Acoustic harmonic generation from fatigue-generated dislocation substructures in copper single crystals

• Published in: Philosophical magazine (Abingdon, England) England), 2013-07, Vol.93 (21), p.2802-2825
• Main Authors: Apple, T.M., Cantrell, J.H., Amaro, C.M., Mayer, C.R., Yost, W.T., Agnew, S.R., Howe, J.M.
• Format: Article
• Language: English
• Subjects: Acoustics; Applied sciences; Condensed matter: structure, mechanical and thermal properties; Defects and impurities in crystals; microstructure; deformation; dislocation dynamics; dislocation structures; Dislocations; Exact sciences and technology; Fatigue; Harmonic generations; Linear defects: dislocations, disclinations; materials characterisation; Mathematical models; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; mechanical property evaluation; Metals. Metallurgy; Nonlinearity; Physics; Plastic deformation; Structure of solids and liquids; crystallography; Substructures; transmission electron microscopy; ultrasonics
• ISSN: 1478-6435; 1478-6443
• DOI: 10.1080/14786435.2013.789144

Dislocations generated during cyclic loading of metals self-organize into substructures that produce substantial changes in the nonlinear response. The nonlinearity is quantified by the material nonlinearity parameter extracted from acoustic harmonic generation measurements. Measurements of on copper single crystals oriented for single-slip ([1 2 3] loading axis) and fatigued in plastic strain control are compared to calculations of obtained from the Cantrell model for which measured values of model parameters associated with the substructures are required. Transmission electron microscopy measurements of the volume fractions of veins and persistent slip bands, dislocation loop lengths, dipole heights and the densities of primary and secondary dislocations in the fatigue-generated substructures are obtained for input into the model calculations. The model predictions agree with the values observed experimentally. In particular, the experimental data show an increase in proportional to where is the cumulative plastic strain and m is 0.7 and 0.4, respectively, for acoustic wave propagation along the and crystal axes. Such dependence is consistent with the Cantrell model and at variance with models, based on assumed variations in the third-order elastic constants, which predict an exponential dependence on .