FE Mesh Generation – Automated Crack Grow Modeling with a View to Stress Intensity Factor Computing

Abstract

The damage tolerance design approach, expects the existence of the initial flaw in any structure. To manage the extension of this flaw during service, the fracture mechanics principles are applied. For this purpose, two domains of analysis must be accomplished: First, the crack growth due to variable, periodical load (fatigue load), second, the residual strength of the damaged structure statically loaded. For both analysis, the computing of the fracture mechanics characteristics in each state of the crack opening is indispensable.In practice, the application of the FE method is necessary. By the help of currently used FEM software NASTRAN, the stress intensity factor – KI and KII – can be compute by application of the special element, called CRAC2D. Unfortunately, CRAC2D element is not implemented into the currently used FE pre-processors. Moreover, one application of the CRAC2D element result only in a single value of the KI and KII for the modeled crack length.For these reasons, the fully automated crack growing modeling was developed. Based on the virgin FE model (base FE model without crack), the developed software application generate the appropriate FE model for each desired crack opening. User have only to indicate the crack initiation node and the crack growing path, so-called crack growing scenario (see fig.1). After the data check, the crack is modeled, the CRAC2D element is applied at the crack tip, the FE model is saved, the related job is executed and the resultant KI and KII values are associated with modeled crack length. This step is repeated for each desired crack opening.