thickness load approached the compressive strength of the laminate, the specimen shear capacity began to decline owing to the transition of fracture mechanisms. Indeed, the specimens exhibited mixed failure modes corresponding to the different stress states, which were induced by the combined effects of through-thickness compressive and shear stresses. As the applied through-thickness compressive stress increased, the dominant failure mode of the laminate specimen changed from fiber-matrix debonding to fiber shearing and then to fiber breakage, resulting in various shear performances.

Key words: Fiber-reinforced composites, Mechanical behavior, Multiaxial loading, Failure analysis