Reliability of piezoceramic patch sensors under cyclic mechanical loading

Piezoceramic patch sensors have to withstand the primary stresses and strains of a structure during operation. In the leading project Adaptronics a lifespan of 106 cycles at 0.1% strain was required for sensors applied on components of steel and carbon fibre reinforced plastics (CFRP). In order to test the reliability of the patches themselves and of their adhesion on the substrate, special four-point bending tests were carried out under quasistatic loading and under cyclic loading at different strain levels. The specimens consisted in sheets of steel and CFRP as substrates on which the newly developed patches with embedded piezo electric foils and fibres were glued (Fig. 4). In the quasistatic bending tests the performance of each sensor was characterised by measuring the sensor signal (charge) as a function of strain before and after cycling. Damage of the specimens would result in a decreasing slope of the charge-strain-curve after cycling. However, all the specimens tested survived 107 cycles up to 0.12 % strain without marked loss of performance.