STATISTICAL NATURE OF FATIGUE CRACK PROPAGATION.

A statistical investigation of the fatigue crack propagation process was conducted. Sixty-eight replicate constant amplitude crack propagation tests were conducted on 2034-T3 aluminum alloy. Distribution determination programs were written for the variables DELTA N/ DELTA a, N, da/dN, and dN/da. The following distributions were considered: two-parameter normal distribution, three-parameter log-normal distribution, three-parameter Weibull distribution, two-parameter gamma distribution, three-parameter gamma distribution, the generalized three-parameter gamma distribution, and the generalized four-parameter gamma distribution. From the experimental data, the distribution of N as a function of crack length was best represented by the three-parameter log-normal distribution.