When setting up a VCCT-based crack-growth analysis, consider the following hints and recommendations:
Differences in the size of the elements ahead of and behind the crack tip/front affect the accuracy of the energy-release-rate calculation. Use equally sized meshes for elements along the predefined crack path whenever possible.
The mesh size itself also affects the solution. Examine mesh-size convergence before attempting the finite element solution.
To ensure accuracy of the energy-release-rate calculation, define the crack extension carefully.
The following assumptions apply to the VCCT calculation:
The strain energy released when a crack advances by a small amount is the same as the energy required to close the crack by the same amount.
The crack tip field/deformation at the crack tip/front location is similar to that which occurs when the crack extends by a small amount.
Neither assumption applies when crack-growth approaches the boundary, or when the two cracks approach each other; therefore, when using the VCCT calculation for problems such as T-joints where the two cracks approach each other, examine the analysis results carefully.
In the case of unstable crack-growth or a rapid extension of the crack, specify smaller DTMAX and DTMIN values (CGROW) to allow time for load rebalancing.