升降法测试疲劳强度均值和标准偏差产生误差的原因

Cause of Error in Average and Standard Deviation of Fatigue Strength Measured by Up-and-down Method

借助计算机模拟研究了应力台阶d与疲劳强度标准偏差σ的比d/σ、应力台阶数i及试样数量N对升降法测试疲劳强度均值μ和标准偏差σ的影响。结果表明:升降法测试疲劳强度均值的可靠度高于测试标准偏差的,同一试验条件下进行多次重复测试可以提高试验结果的可靠度。d/σ>3时,升降图难以满足D>0.3。标准偏差估计值σ的均值和标准偏差均与升降图应力台阶数i相关,升降法试验中应保证i为3或4。提高试样数量可以减小(μ,σ)的估计值(μ,σ)的分散性。

The effects of the ratio d/σof the stress step d to the standard deviation of fatigue strengthσ,the number of stress steps i and the number of sample N on the averageμand standard deviationσof fatigue strength measured by up-and-down method were studied through computer simulation.The results show that the reliability of fatigue strength average measured by up-and-down method is higher than that of standard deviation,and the reliability of test results can be improved by repeated measurements under the same test conditions.When d/σ>3,it is difficult for up-and-down picture to meet the requirement of D>0.3.The average and standard deviation of the estimated value of standard deviation■related to the number of stress steps i in up-and-down picture,and i should be 3 or 4 in up-and-down method test.It is useful to reduce the dispersion of estimated value■by increasing the number of specimens.