Load transfer and bond fatigue in an embedded induced strain actuator

An embedded piezoceramic induced strain actuator transfer actuation to the host composite mainly through shear action over the faces of the actuator. The Synthesis and Processing of Intelligent Cost Effective Structures (SPICES) actuator, analyzed in this paper, is an induced strain actuator, comprising of a co-fired piezoelectric stack, encased within a titanium frame, and excited in the 3-3 mode. The shear stresses are maximum at the edge of the piezoelectric stack, while the normal stresses are uniform over the piezoelectric stack. Both decrease exponentially towards the edge of the frame. The shear stresses though much smaller than the normal stresses are responsible for the load transfer to the composite. The actuator-composite interface is subjected to fatigue. Any failure or deterioration in this bond will significantly reduce the efficiency of the actuator. Debonding starts near the interface of the PZT and the frame and reduces the load transfer to the composite. This reduction is found to be quite low for small amounts of debonding. Experiments show that, specimens fatigued to a million cycles showed an average decrease of 6 percent from the non-fatigued specimen.