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레이저를 이용한 Tailored Blank 용접 판재의 피로거동
오택열,권윤기,이종재,곽대순 韓國工作機械學會 2000 한국생산제조학회지 Vol.9 No.4
For the Tailor Welded Blank sheet used for automobile body panel, the characteristics of fatigue strength and crack propagation behavior were studied. The thickness of specimen was joined to be same (0.9mm+0.9mm) and different (0.9mm+2.0mm). As a base test, mechanical properties around weld zone were examined. The results indicated that there were no significant decreases in mechanical properties, but hardness around weld bead was 2.3 times greater than base material. The fatigue strength was the highest when the loading direction was parallel to the welding direction, which was about 85% of tensile strength of base metal. It was decreased by 8.5% when the thickness of specimen and base metal was different, and it was increased by 25% when pre-strain was applied. The crack propagation rate was noticeably decreased around weld line and rapidly increased as it passed through weld line. Reviewing the shape of the crack propagation, crack width around weld line was wide around the weld zone due to retardation of crack growth, but it became narrow passing weld line due to decreased toughness.
Evaluation of pre-stresses in the menisci of human knee joint using microindentation
Kwak, Dai Soon,Bae, Ji Yong,Kim, Sung Youb,Jeon, Insu,Lu, Tian Jian Professional Engineering Publishing Ltd. 2014 Proceedings of the Institution of Mechanical Engin Vol. No.
<P>To evaluate the pre-stress in the menisci of a human knee joint, the technique of microindentation was adopted. Five specimens each for lateral and medial menisci attached to the tibia were prepared from the knee joints of Korean cadavers to represent the pre-stress state of the meniscus. To create test specimens for the stress-free state of the meniscus, each meniscus was resected from the tibia and cut into three parts, which were subsequently attached to a metal plate. Indentations were carried out in each meniscus in both the pre-stress state and the stress-free state. The pre-stresses in the menisci were evaluated using the load-versus-depth curves. Compressive pre-stresses were found in the menisci. For each indentation region, the pre-stresses in the medial meniscus were higher than in the lateral meniscus. The highest pre-stress in both the lateral and medial meniscus was found in the posterior regions, while the anterior regions experienced the lowest pre-stress. The obtained pre-stresses can be used for the accurate numerical analysis, the fabrication of artificial menisci, and the diagnosis of meniscal disease progression for human knee joints.</P>
Effect of a Single Applied Overload on Fatigue Crack Growth Behavior in Laser-welded Sheet Metal
Dai-Soon Kwak,Seog Hwan Kim,Taek Yul Oh 한국정밀공학회 2006 International Journal of Precision Engineering and Vol.7 No.3
We investigated fatigue crack growth behavior in laser-welded sheet metal caused by a single applied overload. The fatigue specimens were made using butt jointed cold rolled sheet metal that was welded with a CO₂ laser. The effects of the specimen thickness and overload ratio were determined from fatigue crack propagation tests. These tests were performed in such a way that the fatigue loading was aligned parallel to the weld line while the crack propagated perpendicular to the weld line. Overload ratios of 1.0, 1.5, and 2.0 were applied near the tip of the fatigue crack at points located 6, 4, and 2 ㎜ from the weld line. The specimens were either 0.9 or 2.0 ㎜ thick. The size of the plastic zone at the crack tip due to the single applied overload was also determined using finite element analysis.
Effect of a Single Applied Overload on Fatigue Crack Growth Behavior in Laser-welded Sheet Metal
Kwak Dai-Soon,Kim Seog-Hwan,Oh Taek-Yul Korean Society for Precision Engineering 2006 International Journal of Precision Engineering and Vol.7 No.3
We investigated fatigue crack growth behavior in laser-welded sheet metal caused by a single applied overload The fatigue specimens were made using butt jointed cold rolled sheet metal that was welded with a $CO_2$ laser, The effects of the specimen thickness and overload ratio were determined from fatigue crack propagation tests, These tests were performed in such a way that the fatigue loading was aligned parallel to the weld line while the crack propagated perpendicular to the weld line, Overload ratios of 1.0, 1.5, and 2. 0 were applied near the tip of the fatigue crack at points located 6, 4, and 2 mm from the weld line. The specimens were either 0.9 or 2.0 mm thick. The size of the plastic zone at the crack tip due to the single applied overload was also determined using finite element analysis.