PSI - Issue 2_A

Stefan Kolitsch et al. / Procedia Structural Integrity 2 (2016) 3026–3039 Stefan Kolitsch/ Structural Integrity Procedia 00 (2016) 000–000

3033

8

Fig. 4. Experimentally determined and fitted cyclic crack resistance curves for the threshold of stress intensity factor range for different stress ratios.

Table 2. NASGRO parameters.

Parameter

mean 5.318

COV upper

COV lower

Δ K 0 [MPa √ m] C [mm/cyc]

4.365

6.271

2.02E-9

2.42E-9

1.69E-9

m [-] p [-]

3.581 0.198 0.034

3.748 0.149 0.072

3.414 0.248 0.013

l 1 [mm]

3.2. Calculation of the notched specimen

The calculation of a crack starting from a notch is somewhat different from the one for a crack in a smooth specimen. As long as the crack extension is small and the crack tip is near the notch root, the crack tip loading is fully governed by the stress concentration at the notch root; as the crack propagates further, it grows out of the notch stress concentration, which leads to a reduction of the crack tip load. A geometry factor for a crack emanating from a notch is given by Neuber (1977) as

    

    

2.5 0.4

− −

   

   

  

  

+ a t a

( )

(

)

2.5

−

N Y a

1,1215 1

⋅ + − + 1 α

1

=

−

(10)

k

with the notch stress concentration factor