Execution and evaluation of cyclic tests at constant load amplitudes – DIN 50100:2016

Abstract

Tests with constant load amplitudes are used to characterize the fatigue strength behavior of material specimens and components. The S-N curve derived from these test results describes the relationship between the load amplitude and the corresponding cycles to failure. Different concepts for carrying out and evaluating fatigue tests make it difficult to compare the results from different research institutes. The aim of the new version of the German standard DIN 50100:2016 is to define a procedure for determining an S-N curve for metallic alloys that does not allow any scope for interpretation. It is assumed that the test results are subject to logarithmic normal distributions in both load and cycle direction. It is further assumed that the S-N curve in the high-cycle fatigue regime and the long-life fatigue regime can be approximated by a bilinear function. For the determination of the straight line of finite life, the pearl string method and the load level method are available for determining the position parameter and the slope of the power function according to Basquin. Long-life fatigue strength is determined using the staircase method and forms the knee point of the S-N curve on average with the straight line of finite life. For the long-life fatigue regime, a horizontal course or a decrease with low inclination, depending on the material group examined, is assumed. In addition, DIN 50100:2016 contains information on the accuracy of the estimation of the mean values and the scatter of the characteristic values according to the sample size. The goal of achieving comparability of S-N curves is supported by extensive examples. An English translation of DIN 50100:2016 is available also.