Abstract: The present paper presents a method for estimation of the fatigue crack length distribution based on the stochatic processing of time discreted. The strains of the structure containing multiples cracks at each structural detail are changed during the propagation of the cracks. The method can calculate the probability tensity function of each crack. With the crack length distribution, and distribution of the strain level, a model of crack length-KIc interference for the reliability of multi-cracks structure is establised. The reliability - time curve of the structure can be ploted. A sample example is presented.

Key words: probability fracture mechanic, crack growth, reliability