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윤서현,김민헌,남기우 한국산업융합학회 2019 한국산업융합학회 논문집 Vol.22 No.6
Fracture behaviors of SCM435 high strength bolt have been studied including macroscopic and microscopic fracture observation, Energy Dispersive X-ray Spectroscopy, Vickers hardness test and applied stress evaluation. cracks (ratchet marks) were generated by the repetitive loads acting on the bolts, initial stress of bolt and the stress concentration. The applied stress was found to be slightly higher than the fatigue limit of the material. The initial stress of bolt must be removed, and the mold temperature during the process must be maintained by room temperature. Bolts are recommended to be peened to improve fatigue limit.
뜨임한 구조용강 SCM435의 경도 및 충격 흡수에너지에 대한 신뢰성 평가
윤서현,구세훈,남기우 한국산업융합학회 2019 한국산업융합학회 논문집 Vol.22 No.6
SM45C steel, which is widely used for mechanical structure, was carburized at 87 0℃ for 4 hours and tempered at 300℃ and 400℃ for 1, 3 and 6 hours. The tempered materials were evaluated for tensile test, hardness test and impact test. In particular, the hardness and the absorption energy were evaluate the reliability by the Weibull statistical analysis. 300℃-1h specimen is considered to be the best heat treatment condition in the tensile stress and the observation of fracture surface. 300℃-1h specimen showed larger shape and scale parameter than the other specimens, and Rockwell hardness variance was small and showed the best characteristics. 400℃-3h specimen showed larger shape and scale parameter than the other specimens, the dispersion of impact absorption energy is small, and showed excellent characteristics.
자동차 에어 브레이크 스프링 고정용 SCM435 볼트의 파손 해석
윤서현,김민헌,남기우 한국산업융합학회 2020 한국산업융합학회 논문집 Vol.23 No.1
This study analyzed the causes of failure of SCM435 bolts that fix the springs of automobile air brakes that have been fractured during use. The cause of failure was analyzed using SEM, EDS, metallogical microscope and Vickers hardness tester. In the fracture, the ratchet mark began at the outer boundary of crack origin, and the grains at crack origin were found to have clear intergranular corrosion. One SCM435 bolt was subjected to a stress of 398 MPa, it’s a stress of about 80% of the fatigue limit. As a result of such a large applied stress, cracks occurred at the corrosion origin and were fractured. In order to prevent the SCM435 bolt from fracture, it is necessary to use the correct composition, the accuracy of heat treatment, preventing damage by external impact, preventing corrosion of the damage part by moisture, and introduction a compressive residual stress by peening.