The damage tolerance approach is used widely in the aerospace industry today and has a physics-based foundation in fracture mechanics. The down side to traditional fracture mechanics is that an initial crack or damage must be assumed and for most fracture mechanics methods, the crack is assumed to be relatively large compared to the size of any actual damage in the structure. VEXTEC’s proposed approach will use the actual size of the damage and the cycles needed to grow to that damage to a size large enough to use traditional fracture mechanic 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 material and crack closure effects prior to transition to traditional fracture mechanics. Phase I will demonstrate the feasibility of these model to accurately predict small crack growth in beta annealed titanium by comparison with test data. Phase II would result in a fracture mechanics tool for accurate lifing of small cracks.
The benefit of developing a physics-based fracture mechanics methodology is the significant reduction in errors and uncertainty in the life predictions which result in unreliable or excessively conservative designs. The methods and tools developed will facilitate the design of more reliable and efficient aerospace structures. These models and software tools will benefit the United States Air Force and aerospace manufacturers in determining the fatigue life of structures accurately. In the long run, these tools will also help in estimating maintenance and fleet readiness levels. The United States 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 aircraft. This need will be met through better simulation tools.
VEXTEC (http://www.vextec.com) was founded in 2000 and has developed its patented technology with the aid of Department of Defense Small Business Innovative Research programs (http://vextec.com/