Experimental investigation of void effects on the structural integrity of composite laminates using acoustic emission monitoring

Abstract

This thesis involves the experimental investigation of void effect on the structural integrity of composite laminates using acoustic emission monitoring. The novelty of this research is that it improvises the data to theoretical model through understanding the effect of voids using Acoustic Emission (AE) signals to predict the failure mechanism during the service life of composite products that are fabricated using low cost fabrication methods. Voids were created by varying the curing cycles. Optical image was used for calculation of the void volume and parameters. Flexural test was done to understand mechanical behavior. Acoustic Emission monitoring was performed in the failure mechanism during testing. All the stages were validated using designed curing pressure (Non-Void) specimens. Specimens were created by two methods, namely, varying the curing pressure and curing time. Specimens that were created by varying the curing time yielded a large number of voids hence leading to rejection of the specimens. Specimens that were formed by varying curing pressure were subjected to static, dynamic and delamination fracture toughness testing. In the initial study, two sets of experiments were conducted. In the first set, Mode-I testing was performed for correlation of the curing pressure effect and delamination toughness by applying AE monitoring. K-means clustering technique was introduced for better correlation of the acoustic signal with the toughness value. This value derived was be fed to the final model. In the second set, both With Void (WV) and Non Void (NV) specimens were subjected to impact loading under the categories of (a) ambient and elevated temperature impact in carbon specimens, (b) multiple impacts in carbon specimens, (c) ambient temperature impact in glass fiber specimens. The residual strength variation was calculated with the non impacted specimens newline