Computation of SIFs in StressCheck
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. This point is addressed in the following text and practical guidelines are provided.
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The software provides a highly reliable and user-friendly production stress analysis tool that will replace the Finite Element Method (FEM) tools and failure criteria the experts currently employ for analyzing bonded joints. The software includes an FEM-based handbook format, which allows non-experts to utilize models prepared by specialists. The handbook problems include built-in failure criteria, geometric and material nonlinearities, and the modern FEM technology provides better error control and the treatment of very large aspect ratios.”
Dr. Stephen P. EngelstadTechnical Fellow, Lockheed Martin Aeronautics Company, Structural Methods and Analysis