2018 年 67 巻 2 号 p. 170-176
In order to clarify influence of hydrogen on fracture behavior of clinched joint, we performed tensile shear tests and fracture analyses. As verification tests, a hardness test, tensile tests with plate specimens and hydrogen concentration measurement were conducted. The tensile shear tests were conducted with and without hydrogen charging, respectively. The tensile shear test results showed that the maximum load and fracture displacement of the hydrogen-charged specimen were smaller than that of the noncharged specimen. The fracture analyses clarified that macroscopically fracture surface of the joint part on the hydrogen-charged specimen did not deform much, but microscopically showed large dimples with high aspect ratio. Fracture analysis results indicated that a crack growth on the joint part was assisted by hydrogen-enhanced void nucleation, growth and coalescence and hydrogen-enhanced localized plasticity. The hardness of the joint part was higher than that of the material before the joining process. On the tensile test, the maximum load and fracture displacement were not changed by hydrogen charging. The hydrogen concentration measurement showed that the joint was charged with 1 ppm hydrogen. These results show that work hardening and stress concentration have an important role on hydrogen embrittlement on clinched joints.