The application of standard nonlinear solid material models in modelling the tensile behaviour of the supraspinatus tendon

Tendons transmit forces from muscles to bones through joints. Typically, tendons and muscles work together to innovate a motion. In addition, tendons are often subjected to much higher stresses than the muscles that they serve in any given action. As a result, tendons are susceptible to injuries that may lead to a permanent dysfunction in joint mobility due to the fact that the scar tissue that forms after healing often does not have the same mechanical properties of the original tissue. It is therefore very important to understand the mechanical response of tendons. In this paper the performances are examined of two viscoelastic standard nonlinear models in modelling the elastic and plastic behaviour of the tendon in the light of a well-known hyperelastic Yeoh model. The use of the Yeoh model is more for validating the performances of the viscoelastic models within the elastic region than for comparison purposes. The Yeoh model was selected based on its superior performance in modelling the elastic phase of soft tissue, as reported in previous studies, combined with its simplicity. The results show that the two standard nonlinear solid models perform extremely well both in fitting accuracies and in correlating stress results. The most promising result is the fact that the two standard nonlinear models can model tendon behaviour in the nonlinear plastic region. It is also noted that the two standard nonlinear models are physically insightful since their optimisation parameters can easily be interpreted in terms of tendon elasticity and viscoelastic parameters.