Vibration Analysis for Damage Detection in Composite Plate using PZT Sensors

Advanced composite materials have applications in many areas. However, the mechanical performance of composite materials under damage is very complicated. The tensile strength of composite materials is typically much lower than its compressive strength, making the composite material vulnerable to matrix cracking, fiber fracture, delamination and interfacial debonding. Nondestructive testing NDT methods currently used to detect damage in composite materials have several disadvantages; they are expensive, complicated devices that do not readily allow for online health monitoring or monitoring of large areas. These disadvantages limit the usefulness of NDT methods for testing composite materials. For example, in the aviation industry, where composite materials have many applications, ordinary NDT methods can only be used locally. Despite this limitation, these methods are employed because damage cannot readily be located visually. However, the structures are large, so a great deal of time and money is invested in using these NDT methods�yet they cannot test nor locate damage in real time. This study focuses on an active monitoring method for damage detection applied to composite structures. Different specimens made up of fiber epoxy resin in the form of composite structures are studied. Wavelet analysis methods are adopted to post process the raw monitored signal. A new damage signature is introduced to determine the presence and extent of damage in composites, while eliminating the influence of different distances between the active actuator and active monitoring elements. The proposed method is shown to be effective, reliable, and straightforward for the specimens considered in the present study, which are composed of different materials and suffer various levels of damage. An online real-time active monitoring system for damage detection is described that is based on this research.