The paper points out a modality of determination of functioning of a part submitted to a cyclic solicitation undulant positive of eccentric traction. Experimentally, for samples made of general use steel R520, we determined the variation of the fracture length of crack a and the number of N cycles, corresponding to them. Empirical relations of calculation for the time of a part's functioning were obtained, taking into consideration the asymmetry coefficient R and the solicitation loads. The working environment temperature was 213K (-60Â°), and the asymmetry coefficients used were R= 0.1, R= 0.3 and R= 0.5.