Thermal reliability of piezoelectric materials and structures

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Piezoelectric materials are materials which generate electricity when mechanically strained, and deform under an electric field. Due to their distinguished electromechanical coupling effect, piezoelectric materials have widely been used in many applications, such as acoustic emission microsensors, vibration monitors, molecular recognition biosensors, precision positioners, micropumps, and linear stepper motors, energy harvesting devices, and so on. Reliability of functional devices heavily depends on the proper functioning of piezoelectric, smart components.****Thermal fatigue of smart materials results in functional failure like depolarization or structural failure like cracking. As an essential piece, a fatigue strength versus fatigue life curve, the so called S-N curve for piezoelectric materials at various service temperatures lies in the core of design of smart devices. Cyclic electric loading has been widely used to examine the fatigue behavior of piezoelectric materials, however, mechanical cyclic loading, particularly at various temperatures, has rarely been used in the fatigue test of the material. As such, no reliable S-N curve is available. Another issue is the reliability of structures under thermal shock, such as the case of sudden exposure to a high or low temperature environment. Thermal effect will be felt by the material as a time-dependent wave, which is unable to be described by the traditional Fourier heat conduction theory. Non-Fourier heat conduction theories introduced so-called, thermal relaxation times to account for the time lags of heat flux and temperature gradient response with respect to the initial thermal disturbance, leading to a wave-form, hyperbolic heat conduction equation. Theoretical results show that the thermomechanical response is well beyond the static results based on the Fourier heat conduction, leading to a vital reliability issue. However, no experimental results are available for the exact values of thermal relaxation times.****The present research focuses on the two major issues of thermal reliability of the material, thermal fatigue and thermal relaxation. In particular, we will determine the S-N curves at various temperatures, and the thermal relaxation times to account for the non-Fourier, wave-like thermal disturbances in smart structures, and build the multiphysical framework to deal with thermal reliability issues of smart structures. The present research will bring a strong impact on the reliability of smart devices. The results will meet the high demand of both the theoretical and application communities on thermal reliability of smart materials. The successful completion of the proposed program will greatly benefit the advanced materials and manufacturing sectors of Canada. The program will yield many high quality papers which will enhance the profile of Canada in the global scientific community.***