On the constitutive modelling of recruitment and damage of collagen fibres in soft biological tissues

The aim of this work is to propose a recruitment and damage constitutive model for collagen fibres in soft biological tissues. Similarly to other published models, our model employs probability distribution functions in order to capture the progressive recruitment and damage of fibrils in a collagen fibre. We rigorously investigate the continuum mechanical treatment of recruitment and damage using a multiplicative decomposition of the deformation gradient. Our proposed model stems from the correction, generalisation and extension to damage of the recruitment model proposed by Martufi and Gasser (2011, J. Biomech., 44, 2544-2550). We demonstrate that the generalised model is equivalent to the recruitment and damage model proposed by Hurschler et al. (1997, J. Biomech. Eng., 119, 392-399). Finally, we explore the sensitivity of the proposed model to the parameters describing recruitment and damage, implement the model into Finite Elements and show an example of application, which gives good agreement with published experimental data.