PSI - Issue 21

Emre Kurt et al. / Procedia Structural Integrity 21 (2019) 21–30 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

23

3

2. Crack propagation simulation procedure Details of the analysis method performed for the two applications are described in this sub-section. Process steps of fatigue crack growth analysis are given in Fig. 1.

Modeling, Meshing, Applying BC’s & Loads ANSYS

FCPAS

Finite Element Model

Frac3d Fracture Analysis

Material Properties Modulus of Elasticity, Poisson’s ratio etc.

Results Stress, Stress Intensity Factor etc.

Crack Growth Model (Developed New 3-D Criteria) and material constants

Predict next crack profile

Curve Fitting Next Crack Profile

Yes

No

Continue Analysis?

STOP analysis Calculate Life

Fig. 1. Process steps of fatigue crack growth analysis (Ayhan (2011)).

The finite element models are generated using ANSYS™ (2009) and analyzed using FCPAS. At the end of the fracture analysis, three-dimensional SIFs along the crack front are calculated automatically. Crack growth model of Paris-Erdogan (1961); (1963) law as shown in equation (1) is used for prediction of nodal crack growth increments.   n eq C K dN da   (1) In Eq. (1), a is crack length, N is number of loading cycles, Δ K eq is equivalent SIF range under mixed mode fatigue loading, and C and n are material properties. A new and improved empirical crack deflection angle equation (2) from a previous study by Demir et al. (2017) for mixed mode loading problems is used for prediction of nodal crack growth angles.

    

    

2 II

2

  K d K a K K K b K K c K K          2 II I II I I

I

arccos



 

(2)

0

2 II

I

The coefficients of Eq. (2) are given in Table 1.

Table 1.Coefficients of crack deflection angle equation (2). a b c

d

0.1723

5.1062

-2.7483

-1.1636