Study on C-R-S curves of up-and-down test and fatigue limit stress

A technique for dealing with confidence limit-reliability-stress (C-R-S) curves of up-and-down test was presented to obtain a more accurate endurance limit.Firstly,a distribution hypothesis was tested and its parameters were estimated with regard to the random variables of stress level and reliability.According to 3-parameter Weibull distribution,C-R-S curves were fitted by the least square method.Lastly,the endurance limit was obtained concerning reliability.The endurance limit with a confidence limit of 95% and a reliability of 99% was deduced as 283.76 MPa from up-and-down test of gear tooth bending tests on the quenched and tempered alloy steel 38SiMnMo.This result falling into the square chart of Chinese standard GB3480 can verify the technique presented.