ANALYSIS OF THE ACCURACY OF DETERMINATION OF THE ENDURANCE LIMIT BY THE METHOD OF GRADUAL LOAD CHANGE

Abstract

Introduction. The problem associated with the accuracy of the experimental determination of the average probable value of the endurance limit and its root-meansquare deviation using the up-down method is considered. To solve the problem, an example was considered and calculations were carried out, which made it possible to plot the dependences of the errors of these fatigue resistance characteristics on the test modes. It was shown that the average probable values of endurance limits and their root-mean-square deviations significantly depend on both the initial load level and the voltage drop between levels. In this case, it was found by calculation that the minimum error values occur when the initial stress is close to the expected endurance limit, and the voltage drop d is minimal. Purpose of the article is to study the accuracy of the method for determining the endurance limit and its dispersion under different test planning options. Results. The dependences of the endurance limit and its root-mean-square deviation from the interval between stress levels and the initial load level are obtained by calculation, and the values of their errors are determined, presented in tabular and graphical forms. Conclusions. The average probable values of endurance limits and their root-mean-square deviations, determined by formulas (3) and (4), depend both on the initial load level and on the voltage drop between the levels. The minimum error values occur when the initial stress is close to the expected endurance limit, and the voltage drop is minimal. The errors of the root-mean-square deviation of the endurance limit vary within the limits, and their dependence on the voltage drop and the initial level is stochastic.