Dislocation Contribution to the Second Harmonic Generation of Ultrasonic Waves

Abstract

The experimental evidence and the associated theory are presented for the dislocation contribution to the generation of the second harmonic of an ultrasonic wave in solids. The contribution is measured through the changes, as a function of static bias stress, in the amplitude of the second harmonic of a fundamental wave (10 Mc/sec compressional wave) propagating in the specimen. In aluminum single crystals the amplitude of the second harmonic, for a given amplitude of the fundamental, changes markedly with static bias stresses ranging from 0 to 106 dyn/cm2. In alloys, there are essentially no changes of the amplitude of the second harmonic even for bias stresses up to 107 dyn/cm2. These observations are consistent with the predicted dependence of the amplitude on dislocation loop length and on the static stress. The effects of small amounts of plastic deformation were consistent with the proposed model.

Acoustic Harmonic Generation and Dislocation Dynamics of Fatigued Aluminum Alloys

“…The graph in Fig. 1 shows that the nonlinearity parameter ~ for aluminium 2024-T4 is relatively constant over a large stress amplitude range in both the fatigued and unfatigued sample and is thus similar to the results of Hikata et al [2] for 2S and lIS alloys. The graph also shows that a substantial increase in ~, hence acoustic harmonic generation, occurs for the unfatigued sample in the longitudinal acoustic stress range 2.7 MPa to 2.9 MPa.…”

“…The model of Suzuki et al[l] predicts the second hannonic to be linearly dependent on the applied or residual stress in the solid and dependent on the dislocation loop length to the fourth power. Experimental verification of the linear dependence on applied stress is reported by Hikata et al [2] in high-purity single crystal aluminium. However, their second hannonic generation experiments on aluminium alloys 2S and lIS show no dependence within experimental error on applied tensile stresses up to 1.6 MPa.…”

“…It is appropriate then to consider the nonlinear interaction of acoustic waves with such dislocation configurations. We begin with an examination of the theory of Suzuki et al [1] and of the experiments of Hikata et al [2] (performed during the 1960's) pertaining to acoustic harmonic generation from arrays of single dislocations (monopoles) in unfatigued material and discuss the limitations in applying their findings to the dislocation multipole configurations and substructures formed during the fatigue process. We introduce a new theory of the interaction of acoustic waves with dislocation dipoles and with dipole-array approximations to the vein and PSB substructures of fatigued metals and compare the results to experimental measurements of the acoustic nonlinearity parameter in aluminum alloy 2024-T4.…”

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

“…Major sources of acoustic nonlinearity in such materials are material defects such as dislocations and precipitates [30][31][32]. Since damage in metallic materials often involves dislocation activities, by measuring the acoustic nonlinearity parameter, the degree of damage in metals can be assessed nondestructively.…”

“…Back in the early 1960s, several authors, e.g., [1][2][3][4][5][6][7][8][9] , pointed out the feasibility of using nonlinear ultrasound for nondestructive evaluation (NDE) of damage in metallic materials. 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.…”