Predictive Crack Growth Technique for Laser Peening Process Development
Abstract: Laser peening (LP) has shown excellent fatigue life extension in numerous tests with typical treatments garnering 2-4 times the fatigue performance of an untreated component. Initially, large test programs were implemented to determine the best LP parameters for a given scenario, eventually being augmented by physics-based modeling due to the large design space available to the LP process. Approval for these processes continues to be on a case-by-case basis, contingent on multiple factors: cost, applicability, time, % fatigue life extension, and ability to track crack growth. Because LP induces compressive residual stresses in the near surface region, the compensatory tensile residual stresses are shifted sub-surface. While an axial tensile load would be mitigated by surface compressive stresses, sub-surface a crack can propagate rapidly via tensile stresses. Current predictive methods lack the ability to track this sub-surface behavior, limiting the accuracy of fatigue crack growth predictions throughout the various design stages of an LP treatment. This work demonstrates a framework that incorporates user-defined geometry, material data, crack growth data, mechanical loading, and residual stresses to predict the crack front shape evolution in 3D solids. A baseline case with no residual stresses is simulated and compared with a closed form solution.
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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