Reliability of piezoceramic patch sensors under cyclic mechanical loading

Abstract

Piezoceramic patch sensors have to withstand the primary stresses and strains of astructure during operation. In the leading project ‘Adaptronics’ a lifespan of106 cycles at 0.1% strain was required for sensors applied on components of steel and carbonfibre reinforced plastic (CFRP). In order to test the reliability of the patchesthemselves and of their adhesion on the substrate, special four-point bending tests werecarried out under quasistatic loading and under cyclic loading at different strainlevels. The specimens consisted in sheets of steel and CFRP as substrates onwhich the newly developed patches with embedded piezoelectric foils and fibreswere glued. In the quasistatic bending tests the performance of each sensor wascharacterized by measuring the sensor signal (charge) as a function of strain before andafter cycling. Damage of the specimens would result in a decreasing slope of thecharge–strain-curve after cycling. However, all the specimens tested survived107 cycles up to 0.12% strain without marked loss of performance.