Modeling for nonlinear acoustic imaging of an isolated crack via standing waves in a 2D solid

This paper is concerned with numerical modeling for nondestructive imaging of defects in solids via standing waves excited by a periodic sinewave signal. The stationary solution, purely sinusoidal in an intact sample, contains higher harmonics when damage is present. These harmonics are generated by contact acoustic nonlinearity and form their own standing waves whose intensity maximum usually indicates the position of damage, in a way similar to resonant vibrometry experiments. The key point of the developed numerical tool that describes those wave phenomena is a model of planar damage (crack, delamination) considered here as an inner contact with rough surfaces and friction. The corresponding boundary conditions are given by the previously developed contact model based on the Method of Memory Diagrams (MMD) capable of automating the account for hysteretic frictional effects. Combination of the MMD for boundary conditions and a finite element formu-lation for waves in a volume (MMD-FEM model) provides a complete description which represents a numerical code applied here for nonlinear standing waves simulations. We present a number of examples obtained for idealized 2D geometry and reveal conditions in which both position and extent of damage are clearly seen as well as cases where only partial detection is possible.