Issue 61

V. Shlyannikov et alii, Frattura ed Integrità Strutturale, 61 (2022) 46-58; DOI: 10.3221/IGF-ESIS.61.03

C

Cr

Mo

Al

Ti

Nb

Ni

0.03-0.07

13.0-16.0

2.8-3.2

1.45-1.8

2.35-2.75

1.9-2.2

basis

Table 1: Chemical composition for XH73M alloy.

B [1/(MPa*n ⋅ hr)] - 2.5*10 -11

T [ ˚ C]

σ u [MPa] 1298.25 1229.53 1205.93 1079.30

σ 0 [MPa]

E [GPa]

δ [%] 34.94 32.31 27.73 10.67

ψ [%] 54.19 50.88 30.12 18.35 17.90

n

23

904.04 830.50 836.42 866.05 705.46

215.77 192.87 206.18 192.76 161.39

-

400 550 650 750

2.50 3.53 4.80 8.85

4.0*10 -12 2.1*10 -16 4.0*10 -26

839.85

8.27

Table 2: Main mechanical static properties for XH73M alloy.

In the present study, the interpretation of experimental results on the CGR in C(T) specimens of nickel-based alloy at high temperatures are presented in terms of the fracture mechanics characteristics for the conditions of elasticity and creep. Traditionally, the experimental data are presented through the creep C-integral and the elastic SIF which for C(T) specimens is given by the ASTM standard [14] as

   1 1 K P f a w b w

(3)

  

       

   

2

3

4



a w

2

      a w

      a w

      a w

      a w

 



 0.866 4.64







f a w

(4)

13.32

14.72

5.6

1

  a w

1.5

  1

where a is the crack length, w is the length of the working area of the specimen, b is the specimen thickness, and P is the applied load. To interpret the data on crack propagation at high temperatures creep-fatigue interaction loading conditions, the method for determining the C* -integral can be used, which is based on the experimentally measured load-line deflection V FL in the C(T) specimen. The compliance method [14] has been applied in order to determine the force-line displacement rate ∂ V FL / ∂ t . The relationship between compliance and normalized crack size for experimentally measurements made at the load-line for a specimen with a crack subject to constant force, P , are given by the following equation:

  FL

FL C V P

(5)

2

  

   

2

3

4

5

   a w

      a w

      a w

      a w

      a w

      a w

1 1



 12.163 12.219









20.065

0.9925

20.609

9.9314

 

  a w

Eb

1

 

The expression for extending the C* -integral concept to small-scale creep conditions in the form of the C(t) -parameter is described by the equation [14]:

       f

FL P V t

 

(6)



C t

    1 f

bw

df

1



  

f

f

f

f

'

(7)

2

3

4

( d a w

)

   

   

2

3

4

      a w

      a w

      a w

      a w

1

 



 0.866 4.64







f a w

13.32

14.72

5.6

(8)

2





1.5



a w

1

50