PSI - Issue 31

Vera Friederici et al. / Procedia Structural Integrity 31 (2021) 8–14 V. Friederici et al. / Structural Integrity Procedia 00 (2019) 000–000

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investigated differently heat-treated 42CrMo4 material. The Paris coefficient m is independent of the diagram scale, C changes due to the different units used.

Figure 4. Crack propagation curves for R = 0.1 with Paris lines for core and hardened material, in correlation with literature date (Göncz, P., 2010; Lesiuk, G., 2018; Kheder, A.R.I., 2011).

Fracture toughness of the core material was also measured and found to be 151±10 MPa*m 1/2 and 34±1 MPa*m 1/2 for the hardened material. Crack propagation was performed using positive stress ratio (R=K min / K max ) of 0.1, 0.3 and 0.5. During rotating bending test the stress ratio is R = -1. The slope of the measured crack propagation curves can therefore not simply be used to calculate crack propagation in rotating bending specimen. First a propagation curve for R = -1 needs to be calculated from the experimental data. A simple prediction of propagation curves for various R values is stated by Kujawski et al. (Kujawski, D., 2001; Dinda, S., 2004), proclaiming an equation without involving crack closure data as follows: � � � � � � � ∗ ∆ � � � � ∗ ∆ � (3) Table 3. Paris coefficients m and C for the investigated 42CrMo4 material and literature data. Values in green are obtained for material of 28 HRC and 54 HRC hardness (Göncz, P., 2010), values in red for material of 27 HRC in two different heat-treatment states and for 45 HRC hardness (Lesiuk, G., 2018), and values in blue for material of 217 HBN hardness (Kheder, A.R.I., 2011). core state Hardened state Core state (fitted using equal m for all R) Hardened state (fitted using equal m for all R) R C m C m C m C m

2.8762 2.824 [Göncz, P., 2010] 3.15 / 2.77 [Lesiuk, G., 2018] 3.5205 [Kheder, A.R.I., 2011]

1.235E-08 3.398E-09 [Göncz, P., 2010] 2.0E-08 [Lesiuk, G., 2018]

3.3920 3.406 [Göncz, P., 2010] 3.14 [Lesiuk, G., 2018]

6,975 E-08

2.786

1,716E-10

4.186

0.1

3.981E-08 5.135E-08 [Göncz, P., 2010] 4E-09 / 6E-08 [Lesiuk, G., 2018] 5.0E-10 [Kheder, A.R.I., 2011]

0.3

2.282E-07

2.6287

1.0423E-09

3.9399

9,164 E-08

2,789E-10

0.5

7.933E-08

2.8390

5.405E-11

4.5602

1,075 E-07

3,670E-10