In situ fabricated smart material active sensors for structural health monitoring

Abstract

Structural health monitoring (SHM) is currently using piezoelectric wafer active sensors (PWAS) permanently attached to the structure with adhesives. This is often a burdensome and time-consuming task, especially for large structures such as aircraft, bridges, etc. In addition, there are critical applications where the rigid piezoceramic wafers cannot conform to curved surfaces. Another important issue is the long term durability of the bonded interface between the PWAS and the structure, which is often the durability weak link. An in-situ fabricated smart sensor may offer better durability. This paper considers the possibility of fabricating the PWAS directly to the substrate structure in order to alleviate these problems. The paper starts with a review of the state of the art in active composite fabrication. Then, two concepts are considered: the piezomagnetic composite sensor and the piezoelectric composite PWAS. The piezomagnetic composite was fabricated using Terfenol-D magnetostrictive powder in a fiber reinforced composite beam. The strain-induced magnetic field was detected with a Lakeshore gaussmeter. The piezoelectric composite sensor was prepared by mixing lead zirconate titanate (PZT) particles in an epoxy resin. The mixture was applied onto the structural surface using a mask. After curing, the piezo composite was sanded down to the desired thickness and poled under a high electric field. The resulting in-situ composite PWAS was utilized as a sensor for dynamic vibration and impact. Characterization of the in-situ composite PWAS on aluminum structure have been recorded and compared with ceramic PWAS before and after poling. To evaluate the performance of the in-situ composite PWAS, both vibration and impact tests were conducted. Both experiments indicated that in-situ fabrication of active materials composites poses itself as a good candidate for reliable low-cost option for SHM smart sensor fabrication.