Assessment of accumulated structural damage with the help of linear and nonlinear acoustic techniques

Abstract

The paper presents applications of linear and nonlinear acoustic techniques for reliable detection of early stages of fracture, fatigue, and other damage, as well as investigation of structure-sensitive acoustical signatures for fundamental material research. The experimental investigations were conducted on steel samples, carbon bricks, and pavers under different types of loading (static and cycling regimes) in laboratory conditions and, in field, to detect progressive changes in a blast furnace wall. A special effort was made to investigate the changes of acoustical response after aging of materials, but before a warning of damage (necking, crack initiation, crazing, disbonding, surface flow, etc.) is physically observed in service life. Measurements were made periodically as structural damage accumulated, but no visible surface crack formation was observed during the tests. The described techniques can be used for the assessment of structure integrity, remaining life, and adjustment of maintenance schedules in applications as diverse as reactor containment wall damage, inspection of damage in buildings, bridges, furnaces, pipelines, aging aircraft, etc. [Support of Indiana 21st Century Fund is greatly appreciated.]