In-situ Fabrication of Composite Piezoelectric Wafer Active Sensors for Structural Health Monitoring

Structural health monitoring (SHM) is important for reducing maintenance costs while increasing safety and reliability. Traditionally, structural integrity tests required attachment of sensors to the material surface. This is often a burdensome and time-consuming task, especially considering the size and magnitude of the surfaces measured (such as aircraft, bridges, structural supports, etc.). Temporary sensors are a hassle to install; there are some critical applications where they simply cannot accomplish the task required. Piezoelectric wafer active sensors (PWAS) can be permanently attached to the structure and offer a permanent sensor solution. Existing ceramic PWAS, while fairly accurate when attached correctly to the substance, may not provide the long term durability required for SHM. The bonded interface between the PWAS and the structure is often the durability weak link. Better durability may be obtained from a built-in sensor that is incorporated into the material. This paper describes the work on the in-situ fabrication of PWAS using a piezoelectric composite approach. The piezoelectric composite was prepared by mixing small lead zirconate titanate (PZT) particles in an epoxy resin matrix; the mixture was then directly applied onto the surface of a host structure using a designed mask. The curing of the piezo composite was carried out at elevated temperature. After curing, the cured composite was sanded down to the desired thickness. Finally, the piezo composite was poled under a high electric field to activate the piezoelectric effect. The resulting insitu 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. In-situ composite PWAS are believed to be a good candidate for reliable low-cost sensor fabrication for SHM.