Sensors constructed with single-crystal PMN-PT, i.e. Pb(Mg1/3Nb2/3)O3-PbTiO3 or PMN, are developed in this paper for
structural health monitoring of composite plates. To determine the potential of PMN-PT for this application, glass/epoxy
composite specimens were created containing an embedded delamination-starter. Two different piezoelectric materials
were bonded to the surface of each specimen: PMN-PT, the test material, was placed on one side of the specimen, while
a traditional material, PZT-4, was placed on the other. A comparison of the ability of both materials to transmit and
receive an ultrasonic pulse was conducted, with the received signal detected by both a second surface-bonded transducer
constructed of the same material, as well as a laser Doppler vibrometer (LDV) analyzing the same location. The optimal
frequency range of both sets of transducers is discussed and a comparison is presented of the experimental results to
theory. The specimens will be fatigued until failure with further data collected every 3,000 cycles to characterize the
ability of each material to detect the growing delamination in the composite structure. This additional information will be
made available during the conference.
In this study, the guided wave technique is applied to nondestructively assess the damage in various engineering materials, like alumina, laminated composites, and composite sandwiches. A combined theoretical, numerical and experimental investigation of the pulse-echo method using piezoelectric sensors and actuators is conducted. The dispersion effect of wave guides on these materials is first analyzed, and the transient propagation process of wave guides and its interaction with inside damages are then numerically simulated. The implementations of the pulse echo method are illustrated in experimental testing and damage detection of aluminum beams, carbon/epoxy laminated composite plates, and composite sandwich beams. In particular, the experimental results on damage detection of the composite sandwich beams are reported and discussed. As illustrated in this study, the pulse-echo method combined with piezoelectric material can be used effectively to locate damage in various engineering materials and structures.
Accurate interpretation of data measurement is a major challenge for development of reliable and effective diagnostic system. This paper presents experimental results of a proposed damage identification candidate based on Lamb wave propagation analysis. Carbon/epoxy laminated composite plate specimens with various damage, i.e., delamination and impact damage, are evaluated. Damage location is extracted from the measured time history data of the propagated wave and the wave traveling time. Assuming the wave propagates with a constant speed, the summation of the distance from the transmitter to the damage and the distance from the damage to the receiver is constant. The possible damage location combining with the locations of the transmitter and receiver forms an elliptical path, where the locations of the transmitter and receiver serve as the foci of the ellipse. Piezoelectric transducers (PZTs) are used as the wave transmitters and receivers. Post-processing of the recorded signals using wavelet transform allows better isolation of the interested propagation mode and the extraction of the traveling time, which enhance the accuracy of damage localization. Results of the damage location estimation are presented.
Fiber reinforced polymer (FRP) composites have been increasingly used for civil infrastructure in recent years, and the applications have promoted interest in health monitoring of structural composites. Although primary layouts of these composite structures are similar, the FRP composites used in civil engineering structures are usually relatively thicker and larger in size. Hence, more power authority is needed in the experimental procedure for health monitoring purposes. In this study, health monitoring of thick composite structures using smart piezoelectric materials is presented. Monitoring technique based on wave propagation is evaluated for possible damage detection in civil composite structures. For comparison purposes, the composite laminated beams with two different thickness are made of E-glass fiber and epoxy resins by vacuum bagging process, and the damage in the form of delamination is created by inserting Teflon sheet between the lamina at certain location. Smart piezoelectric materials are used as both the emitter and receiver of the wave. The exploratory experimental program developed in this study can be used for better understanding of the possibility of wave propagation based technique in health monitoring and damage detection of large civil FRP composite structures.