THE RELATION BETWEEN CRACK BLUNTING AND FATIGUE-CRACK GROWTH-RATES

Previous work has shown that the inclusion of the strain energy releas ed by crack blunting leads to an energy minimum for fatigue crack grow th that can be used to predict stage II fatigue crack growth. The pres ent work assumes a polynomial relation between crack blunting and crac k extension to derive an expression for the rate of fatigue crack grow th that is dependent upon only the applied DELTAK, E, sigma(ys) K(c) a nd the exponent p in the relation between crack blunting and crack ext ension. This expression is thought to be generally valid since it accu rately predicts fatigue crack growth rates for a wide variety of titan ium, nickel, aluminium and steel alloys. A unique characteristic of th e model is its ability (for long crack, slow crack growth) to account for the different slope for different materials in the Paris Law regio n of the da/dN vs. DELTAK curve. The model specifically shows that thi s slope, m, is dependent solely upon the exponent, p, in the relation between crack blunting and crack extension.