II.11 - Acoustic Emission Detection of Micro-Cracks Initiation and Growth in Polymeric Materials

Abstract

The Acoustic Emission (AE) signals are stress waves. They are generated at critical sections of the stressed materials as a result of micro-cracks advancement or deformation process. The theme is very important as a non-destructive testing technique for observing critical parts in the components of structures or machinery. Utilizing the AE signals produced by the stressed components during normal working enables one to monitor the condition of the important element continuously. When the material is loaded or strained, it produces a certain acoustic characteristic pattern. If the component begins to fail, its acoustic pattern changes. The detection of such change serves warning for the replacement of the component before it causes sudden failure of the entire structure. An AE monitoring system is developed and employed to detect the AE signals originating in the vicinity of a single edge crack in a Poly-methyl-methacrylate (PMMA) sheet. Different loading modes are applied in one loading spectrum on each test specimen. Throughout the entire loading spectrum, the AE signals are recorded simultaneously with the load. The relationship between the crack advancement and AE signals are also briefly discussed in the chapter.