PSI - Issue 5

Lars Sieber et al. / Procedia Structural Integrity 5 (2017) 1019–1026 Sieber, Stroetmann / Structural Integrity Procedia 00 (2017) 000 – 000

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extensive tests to analyze the material toughness was carried out. As expected, the Siemens-Martin steels had a significantly lower reference temperature T 0 than Thomas steels. The two material samples in Figure 2 which are labeled with M31 and M56 can also be identified as Siemens Martin steels. If one evaluates the fracture toughness of those specimens with the three rimmed mild steels B1, B2 and B4 according to ASTM E1921, a reference temperature T 0 = – 45 °C (Figure 3) is obtained. This is about 15 °C lower than for the mild steels according to Figure 2. Comparable to Equation (3) the characteristic value of the fracture toughness can be obtained for Siemens-Martin steels with     45 25,2 36,6 exp 0,019 1 ,5%       T K Jc T . (4)

Fig. 3. Evaluation of all test series of Siemens-Martin steels according to ASTM E1921 by Sieber (2016)

2.4. Correlation of fracture toughness and Charpy impact energy

Since the dermination of the fracture toughness is sometimes not possible or should be avoided due to extensive effort many research projects were carried out to derive correlations to other material properties. Most of the research was focused on an estimation of K Jc from the Charpy impact energy KV 2 . Some of those correlations are explained, evaluated and critically discussed in Phall and Macdonald (1991). In general these relationships are based on empirical data and are only valid for some certain materials or material states. Their suitability must be examined critically for the respective application. For the old mild steels (see Figure 2) the recommended estimations of the fracture toughness from the results of the Charpy impact energy according to the SINTAP-guidelines (Bannister and Webster (1999)) were checked. The lower threshold value of the fracture toughness K mat in a brittle material state can be determined with   20 20 25 12 0,25 2     KV K mat . (5)

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