In order to investigate the statistical distribution and its characteristics (parameters of the distribution) of fatigue crack length at an arbitrary time during the process of fatigue crack propagation, pulsating-tension fatigue tests were carried out under the condition of the same constant stress amplitude on many specimens of a high-tension steel, and the results were discussed by means of the statistical analysis.
In the first place, the constants in the Paris-Erdogan equation of fatigue crack propagation were randomized and the results obtained by computation were compared with the experimental results and discussed. Next, from these results a new parameter was considered, which is constant irrespective of crack length and represents the statistical variability of crack propagating-life. Finally, by using the method of Markov chain, it was revealed that this parameter really represented the variability of lives in the transition propability matrix of Markov chain, and thus the physical meaning was given for this parameter. It was also found that the above parameter was applicable for the crack propagating behaviour in both cases of constant and variable stress intensity factor ranges.
