ABSTRACT
In this chapter we consider methods for evaluating crack tip parameters for practical applications. In view of the complex nature of the equations of state which exist even in the most simple test pieces, a desirable approach is to compute the displacements, stresses and strains at required points in the structure being analysed by suitable numerical techniques. Crack tip parameters may then be evaluated such as the J integral defined in Chapter 2. In this case, by the path independence discussed in Section 2.2.2.3, the contour of integration may be chosen to pass through areas of structure away from the tip, where stress and strain gradients are relatively mild. This in turn enhances the accuracy of the numerical integration in techniques such as the finite-element method. It also reduces the importance of the actual crack tip modelling, such as the effects of blunting with increased local plasticity.
