Quasi-brittle fracture diagrams under low-cycle fatigue (variable amplitude loadings)

Stepwise propagation of the internal mode I crack under cyclic loading is considered. Variable amplitude loads under cyclic loading conditions are studied for elastoplastic material. For analysis of this process, it is proposed to use diagrams of quasi-brittle fracture of solids under variable amplitude cyclic loading conditions. One of curves of the proposed diagram bears resemblance to the Kitagawa-Takahashi diagram. Estimates of average dimensionless velocity of stepwise crack propagation per loading cycle have been obtained in an explicit form for plain specimens of finite width. The relations derived for the average crack growth rate can be considered as structural expressions for plotting Paris’ curves.