Fatigue behaviour of metallic fibre-reinforced materials: a study of steel fibre-reinforced silver

Abstract

Fatigue damage and crack propagation modes in composites with unidirectionally aligned fibres may be affected by several variables such as fibre and matrix strength, fibre—matrix interfacial bonding and possible fluctuations in the strength of the reinforcing fibres. The influence of the different parameters on the behaviour of metallic fibre-reinforced materials was investigated up to 108 cycles in a model compound of steel-fibre-reinforced silver. The fatigue tests were carried out at a frequency of 20 kHz using an ultrasonic equipment. Two fundamentally different failure mechanisms and several transitional modes have been observed: (a) failure by nucleation and propagation, usually of one matrix fatigue crack, with simultaneous failure of the reinforcing fibres, (b) failure by gradual accumulation of matrix and interface fatigue damage and fibre-inhibited propagation of the final fatigue crack. The occurrence of both mechanisms depends mainly on the development of the local stress conditions when a matrix fatigue crack is approaching a fibre. This is discussed in terms of a simple model. Additionally, the effect of the failure mechanism on fatigue life and on the design of an appropriate failure criterion is considered.