Effect of Notch on Tensile and Fatigue Strengths of Lead Free Copper Alloy Castings

The fatigue strength of lead free copper alloy castings such as bismuth, bismuth-selenium, and silicon-zinc copper alloy castings was investigated by conducting fatigue tests at a constant stress amplitude under tension-tension cyclic loading. No fatigue limit was observed in the S-N curves obtained for the copper alloy castings, therefore, the endurance ratio, defined as the ratio of the stress amplitude at 107 cycles to the tensile strength of the material, was evaluated from the S-N curve. Results of the fatigue tests showed relatively small values of endurance ratio ranging from 0.1 to 0.2 for the lead free copper alloy castings. Effects of notch on the fatigue strength were also examined. For the bismuth and bismuth-selenium copper alloy castings, the fatigue strength of notched samples was higher than the tensile strength of the castings. The triaxial stress state in tension was thought to be created at the cross section of the notch root due to plastic constraint. Meanwhile, in the case of silicon-zinc copper alloy castings which have higher tensile strength, the notched sample showed lower fatigue strength than the tensile strength. Basic mechanical properties including notch effects on the tensile strength of the copper alloy castings tested are also described in the present report.