PSI - Issue 65

A.N. Romanov / Procedia Structural Integrity 65 (2024) 200–208

203

A.N. Romanov / Structural Integrity Procedia 00 (2024) 000–000

4

a

b

800

600

400

200

0 5 101520253035 Strain, % 0

Fig. 1. Static tensile diagram of steel 22k under conditional and true stresses: (a) as a function of plastic strain and (b) as a function of relative strain.

In quasi-static fracture, the ultimate accumulated damage, as shown below, is determined predominantly by the first two terms, and elastic deformation does not contribute significant damage at the time of fracture. With increasing durability (decreasing load level), the damaging effect of elastic deformation increases and becomes major in multicycle fatigue. Under rigid loading (with a given elastic-plastic strain range) in the low-cycle fatigue region is determined by the first term in Eqs. (1) - (6):

2

 

  N

st p dN 2

(7)



0

2

 f N

 

2 st p dN

(8)

1



0

If we assume that, under rigid loading, the width of the hysteresis loop does not change in practical terms, then

st p   2 2  

2

2 2 p st

 

 

2 st p N 

,

,

,

(9)

N

f N

1



 f



and considering the damaging role of elastic deformation as follows:

st p ep dN 2   

  N

(10)



0

f N

st p ep dN 2   

(11)

1



 0

3 cycles) under hard and soft loading, it is necessary to calculate by Eqs. (4) and (11),

At high durability (N f > 10

which consider damage from elastic deformation. Other approaches, including damage modeling, have also been discussed by Carpinteri et al. (2016), Gates and Fatemi (2017), Iacoviello et al. (2019). All existing criteria can be divided into force, strain, energy, and thermodynamic approaches. As a rule, they are used to solve specific practical problems under given loading conditions. In most cases, they are not widely used or can be applied to a limited range of tasks.