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Acoustic emission detection in composites is complicated in comparison with metallic structures due to the complex nature of acoustic emission wavelet transform in anisotropic materials. In this study, the adhesively bonded single-lap joints with zero-degree orientation are used to trigger different failure mechanisms when subjected to tensile test with acoustic emission monitoring. Acoustic emission signals which are studied for damage characterization are obtained during tensile tests. The range of peak frequency with time, pertaining to the failure mode in adhesively bonded single-lap joints has been identified using wavelet transform. Signals and their characteristics representing different failure modes are identified and validated using wavelet transform analysis. Continuous wavelet transform is then applied to identify the frequency range and time history for failure modes in each signal. The fractured surface area of the bonded single-lap joint specimen was examined directly using a scanning electron microscope and also identified the failure mechanism of bonded single-lap joints. The results obtained from acoustic emission technique are compared with scanning electron microscope results, to find the evidence of predicted damage. This study of the frequency content of each test using continuous wavelet transform is then performed and the classification of several failure modes is identified.

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Experiments were carried on nozzles with different exit geometry to study their impact on supersonic core length. Circular, hexagonal, and square exit geometries were considered for the study. Numerical simulations and schlieren image study were performed. The supersonic core decay was found to be of different length for different exit geometries, though the throat to exit area ratio was kept constant. The impact of nozzle exit geometry is to enhance the mixing of primary flow with ambient air, without requiring tab, wire or secondary method to increase the mixing characteristics. The non-circular mixing is faster comparative to circular geometry, which leads to reduction in supersonic core length. The results depict that shorter the hydraulic diameter, the jet mixing is faster. To avoid the losses in divergent section, the cross section of throat was maintained at same geometry as the exit geometry. Investigation shows that the supersonic core region is dependent on the hydraulic diameter and the diagonal. In addition, it has been observed that number of shock cells remain the same irrespective of exit geometry shape for the given nozzle pressure ratio.

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