Over the last few decades, as material science and damage detection techniqueshave improved an increasing number of structures are now designed based onreliability and ‘Safe Life’ criteria requiring much better knowledge of crack growth profiles and residual life details. This renders using experimental methods rather impractical and highlights the importance of fracture mechanics based computational mechanics algorithms used in an evaluation of 3D mixed mode crack propagation.

The total fatigue life of a component consists of crack initiation and crack propagation phases. The crack initiation phase which could be as much as 75-80% of the component life is largely affected by the strain field in the process-zone immediately ahead of a void or a notch type flaw where the damage due to dislocation and migration of grain boundaries at a micro-scale level accumulates and allows a crack to nucleate. Once the crack is fully initiated and grown to a discernable size, larger than the process zone, the size, shape and the orientation of which can be measured by a Nondestructive Testing (NDT) tool. Finite Element Analysis (FEA) Codes can then be used to simulate 3D crack propagation to assess the integrity of a component. Most crack propagation codes are based on Linear Elastic Fracture Mechanics (LEFM) principles. In the Small ScaleYielding (SSY) regime where the plastic strains in the process-zone remain small, LEFM may still be used to assess crack growth provided the constraint (triaxiality) at the crack-tip remains positive.