Abstract
Acoustic emissions (AE) generated by a structure under stressed condition provide a passive method to understand the flaw growth phenomenon. In complex structures, such as composites, characterisation of AE signals generated by various failure mechanisms enhances such understanding. Sample level tests have been carried out on carbon epoxy unidirectional laminate in longitudinal direction of fiber to study the AE characteristics of different failure mechanisms, namely, fiber breakage and inter layer de-lamination. The AE parameters such as amplitude, energy, duration, rise time and signal strength have been acquired and analysed using various correlation plots. The fiber breakage is represented by high energy and longer duration hits with an amplitude of above 90 dB. The de-lamination mechanism is producing AE hits of medium energy of about 1000 units and long duration up to 106 µs. The duration per unit energy and the rise time per unit energy graphs portray a vivid picture of the occurrence of fibre breakage and delamination. Key words: Carbon-epoxy composites, failure modes, acoustic emission (AE).
Highlights
Composites are widely being used as structural members in the aerospace industry, because of its high specific strength, stiffness and good corrosion resistance
The observations on the failure modes of the specimens and Acoustic Emission (AE) test data are as follows: Fibre breakage is the principal failure mode in the longitudinal tensile specimens [UDL(T)] and they have shown the highest failure loads
AE signatures corresponding to failure mechanisms of fibre breakage
Summary
Composites are widely being used as structural members in the aerospace industry, because of its high specific strength, stiffness and good corrosion resistance. Structural integrity assessment and quality control of composite structures have been a challenging task. Experience has shown that using non-destructive testing (NDT) for structural integrity assessment has greatly improved the quality and performance of composite systems. Non destruction evaluation (NDE) of composite structures is complex in terms of testing and data interpretation owing to its anisotropy and nonhomogeneity. Acoustic Emission (AE) testing is found to be a reliable and cost effective non-destructive tool for use with composite structures for on line structural health monitoring (American Society for Non-destructive Testing, 2005). The rapid release of strain energy at localized stress concentration points of microscopic or macroscopic defects within the structure under strain generates acoustic emissions.
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