PSI - Issue 40

Vladlen Nazarov et al. / Procedia Structural Integrity 40 (2022) 334–340 Vladlen Nazarov / Structural Integrity Procedia 00 (2022) 000 – 000

336

3

material parameters of the fractional power dependence Shesterikov et al. (1984) take the physical meaning of the ultimate creep stresses. They are starting creep stress (the maximum possible stress at which the creep process is absent) and the break creep stress (the minimum possible stress at which instantaneous fracture occurs). The power dependences Norton (1929) and Bailey (1929) with two material parameters have the form:

n

  

  

1



app

dim nom

0   n

0

A

A

 



(1)

1 sec

1

1



m



app rupt

t

  

  

1



dim nom

0 B m 

0





(2)

1

1

B



1

where app sec   is elongation rate at the secondary creep in approximation, app is nominal stress (the stress at the initial time of impact of the force), 1MPa dim   is dimensionless stress, 1 n and 1 m are dimensionless parameters, as well as parameters 1 A and 1 B with dimensions h/mm and h . The fractional power dependences Shesterikov et al. (1984) with four material parameters have the form: rupt t is rupture time in approximation, nom 

n

  

  

2







app

nom

start

0

0

A

A

n



nom   







 



(3)

2 sec

start

break

2

2







break

nom

m

app rupt

t

  

  

2







break

nom

0 B m 

0



nom   







(4)

start

break

2

2

B







2

nom

start

where app rupt t is the rupture time in approximation, 2 n and 2 m are dimensionless parameters, as well as parameters 2 A and 2 B with dimensions h/mm and h . The approximations (3) and (4) has limits the starting creep stress start  and the break creep stress break  (Fig. 1). sec   is elongation rate at the secondary creep in approximation, app

Fig.1. Two types of approximations (2) and (4) for experimental data on creep rupture.

Nazarov et al. (2017) had been shown that the total error of the fractional power dependence Shesterikov et al. (1984) with four material parameters is less than the total error power dependence Norton (1929) and Bailey (1929)