Anisotropic stress-softening effect on fast dynamic crack in filler-reinforced elastomers

Deformation of filler-reinforced elastomers is accompanied by a complex internal damage due to stress softening (Mullins effect). The crack growth behavior of filler-reinforced elastomers is made significantly complex by the occurrence of a simultaneous directional stress softening. The influences of the directional stress softening on fast crack propagation normal to the pre-stretching direction are revealed by the comparison using three types of specimens: (I) a low-filled elastomer with almost no stress softening, (II) a pristine highly filled elastomer with a pronounced stress-softening feature, and (III) an elastomer obtained by imposing before uniaxial loading-unloading cycles with a large maximum stretch of specimen (II). The previous directional softening causes a reduction in the threshold tearing energy for velocity transition, and an increase in local strain in the softening direction. In contrast, the previous directional softening has no appreciable effect on the tearing energy dependence of velocity, crack-tip shape, strain field behind the crack-tip, and the strain singularity near the crack-tip.