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 increasing 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-propagation behavior of physically small cracks. The application of the R-curve technique results in the Kitagawa diagram where one can estimate the fatigue limit of components containing "small" flaws. R-curve tests and standard fatigue experiments at different stress ratios were performed oil a 20 vol% SiC particle reinforced 359 TG cast aluminum alloy which contains naturally small flaws up to 400 mu m. Application of the R-curve concept is demonstrated and the estimations are compared with experimental results of the fatigue tests, Good agreement between the predicted and measured failure behavior was found.