Evaluating Plastic Deformation and Damage as Potential Mechanisms for Tendon Inelasticity using a Reactive Modeling Framework

Abstract

Inelastic behaviors, such as softening, a progressive decrease in modulus before failure, occur in tendon andare important aspect in degeneration and tendinopathy. These in elastic behaviors are generally attributed to two potential mechanisms: plastic deformation and damage. However, it is not clear which is primarily responsible.In this study, we evaluated these potential mechanisms of tendon in elasticity by using a recently developed reactive in elasticity model (RIE), which is a structurally-inspired continuum mechanics frame work that models tissue in elasticity based on the molecular bond kinetics. Using RIE, we formulated two material models, one specific toplastic deformation and the other to damage. The models were independently fit to published experimental tensiletests of rat tail tendons. We quantified the inelastic effects and compared the performance of the two models infitting the mechanical response during loading, relaxation, unloading, and reloading phases. Additionally, we validated the models by using the resulting fit parameters to predict an independent set of experimental stress-straincurves from ramp-to-failure tests. Overall, the models were both successful in fitting the experiments and predicting the validation data. However, the results did not strongly favor one mechanism over the other. As a result, to distinguish between plastic deformation and damage, different experimental protocols will be needed. Nevertheless, these findings suggest the potential of RIE as a comprehensive framework for studying tendon inelastic behaviors.