Identification of mode I and III fracture toughness of a structural silicone sealant

The present study focusses on the experimental determination of mode $I$ and $III$ fracture toughness for structural silicone sealants. Large deflections are explicitly considered in the theoretical framework employed for evaluating the experiments. Tests are performed with a structural silicone sealant manufactured in thin layers. Double cantilever beam specimen are loaded with out-of-plane shear to measure the mode $III$ fracture toughness of the adhesive. The methodology of the evaluation is validated numerically. The assumptions made in the development of the theoretical framework result in a maximum deviation between numerical results and the approximation formula of less than 10%. Additionally, double cantilever beam specimen are submitted to cleavage loading in order to determine the mode $I$ fracture toughness. We measure a mode $I$ fracture toughness of DOWSIL™ TSSA of $G_{Ic}=(3.64\pm 0.91)\mathrm{N/mm}$. In case of out-of-plane shear loading, the fracture toughness is found to be $G_{IIIc}=(7.03\pm 0.94)\mathrm{N/mm}$. The outlined experiments are suitable for arbitrary nonlinear elastic materials undergoing large deflections during fracture toughness testing.