Elastoplastic treatment of discontinuities: The risk of fracture

The first part of Chapter 4 presented toughness for an overall elastic behaviour of the cracked component. This toughness is given in terms of a critical value K _lC or under the representation of a crack growth resistance curve K — R, these quantities being amenable of an experimental determination. The effect of thickness was presented: for great thickness, toughness appears as a characteristic of only material and for small thickness, toughness is a function of material and thickness. Here toughness is described in the general case by utilising the microscopic models of fracture that were treated in Chapter 5 and the stress and strain fields that were described in Chapters 6 and 7. Moreover some assumption has already been introduced in Chapter 3 in the case of brittle fracture with the a-priori assumption of a critical tangential stress. This postulate is here more thoughtfully evaluated with a complete analysis of mixed mode fracture, which allows a discrimination between the postulated basic fracture criteria.