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This paper demonstrates the results of an experimental study on cross ply carbon/epoxy composite laminates fabricated from high temperature hardener HT972 subjected to impact loading at different velocities and temperatures. The carbon fiber reinforced plastic (CFRP) samples were impacted at velocities 1.5 m/s and 2.5 m/ s, each at a temperature level of 308C, 608C, 908C, and 1208C. The impact response of the material towards various velocities and temperatures was determined using impact parameters like peak force, absorbed energy, maximum deflection, and rebound velocity. Result reveals that the velocity and temperature play a significant role in the impact response of the material. The variation in the trend of Flexural After Impact (FAI) strength of composite laminates at different velocities and temperatures was determined using FAI test and these results were further correlated with impact results. The dominating failure modes affecting the residual strength of the samples were found using acoustic emission (AE) monitoring. POLYM. COMPOS.,

In this article, to overcome the challenges encountered during the discrimination of various failure modes in post impacted/indented glass-fiber-reinforced plastic, techniques like pattern recognition method and advanced signal processing were employed. The significant acoustic emission parameters such as amplitude, rise time, counts, energy, duration, and peak frequency that are acquired during compression after impact test are considered as inputs to cluster validity index and for various clustering techniques such as k-means, fuzzy C-means, and Kohonen's self-organizing map. The acoustic emission count-frequency and amplitude-frequency have no overlapping, whereas other combinations of acoustic emission parameters result in overlapping with four clusters. The clustering techniques are validated by discrete wavelet transform of acoustic emission signals. The discrete wavelet transform was performed on the clustered acoustic emission signals to identify the percentage of energy and frequency content of each level which correlates the different failure modes. The results infer that k-means, fuzzy C-means clustering, and Kohonen's self-organizing map are 94.5%, 97.1%, and 98.6% reliability, respectively, clearly suggesting Kohonen's self-organizing map as the most appropriate technique for the classification of acoustic emission signature.

In this paper, symmetric cross ply CFRP laminates were fabricated using hand layup with LY556 epoxy resin as matrix and the specimens were cut without cut-out, with circular, vertical elliptical and horizontal elliptical cut-outs according to the ASTM D 7137 standard using water jet cutting. The CFRP specimens with and without cut-outs were subjected to compression under controlled condition accompanied by acoustic emission (AE) monitoring. The ultimate compressive strength for specimens with and without cut-outs were determined and compared. The optimum cut-out with lesser reduction in compressive strength was determined. The nature and dominance of different failure modes in each type of cut-out were investigated using AE. Finally the result gives useful information about improved design of laminated composites with cut-outs suitable for different applications.

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