PSI - Issue 13

Daisuke Sasaki et al. / Procedia Structural Integrity 13 (2018) 1006–1009 Author name / Structural Integrity Procedia 00 (2018) 000–000

1009

4

Figure 4 shows the SEM observation results. Figure 4(a) shows the enlarged view of the step on the fracture surface. In Figs. 4(b), (c) and (d), the brittle-like fracture surface is confirmed and a few dimples are confirmed. The width of brittle-like fracture surface is near to the initial crystal grain size. Lambiase and Di llio (2016) reported that when the upper sheet fractures at a clinching, dimples are observed on the fracture surface. Birnbaum and Sofronis (1994) reported that hydrogen enhances dislocation mobility, resulting localization of plas tic deformation. Sasaki et al. (2015) showed that hydrogen localization has an important role on a crack formation and a fracture surface is brittle-like. According to these reports, it is suggested that at the specimen with 19.6 x 10 4 A / m 2 charging, hydrogen in SPCC270 promotes dislocation ability and the crack formation. In this study, cracks formed at the minimum thickness part of the plastic joining part on the specimen with 19.6 x 10 − 4 A / m 2 . These results indicate that decreasing hydrogen content in SPCC270 suppresses hydrogen-induced crack formation. To investigated influence of hydrogen on the crack formation behaviour in a mechanical clinching process, joining tests and fractography were conducted after di ff erent hydrogen charging. In this study, we found the followings. 1. A load-displacement diagaram shows that At both specimens without charging and with 19.6 x 10 − 4 A / m 2 charg ing, the load increases as the cross head displacement increases. At specimen with 19.6 A / m 2 charging, the load once falls at displacement of 2.6 mm and increases as the cross head displacement increases. 2. The cross sectional observation shows that at specimens without charging and with 19.6 × 10 − 4 A / m 2 charging, cracks do not form near minimum plate thickness parts and the interlocks form. Additionally, at the specimen with 19.6 × 10 A / m 2 charging. cracks form and the joining part fractures. 3. Fractography shows that the specimen with 19.6 x 10 A / m 2 charging had a uniform fracture surface thickness. On the fracture surface, there are many steps. 4. Fractography using SEM shows that the brittle-like fracture surface is confirmed and a few dimples are confirmed. The width of brittle-like fracture surface is near to the initial crystal grain size. 5. Based on the above 1, 2, 3 and 4, it suggests that hydrogen embrittlement in mechanical clinching depends on pickling condition. 4. Conclusion

References

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