| Abstract [eng] |
For determination of lifetime of structural elements number cycles Nc before fatigue crack appearance must be known. Dependence of cyclic plastic strains δ on the number of cycles Nc can be expressed by Coffin’s law. δ=CN^(-m), but determining of material cyclic constants C and m for cyclic non – stable materials is complicated because in this case the cyclic plastic strain δ depends on number of cycle N. Therefore an equation ε=C_ε N^(〖-m〗_ε ) proposed by M. Daunys, which approximately may be used for determination lifetime on the interval of cyclic strains (3…3,5) ε_(e_pl )≤ε≤0,026…0,038. In this work is used the analytical method of calculations by using results of experimental investigations. The highest value of this curves validity is ε_2, which corresponds number of cycles N=N_2 and was determined in this work. As well is proposed to change this curve in interval of cycles 1≤N≤〖10〗^7 by broken line, which consists from tree linear elements and were determined constants of these zones. Expression for simplified determining of the highest interval validity of this curve ε2 with the sufficient accuracy is proposed. |
