Large deformation of hyperelastic thick-walled vessels under combined extension-torsion-pressure: analytical solution and FEM

Abstract

The mechanical behavior of a thick-walled pressure vessel composed of an incompressible isotropic nonlinearly elastic material subjected to the combined pressure and extension-torsion loading is investigated. An analytical solution is proposed for the general form of the free strain energy density, and different models including well-known Neo-Hookean, Mooney-Rivlin, and recently presented free energy contained two exponential terms -exp-exp model- which is strongly stable and compatible with experimental data, are employed. Comparing different constitutive models involves compatible calibration for a specific material. Thus, the uniaxial and equi-biaxial experimental data of silicon-rubber are simultaneously considered to be used in a calibration optimization procedure. Regarding the application of extension-torsion problem, e.g., biological application in papillary muscles, it is required to inspect this loading on a hollow cylinder and considering the internal and external pressure make the problem more realistic to be employed as capillary muscle. After proposing a closed-form solution for this problem, the finite element analysis of the same problem is conducted to verify the proposed analytical solution. Comparing the results of non-dimensional stress, force and moment distribution of analytical and finite element methods illustrate excellent agreement which confirms the accuracy of the presented solution. Some designing factors including the value of applied twist, axial stretch and pressure, and radius ratio are studied. Results demonstrate that the exp-exp model is more conservative in a small amount of twist and axial stretch. However, it yields a higher value for the stress, force, and moment in larger twists and stretches.