Oznaczanie granicy zmęczenia tworzyw sztucznych metodą schodkową

The statistical analysis of 60 up-and-down method diagrams was carried out to find the minimum number of samples required for determination of the fatigue strength of plastics. Basing on the sequential analysis the evidence was given that if the value of cumulative function is not greater than 3 per cent of the size of set taken as parent population, then the determination of fatigue strength can be carried out with the number of samples not less than 22. The applicability of modyfied up-and-down method for determination of the fatigue limit was verified. It was found that in this pattern of calculation the number of samples may be reduced by 10 per cent. As the experimental set of diagrams represents a relatively wide class of plastics and test parameters, the applicability of conclusions to other materials with dispersion within the limits of tested set, was found possible.