The effect of hygrothermal environments upon the tensile and compressive strengths of notched CFRP laminates. Part 2: Fatigue loading

Abstract

The effects of several hygrothermal environments upon the residual strength of centre-notched laminates, fabricated from a standard carbon fibre-reinforced epoxy system were investigated. Conditioned dry or wet specimens were fatigue tested in tension-compression in a range of hygrothermal conditions (RT/dry, 90°C/dry, RT/wet and 90°C/wet) for a predetermined number of fatigue cycles. Subsequently, both the tensile and compressive residual strengths were evaluated in a range of test temperatures: RT, 90°C and 130°C. Two stacking sequences were studied: (±45°/0° 3/±45°/0°) s denoted A and (0°/±45°/0° 2/±45°/0°) s denoted B. In the case of sequence A, two notch geometries were considered: a sharp 10 mm notch, and a circular 5 mm diameter hole; sequence B was investigated with a sharp notch only. The results indicated that, for a given stress amplitude, the residual strength appeared to be dependent upon factors such as: notch geometry, environmental exposure, the number of fatigue cycles, and/or a combination of these. The interactions of damage modes responsible for the observed behaviour were isolated and have been schematically presented in a ‘flow diagram’.