Micro-damage diagnostics using nonlinear elastic wave spectroscopy (NEWS)

Nonlinear elastic wave spectroscopy (NEWS) represents a class of powerful t ools which explore the dynamic nonlinear stress-strain features in the comp liant bond system of a micro-inhomogeneous material and Link them to micro- scale damage. Hysteresis and nonlinearity in the constitutive relation (at the micro-strain level) result in acoustic and ultrasonic wave distortion, which gives rise to changes in the resonance frequencies as a function of d rive amplitude, generation of accompanying harmonics, nonlinear attenuation , and multiplication of waves of different frequencies. The sensitivity of nonlinear methods to the detection of damage features (cracks, flaws, etc.) is far greater than can be obtained with linear acoustical methods (measur es of wavespeed and wave dissipation). We illustrate two recently developed NEWS methods, and compare the results for both techniques on roofing tiles used in building construction. (C) 2001 Elsevier Science Ltd. All rights r eserved.