Control of Tension-Compression Asymmetry in Ogden Hyperelasticity with Application to Soft Tissue Modelling

TL;DR

This paper introduces a new hyperelastic model that independently controls tension-compression asymmetry, improving soft tissue modeling by separating asymmetry effects from non-linearity, and demonstrates its application to skeletal muscle tissue.

Contribution

A simple hybrid Ogden-based formulation is proposed, enabling separate control over tension-compression asymmetry in hyperelastic materials, with applications to soft tissue modeling.

Findings

The hybrid model allows independent tuning of asymmetry and non-linearity.

The symmetric form is suitable for modeling ground matrix contributions in tissues.

Application to skeletal muscle demonstrates the model's effectiveness in biological tissues.

Abstract

This paper discusses tension-compression asymmetry properties of Ogden hyperelastic formulations. It is shown that if all negative or all positive Ogden coefficients are used, tension-compression asymmetry occurs the degree of which cannot be separately controlled from the degree of non-linearity. A simple hybrid form is therefore proposed providing separate control over the tension-compression asymmetry. It is demonstrated how this form relates to a newly introduced generalised strain tensor class which encompasses both the tension-compression asymmetric Seth-Hill strain class and the tension-compression symmetric Ba\v{z}ant strain class. If the control parameter is set to q=0.5 a tension-compression symmetric form involving Ba\v{z}ant strains is obtained with the property {\Psi}({\lambda}_1,{\lambda}_2,{\lambda}_3 )={\Psi}(1/{\lambda}_1 ,1/{\lambda}_2 ,1/{\lambda}_3 ). The symmetric form may be desirable for the definition of ground matrix contributions in soft tissue modelling allowing all deviation from the symmetry to stem solely from fibrous reinforcement. Such an application is also presented demonstrating the use of the proposed formulation in the modelling of the non-linear elastic and transversely isotropic behaviour of skeletal muscle tissue in compression (the model implementation and fitting procedure have been made freely available). The presented hyperelastic formulations may aid researchers in independently controlling the degree of tension-compression asymmetry from the degree of non-linearity, and in the case of anisotropic materials may assist in determining the role played by, either the ground matrix, or the fibrous reinforcing structures, in generating asymmetry.