Scatter Factor Analysis for Sample Fatigue Life Based on a Three Parameter Birnbaum-Saunders Distribution

The Birnbaum-Saunders (B-S) distribution was derived as a lifetime model for specimens subjected to cyclic patterns of stresses and strains. A new model of three-parameter Birnbaum-Saunders distribution was derived by proposing a dependence assumption on account of the assumption of independence of crack growth from cycle to cycle being unrealistic. A method for reliable fatigue life analysis and assessment based on three-parameter Birnbaum-Saunders distribution was studied, and fatigue life scatter factor formulae of three-parameter Birnbaum-Saunders distribution based on median value was derived, and based on the order statistic theory, the scatter factor formulae corresponding to maximum and minimum test life were presented. The results of calculating examples show that life scatter factors of three-parameter Birnbaum-Saunders distribution are usually better than that of the lognormal distributions as well as that of the original Birnbaum-Saunders distribution.