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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“At DST Group, we have effectively used StressCheck® over the last 10 years to determine accurate stress intensity factors. The results have been used to improve our residual strength and structural life estimates for aircraft in service with the Royal Australian Airforce, including C-130, P-3C and F/A-18 A/B. We have found it to be extremely easy to use and a very versatile code with which to create parametric models.
We have recently used StressCheck® to obtain improved stress intensity factor solutions (Improved stress intensity factors for selected configurations in cracked plates and Improved stress intensity factors for a single corner crack at a loaded fastener hole) for five key generic configurations. These transferable parametric results have been published externally. One specific example is the non-linear contact analysis of a cracked, filled fastener hole, with both fastener and remote plate loading.”
Dr. Manfred Heller, HeadStructural & Damage Mechanics, DST Group