Experimental investigation of damages in the bimorph piezoelectric energy harvester with multilayer composite substrate

Composite materials, regarding their lightweight, can be considered a suitable option for the next generation of piezoelectric energy harvesters, which are used for supporting low-power applications. Also, due to the broader selection range and different stacking sequences, one of the advantages of these materials is that they can provide better stiffness adjustment of the structure to achieve the desired frequency of energy harvesting from the ambient vibration. Despite all these advantages, one of the challenges in the widespread use of this type of material is the complex damage behavior and less information about their damage behavior compared to other traditional materials. The bimorph piezoelectric energy harvester studied in this work has a three-layer woven substrate in the form of [0/90]; its behavior and performance in the presence of some well-known damage mechanisms in the composite structures, such as the mid-layer transverse cracks are investigated. A crack density-based stress transfer method, from a micromechanical point of view, is employed to calculate stiffness reduction due to damages in the bimorph. The effect of the damping coefficient on analytical modeling is considered, and the parameter of the damping ratio is given by the experimental test. Effects of damages on the mechanical parameters like resonance frequency, as well as the electrical parameters like output voltage, are investigated. It is observed that the presence of fabricated transverse cracks in the mid-layer of the bimorph piezoelectric energy harvester increases the value of the damping ratio and also decreases its stiffness. Finally, the output voltage is investigated, which reduces by the mid-layer transverse cracks.