PSI - Issue 13

Mirko Maksimović et al. / Procedia Structural Integrity 13 (2018) 1888 – 1894 Author name / Structural Integrity Procedia 00 (2018) 000–000 5 propagation angle θ 0 can be expressed by using the angle between the line of crack and the crack growth direction, with the positive value defined in the anti-clockwise direction: 1891

   

   

2

I K     II   K

1

K

1

2 tan

8  

0



for K 

 

4 4 I K 



o

II

II

   

   

2

(4)

I K     II   K

1

K

1

2 tan

8  

0



for K 

 

4 4 I K 



o

II

II

To initiate crack propagation, it needs that the maximum circumferential tensile stress σ reaches a critical value. This results in an expression for the equivalent SIF in mixed mode condition as

3

3 0 



cos

0 cos sin

eq K K 

K





(5)

0

I

II

2 2

2

However, when the plastic zone size can’t be ignored, it is necessary to use the stress state at a material dependent finite distance from the crack tip. 3. Numerical and experimental results Here two type problems are considered: i) Determination crack growth trajectory and ii) Residual life estimation along „curve” mixed mode crack growth trajectory. To illustrate determination crack growth trajectory under mixed modes I/II here is considered duraluminum plate with two holes and initial crack, as shown in Figure 1. To determine stress intensity factors K I and K II here Msc/Nastran softwer code is used. In Figure 2 finite element model with stress distributions of cracked specimen is shown.

Fig. 1 Geometry of specimen for modeling of crack growth trajectory

Fig. 2 Stress distributions of cracked specimen using finite elements (F y =6000 N)