Summartion of fatigue fractures during cyclic loading transient conditions of carbon steels

The effect is studied of preliminary cyclic strain at the first stress level on the change rate of the fatigue fracture accumulation when passing to the tests of the second level. Samples from carbon steels 20,40 and U8 have been tested for fatigue at pure bending with rotation. It is shown that during cyclic loading transient conditions all the materials under study display, to a lesser or greater extent, hereditary properties manifesting themselves as a change of inelastic properties at the second testing level, which leads to delayed or premature metal fracture. It is proposed that the material susceptibility to displaying hereditary properties be characterized by the hereditary coefficient. The corresponding coefficients for a number of carbon steel types are presented. An improved calculating formula for the summation of fatigue fractures during cyclic loading transient conditions is given, which accounts for the material susceptibility to displaying hereditary properties, experimetanl checking is presented as well