Experimental investigation of performance reliability of macro fiber composite for piezoelectric energy harvesting applications

Macro fiber composite (MFC) has been extensively used in actuator/sensor/harvester applications. Fatigue due to cyclic high electric fields in actuator applications has been studied extensively. However, fatigue failure of MFC due to high stress or strains in energy harvesting applications has attracted little attention. The aim of the study is to obtain the upper limit of dynamic strain on MFC which can be used as failure limit in the design process of piezoelectric energy harvesters (PEHs). The examined PEH is comprised of a cantilever beam made of aluminum and a patch of MFC bonded at its root for power generation. Energy harvesting tests are conducted at various base accelerations around 30 Hz (near resonant frequency) and the voltage output and maximum strain on MFC are measured. Severe loss in the performance of the harvester is observed within half million cycles of testing at high strain amplitude. Hence several reliability tests for extended periods of time are carried out at various strain amplitudes. The harvesters are tested at resonant frequencies around 30 Hz and 135 Hz for over 20 million and 60 million cycles, respectively. Degradation in voltage output, change in natural frequency and formation of cracks are considered as failures. Based on the experimental results, an upper limit of 600 μϵ is proposed as the safe amplitude of strain for reliable performance of MFC. Tensile tests are also carried out on MFC patches to understand the formation of cracks and shift in resonant frequency at low strains. It is observed that cracks are formed in MFC at strains as low as 1000 μϵ. The observations from this work are also applicable to MFC bending actuators undergoing cyclic strains.