1. Experimental Verification of the Survivability Model Under Mixed I+II Mode Fracture for Steels of Rolling Rolls

The model of fatigue mixed fracture, which follows from the amalgamation rule of resource safety indices, has been experimentally confirmed. It does not require finding an effective SIF, but is based on the construction of survivability curves for pure modes. Survivability in a mixed process is defined as the result of combining individual fracture processes. Peculiarities of steels of rolling rolls fracture under conditions of cyclic deformation according to the scheme of four-point asymmetric bending are revealed. Although such a test scheme is designed to obtain the fracture of the II mode, in existing studies, this has not been achieved. The crack from the notch, practically, immediately went away at an angle ~45° toward the tensile zone, which indicates a mixed I+II fracture. With sufficient accuracy to predict survivability, the exponent of the Paris's region of the fatigue crack growth diagram (FCG) can be taken as n_I = 4 (I mode), n_II = 3 (II mode). As a parameter of schematization, it is possible to use the value of SIF at an FCG rate of 10^–7 m/cycle. Its value for steels of rolling rolls can be 60–70 MPa√m in mode I. For mode II, this index decreases by 2.5–3 times.