Effect of fatigue on the interface integrity of unidirectional Cf-reinforced epoxy resin composites

The current study reports on the fatigue behaviour, micromechanics of reinforcement and stress transfer efficiency of the interface of an autoclave-processed Cf-epoxy laminate. Throughout fatigue loading at a maximum strain below the critical fatigue limit of the matrix material, testing was interrupted at discrete fatigue levels of 100, 103, 104 and 105 cycles to allow for laser Raman microscopy measurements of the axial stresses developing along natural and induced discontinuities on fibres in the composite. The established axial stress profiles were regressed to establish the corresponding interfacial shear stress (ISS) profiles at each fatigue level. The effect of fatigue on the stress transfer efficiency of the interface was calculated through the evolution of three interfacial performance parameters (maximum ISS, length required for its attainment and transfer length) as a function of loading cycles. Additional measurements on “random” locations helped identify the main damage mechanisms developing at the microscale.