Large deformation mechanics of a soft elastomeric layer under compressive loading for a MEMS tactile sensor application

• We modeled the non-linear response of an infinite elastomeric soft layer under uniform compression.
• Analytical and numerical finite element deformation and stress predictions are reported for severe layer compression up to 40%.
• Excellent agreement was found to exist between the analytical and finite element results.
• The analytical model was developed with the purpose of predicting the response of a MEMS pressure tactile sensor.
• The layer deformation is used to predict the electrode separation for capacitance measurements in tactile sensing.

The study is motivated by the need to develop highly sensitive tactile sensors for both robotic and bionic applications. The ability to predict the response of an elastomeric layer under severe pressure conditions is key to the development of highly sensitive capacitive tactile sensors capable of detecting the location and magnitude of applied forces over a broad range of contact severity and layer depression. Thus, in this work, a large deformation Mooney–Rivlin material model is employed in establishing the non-linear mechanics of an elastomeric layer of finite thickness, subjected to uniform displacement of controlled compression. Thus, an analytical non-linear model for the above described problem which is validated numerically via the method of finite elements is developed. Two dimensional, plane strain conditions of an infinitely long and of finite thickness elastomeric layer are assumed. The layer is subjected to a uniform vertical large displacement with symmetry conditions applied at the contact center. Cauchy normal and shear stress profiles as well as displacement profiles are established over a broad range of a layer compression including up to 40% of layer thinning. The model allows for the determination of the non-linear relationship between the relative separation of embedded conducting electrodes and thus the sensor capacitance during touch, to the force magnitude of the force concentrated at the symmetry plane or sensor center. The current model is expected to further improve the sensitivity and range of polymeric tactile sensors currently under development (Charalambides and Bergbreiter, 2013) [1]. As shown elsewhere (Kalayeh et al., 2015) [2], capacitance–force model predictions are found to be in remarkable agreement with experimental measurements for a broad family of self-similar pressure sensors.