Abstract: Based on PFDM (Probabilistic Fatigue Damage Mechanics) system established by combining statistic fatigue analysis and damage mechanics from the macroscope aspect, a simplified model (four-parameter model on Lognormal distribution) is proposed here in hopes of finding applications in engineering. If the materials constant concerned in the model are obtained by experiment, the propabilistic distribution of the (N) or log-life (t) of a component with original damage D0(x, y, z) could be predicted. The forms of damage parameter Deq and relative damage gradient RG0 in the model is discussed also. Some examples are given.

Key words: fatigue, Damage mechanics, Lognormal distribution.