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Acoustic emission testing is a quasi-non-destructive testing method to detect and record the ignition and propagation of irreversible damage in materials under load. In tensile testing of fiber reinforced plastics, first micro cracks occur as soon as a critical strain is exceeded. They emit a characteristic sound, which can be detected via acoustic emission analysis. By increasing the load, the amount of acoustic emissions rises. Even, if the plastic's matrix causes a high damping rate, a sudden change in amplitude is indicating the critical strain. Further, the analysis shows signals of the whole frequency range which can be distinguished into three different damage mechanisms (matrix cracking, interfacial failure and fiber breakage) by using pattern recognition techniques. It can be shown that the appearance of micro cracks can be correlated with a specific strain value which is interpreted as the critical strain. [ABSTRACT FROM AUTHOR]