PSI - Issue 66

Slobodanka Boljanović et al. / Procedia Structural Integrity 66 (2024) 535– 542 S. Boljanovi ć and A. Carpinteri/ Structural Integrity Procedia 00 (2025) 000–000

536

2

semi-elliptical flaw via the weight function method. Peng et al. (2005) have generated relevant solutions for the stress intensity factors in the case of a tubular member with a surface flaw. Moreover, Mikheevskiy et al. (2012) have employed the crack growth concept developed by Noroozi et al. (2007) and the weight function method for analyzing the failure due to the quarter-elliptical corner flaw. Boljanovi ć et al. (2017) have evaluated the fatigue stability of the same part-through flaw taking into account the crack growth law proposed by Zhan et al. (2014) and the J -integral method. Through the residual strength design, Boljanovi ć et al. (2019) have assessed the durability of two notches with the same elliptical flaw using the crack growth concept proposed by Huang and Moan (2007) and the finite element method. Further, Boljanovi ć and Carpinteri (2021) have developed novel damage tolerance-based solutions in order to estimate the fatigue performance of the surface elliptical flaw. The aim of this research work is to explore the mechanisms of system capacity degradation due to a semi-elliptical flaw. Novel design solutions are generated to analyze the fatigue strength combining the part-through flaw effect and the stress ratio effect. Through case studies by taking into account relevant experimental datasets, the viability of the developed design strategy is discussed. 2. Crack tip intensity analysis under cyclic loading The fatigue behavior of a semi-elliptical flaw (Fig.1) is evaluated through the stress intensity factor (Newman and Raju, 1984, Carpinteri, 1994), expressed as follows

a



K f    sec

S

(1)

.

Q

where  S is the applied stress range, a and Q are the crack growth length in depth direction and the ellipse shape factor, respectively, and  K is the stress intensity factor range. Through the driving mode analysis, the shape effects of a surface crack-like flaw are herein generated by means of correction factor f sec , via relevant parameters M 1 , M 2 , M 3 , g , and Q (Newman and Raju, 1984), expressed as follows:

2

4

t a

t a

  

   

  

  

f

M M

M

w g f f 

 

(2)

sec

1

2

3

where t is the thickness, f  and  f w are the correction factors involved to quantify the angle location effect and the width effect, respectively, for the structural component with a part-through stress raiser. Moreover, in order to quantify the crack size effect, the crack shape effects and the elliptical shape effect of surface flaw ( a / b ≤ 1), the following parameters are involved:

b a

M 1.13 0.09 1  

(3)

0.89

  0.54

M

(4)

b a

2

0.2



24

0.65 1

b a

14 1     

  

0.5  

M

(5)

b a

3



1.65

1 1.464       b a

Q

 

(6)