The variety of possible requirements is tackled in Zencrack by the combination of two processes:

• extraction of the results of one or more load increments from the finite finite element analysis
• a load system methodology for defining the load sequence during crack growth calculations

The processing of multiple increments from the finite element analysis is sufficient for cases without crack growth. It allows, for example, creation of K vs time plots through a transient loading sequence.

Any local mixed mode effects arising at the crack front as a result of the geometry and loading are embodied in the stress and displacement solution of the finite element analysis. A crack growth direction can therefore be calculated for each processed load increment and this direction may change through the loading sequence.

For crack growth, the load system approach allows a framework to be constructed that defines the loading history applied to the structure. The load system framework is then cross-referenced to the results from the finite element analysis. This load system approach can be used to define simple cases such as constant amplitude fatigue loading through to complex general cycles which have combined fatigue and time dependent crack growth effects.

¹ The term "load increment" is used here to describe the solution of a single load state in the finite element analysis. In Abaqus terminology this is the solution of an increment within a step. In Ansys terminology it is the solution of a sub-step within a step.