The 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 2024-T3 aluminum alloy. From the experimental data, the distribution of N was found to be represented best by the 3-parameter log-normal distribution. Six growth rate calculation methods were investigated and a modified secant method was found to introduce the least amount of error into the growth rate data. No one single distribution was found to describe the distribution of da/dN. A prediction scheme using the distribution parameters of da/dN was partially successful.