Effects of Material Variation on Acoustic Emissions-Based, Large-Crack Growth Model

Acoustic emissions (AE) collected during fatigue crack-growth in a titanium alloy were analyzed and compared with a previously proposed AE-based, crack-growth model used for an aluminum alloy. Acoustic emission technology has the potential for on-line structural health monitoring; a desired procedure for evaluating material degradation in military and commercial aircraft. Both aluminum and titanium alloys are prevalent materials in aerospace structures which prompted this current investigation. Acoustic emissions are stress waves that propagate through a material as a result of applied stresses. When a material is subjected to cyclic fatigue loading, AE signals are generated due to dislocation movements and microstructural changes. These waves can be detected by piezoelectric sensors when placed on the surface of the material. Previous research proposed a linear relationship between the logarithm of AE count rate (dc/dN) and the logarithm of crack growth rate (da/dN) for the aluminum alloy, Al7075-T6, at various loading conditions and loading frequencies. This paper summarizes and compares the results obtained from identical experiments using titanium alloy Ti-6Al-4V with the previous study. The results suggest the linear model used to relate AE and crack growth in Al7075-T6 holds true for the titanium alloy while, as expected, the model parameters are material dependent. With each material, the model parameters and their distributions were estimated using a Bayesian regression technique.

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