PSI - Issue 43

Yoshikazu Nakai et al. / Procedia Structural Integrity 43 (2023) 221–227 Nakai et al./ Structural Integrity Procedia 00 (2022) 000 – 000

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3.2. Measurement of misorientation by DCT Figure 5 shows the results of tensile tests of the (a) Untreated and (b) MM series, where the numbers in the figure indicate the location of the DCT and/or RCT image. The blue circles in the figure indicate points where both RCT and DCT imaging were conducted, and the orange diamonds indicate points where only RCT imaging were conducted, meaning that imaging was conducted 11 times for the Untreated series and 13 times for the MM series, including postfracture imaging. The tensile strength of the MM series is higher than that of the Untreated series, while the elongation upon fracture of the Untreated series is greater than that of the MM series unlike the conventional-size specimens. The difference in the necking process may be affected by the specimen dimensions, especially the length of the parallel section. Using the results of the measurement by DCT, the change in misorientation from the initial state (#1 in Fig. 5), Δβ ave , was calculated for #2 to #5 in Fig. 5, where the average Δβ for each grain at each diffraction plane was obtained. The relationship between Δβ ave and the applied stress in the tensile test is shown in Fig. 6, indicati ng that Δβ ave of both

Fig. 3. Shape and dimensions of tensile test specimen.

Fig. 4. Image quality (IQ) map and grain boundary map obtained by EBSD analysis for MM series (Kikuchi, 2018).

Fig. 5. Stress-displacement relationships and imaging points, where displacement is defines as change in distance between grips.

series increases with applied stress; h owever, the increase in Δβ ave of the Untreated series is greater than that of the MM series.