Stress and strain dielectric response for sensing and actuator applications

Electrostriction, a deformation caused by the electric field-induced stress, and dielectrostriction, a variation of dielectric properties with deformation, are the electro-active responses which can be observed in any dielectric material. Thermodynamic consideration links these two phenomena to the same set of material parameters including dielectric constants and the derivatives of dielectric constants with strains. A traditional approach to electrostriction through measuring the field-induced deformations is challenging and unreliable for soft materials due to the inherent uncertainties with the constraints at the material-electrode interface. This work deals with variation in the dielectric properties of a material caused by the deformations, e.g., the stress/strain-dielectric response of elastic solids, and adopts this approach for evaluating the electrostriction response of an elastic dielectric material.;In this study, the stress/strain-dielectric response of elastic solids is formulated for arbitrary deformations. Background for a planar capacitor sensor and the sensor rosettes for dielectrostriction study are introduced. Such sensor and sensor rosettes would not require any mechanical contact with the specimen, which removes uncertainties with the boundary constraints. Experimental study of stress/strain-dielectric response is conducted for several polymeric and composite specimens loaded in linear and non-linear elastic regions. Stress and strain descriptions of dielectrostriction are equivalent for a linear elastic range. However, only the stress-dielectric relation remains linearly even for a non-linear elastic range. It is demonstrated that the principal strains and the principal directions of strains can be measured by using the sensor rosettes. The electrostriction parameters of isotropic dielectrics are obtained through the dielectrostriction responses to uniaxially tensile loaded specimens, which show good agreement with the predicted values. Finally, the actuation of silicone-Barium Titanate (BaTiO3) composites is investigated for different volume fractions of the inclusions and different material structures, which is an avenue for optimizing future actuator designs. These results constitute an approach for a self-sensing and self-actuation of materials which combines dieletrostriction and electrostriction phenomena. Potential applications include stress or strain sensing, in-line health monitoring and NDE (Non-Destructive Evaluation) of structural materials, self-sensing and self-actuating in smart materials.