Stress Wave Emission - An Important New Tool for the Technical Community

Engineers and scientists in increasing numbers are beginning to use a technique for determining the inception and continuation of crack growth and/or general specimen deformation as a means of establishing a variety of objectives. These objectives range from the detection and location of a growing flaw or a grossly deforming area of a structure, simple or complex, to all phases of research into the mechanisms of material failure. Stress waves, the elastic energy released by material undergoing deformation, are a measurable entity traveling through the structure in which they occur. Instrumentation techniques allow these waves to be correlated with other physical parameters and provide capability to detect deformations within the material which are undetectable by other techniques. Practical applications of stress-wave emission technology encompasses systems for use in sensing and locating undetected flaws in supposedly flaw-free structures, systems for preventing the unexpected catastrophic failure of structures and many techniques for studying failure processes in both flawed specimens (fracture mechanics studies, for example) and unflawed materials, including metals, glass, concrete, and composites. We at the Aerojet-General Corporation in Sacramento, California, have been working in the field of stress wave emissions for nine years, on a continuous and ever-increasing basis. As with any new exciting technology, we have watched as the number of groups using the technique has grown rapidly, particularly in the last year or so. Primarily because of this wide-spread interest, the applicational uses and the number of users can be expected to continue to increase dramatically. Prime impetus to the use of the stress-wave-emission technology (also referred to as acoustic emission) rests with the Aerospace programs, and has been directed towards the increased reliability of DOD, NASA and other Government agencies products, either by direct inclusion into hardware programs, or by research tasks on improved nondestructive inspections, on-line failure warning systems, materials evaluation, materials research, and test and inspection process revisions. Developments made under these programs have found their way into commercial industry, and we confidently predict their continued growth as one of the very clearly defined spin-off developments of the aerospace industry