#### Location

Thousand Oaks, CA

#### Start Date

1975 12:00 AM

#### Description

Before going into acoustic harmonic generation, I should bring to your attention the definition of internal stresses which was made about 40 years ago. Basically, we have to distinguish between two kinds of internal stresses. Internal stresses of the first kind are those which spread out over macroscopic distances of the order of millimeters. Applying x-rays, one obtains a line shift in the Bragg reflection due to a lattice parameter change. A simple example of internal stresses of the first kind is shown in Fig. 1, top: in bending a piece of material elastically, a line shift in the Bragg reflection will be found on the upper and lower surface. Internal stresses of the second kind are restricted to much, much smaller dimensions, say of the order of 1 um or below. Bragg reflection does not show a line shift, but merely a line broadeninq. A typical example is shown in Fig. 1, bottom. Assume dislocations are distributed in a material. The· variation of the elastic stress field surrounding the dislocations is assumed to be sinusoidal and of the periodicity of the dislocation arrangement. If another dislocation is pushed against this chain of dislocations, it will see the stress field of the dislocation arrangement. In work hardening theories, this model is used to calculate the work hardening coefficient. The present paper will be concerned mainly with the internal stresses of the second kind.

#### Book Title

Proceedings of the ARPA/AFML Review of Quantitative NDE

#### Chapter

10. Residual Stresses

#### Pages

735-748

#### Language

en

#### File Format

application/pdf

Measurement of Flow Stress Related Phenomena by Nonlinear Acoustics

Thousand Oaks, CA

Before going into acoustic harmonic generation, I should bring to your attention the definition of internal stresses which was made about 40 years ago. Basically, we have to distinguish between two kinds of internal stresses. Internal stresses of the first kind are those which spread out over macroscopic distances of the order of millimeters. Applying x-rays, one obtains a line shift in the Bragg reflection due to a lattice parameter change. A simple example of internal stresses of the first kind is shown in Fig. 1, top: in bending a piece of material elastically, a line shift in the Bragg reflection will be found on the upper and lower surface. Internal stresses of the second kind are restricted to much, much smaller dimensions, say of the order of 1 um or below. Bragg reflection does not show a line shift, but merely a line broadeninq. A typical example is shown in Fig. 1, bottom. Assume dislocations are distributed in a material. The· variation of the elastic stress field surrounding the dislocations is assumed to be sinusoidal and of the periodicity of the dislocation arrangement. If another dislocation is pushed against this chain of dislocations, it will see the stress field of the dislocation arrangement. In work hardening theories, this model is used to calculate the work hardening coefficient. The present paper will be concerned mainly with the internal stresses of the second kind.