Energetic Considerations with Modified Relaxation Integral on Fast Propagating Crack in a Viscoelastic Strip

Abstract

The energy balance concept was applied to the analysis of crack propagation in a viscoelastic material through the estimation of several kinds of energies, which are derived from a modified relaxation integral law, e.g., the instantaneously released elastic energy, the dissipative energy and/or the residual energy. For this purpose, non-linear relationship between stress and strain due to the intrinsic material properties under large deformation as well as the change of boundary condition during crack extension should be described quantitatively. The experimental results for an epoxy resin used as the tested material showed that the modified linear viscoelastic relaxation integral equation is applicable for the aforementioned analysis up to about 100% straining by use of the logarithmic strain rate instead of the nominal one. Also, it was ascertained experimentally that he average crack can be represented in similar ways by introduction of a correction factor depending on the change of crack length, namely the compliance reduction ratio. Finally, a criterion for the crack propagation in a viscoelastic strip was proposed from a macroscopic view point of the internal energies depending on time.