Elastic waves from localized sources in composite laminates

This paper is concerned with the analysis of elastic waves generated by localized dynamic sources in structural composites. The source can be external, involving acoustic wave loading as in the so called leaky Lamb wave experiment, and low-velocity foreign object impact on the surface of the structure, or internal, as in sudden crack initiation and its rapid growth from existing internal flaws. All three problems are of critical importance in the safe operation of composite structures, due to their vulnerability to hidden delaminations that can occur in composite materials when they are subjected to this type of loads. It is well known that both the dynamic surface loading associated with impact, and the sudden "opening" of an internal crack associated with the extension of a preexisting flaw act as sources of elastic waves in the material of the structure. The research reported here consists of model-based analysis of the guided waves generated by surface loading and microcrack initiation in graphite epoxy composite laminates commonly used in aircraft and aerospace structures. The objective of this study is to develop a mechanics based understanding of the causal relationship between the properties of the source and the characteristics of the waves generated by its initiation and propagation. The results of this research are expected to be useful in developing effective health monitoring systems for new as well as aging aircraft and aerospace structures. (C) 2002 Elsevier Science Ltd. All rights reserved.