by V.-X. Tran, EDF R&D / AMA
More than forty fatigue crack initiation criteria are available in literature. However, a mechanical engineer/researcher often needs to build up new criteria. Its implementation in a finite element software is not usually easy due to significant code modification. Recently, a new functionality has been developed in Code_Aster: user-defined crack initiation criteria. The new criterion to be tested is provided in the command file (.comm) as an analytical formula of pre-defined parameters, thanks to the operator FORMULE. The new functionality facilitates the evaluation of different crack initiation fatigue models with a lower labour cost.
The user-defined crack initiation criteria are based on a general relation between an equivalent parameter and an associated fatigue life curve. The expression of the equivalent parameter is provided by the user as a function of pre-defined parameters. Actually, 20 parameters for constant amplitude loads and et 12 parameters for variable amplitude loads are available in Code_Aster. The fatigue life curve, in turn, can be provided with a name previously given in material properties or with a function (either in formula or in table).
For basic applications, the 5 existing criteria historically developed in CALC_FATIGUE have been reserved.