The Probability of Failure of a System Subjected to the Joint Effect of Cyclic Loading and Randomly Distributed Discrete Load Peaks.

摘要

If a specimen is subjected to some kind of cyclic loading with a maximum load level S, which is larger than the fatigue limit of the specimen, then the strength of the specimen will gradually decrease until its residual strength R reaches the value S, when static failure occurs. This deterioration process may, as indicated, be described graphically by an R-S-N-diagram or analytically by a set of parameter functions of S and N. If now a discrete load peak of known level L is imposed upon the specimen after N fatigue cycles, then the probability of failure may be directly read from the diagram or computed by use of the parameter functions. A generalization of the R-S-N-diagram is proposed in order to make it applicable to the case, when the discrete load peaks are replaced by sequences of different cyclic loadings. By use of this diagram it has been proved that Miner's measure of cumulative fatigue damage M = sum over n sub i/N sub i depends on the order in which the different sequences are applied, a defect which has been repeatedly verified by experiment. (Author)