The temperature stability of guided wave structural health monitoring systems

Abstract

It is desirable for any structural health monitoring (SHM) system to have maximumsensitivity with minimum sensor density. The structural health monitoring systemdescribed here is based on the excitation and reception of guided waves usingpiezoelectric elements as sensors. One of the main challenges faced is that in all butthe most simple structures the wave interactions become too complex for thetime domain signals to be interpreted directly. One approach to overcoming thiscomplexity is to subtract a baseline reference signal from the measured systemwhen it is known to be defect free. This strategy enables changes in the structureto be identified. Two key issues must be addressed to allow this paradigm tobecome a reality. First, the system must be sufficiently sensitive to small reflectionsfrom defects such as cracking. Second, it must be able to distinguish betweenbenign changes and those due to structural defects. In this paper the baselinesubtraction approach is used to detect defects in a simple rectangular plate. Thesystem is shown to work well in the short term, and good sensitivity to defects isdemonstrated. The performance degrades over the medium to long term. The principalreason for this degradation is shown to be the effect of change in temperature ofthe system. These effects are quantified and strategies for overcoming them arediscussed.