FULL-FIELD MEASUREMENTS OF THE DYNAMIC DEFORMATION FIELD AROUND A GROWING ADIABATIC SHEAR-BAND AT THE TIP OF A DYNAMICALLY LOADED CRACK OR NOTCH

The method of Coherent Gradient Sensing (CGS) is used to record the deformation held around an adiabatic shear band emanating from a pre-crack tip in C-300 steel loaded dynamically in mode II. At early times after impact, the resulting fringe pattern surrounding the shear band seems to exhibit the deformation characteristics of a mode II Dugdale plastic zone evolving under small-scale yielding conditions and, as a result, the experimental fringe patterns are fitted to the theoretical Dugdale crack deformation field by using a least squares fitting scheme. This results in values for the shear band length and the average shear stress acting on the shear band as functions of time. The shear band is observed to initiate when K-II(d)(t) = 140 MPa root m and subsequently propagate with an average speed of 320 m s(-1). The average sheer stress on the shear band decreases from 1.6 GPa at initiation to 1.3 GPa during the later stages of propagation.