Abstract

Nondestructive evaluation (NDE) techniques have been widely used in industry but its application is limited to end-of-life events when the size of defects is already critical. Compared to conventional NDE techniques, nonlinear ultrasound (NLU) is a promising tool for diagnosing early-stage damage, since it is sensitive to nano- and microstructural features such as dislocations and precipitates. Presented in this work is an approach to evaluate the acoustic nonlinearity parameter (?) due to accumulated plastic strain. A dogbone sample of Al2024 was subjected to fatigue cycles and the spatial distribution of accumulated strain fields were measured using digital image correlation (DIC). DIC can capture localized strain at microscale and thus high resolution strain distributions can be obtained. A map of accumulated acoustic nonlinearity was then calculated based on a power law relationship. Using this spatial map of ?, we calculated the dependence of A2/??12 on propagation distance, as typical in Rayleigh surface wave measurements. Results showed that measure ? depends on the propagation path, since there is a spatial distribution of plastic strain. This approach will be useful understanding second harmonic generation at microscale.

How to Cite:

Kim, C. & Matlack, K., (2019) “An experimental method for mapping acoustic nonlinearity from accumulated plastic strain field”, Review of Progress in Quantitative Nondestructive Evaluation .