A generalized grain-size dependence of the fatigue limit

A generalized model is developed for calculating the fatigue limit of the material based on the data on its microstructure. The experimental results of fatigue and cyclic fracture toughness tests and the data on the analysis of the microstructure of two-phase (α + β) titanium VT3-1 alloy with a different microstructure (globular, bimodal and fine lamellar microstructure) have shown that the dependence of the fatigue limit on the structural parameter, which is responsible for the material fatigue strength, has a nonlinear S-like nature. The formula for calculating the fatigue limit is justified by the data on the microstructural parameters and by the results of static tensile tests of the material, with a fair agreement obtained between the calculated and experimental results. The model has been validated for materials with another type of the crystal lattice [steel containing 0.16% C with a body-centered cubic lattice (bcc) and brass 70/30 with a face-centered cubic lattice (fcc)] and has shown a satisfactory agreement between the experimental and calculation results.