Fiber reinforced composite materials are being used in an increasingly wide range of structural applications. However, many types of composite laminates are extremely susceptible to impact damage [1,2]. Relatively low energy impacts may induce significant internal damage, generally in the form of matrix cracks and delaminations, which are not accompanied by visual evidence [3–5]. This damage has been shown to significantly reduce the strength, stiffness and fatigue life of compression loaded, flat composite laminates [1,2,4–7], as well as the strength of thin walled composite tubes [8]. Residual strength and life are closely related to the nature and extent of damage [6,7]; thus, the capability to perform detailed nondestructive evaluation of damage represents a critical component in the damage tolerant design of composite structures.
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