Piecewise fitting of silicone rubber for soft robot based on the Neo-Hookean constitutive model

A number of pneumatic soft robots are made of hyperelastic silicone rubber. The dynamic modeling and control of the soft robot require the establishment of a constitutive model of the silicone rubber. The Neo-Hookean constitutive model was established according to the material properties of silicone rubber. In this study, using the optimization module of COMSOL Multiphysics, we fitted uniaxial and equibiaxial measured data against the Neo-Hookean constitutive model. We obtained the stretch-stress relationship of the silicone rubber material from the uniaxial tension test. For the uniaxial and equibiaxial measured data, different weights are assigned to improve fitting accuracy. For silicone rubber with a large range of stretch factor, the measured data are fitted piecewise against the Neo-Hookean model. The Neo-Hookean material model fits both test data quite well for the case of different weight and piecewise fitting for uniaxial and equibiaxial data set.