Piezoceramic patch sensors have to withstand the primary stresses and strains of a structure during operation. In the leading project 'Adaptronics' a lifespan of 10 6 cycles at 0.1% strain was required for sensors applied on components of steel and carbon fibre reinforced plastic (CFRP). In order to

Deformation and failure of fiber-reinforced materials (FRM) can cause electric charge displacements. This, consequently, leads to variations in the external electric field. These can be observed and recorded during the loading process without any contact to the sample. Analyzing, these signals named electric emission (EE) can be done individually and also statistically when an acoustic emission equipment is used. Fracture of carbon and glass fibers yields EE signals of large amplitudes, whereas the polycarbonate matrix material exhibits smaller ones. The signals obtained in a tensile test with the composite materials exceed the ones of the matrix material but do not attain those of the fiber material. From the shape of the EE signals conclusions can be made on the elementary fracture process. From these experiments it can be concluded that the EE method is a valuable tool with respect to the detection of failure occurence of composite materials as is the acousti emission technique. The EE Technique is a field method and does, therefore, not require any sample preparation. This makes it a low cost technique which can be possibly applied in the field as well as in the laboratory

The performance and reliability of piezoceramic patches based on Lead-Zirconate-Titanate (PZT) wafers were investigated under both quasi-static and cyclic loading conditions in sensor and actuator applications. A 4-point bending setup was used to study the patches loading limits and damage behavior under mechanical tensile and compressive loading at varied strain levels. The patches performance under electric actuation was tested in a bending actuator setup. As opposed to irreversible damage by cracking of the PZT wafers under tensile loading (strain at failure: ca. 0.35 %), no mechanical damage was observed under compressive loading at strain levels of up to -0.6 %. Instead a partly reversible degradation of the piezoceramics electromechanical properties was noted. A strain-cycle diagram was established for tensile loading at room temperature. Finite-element analyses were performed using 3D material modeling with electro-mechanical coupling behavior. Very good predictability of the sensor and actuator performance was achieved by FE-simulation. Through numerical investigations the degradation of the patches sensor performance under tensile loading could be correlated to the increasing number of cracks in the PZT wafers

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Efficient application of piezoelectric sensors and actuators requires extensive investigations of their loading limits, failure-behavior and life-span under service conditions. Here the performance of laminar PZT-patch-modules is studied, applying a combined approach of experimental and numerical tests. Four-point bending tests are used to evaluate the sensor performance. Linear electro-mechanical coupling is implemented in an 8-node brick user element of the research finite element code FEAP to develop a flexible FE-tool for piezoelectric problems. Comparative FE-analyses of the bending test are carried out in order to assess the capability of the implemented FEAP user element versus the commercially available FE-code ABAQUS. FE-results show good agreement with the experimental tests, different element types yield slight deviations which are discussed.