Residual stiffness and actuation properties of piezoelectric composites: Theory and experiment

This work attempts to characterize and model the effective stiffness and actuation properties of active composite materials under high uniaxial tensile loads. The motivations for this undertaking are to obtain effective material properties as damage accumulates in the active element and to identify the mechanisms affecting stiffness and actuation to improve the material. A unified model with predictive capability for overall laminate effective material properties was developed. Key model assumptions include a constant linear elastic fiber recovery length and a Weibull form for fiber strength. A one dimensional shear lag model was employed to characterize the load transfer between the composite's layers. In order to validate this model several experiments were conducted on interdigitated electrode piezoelectric fiber composites embedded in E-glass laminae. Actuation data were obtained by performing active tests: specimens were subjected to increasing tensile loads and measurements of actuation under load were taken at selected strain levels. Stiffness data was collected during actuation tests. Very good correlation was demonstrated in most cases between predicted behavior and experimental results.