Critical stress criterion to model the propagation and stop of brittle crack

12 June 2012

by A. Dahl, EDF R&D / MMC

A local criterion based on a critical stress, allowing to model the propagation and stop of cleaving crack has been implemented in Code_Aster. For this, a new feature POST_ITER = ’CRIT_RUPT’ available in STAT_NON_LINE and DYNA_NON_LINE was developed for constitutive laws VISCOCHAB, VMIS_ISOT_TRAC (_LINE) and VISC_ISOT_TRAC (_LINE) (see test SSNV226A, B, C).

This criterion is formulated as follows: the crack is propagating when the maximum principal stress, averaged over one element, reaches a critical stress SIGM_C. The crack propagation in an element is obtained by dropping the Young’s modulus of the element.

This criterion was successfully used in the PhD thesis of Anna Dahl (2012) for modeling of isotherm crack stop tests on CT specimens and compression rings. The following figure shows the comparison of the evolution of the advancing crack a with time between simulation (solid lines) and the experience of two CT tested at -150° C. In both cases, the test is able to accurately simulate the propagation velocity and the experimental average crack length at stop, af .

The illustration below shows the progress of crack obtained on a CT specimen, also tested at -150 ° C. It is clear that crack propagation is done in stages with a series of propagation and stops. the test closes after the final stop.

Available in the 11.2.1 version and future releases