Coupled ductile–hydrolytic damage model based on variational constitutive updates

Mechanical characterization of hydrolysis effects on the stiffness of bioabsorbable polymeric filaments: An experimental and modeling approach based on a simple constitutive damage model

“…As can be seen in Figure 4a, both stiffness and strength of yarns reduce their values proportionally to the period of bath immersion, behavior that was already expected and clearly indicates mechanical degradation. 1,3,7 Nevertheless, due to the nonlinearities involved—both material and geometrical—the understanding of how much the hydrolytic degradation changes the stiffness over time is not straightforward in the present case.…”

“…These mechanical states are usually found in bioabsorbable polymeric medical devices. 1,3 It is worth mentioning that the terms creep and stress relaxation are commonly employed in the context of viscoelastic materials. On the other hand, continuum damage formulations, as the present one, can induce creep and stress relaxation, even if no viscous effects are accounted for.…”

“…13,30,41 Despite stress at failure concerns an important quantity to be taken into account in mechanical design, biomedical devices could consider other design criteria, such as deformation level and stiffness. 1,3 For the present application, if at a certain time of degradation the surrounding tissue is not properly healed, the load continues to be fully supported by the suture which, if degraded, can deform more than is necessary to fulfill its function. Such mechanical behavior, namely, damage-induced creep , is better explored in the numerical results discussed in Section 4.2.…”

“…3,18,32-35 Moreover, this damage theory is consistently grounded within the Continuum Thermodynamics , 36 providing then a sound constitutive formulation. 3,18,19,32…”

“…Although the damage could be an anisotropic tensorial variable, an isotropic assumptiongoverned by one scalar damage variable-is generally suitable to capture a broad range of mechanical degradation phenomena. 3,18,[32][33][34][35] Moreover, this damage theory is consistently grounded within the Continuum Thermodynamics, 36 providing then a sound constitutive formulation. 3,18,19,32 Within the present context, the degradation of the material is represented by a total damage variable D that is a function of two other damage variables, i.e.…”