The steady state fracture kinetics of crack front spreading

The kinetics study is based on the energetically favourable crack propagation mechanism of double kink nucleation and its subsequent sideways spreading. The analysis was carried out on linearly elastic solids for the case when kink spreading is the rate controlling mechanism. The kink spread distribution is described by a differential equation that is identical with the mass and heat transport equations. The solutions of the differential equation represent the distribution function and the crack propagation velocity as a function of the bond breaking energy G, the work W contributed by the applied stress, and of the temperature. When WG/2 the crack velocity increases exponentially with increasing work, decreases steeply with decreasing work, and reduces to zero when WG/2. The theory represents well the behavior of ceramic materials and some metals in Region 1 and at the threshold region of stress corrosion cracking. It is of special interest for stress corrosion cracking designs that the threshold stress intensity is independent of the temperature under the conditions of the present investigation.