The Biot stress -- right stretch relation for the compressible Neo-Hooke-Ciarlet-Geymonat model and Rivlin's cube problem

TL;DR

This paper investigates the stress-strain relations in a hyperelastic cube model, analyzing conditions for unique solutions, symmetry breaking, and bifurcations under tensile loads, with implications for stability and deformation behavior.

Contribution

It establishes conditions on volumetric functions ensuring unique radial solutions in the Neo-Hooke-Ciarlet-Geymonat model and explores symmetry-breaking bifurcations in Rivlin's cube problem.

Findings

Conditions on volumetric function h for unique radial solutions

Discontinuous equilibrium trajectories with non-symmetric deformations

Monotonicity holds up to bifurcation load, then fails

Abstract

The aim of the paper is to recall the importance of the study of invertibility and monotonicity of stress-strain relations for investigating the non-uniqueness and bifurcation of homogeneous solutions of the equilibrium problem of a hyperelastic cube subjected to equiaxial tensile forces. In other words, we reconsider a remarkable possibility in this nonlinear scenario: Does symmetric loading lead only to symmetric deformations or also to asymmetric deformations? If so, what can we say about monotonicity for these homogeneous solutions, a property which is less restrictive than the energetic stability criteria of homogeneous solutions for Rivlin's cube problem. For the Neo-Hooke type materials we establish what properties the volumetric function $h$ depending on ${\rm det}\, F$ must have to ensure the existence of a unique radial solution (i.e. the cube must continue to remain a cube) for any magnitude of radial stress acting on the cube. The function $h$ proposed by Ciarlet and Geymonat satisfies these conditions. However, discontinuous equilibrium trajectories may occur, characterized by abruptly appearing non-symmetric deformations with increasing load, and a cube can instantaneously become a parallelepiped. Up to the load value for which the bifurcation in the radial solution is realized local monotonicity holds true. However, after exceeding this value, monotonicity no longer occurs on homogeneous deformations which, in turn, preserve the cube shape.