Schedule

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1975
Wednesday, January 1st
12:00 AM

Acoustic Emission from Plastic Deformation

Steve H. Carpenter, University of Denver

Thousand Oaks, CA

12:00 AM

I would like to discuss some recent work at the University of Denver concerning acoustic emission generated during plastic deformation. I must emphasize that this is a preliminary progress report and that the investigation is still in its early stages. I would like to acknowledge two people who have been working with me on this investigation, Robert Wittman of the Denver Research Institute and Frank Higgins, a graduate student of mine at the University of Denver.

Energy Dependence of Fatigue-Enhanced Photoemission

Otto Buck, Rockwell International

Thousand Oaks, CA

12:00 AM

This is a progress report on the subject of fatigue-enhanced photoemission. In our studies on fatigue-enhanced photoemission, the ultimate goal is to see whether or not the photoyield can be used as a tool to uniquely define the early and later stages of fatigue on structural materials. This yield results in an electron current off the specimen.

Sources of Acoustic Emission in Aluminum Alloys

Lloyd J. Graham, Rockwell International

Thousand Oaks, CA

12:00 AM

I'd like to start the talk with a brief description of this task on acoustic emission (AE) source identification in terms of its immediate aims and ultimate goals. The _immediate aims were to, first, identify the sources of AE in a variety of materials, making a survey of just where they originate, and their dependence on changes in microstructure. The second aim was to identify characteristics of the AE signals which might be related to these sources and, therefore, indirectly to the microstructural effects. These aims were realized for the materials studied. The ultimate goals of such a study would be the extrapolation of AE data from one test situation or from one material to another, and, ideally, to relate the emissions to a determination of flaw criticality.

The Current Status of Nondestructive Testing with Positron Annihilation

J G. Byrne, University of Utah

Thousand Oaks, CA

12:00 AM

The existence of the positron was verified more than 40 years ago by Anderson but only in the 1950's was much attention given to its usefulness in terms of understanding the electronic structure of solids. As more workers became involved in the 1950's and 1960's work began to appear on metals, gasses and insulators and it was realized that positrons were sensitive to lattice defects. This realization has caused a new burst of interest in experimental and theoretical work using the positron as a probe for defects. Advantages of the positron technique are that it is nondestructive, very fast (106 counts in about 10 minutes), and highly sensitive to very low defect concentrations.

Theoretical Analysis of Acoustic Emission Spectra

William J. Pardee, Rockwell International

Thousand Oaks, CA

12:00 AM

Frequency analysis of acoustic emission spectra has been done by our group and others for several years now. Lloyd Graham presented some of the results in a previous paper. One would like, of course, to extract as much information as possible from these spectra. We hope, for example, that at least some fracture or failure processes, microscopic failure processes, will have distinctive frequency signatures: perhaps certain kinds of phase transformations or, as has been discussed, microcrack initiation by brittle fracture of intermetallic particles.