In this study the loading limits, damage behavior and long-term integrity of piezoceramic patch transducers, based on monolithic PZT (lead zirconium titanate) wafers (PIC 255), were investigated. The study involved quasi-static and long-term cyclic testing under tensile and compressive mechanical loading of the patches, at different temperatures. A strain-cycle lifetime diagram was established for tensile loading at room temperature, and +60, +100 and −40 • C. In all cases of tensile loading, cracking in the PZT ceramic was found to be the relevant failure mechanism which was shown to be correlated with the observed degradation of sensor performance of the patches. No mechanical damage was found under compressive loading at strain levels of up to −0.6%. Finite element (FE) analyses were performed using 3D material modeling with electromechanical coupling, achieving very good predictability of the sensor and actuator performance. Analytical calculations and numerical simulation were used to interpret experimental findings and to allow the transfer of results to various applications. Based on micro-structural investigations of the cracked PZT wafers and FE simulation, fracture mechanics analyses of the local stress situation in the PZT ceramic were carried out.

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

Objective of the present study is the definition of a material model accounting for fatigue damage and degradation. The model is formulated as a brittle damage model in the otherwise linear elastic framework. A stress driven damage evolution equation is derived from microplasticity considerations. The model is implemented as a user-defined material model into a commercial finite element program. In a comparison with experimental data in the low cycle fatigue regime, a good agreement with the numerical prediction is obtained.

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Objective of the present study is the definition of a continuum damage mechanics material model describing the degradation of fiber reinforced materials under fatigue loads up to final failure. Based on the linear elastic framework, a brittle damage model for fatigue conditions is derived, where the damage constitutes the only nonlinearity. The model accounts for damage effects by successive degradation of the elastic moduli. Assuming that material damage is driven by microplastic work, a stress-driven damage evolution equation is defined. For generality, a fully three-dimensional formulation on single ply level is employed. The model is implemented into a finite element program. In a validation against experimental data on filament-wound carbon fiber reinforced material, the model proves to provide a good numerical approximation of the damage during the cyclic loading history up to final material failure.