Nonlinear elastic finite fracture mechanics: Modeling mixed-mode crack nucleation in structural glazing silicone sealants

Requiring both stress and energy conditions to be met simultaneously proved key to modeling brittle crackformation at singular and nonsingular stress concentrations in linear elastic materials. The present workextends this so-called coupled stress and energy criterion to brittle crack nucleation in hyperelastic mediausing the example of silicone adhesives. For this purpose, we provide a comprehensive constitutive as wellas fracture mechanical characterization of the structural silicone adhesive DOWSIL™ 993 using a large setof experiments and propose a mixed-mode failure model for crack initiation in nonlinear elastic materials.Characterized in independent experiments, the model is used to determine critical loads of hyperelasticadhesive bonds in both shear and tension dominated configurations. For any of the examined adhesive jointconfigurations the model predicts and explains size effects and agrees well with experimental findings. Westudy stable and unstable crack propagation observed in video recordings of our experiments. It is shownthat crack initiation, crack growth and crack arrest are caused by nonmonotonic energy release rates andcan be predicted. Effects of excess energy available after crack nucleation and initial unstable crack growthare discussed.