PSI - Issue 23

I.S. Nikitin et al. / Procedia Structural Integrity 23 (2019) 131–136 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

134

4

,max H    was found:

In a similar way, the time within the loading cycle that determines the greatest value of

,max max ( ) / 3 H kk t P t    

a)

b)

Fig. 2. Fatigue life in terms of cycles N as a function of phase shifts 2  , 3  .

It is possible to evaluate the amount of cycles N for arbitrary amplitude values of a multiaxial cyclic loading as a function of phase shifts. The significant effect on fatigue life caused by phase shifts was found by calculations and can be seen in fig. 2. a and b. The proposed semi-analytical procedure was performed: at a given stress values and phase shifts the times 1 t and 2 t were determined and then the components by the n vector were calculated from the formulas obtained. These components of the critical plane orientation vector were used to calculate fatigue life by the criterion. 3.2. Bi-axial bending-torsion test A similar analysis was conducted for the case of a widely used bending-torsion cyclic loading with an arbitrary phase shift. Let us again assume a harmonic law for principal stresses variation in time with frequency  and an arbitrary phase shift  :   23 cos m a t t       ,     33 cos m a t t         . where m  , m  are mean stress components and a  , a  are their amplitudes. Ranges of the stresses within a loading cycle are:

t t

t t

2 

2 

 

sin      

  

23   (cos t t          cos ) 2 sin a a 1 2



2 1

2 1