The cyclic stress behaviour of a 355 stainless steel 2024-T8 aluminium alloy

The push-pull fatigue behaviour of a 355 stainless steel 2024-T8 aluminium alloy composite, has been studied at constant stress. The S-N curve shows a fatigue strength of 20 kg/mm². Microhardness measurements reveal that little fatigue hardening takes place within the matrix; also, hardness numbers are similar in fatigued specimens, irrespective of the applied stress amplitude.The increase in damping capacity for increasing stress amplitudes, is attributed to increased delamination at the fibre-matrix interface, in the early fatigue stages. This result is also confirmed by optical microscopy. It is inferred that the sequence of failure weakness in the composite is: fibre-matrix interface, matrix and, finally, fibres.A fatigue strength/tensile strength ratio of 0.16 for this material is noticeably low, but fatigue properties of the composite can be improved by enhancing the fibre-matrix bonding.