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Many composite materials and structures are susceptible to defects, which can significantly reduce the strength of structures and may grow to failure. To avoid the catastrophic failure of structures, development of a reliable method of structural health monitoring is one of the most important keys in maintaining the integrity and safety of structures. Dynamic response-based damage detection offers a simple procedure as an alternative to the conventional nondestructive evaluation techniques. However, this technique depends on the quality of measured data for its identification accuracy. In this article, experimental aspects of dynamic response-based damage detection technique on carbon/ epoxy composites are addressed. Smart piezoelectric materials are used as sensors or actuators to acquire the curvature modes of structures. These materials are surface-bonded to the beams. An impulse hammer is used as an actuating source as well. Four types of damage detection algorithms are evaluated for several possible damage configurations with two different excitation sources. The quality of damage identification with the four different detection algorithms is discussed. These experimental damage identification techniques using curvature modes and piezoelectric materials can be effectively used in damage detection and health monitoring of composite structures.

The need to understand and monitor the integrity of structural components made of composite materials is becoming critical, due to an increase of the use of composites in aerospace, civil, wind energy, and transportation engineering. Off-the-shelf piezoelectric transducers embedded inside the composites or bonded onto the structure surface are a possible solution for on-line structural health monitoring and non-destructive evaluation: they can be used to generate Lamb waves, which are able to detect damage. This article focuses on the behavior of two sets of woven fiberglass/epoxy specimens, one with embedded, one with surface-mounted piezoelectric wafer transducers (lead zirconate titanate). The specimens are tested under axial tensile fatigue at high stress ratio, and the transducers are interrogated in pitch-catch mode at different stages of the specimens’ life, while they are subjected to the mean test load (the testing machine is paused). A novel signal processing technique based on wavelet thresholding/denoising and Gabor wavelet transform is discussed. This technique identifies changes in boundary conditions, loading/unloading prior to damage and during damage. It appears to correlate the contour area changes with the so-called characteristic damage state observed in the literature in composite laminates under tensile fatigue.

In this article, a combined analytical and experimental damage assessment method using curvature mode shapes is developed. The curvature mode is selected due to its sensitivity to the presence of the damage and the localized nature of the changes. An analytical relationship between the damaged and the healthy beams is formulated, for which the effect of damage in the form of stiffness loss is accounted. This relationship is later used to estimate the extent of damage from the experimentally identified changes in structural dynamic characteristics. Surface-bonded piezoelectric sensors are used to directly acquire the curvature modes of composite structures, which simplify the identification procedure. The specimens are made of carbon/epoxy laminated composite beams. Several different types of damages are introduced in the beams (i.e., delamination, impact, and saw-cut damages) to simulate possible damage scenarios. Several limitations and remarks of the proposed experimental and damage identification approaches are discussed. The study shows that the present technique using curvature mode shapes and piezoelectric materials can be used effectively to locate the damage in the laminated composite structures.

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