DYNAMIC CRACK-PROPAGATION IN A LAYER

Mode I crack propagation in an elastic layer is discussed. Previous investigations have dealt with cases in which the crack edge travels with sub-Rayleigh velocity with respect to the surrounding medium, and with either sub-Rayleigh or supersonic velocity with respect to the layer. In the present paper, the third fundamental case is studied; crack edge travel at sub-Rayleigh velocity with respect to the layer and supersonic velocity with respect to the outer medium. Comparison is made between the three cases, and the theoretical basis for expecting the plane stress Rayleigh wave velocity of the outer medium as an upper limit of the crack velocity in the recent experiments by Washabaugh and Knauss (1994, Int. J. Fract. 65, 97-114) is discussed.