ABSTRACT
Kakavas has proposed a strain energy function based on the logarithmic strain approach for predicting the experimental data of tests on rubber materials. Due to the incompressibility constraint the first logarithmic invariant vanishes, and the function is expressed in terms of the second and third invariants. The proposed function was applied for the prediction of the twisting moment and the axial force for a cylinder under simple torsion. To test the validity of the proposed strain energy function for moderate deformations, its predictions for the twisting moment and the axial force in simple torsion and combined extension and torsion of solid cylinders of incompressible materials were calculated. The proposed four parameter model is proved that predicts the experimental behavior of rubber materials for all the range of deformation. Equations for the estimation of twisting moment and resulted axial force were evaluated using simple numerical analysis methods.
