The dynamic energy release rate for two parallel steadily propagating mode III cracks in a viscoelastic body

The dynamic steady-state propagation of two parallel semi-infinite, mode III cracks is considered for a general, infinite, homogeneous, and isotropic linearly viscoelastic body. A Barenblatt type failure zone is assumed to exist at the crack tip and a formula for the energy release rate is derived which provides immediate comparisons with the corresponding single crack problem. The influence of crack speed, crack separation, and material properties upon the energy release rate are illustrated with numerical calculations for both power-law material and a standard linear solid. Results for the elastic and quasi-static viscoelastic problems are deduced as limiting cases of the analysis.