Reliability investigation of piezoelectric macro fibre composite (MFC) actuators

Multi-functional materials are the key to integrated sensor and actuator functions which enable adaptronic systems to intelligently react on varying forces and environment. The reliability of adaptronic systems has not extensively been investigated in the past, but it is evident that it strongly depends reliability of the functional material systems. The present study is a contribution to the reliability investigation of a special group of piezoelectric composite materials, the so called Macro Fibre Composite (MFC) patch actuators. Commercial Piezoelectric Macro Fibre Composite (MFC) actuators show high potential for vibration and noise reduction of flat mechanical structures like car roofs, windshields, and building facades. Within the European project InMAR, the reliability of these devices lias been investigated experimentally. The reliability assessment strategy of such complex material systems differs from the one applicable to monolithic materials. Failure modes different from the material immanent failures may occur randomly along the desired life span of the device. Therefore, a combined strategy of qualitative and quantitative methods as well as design weakness and accelerated testing techniques has been applied. Different test scenarios of combining the damage relevant parameters like electric field, mechanical strain and temperature were realized. It was found that the investigated devices exhibit a high reliability even on a lab scale production process. Cycles of more than 108 were survived without obvious degradation, despite high electromechanical cycling amplitudes and elevated temperatures. Microscopic investigations of cycled but still undegraded samples revealed intensive cracking all along the macro fibres, leading to the conclusion that this internal damage is tolerated as a system immanent procedure and does not affect the macroscopic performance. It is concluded that the MFC actuators show excellent reliability performance when applied within the specification range.