Computation of SIFs in StressCheck
This document revisits the 2016 tech brief of the same name, introducing the new Mixed Mesh option for the Crack Front automesh method implemented in StressCheck Professional v11.1. In this revised version, we provide a brief overview of the mixed mesh capabilities in the context of the model problem covered in the original tech brief. The Mixed Mesh option for the Crack Front automesh method allows the generation of pentahedral and hexahedral elements around the crack front boundary. Additionally, we expand upon the original material by presenting a new example involving a corner crack in a plate with an offset hole.
There are three considerations when solving a 3D-elasticity problem for cracked bodies when the goal is the accurate computation of Stress Intensity Factors (SIFs):
- Approximability of the exact solution: The best rate of convergence is obtained by p-extension with a mesh graded in geometric progression towards the crack front with a grading factor of 0.15.
- Element mapping: Distorted elements decrease the quality of the computed stress field which is used in the extraction of SIFs by means of the Contour Integral Method (CIM).
- Path-independence: When computing SIFs by the CIM for corner and thru-thickness cracks in 3D, the SIFs are not independent of the radius of the integration path. It is necessary to use the stress field in the close vicinity of the crack front for the computation of SIFs.