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1975
Wednesday, January 1st
12:00 AM

Deducing Subsurface Property Gradients from Surface Wave Dispersion Data

John Richardson, Rockwell International

Thousand Oaks, CA

12:00 AM

My talk deals with the same subject as that of the previous speaker, Dr. Szabo, except I am not going to assert that it involves residual stresses necessarily. I consider some kind of a perturbation of the elastic properties and/or density due to some kind of surface treatment. As in all problems of this kind I assume, at least for the time being, some kind of an ansatz about mutual proportionality between the various kinds of perturbed physical properties as they vary with depth.

There are, perhaps, four ways of classifying approaches to this kind of problem. One is a parametric approach where one assumes that the candidate profile is defined by a finite set of parameters which are adjusted to give the best fit to the experimental data. Another is a nonparametric approach in which one does not have a finite set of parameters but an essentially infinite set of parameters. Another dimension of classification is whether one is using a probabilistic or a nonprobabilistic approach. In the nonparametric case one is forced to use a probabilistic approach. Here one treats every conceivable profile as being present in a statistical ensemble but with probability weightings reflecting one's a priori knowledge of what is more or less reasonable.

Measurement of Flow Stress Related Phenomena by Nonlinear Acoustics

Otto Buck, Rockwell International

Thousand Oaks, CA

12:00 AM

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.

Measurement of Residual Stress Using Magnetic Barkhausen Noise Analysis

G A. Matzkanin, Southwest Research Institute
C G. Gardner, Southwest Research Institute

Thousand Oaks, CA

12:00 AM

In this presentation we very briefly review the concepts involved in stress measurement by means of the Barkhausen effect, and cite the major instances of its practical application; the major part of the paper is devoted to a presentation of some recently obtained results regarding the effects of plastic deformation, and of biaxial stress fields.

Measurement of Surface Strain by Surface Reflection Raman Scattering

Susan Ushioda, University of California - Irvine

Thousand Oaks, CA

12:00 AM

My talk today sort of comes from the unreal side of the world in the sense that this method of nondestructive testing is quite new and nobody has used it, and I am presenting this method as a possible method for the future. Of course, the unreal world today often becomes the real world tomorrow, so there is a good possibility that the method that I present here will become a useful one. At the moment, of course, the equipment that I use for these measurements can't be hung on the airplane wing or anything of that sort.

Residual Stress Detection by Measurement of Efficiency of Electromagnetic Generation of Ultrasound

R Bruce Thompson, Rockwell International

Thousand Oaks, CA

12:00 AM

I think I should thank George Matzkanin for starting everyone thinking in terms of magnetic phenomena. Yesterday we heard three papers describing the performance of electromagnetic transducers on nonmagnetic materials. The question was asked at the close of one, "Do these transducers work on ferrous materials?" The answer that I will give you is, "Yes, they do, and furthermore, the efficiency of the operation is directly related to the stress within the material." The mechanism of this relationship is very similar to the mechanism of the stress dependence of the Barkhausen effect. However, the information gained is distinct and complimentary.

Residual Stress Measurements from Surface Wave Velocity Dispersion

Thomas L. Sazbo, United States Air Force

Thousand Oaks, CA

12:00 AM

I'm going to try to keep you awake and I hope to tie some of the subjects that were discussed earlier today in with this paper. You may be asking, "What do I mean by velocity dispersion?" and even more, "What do I mean by residual stress?"