Experimental investigation on the influence of a ``soft layer'' on the structural performance of a smart composite structure

The composite structures embedding piezoelectric implants are developed due to their abilities of modifying mechanical properties according to the environment, of keeping their integrity, of interacting with human beings or with other structures. One way to functionalize a mechanical device consists in embedding the transducers inside the final composite structure via a ``soft'' layer. This layer consists of two plies sandwiching the transducers, impregnated with a resin compatible with the one of the final composite structures. The test structures are laminates made of a glass-fiber reinforced plastic with a polyester resin. In this paper, we propose to experimentally investigate the influence of the through-the-thickness position of the ``soft layer'' on specific parameters of design such as eigenfrequencies, modal amplitude, damping ratio and Lamb wave propagation properties. Results show that the ``soft'' layer behavior can not be neglicted to predict the behavior of the final product in particular for the eigenfrequencies and the modal amplitudes. However, the ``soft layer'' has no impact on the damping ratio and the Time-of-Flight of a wave train.