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

Previous work has shown that the inclusion of the strain energy released by crack blunting leads to an energy minimum for fatigue crack growth that can be used to predict stage II fatigue crack growth. The present work assumes a polynomial relation between crack blunting and crack extension to derive an expression for the rate of fatigue crack growth that is dependent upon only the applied DELTAK, E, sigma(ys) K(c) and the exponent p in the relation between crack blunting and crack extension. This expression is thought to be generally valid since it accurately predicts fatigue crack growth rates for a wide variety of titanium, nickel, aluminium and steel alloys. A unique characteristic of the model is its ability (for long crack, slow crack growth) to account for the different slope for different materials in the Paris Law region of the da/dN vs. DELTAK curve. The model specifically shows that this slope, m, is dependent solely upon the exponent, p, in the relation between crack blunting and crack extension.