Algorithms for the estimation of fatigue crack growth using energy method

A new method of producing kinetic fatigue failure diagrams (KFFD) has been developed by the authors on the basis of experimental results obtained from the study of the hysteresis loop area. For experimental verification of KFFD the results of fatigue crack propagation studies for 41Cr4 (40H) and S355JR (18G2A) steels have been used. Two kinds of kinetic fatigue failure diagrams have been produced. In the first diagram (the classic one), the stress intensity factor K that characterizes the intensity of deformation in the precrack zone ahead of a crack tip was used for building the diagram. In the second diagram (the new one), energetic parameter ΔH that corresponds to the searched energy dissipation of deformation was applied. In contrast to the da/dN – Kmax diagrams, in the da/dN – ΔH diagrams obtained for a given range of the crack growth rate no difference in failure kinetics has been found. It means that the energetic parameter ΔH describes fatigue crack growth rate regardless of stress ratio R in opposition to the force