PSI - Issue 28

B.W. Williams et al. / Procedia Structural Integrity 28 (2020) 1024–1038 Author name / Structural Integrity Procedia 00 (2019) 000–000

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To confirm rate sensitivity of TC128B, quasi-static Charpy tests were performed at 24 °C. Quasi-static Charpy tests were performed in a standard load frame at a strain-rate of about 0.001 s -1 compared to dynamic tests performed at 100 s -1 using a drop tower. All other aspects of the test setup, including the sample size and fixture, were identical. The quasi-static versus dynamic Charpy response is shown in Errore. L'origine riferimento non è stata trovata. . The results show that the energy absorbed (area under the curve) is significantly greater for the dynamic case. Consequently, it was necessary to account for strain-rate effects in the FEA model. 3. FEA Model for TC128B 3.1. Strain-Rate Sensitivity of TC128B The high strain-rate response of metals is often characterized by using split-Hopkinson bar apparatus. However, the high strain-rate response of steel alloys has been well characterized such that it was not deemed necessary to perform such testing. Hence, the strain-rate response of pipeline steel was used to describe that of TC128B. The high strain-rate relationship data for structural steel detailed by Xu and Tyson (2015) was used in the current work for TC128B. The dynamic stress versus strain response at 100 s -1 is compared to the quasi-static tensile responses in Figure 5. This true stress versus strain response was then used to obtain the hardening laws required for the FEA model described according to the following discontinuous yielding hardening law, where � and � are the effective stress and plastic strain, ��� and ��� are the yield parameters to describe the Lüders affect observed at low temperatures for TC128B, with �� being the effective strain at which Lüders strain stops and the response transitions to strain hardening. The quasi-static and dynamic hardening law parameters for TC128B are shown in Table 1 and Table 2, respectively. ��� �� � �� � � �� �� � for � � �� (1) � � � ��� � � ��� � ��� � � �� for � � ��

Figure 5: Quasi-static vs. dynamic stress vs. strain curves for TC128B at various temperatures