PSI - Issue 22

Z. Marciniak et al. / Procedia Structural Integrity 22 (2019) 393–400 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

397 5

2

2   

4   

  

    

  

  









  2 2  

a

a

a

a

1 2 

1 2 2

cos





(3)

eq







2

a

a

a

2

2 a 4 







  

where for  = 0  ,

a

T G 

a T G  ,

a

,mod

- the Nishihara-Kawamoto criterion (N-K) for  = 0      2 3 k k 1 a 2 a 2 2 eq      

2   

4 4 k 2 2 a 2 a 

 

a

(4)

for  = 90 



   2 a



  

  

2

2

2

   2

 4 4 k 2 2 a 2 a

4

1 k

3 k



  

 

 

a

a

a

(5)





 4 1

 

eq



af af    

3

limit ratio (for calculation assumed  af /  af = 1.85),  = 1 – coefficient of sensitivity for

where k

loading phase shift. The lifetime N cal shown in Figs. 4 – 6 were calculated from Eqs. (2) – (5) and compared with the experimental lives N exp . Figs. 4 – 6 present comparison of N cal and N exp for specimens with round cross-sections, phase shift  = 0°, 90° and various stresses amplitude ratios σ a = 0.5τ a ,  a =  a ,  a = 2  a . The solid lines indicate perfect agreement between N cal and N exp , and the dashed lines present the result scatter bands of coefficients N cal / N exp = 3 (1/3). From Figs. 4 – 6 it appears that the fatigue lives N cal calculated according to the modified Tresca-Guest criterion (3) are the most similar to the experimental lives N exp and they are included into the scatter band of coefficient 3 for all the applied amplitude ratios and stress phase shifts. a) b)

Fig. 4. Comparison of fatigue lives of specimens obtained from calculations N cal and experiments N exp for phase shift: a)  = 0°, b)  = 90° and stress amplitudes σ a = 0.5τ a .