Engineering materials to determine 1 what noises are

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engineering materials to determine: (1) what noises are generated from within the test object, (2) the acoustic processes involved, (3) the frequency levels found and (4) the relation between the stress-strain curve and the frequencies noted for the various stresses to which the test objects were subjected. His most significant discovery was the irreversibility phenomenon that now bears his name, the kaiser effect. He also proposed a distinction between burst and continuous emission. Kaiser concluded that the occurrence of acoustic emission arises from frictional rubbing of grains against each other in the polycrystalline materials he tested and also from intergranular fracture. Kaiser continued his research in Munich until his death in March 1958. His work provided the momentum for continued activities at his institute and elsewhere in the world. Research in the United States The first extensive research into acoustic emission phenomena following Kaiser’s work was performed in the United States by Bradford H. Schofield. In December 1954, Schofield initiated a research program directed toward the application of acoustic emission to the field of materials engineering. His initial research was to verify the findings of Kaiser and the primary purpose of this early work was to determine the source of acoustic emissions. Schofield performed an extensive investigation into how surface and volume effects related to acoustic emission behavior. Experimental data obtained from oriented single crystals of aluminum (both with and without an oxide layer) and from oriented single crystals of gold helped him conclude that surface condition does have a measurable influence on the acoustic emission spectrum. However, Schofield’s most important conclusion was that acoustic emission is mainly a volume effect and not a surface effect. Schofield published this pioneering work in several reports introducing the term acoustic emission . 23,24 In 1956, Lawrence E. Malvern at Michigan State University came across a one-page article on audible vibrations during deformation by Wilhelm Späth. 25 The article referenced the observations by Kaiser and others about noises. Interested in studying the asperity theory of friction, Malvern suggested to a new faculty member, Clement A. Tatro, that this acoustic technique would be interesting to investigate. Consequently, Tatro initiated laboratory studies of acoustic emission phenomena. In 1957, Tatro became aware of the work of Schofield and the two began collaborating. Tatro thought that research programs in acoustic emission could follow one of two rather well defined branches: (1) to pursue studies concerned with the physical mechanisms that give rise to acoustic emission to completely understand the phenomenon; or (2) using acoustic emission as a tool to study some of the vexing problems of behavior of engineering materials. 26 Tatro also foresaw the unique potential of acoustic emission as a nondestructive test procedure. 27 His enthusiasm for this new technology
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  • Fall '19
  • Nondestructive testing, Acoustic Emission

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