Issue 51

A. S. Yankin et alii, Frattura ed Integrità Strutturale, 51 (2020) 151-163; DOI: 10.3221/IGF-ESIS.51.12 157 2 1 0 0 1 a m I I A B +  (19) 1 11 22 33 m m m m I    = + + (20) where I 1m is the mean value of the first invariant of the stress tensor, A 0 and B 0 are the model parameters. In this article the Eqn. (19) was modified similarly to the modified Crossland method [31] to take into account the static torsional stress effect 2 2 2 2 1 1 1 1 1 a m m I I I A B C         + +          (21) where A 1 , B 1 and С 1 are the model parameters, which were determined as follows: - the parameter A 1 was determined by means of the axial S-N curve σ a 0 ( N ) 0 a m m    = = = , 2 0 m I = , 1 0 m I = , 0 ( ) a a N   = , 1 2 0 3 ( ) a a I N  = (22) 1 1 0 3 ( ) a A N  = (23) - the parameter B 1 was determined by means of the axial S-N curve σ a τ ( N ) with torsional mean stress τ m =126 MPa 2 m m I  = , 0 a m   = = , 1 0 m I = , ( ) a a N    = , 1 2 3 ( ) a a I N   = (24) 1 2 1 ( ) 1 3 m a B N A    =   −     (25) - the parameter С 1 was determined by means of the torsional S-N curve τ a σ ( N ) with tensile mean stress σ m =202 MPa 0 a m   = = , 1 2 3 m m I  = , 1 m m I  = , ( ) a a N    = , 2 ( ) a a I N   = (26) 1 2 2 1 1 ( ) 1 3 m a m C N A B     =     − +         (27) S-N curve τ a σ ( N ) were plotted according to the experimental data from Tab. 2 similarly to curve σ a 0 ( N ) (see section 3.1). This model has all the advantages and disadvantages of the previous modified Crossland method. Extension of the Sines method to take into account different slopes of the S-N curves under tension-compression and torsion (Sines++) In some cases, experiments show different slope of the S-N curves in tension-compression σ a 0 ( N ) and torsion τ a 0 ( N ) tests. It means that the ratio σ a 0 ( N i ) / τ a 0 ( N i ) will not be constant. The modified Sines method (Sines+) does not take