Methodology for extracting interface damage properties of FRP composite laminates under cyclic shear loading conditions

A damage-based fatigue model for cohesive interfaces in fiber-reinforced polymer (FRP) composite laminates has been proposed. This paper described a combined experimental-computational approach to determine the properties and material parameters for the fatigue model. The approach is demonstrated for the cyclic shear loading. For this purpose, carbon fiber-reinforced polymer (CFRP) composite laminate beam specimens ([0]8), each with a pre-cracked interface is tested under 3-point bending setup. Interfacial fatigue damage is introduced by subjecting the specimens to fluctuating load (ΔP = 75 N, R = 0.25) and varying numbers of accumulated cycles (50, 100 and 200 kcycles). Subsequent quasistatic test to catastrophic failure establishes the characteristic residual strength responses of the damaged specimen. A complementary validated finite element (FE) simulation of the load-displacement response establishes the stress and strain states at the damaged interface. These internal local variables at the crack front are employed to determine the fatigue-related damage model parameters. The resulting interfacial shear strength, penalty stiffness and critical shear energy release rate are found to vary non-linearly with the accumulated number of load cycles.