Résumé
Vaginal delivery frequently induces large deformations of the perineal tissues, which may result in severe obstetric injuries involving the internal anal sphincter (IAS). From a mechanical standpoint, the IAS undergoes complex loading paths combining large strains, anisotropy, and time-dependent effects, which remain insufficiently characterized. This work presents the development of a thermodynamically consistent constitutive model describing the tensile behavior of the IAS up to failure. Mechanical tensile tests combined with microscopic observations are conducted on porcine tissues to characterize fiber organization and to support the development of an anisotropic hyper-viscoelastic model with stress-softening behavior. Current efforts focus on parameter identification and on assessing the model’s ability to reproduce nonlinear and history-dependent tissue behavior. By linking macroscopic mechanical behavior to microstructural characteristics, this approach aims to improve the understanding of IAS injury mechanisms and to identify mechanically based indicators relevant for predictive biomechanical biomarkers.