Improved Design Package for Fracture Mechanics Analysis

ABSTRACT: The damage tolerance approach is used widely in aerospace industry and has a physics-based foundation in fracture mechanics. The fatigue crack growth rate can be determined by calculating the SIF and knowing empirically derived material parameters. Similitude is achieved for different loads, different crack sizes, and different crack shapes. The down side to fracture mechanics is that a crack must be assumed and for most fracture mechanics methods, the crack is assumed to be relatively large compared to the size of the plastic zone and the material microstructure. VEXTEC"s proposed approach will provide the actual size of the flaw and the cycles needed to grow to that size by applying probabilistic, physics-based fatigue crack growth models developed under this program. The damage is modeled as microstructurally small and physically small cracks by capturing the microstructure of the beta annealed titanium material and crack closure effects prior to transition to long crack regime. Phase I will demonstrate the feasibility of these model to accurately predict small crack growth by comparing with test data. Phase II will result in a fracture mechanics tool for accurate lifing of small cracks. BENEFIT: The benefit of developing a physics-based fracture mechanics methodology for analysis of cracks smaller than the linear elastic fracture mechanics (LEFM) regime is the significant reduction in errors and uncertainty in the life predictions which result in unreliable or excessive conservative designs. The methods and tools developed in this SBIR will facilitate the design of more reliable & efficient aerospace structures. These models and software tools upon further development in Phase II will benefit the USAF and OEMs in determining the fatigue life of structures accurately by directly linking to tools used for structural design. In the long run, these tools will also help in estimating maintenance and fleet readiness levels. The US military is, out of necessity, focusing on sustainment of its existing weapon systems, as opposed to procurement of new fleets. One important aspect of improved sustainment is better, higher fidelity models for existing aircrafts. These needs will be met through investment by OEMs and the military in better simulation tools. Assuming VEXTEC captured only a fractional percent of the discussed market potential, it would equate to many millions of dollars in annual revenue to the company. Moreover, VEXTEC foresees this opportunity following in the footsteps of previous successful technology transitions into the aerospace markets.