Abstract

Acoustic Nonlinearity Described by Hysteretic Crack Closure Model

B.Gommerstadt (MIME Department, Northeastern University, Boston, MA, USA); A.Sutin (Stevens Institute of Technology, Hoboken, NJ, USA)

e-mail: gommers@coe.neu.edu

Nonlinear Elastic Wave Spectroscopy (NEWS) is a novel technique for nondestructive evaluation based on the nonlinear acoustic effects due to cracks leading to the amplitude dependence of the resonance frequency shift, modulation of ultrasound by vibration, high harmonics generation, and amplitude dependence damping. This technique has been developed as an empirical method. The objective of present work is to formulate a simple mathematical model for a breathing crack suitable for the NEWS technique. We employ the crack closure model that also describes hysteretic behaviour of a structural element containing a single crack. This model is adequate to reveal major nonlinear features the NEWS technique is built upon. The proposed model relates modulation parameters to a characteristic crack dimension. It explains the basic features of the observed nonlinear phenomena and it could be applied to crack characterisation needed to assess the lifetime of structures.

Section : 3