Defect sensitivity of highly deformable polymeric materials with different intrinsic qualities at various strain rates

Highly deformable materials, such as elastomers and gels, can withstand very large deformation without failure, and this response is usually insensitive to the presence of macroscopic defects. These polymer-based materials, different from the traditional ones which are usually characterized by an enthalpic elasticity, show a mechanical response which is governed by the state of internal entropy of their molecular network. If fracture energy is large, the noticeable ability of soft materials to rearrange their network at the microscale, to display large deformation and to dissipate energy thanks to their viscoelasticity, allows the minimization of the local detrimental effect of existing flaws. In the present paper, the mechanical behavior of silicone-based edge cracked plates with different crack sizes and severity of the intrinsic flaws embedded in the material is examined by taking into account the time-dependent effects. Experimental and theoretical aspects are discussed to explain the defect tolerance of such materials. The detrimental effect of intrinsic voids is quantified and the beneficial effect due to strain at low rates is analysed. The critical distance is related to the ultimate stretch value, the quality of the material and the crack size.