The Influence of Fracture Mechanisms on Fatigue Crack Propagation

Although fatigue crack propagation is generally considered to be solely an engineering problem of continuum mechanics, it is clear that accelerated propagation rates, which may arise from monotonic fracture modes, are very much a characteristic of the metallurgical structure of the material involved. It is therefore necessary that the basis for design against failure by fatigue be concentrated on metallurgical evaluation of materials such that the occurrence of these static fracture mechanisms during fatigue crack propagation is avoided. This should then entail the use of high toughness materials which, apart from not showing propagation rates which are liable to be subject to static mode accelerations, have the added advantage of being able to tolerate longer flaws prior to catastrophic failure.