PSI - Issue 66

3

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

537

Fatigue-induced interactions between the thickness effect, the angle location effect and the width effect are generated through the correction factors g , f  and  f w , expressed as follows   2 2 1 sin 1 0.1 0.35      g

   

   

t a

  

  

(7)

0.25

   

   

2

b a

  

  

2

2   sin 

cos

f



(8)



0.5

   

   

   

   

w b

t a



sec

(9)

f w



2

Fig.1. Geometrical sizes for considered configurations with semi-elliptical flaw: (a) Plate and (b) Pipe.

3. Residual life evaluation Fatigue process coupled with the continuous aging of large systems requires the development of fracture mechanics-based analytical or numerical models (Mikheevskiy et al., 2012, Boljanovi ć et al., 2017, Boljanovi ć and Carpinteri, 2021) that can effectively support informed durability decision-making. In this context, safety-relevant performance of a surface elliptical flaw is theoretically analyzed via the crack growth concept proposed by Kujawski (2001), which is extended here with respect to two critical crack length directions ( a and b ), expressed as follows   A m A A C dN da *    with   0.5 max *     A A A K K  (10a)   B m B B C dN db *    with   0.5 max *     B B B K K  (10b) where a , b are crack growth length in depth and surface direction, C A , C B , m A , m B are material parameters experimentally obtained, and * A   , * B   are relevant functions dependent on the stress intensity factor and stress ratio R . Further,   A K ,   B K are positive parts of applied stress intensity factor ranges examined through relevant domains of the stress ratio, that is: A A K K    and B B K K    for 0  R , and if 0  R , max A A K K    and max B B K K    , whereas  K A  K B are stress intensity factor ranges for depth and surface direction, and K Amax  K Bmax denote maximum stress intensity factors in depth and surface direction, respectively. Through the safety-relevant analysis herein presented, by integrating the crack growth rate (Eq.10) from initial a 0 , b 0 to final a f , b f crack length, the number of loading cycles N can be evaluated as follows: