Experimental research on strain monitoring in composite plates using embedded SMA wires

Shape memory alloy (SMA) materials possess complete superelasticity or pseudoelasticity above the austenite finish temperature (Af) and many unique mechanical, thermal, thermal-mechanical and electrical properties compared with other conventional materials. Many studies have reported that the superelastic and hysteresis properties of SMA materials can absorb energies coming from external excitations or sudden impacts. In addition, due to the special electrical properties of NiTi superelastic wires, they can also be used as a strain-sensing element to monitor structural health conditions. In this paper, composite laminated specimens embedded with SMA wire sensors were fabricated and a detailed testing system was designed, for example for multi-parameter measuring for impact and weak signal processing for SMA sensors. A low-velocity impact test shows that SMA wire sensors embedded in fibre-reinforced plastic (FRP) laminate can be used to monitor impact responses, such as the location of impact damage, impact degree, and strain distribution. Experimental results and theoretical predictions reveal almost the same results. Compared with other methods, the research provides a simple, economic and reliable technique for monitoring important engineering structures online. © 2006 IOP Publishing Ltd.