PSI - Issue 76

Jürgen Bär et al. / Procedia Structural Integrity 76 (2026) 27–34

33

KT diagrams in Figs 6 and 7, the notches are shown in the same colors as in Table 3. Crack arrest is shown by an upright triangle, failure is indicated with a triangle with the tip down.

(a)

(b)

700 800

700 800

600

600

500

500

Steel N, R=-1  e  th,LC  th,a,EH

400

400

Steel N, R=-1  e  th,LC  th,a,EH

300

300

 th,Chapetti  th,d,Chapetti  crack arrest  failure

stress range [MPa]

stress range [MPa]

 crack arrest  failure

200

200

0,001

0,01

0,1

1

10

0,001

0,01

0,1

1

10

Ö area [mm]

a [mm]

Fig. 6. KT diagram for the normalized steel plotted over (a) crack depth; (b) Murakami parameter √ . The triangle with tip up indicates the stress range at crack arrest, with the tip down at failure. Notch 1: black, Notch 2: blue, Notch 3: red and Notch 4: green.

For Steel N (Fig. 6), all measured values except those obtained for notch 1 are below the three models in the representation over the crack depth a (Fig. 6a) as well as in the representation over the Murakami parameter √ (Fig. 6b). As can be clearly seen in Fig. 6a, the values for the fatigue limit ∆ σ th for notches 2 and 4 differ significantly despite the same notch depth. This shows that the notch depth is obviously not the appropriate parameter to describe ∆ σ th . On the other hand, in Fig. 6b, the ∆ σ th values for notches 3 and 4 are also clearly separated despite identical Murakami parameters. This means that the KT diagram plotted over the Murakami parameter is also not a suitable representation for Steel N.

(a)

(b)

600 700 800 900 1000

600 700 800 900 1000

Steel V, R=-1  e

500

500

Steel V, R=-1  e

 th,LC  th,EH

400

400

 th,LC  th,EH  crack arrest  failure

 th, Chapetti  th,d,Chapetti  crack arrest  failure

300 stress range [MPa]

300 stress range [MPa]

200

200

0,001

0,01

0,1

1

10

0,001

0,01

0,1

1

10

a [mm]

Ö area [mm]

Fig. 7. KT diagram for the hardened steel plotted over (a) crack depth; (b) Murakami parameter √ . The triangle with tip up indicates the stress range at crack arrest, with the tip down at failure. Notch 1: black, Notch 2: blue, Notch 3: red and Notch 4: green.