Review of Second Harmonic Generation Measurement Techniques for Material State Determination in Metals

Abstract

This paper presents a comprehensive review of the current state of knowledge of second harmonic generation (SHG) measurements, a subset of nonlinear ultrasonic nondestructive evaluation techniques. These SHG techniques exploit the material nonlinearity of metals in order to measure the acoustic nonlinearity parameter, β. In these measurements, a second harmonic wave is generated from a propagating monochromatic elastic wave, due to the anharmonicity of the crystal lattice, as well as the presence of microstructural features such as dislocations and precipitates. This article provides a summary of models that relate the different microstructural contributions to β, and provides details of the different SHG measurement and analysis techniques available, focusing on longitudinal and Rayleigh wave methods. The main focus of this paper is a critical review of the literature that utilizes these SHG methods for the nondestructive evaluation of plasticity, fatigue, thermal aging, creep, and radiation damage in metals.

Acoustic nonlinearity parameters for transversely isotropic polycrystalline materials

“…The wave displacements of the qL and qSV modes are calculated using Eqs. (19) and (20). Figure 2 gives the rotation angle w 0 as a function of the angle h 0 ; which we use to define the wave propagation directionn in Eq.…”

“…Recently, the measurements of the second-harmonic, generated from a high amplitude input harmonic excitation, have become a popular and important tool used to detect and characterize various forms of material damage. 19 A comprehensive review of this topic has recently been given by Matlack et al 19 The contribution to the second-harmonic amplitude caused by the damage is in addition to the bare nonlinearity accompanying an undamaged material state. The bare nonlinearity is sometimes referred as the virgin nonlinearity and is often assumed to be manifest solely through the lattice anharmonicity.…”

“…The extension to in situ absolute measurements of b is extremely difficult because a baseline measure of the bare nonlinearity is typically unknown. This deficiency amongst others 19 has relegated SHG techniques to relative measures. Thus, many of the theoretical efforts have been aimed toward accurately defining the various contributions to b damage .…”

Extraction of depth profiles of third-order elastic constants in cracked media

“…Especially, second harmonic generation of surface acoustic waves with their frequency-dependent depth sensitivity has been intensively used for monitoring changes of material properties. (For a recent review see [3] and references therein. )…”

A micromechanics model for the acoustic nonlinearity parameter in solids with distributed microcracks

“…Since then, a number of researchers, e.g., [10][11][12][13][14], have pursued the use of nonlinear ultrasound as a tool for nondestructive material characterization. In recent years, there has been a resurgence of interest in nonlinear ultrasonic methods [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].…”