PSI - Issue 16

Yuri Lapusta et al. / Procedia Structural Integrity 16 (2019) 105–112 Yuri Lapusta, Oleksandr Andreikiv, Nataliya Yadzhak / Structural Integrity Procedia

109

5

1

      

      



v v 

   

   

   

r E

  





   

t fc

2 K l fc fc p

2

2

max K l K l   fc I I fc p 

1    l





2

K

4

fc

l

2 K l (1 ) fc fc p fc R 

 

* 

N

dl





.

(9)

*

2

1 2 

      

l



v v 

    

0

     

   

   

r E

  





   

t fc

2

2

2 4 2 th fc p K l 

max K l K l   fc I I fc p 

1   l



2

K

4

fc

3. Approbation of the model

Consider a special case, when the initial crack length 0 l is equal to zero. In this case, the computational models known in literature may give incorrect results, namely * subcr N   . Based on the proposed model, the fracture process should start with the mechanism of crack initiation. Hence, the period of subcritical crack growth * subcr N consists of two components: the initiation period of a macrocrack i N and the period of its subcritical growth subcr N * subcr i subcr N N N   . (10) Then the initiation period of a macrocrack i N can be determined by the relation (9) when 0 0 l  . As an example of the application of the formula (9) for this case, its correctness and preciseness, we consider tension of a strip with two symmetrical stress risers with bending radii r subject to symmetrical loading p (Fig.2). The problem is to determine the number of load cycles N , when the plate fractures. To solve the problem the proposed formula (9) is applied. Considering a plate with two side stress risers, the stress intensity factors I K and max I K are determined by the formulas (Andreikiv et al. (2011)):

Fig. 2. Loading scheme of a plate with two stress risers.