Energy release rate of a single edge cracked specimen subjected to large deformation

The single edge notch specimen (SEN) is commonly used to measure the fracture toughness, or critical energy release rate of soft elastic materials. To measure toughness, an expression for the energy release rate,J, the mechanical energy available for growing the crack per unit area, is needed. Since strains in these fracture experiments can easily exceed several hundred percent, large deformation analysis is needed to calculateJ. An approximate formula forJin SEN samples subjected to moderately large deformation was given by Rivlin and Thomas in J Polym Sci 10:291-318. 10.1002/pol.1953.120100303 (1953) and Greensmith in J Appl Polymer Sci 7:993-1002. 10.1002/app.1963.070070316 (1963). However, this formula works only for small crack lengths, for stretch ratio up to two and does not match the linear elastic result in the limit of small strains. In this paper we carry out a series of finite element (FE) simulations to obtain accurate approximations that are valid for all practical crack lengths and strain levels. Our FE result shows that the small crack approximation of by Rivlin and Thomas in J Polym Sci 10:291-318. 10.1002/pol.1953.120100303 (1953) does not work well in the small strain regime, and in particular, result of Greensmith in J Appl Polymer Sci 7:993-1002. 10.1002/app.1963.070070316 (1963) underestimates the energy release rate for stretch ratios less than 1.5.