A Mode-III Crack Subjected to High-Strain Rates

THE DISPLACEMENT rate is given for a mode III crack growing in a steady state under dynamic conditions. The material is assumed to be visco-plastic and high strain rates are considered. A regular perturbation expansion is performed. First-order perturbing strains are, with one exception, square root singular near the crack-tip. For overstress exponents less, or equal to 2, a reasonably large region around the crack tip, i.e. > 10(-3) of the linear extent of the plastic zone, is dominated by the square root singular strain field. For an overstress exponent of 5/2 the region extends to about 10(-5) of the plastic zone size, which significantly reduces the possibilities of using the strength of the square root singular field as a fracture parameter. For the overstress exponent 3 the region vanishes.