SUMMARY

Turbine engine components such as fan and compressor blades experience complex combinations of steady and vibratory loads that lead to in-service cracking in directions that cannot be predicted by current fracture criteria. In addition, under mixed Mode I/Mode II loading conditions, crack growth direction has been observed to shift from tensile-dominated to shear-dominated crack growth at higher proportions of Mode II loading. Accurate 3D crack path predictions are required in order to characterize the risk and extent of foreign object damage (FOD) resulting from liberation of a fractured component. A new, extensive database of crack growth direction under various 3D mixed-mode loading conditions is required to develop and validate new crack path prediction models, extending current 2D mode mixity criteria to include Mode III loading experienced in fan blade vibration. Titanium 6Al-4V will be tested with two novel crack growth specimen designs to generate a range of mode mixities (I/II/III) and crack tip stress intensities will be calculated with boundary and/or finite element modeling software. Quantitative microscopy will be used to characterize the crack path and growth rate. This crack growth data will be used to extend or replace current crack path prediction criteria.