Fatigue Reliability Analysis And Crack Initiation Micromechanism For 42CrMo Steel

High reliability for alloy structure steels has got more and more emphasis with the development of high-speed and large-scale machineries. The traditional mechanical strength certainty analyses characterized by safety factors are moving towards reliability methods, so that precise and reliable information is offered to fatigue design.With the vital transformation of mechanical strength analysis methods, parametric estimation, hypotheses verification, and reliability models of fatigue life and performance prediction were researched. The influence of short fatigue crack initiation micromechanism on randomness of fatigue was discussed. Hardened gear-tooth bending stress fatigue experiments, strain fatigue experiments, and microscopic experiments of short fatigue cracks of 42CrMo alloy steel were conducted, and the experimental results were analyzed respectively. The researches in this dissertation are supported financially by Natural Science Foundation of Shandong Province(Y2002F19).Firstly, parametric estimation, hypotheses verification and total fitting evaluation of fatigue probability distributions were researched to explore statistical law of the fatigue data. Probability distribution functions commonly include Normal Distribution(ND), Lognormal Distribution(LND), Exponential Distribution(ED), Two-parameter Weibull Distribution(2-PWD), and Three-parameter Weibull Distribution(3-PWD). In order to assess these functions, their linear regression equations were given. The parametric estimation of 3-PWD obtained by analytical or graphic method is usually difficult, so that a parametric estimation method of probability distribution function based on binominal formula expansion was proposed. In the method, the value of fatigue parameter obtained by graphic estimation was introduced into the probability model, and the estimate of the value was achieved by expanding binominal formula of Newton. A hypotheses verification method, that is widely used for various common fatigue reliability distribution models, was developed by introducing non-parametric statistical D_n-testing procedure. The evaluating method of total fitting effect of fatigue probability distributions was presented so that the best fitting probability function could be accepted.Secondly, the general reliability models of fatigue life and fatigue performance...