Issue 51

A. S. Yankin et alii, Frattura ed Integrità Strutturale, 51 (2020) 151-163; DOI: 10.3221/IGF-ESIS.51.12

2 I A B 1 a I

m

+ 

1

(19)

0

0

 = + + 



I

(20)

1

m

11

m

22

m

33

m

where I 1m 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 is the mean value of the first invariant of the stress tensor, A 0 and B 0

   

    +  

   

I

I

I

2

a

2

m

1

m

+ 

(21)

1

A B  

C

1

1

1

and С 1

where A 1

, B 1

are the model parameters, which were determined as follows: was determined by means of the axial S-N curve σ a 0 ( N )

- the parameter A 1

1

0 = ,

0 = ,



=





0  = = = , m m 

=



I

I

( ) N

,

(22)

I

0 3 N

( )

1

m

a

a

0

a

2

m

2

a

a

1

=



A

( ) N

(23)

1

a

0 3

was determined by means of the axial S-N curve σ a τ ( N ) with torsional mean stress τ m

- the parameter B 1

=126 MPa

1

=





0  = = ,

0 = ,



=



=



I

I

( ) N

,

,

(24)

I

( ) N





a

m

1

m

a

a

2 m m

2

a

a

3



m

=

B

(25)

1

2



  



( ) N



a

− 

1

3

A



1

- 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

1

=





0  = = ,

=





=



=



I

( ) N

I

( ) N

I

,

,

,

(26)





a

m

1 m m

a

a

2

a

a

2

m

m

3



m

=

C

(27)

1

2

2



  

  

 





( ) N



a

m

−

+ 

1

A

3

B

 

1

1

S-N curve τ a σ ( N ) were plotted according to the experimental data from Tab. 2 similarly to curve σ a 0 This model has all the advantages and disadvantages of the previous modified Crossland method.

( N ) (see section 3.1).

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

157