Non-destructive fatigue damage characterization of laminated thermosettingfibrous composites

The fatigue behaviour of the laminated thermosetting Fiberdux 6376-HTA comp osite material is studied experimentally for both constant and variable amp litude stress reversal loading. The fatigue-induced material degradation is correlated to nondestructive evaluation data obtained from C-scan graphs t hrough the concept of the damage severity factor (DSF). The DSF is able to account for the varying severity of damage at the different specimen locati ons and is used to quantify the fatigue-induced damage. The concept of the DSF, introduced earlier by the authors for constant amplitude fatigue loadi ng of thermoplastic fibrous composites, is applied to characterize fatigue damage of thermosetting fibrous composites and is extended to account for v ariable amplitude loading. Constant amplitude fatigue tests at various stre ss levels were performed to correlate fatigue damage to the change of mecha nical properties, such as axial stiffness, residual tensile strength and in terlaminar shear strength, and to develop expressions to relate DSF to the degradation of the mechanical properties with increasing fatigue damage. Co rrelation between DSF evolution and consumed fatigue life is made and fatig ue damage functions involving stress amplitude dependency are formulated. T hese expressions together with a modified rainflow method are then used to assess fatigue life under variable amplitude fatigue loading; computed fati gue lives are compared against experimental results.