Composites are used extensively in engineering applications. A constant concern is the effect of foreign object impacts on composite structures because significant damage can occur and yet be undetectable by visual inspection. Such impacts can range from the most ordinary at low velocity - a tool dropped on a product - to the hypervelocity impact of space debris on a spacecraft. This book explains how damage develops during impact, the effect of impact-induced damage on the mechanical behavior of structures, and methods of damage prediction and detection. Numerous examples are included to illustrate these topics. Written for graduate students, as well as researchers and practising engineers working with composite materials, this book presents state-of-the-art knowledge on impact dynamics while requiring only basic understanding of the mechanics of composite materials.

Laminated composite materials are used extensively in aerospace and other applications. With their high specific modulus, high specific strength, and the capability of being tailored for a specific application, these materials offer definite advantages compared to more traditional materials. However, their behavior under impact is a concern, since impacts do occur during manufacture, normal operations, or maintenance. The situation is critical for impacts which induce significant internal damage, undetectable by visual inspection, that cause large drops in the strength and stability of the structure. Impact dynamics, including the motion of both the impactor and the target and the force developed at the interface, can be predicted accurately using a number of models. The state of stress in the vicinity of the impact is very complex and requires detailed analyses. Accurate criteria for predicting initial failure are generally not available, and analyses after initial failure are questionable. For these reasons, it can be said that a general method for estimating the type and size of impact damage is not available at this time. However, a large amount of experimental data has been published, and several important features of impact damage have been identified. In particular, interply delaminations are known to occur at the interface between plies with different fiber orientation. Their shape is generally elongated in the direction of the fibers in the lower ply at that interface. The delaminated area is known to increase linearly with the kinetic energy of the impactor after a certain threshold value has been reached. The effect of impact damage on the properties of the laminate has obvious implications for design and inspection of actual structures. Experimental results concerning the residual strength of impact damaged specimens subjected to tension, compression, shear, bending, and both static and fatigue loading are available. Analyses concentrate primarily on predicting residual tensile and compressive strength. In order to fully understand the effect of foreign object impact damage, one should understand impact dynamics and be able to predict the location, type, and size of the damage induced and the residual properties of the laminate. This article is organized along these lines and presents a comprehensive review of the literature on impact of laminated composites, considering both experimental and analytical approaches.

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Currently, there is strong interest in the effects of impact induced damage to composite structures as evidenced by the large number of articles on this topic that have appeared in the literature in recent years. With laminated composite structures, foreign object impacts, that are expected to occur during the life of the structure, can introduce damage that is often difficult to detect and can significantly reduce the strength of the structure. Research efforts concentrate on monolithic laminates while sandwich structures with laminated facings, which are also used extensively in aerospace and other applications, received less attention. A comprehensive review of the literature dealing with impact on sandwich structures is presented in this review article. The mechanics of contact between a rigid indentor and a sandwich structure is discussed in detail since it is very important to account for the local deformation in the contact zone in developing a model for predicting the contact force history. The mechanical behavior of foam and honeycomb core materials is reviewed along with experimental results and models for predicting the contact law between a smooth indentor and a sandwich structure. The development of mathematical models for predicting the contact force history and the overall response of the structure is also discussed. Finally we review the failure mechanisms involved in impact damage development, the parameters affecting damage size, and the residual properties of sandwich structures. This review article has 85 references.

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