PSI - Issue 21

24 4

Author name / StructuralIntegrity Procedia 00 (2019) 000 – 000

Emre Kurt et al. / Procedia Structural Integrity 21 (2019) 21–30

Furthermore, a new developed 3-D equivalent SIF equations (Eqs. 3 and 4) are used and substituted in Eq. (1). First, a relationship between K II and K III is determined in Eq. (3);

2 II

2

0.6890

0.6796

K

K

K









(3)

( III eq II 

)

III

Subsequently, by combining the above equation (3) with K I , the following equation (4) is defined to determine the equivalent SIF ;   0.25 3 ) ( 4 ) ( 2 ) ( 2 III I eq II I III I eq II III eq II I eq d K e K K c K K a K b K K              (4)

The coefficients of Eq. (4) are given in Table 2.

Table 2.Coefficients of new developed equivalent SIF equation (4). a b c d

e

0.5263

0.3322

-0.1112

0.0257

-0.0004

Combining and curve fitting of the new locations of all crack front nodes on the existing crack front, the predicted subsequent crack front profile is determined. The process described above (Fig. 1) is repeated until the equivalent SIF ( K eq ) reaches the fracture toughness ( K Ic ) value of the corresponding material. 3. Numerical Applications In this section, results of numerical applications on three-dimensional fatigue crack propagation are presented to demonstrate the application of the described analysis procedure and validate the developed fatigue crack growth criteria. First, an inclined penny shaped crack in a large body under tensile load is considered. As a second application, multiple semi-elliptical surface cracks in a dog bone shaped specimen under tensile load are studied. 3.1. Inclined penny shaped crack in a large body In this subsection, the study performed by Ren and Guan (2017) is considered as an application example. Fatigue crack propagation analyses performed for slant penny shaped crack under far-field uniaxial tension (Fig. 2) are presented. Predicted fatigue crack growth surfaces and lives are compared to the reference study (Ren and Guan (2017)).

Fig. 2. A slant penny shaped crack under far-field uniaxial tension.