PSI - Issue 40

Vladlen Nazarov et al. / Procedia Structural Integrity 40 (2022) 325–333 Vladlen Nazarov / Structural Integrity Procedia 00 (2022) 000 – 000

330

6

The torsion under the action of the stationary torque and tension under the action of the stationary axial tensile force of tubular specimen realize the uniform complex stress with normal stress  and tangential stress  . Under the influence of normal stress  and tangential stress  the tube specimen undergoes the normal creep strain  and the tangential creep strain  . For describing the secondary creep process Nazarov (2015b) for the tubular specimen under torque and axial tensile force the principal stresses 1 2 3      and the principal strain rates 1 2 3         are used

2





   

2

,

0   

2 2    

(1)



2

1,3

2

2  

3





      









,

where ,

( ) and t  

( ) t  

(2)





   

 

  

  





1,3

2

4

4

2

2

Experimental creep curves (the dependence of the rotation angle on time) (Fig. 6) had been obtained Nazarov (2017) on tubular specimens (Fig. 7) and given at different ratio values   / (Table 4) for the maximum normal stress MPa 100 max   (experiments 1 – 3) and doubled maximum tangential stress MPa 100 2 max   (experiments 4 – 8). Table 4. Mechanical characteristics Nazarov (2017) of secondary creep for titanium alloy VT1−0 (English equivalent is Grade−2) at 550 o C.

Experiment

1

2

3

4

5

6

7

8

Ratio of normal stress to tangential stress

1.0

2.0

3.0

1.0

1.5

2.0

2.5

3.0

Normal Stress ( MPa ) Tangential Stress ( MPa ) Elongation Rait ( mm/h ) Torsion Rait ( degr./h )

61.8 61.8

82.8 41.4

90.8 30.2 11.0

44.7 44.7

60.0 40.0

70.7 35.4

78.1 31.2

83.2 27.7

6.1

9.9

1.5

1.5

2.1

3.3

3.6

111

78

50

27

20

19

15

13

Force ( N )

3066 4110 4508 2219 2977 3509 3875 4129

Torque ( Nm )

21.6

14.6

10.6

15.7

14.0

12.4

10.9

9.7

A visual inspection of the tested specimens (Fig. 7) shows that the specimens underwent a shape change during the creep tests, where for experiments 1 – 3 the tangential stress has calculated by the formula

   

   

2

max  

 

 

   

(3)

4

where ,

MPa 100



  





max

2

and for experiments 4 – 8 the tangential stress has calculated by the formula

2



max

(4)

2 where ,

MPa 100









max

2  

 

4

  

Formulas (3) and (4) had expressed the specified conditions for stresses in the experiment.