Strain-Field Analysis of Subsonic and Supersonic Cracks in Filled Elastomers

In the present study, the transition in the characteristics of local crack-tip strain-field from the subsonic (V/C_s < 1) to supersonic (V/C_s > 1) cracks in filled elastomers is investigated, where V and C_s are crack-growth velocity and shear wave speed, respectively. The crack propagation of the specimens stretched by pure shear deformation is observed by a digital high-speed camera. The crack-tip strain-field is evaluated by the two-dimensional digital image correlation technique (DIC) on the basis of the captured speckle images. The critical behavior of the vertical strain field (e_yy) near the crack-tip is characterized by the exponent α in the power law, e_yy ~ (1/r)^α, known as a crack-tip singularity field. The exponent α in the subsonic crack is constant and larger than those of the linear elastic fracture mechanics (LEFM, α = 0.5) as well as weakly nonlinear fracture mechanics (WNLM, α = 1). In contrast, the exponent α in supersonic crack significantly increases with an increase in the crack growth rate.