Resistance curves for the threshold of fatigue crack propagation in particle reinforced aluminium alloys

The threshold of stress intensity factor range Delta K-th increases with in creasing crack extension until it reaches the constant value of long cracks . Such curves: can be interpreted as resistance cur;es for the threshold of fatigue crack propagation. In the paper a very simple method to measure such R-curves is presented and a concept based on the R-curve is used to describe the propagation/non-pro pagation behavior of physically small cracks. The application of the R-curv e technique results in the Kitagawa diagram where one can estimate the fati gue limit of components containing "small" flaws. R-curve tests and standar d fatigue experiments at different stress ratios were performed oil a 20 vo l% SiC particle reinforced 359 TG cast aluminum alloy which contains natura lly small flaws up to 400 mu m. Application of the R-curve concept is demon strated and the estimations are compared with experimental results of the f atigue tests, Good agreement between the predicted and measured failure beh avior was found.