SBIR-STTR Award

The United States Air Force (USAF) has identified the need for the development of damage tolerance methodologies to address grinding burns in high strength steel.Our team proposes a holistic approach for damage tolerance assessments in landing gear components (and other high-strength steel components) that focuses not only on grinding burns but also on other failure mechanisms, such as corrosion pitting, the attempted repair of which is often the precipitating event for introducing grinding burns. Our team proposes a technical plan that considers component criticality, defect criteria for grinding burns and other physical damage states (such as corrosion pitting), residual stress effects in crack growth analyses, and mitigation schemes to stop damage propagation using engineered residual stress.The technical plan defined in the first phase shall be implemented in Phase II to provide robust data for model development. Delivery of a fully functional analytical toolkit is scheduled, per USAF guidelines, in Phase III.Our team plans to use previously developed corrosion structural effects analysis methods, residual stress / crack growth analysis methods, successful experience with laser peening, and a strong transition record to provide the USAF with a comprehensive solution package that works seamlessly within the ASIP framework.

Landing gear are often made from high strength steels, such as 300M , which are known to have excellent damage resistance when properly manufactured and maintained but to have lesser damage tolerance when compromised. For example, the grinding process, when done improperly, can heat the steel excessively and cause undesirable microstructural transformations, called grinding burns, which often contain cracks. These burned microstructures are extremely detrimental to fatigue and stress corrosion resistance.The USAF seeks methods to incorporate grinding burns into damage tolerance methods. The Phase I program recently completed by APES illustrated that grinding burns can be readily incorporated into the ASIP process. Methods for systematic, repeatable generation of grinding burns are presented in this proposal, and an analytical framework for transforming these burns into defect criteria is defined.Analytical and physical damage correlation of grinding burns is supported by a research program featuring destructive metallography, non-destructive testing, fatigue testing, failure analysis, stress intensity development and validation, and crack growth modeling. Mitigation strategies for grinding burns were also scoped using laser peening as the solution path.Potential benefits of the technology to warfighter can be recognized through increased safety, reduction in unscheduled or unnecessary maintenance, and increased aircraft readiness rates.