Description: When the VCCT technique is used, crack propagation analysis is carried out on a nodal basis. The crack-tip node debonds when the fracture criterion is reached within a given tolerance. The time increment will be cutback if the tolerance is exceeded. For an unstable crack growth problem, however, it is more efficient to allow multiple nodes at and ahead of a crack tip to debond in one increment without cutting back the increment size when the VCCT fracture criterion is satisfied. The original VCCT technique has been enhanced to allow more nodes at and ahead of the crack tip to debond in one increment (rather than cutting back the increment size until the fracture criterion is no longer satisfied for all the nodes ahead of the crack tip). The forces at the debonded nodes are released completely immediately during the following increment.

The original VCCT criterion uses the principles of linear elastic fracture mechanics (LEFM). To account for ductile resistance, you can specify two different critical fracture energy release rates: one for the onset of a crack and the other for the growth of a crack with the reduction of the debonding force being governed by a user-specified critical fracture energy release rate for crack growth.