PSI - Issue 28

D. Weiß et al. / Procedia Structural Integrity 28 (2020) 2335–2341 D. Weiß et al. / Structural Integrity Procedia 00 (2019) 000–000

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First, the influence of the different rolling directions along and across in relation to the initial crack on the crack growth rate curve is investigated. Each test series contains a minimum of three specimens. The resulting crack growth rate curves for the different rolling directions are shown in Fig. 4.

Fig. 4. Comparison of the crack growth rate curves of the different rolling directions along (blue) and across (orange)

The results show, that the determined curves are almost the same. The average threshold of the longitudinal tests is 6.27 MPaꞏm 1/2 with a small standard deviation of 0.18. The average cyclic fracture toughness is 54.88 MPaꞏm 1/2 and has a standard deviation of 2.81. Looking at the results of the across tests the average threshold is 6.21 MPaꞏm 1/2 with a very small standard deviation of 0.03 and an averaged cyclic fracture toughness of 56.30 MPaꞏm 1/2 and a standard deviation of 1.04. In summary, the rolling direction has no influence on the fracture mechanical parameters. Second, a further R -ratio of 0.3 is considered in the experimental investigations to examine the influence of the mean stress on the crack growth rate curve. Fig. 5 shows the average crack growth rate curve for R = 0.1 in comparison with different crack growth rate curves for R = 0.3.

Fig. 5. (a) Crack growth rate curves for R = 0.1 and R = 0.3; (b) Experimental parameters and results.