세라믹/금속접합재의 고온 열사이클에 따른 잔류응력분포 및 굽힘강도 특성

박영철,허선철,부명환,김현수,강재욱,Park, Young-Chul,Hue, Sun-Chul,Boo, Myoung-Hwan,Kim, Hyun-Su,Kang, Jae-Wook 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.10

Since the ceramic/metal joint material is made at a high temperature, the residual stress develops when it is cooled from bonding temperature to room temperature due to remarkable difference of thermal expansion coefficient between ceramic and metal. As residual stress at ceramic/metal joints influences the strength of joints, it is important to estimate residual stress quantitatively. In this study, it is attempted to estimate joint residual stress of Si$_3$N$_4$STS304 joints quantitatively and to compare the strength of joints. The difference of residual stress is measured when repeated thermal cycl is loaded, under the conditions of the practical use of the ceramic/metal joint. The residual stress increases at 1 cycle of thermal load but decreases in 3 cycles to 10 cycles of thermal load. And 4-point bending test is performed to examine the influence of residual stress on fracture strength. As a result, it is known that the stress of joint decreases as the number of thermal cycle increases.

TiNi 합금을 강화한 TiNi/Al 복합재료의 피로균열제어특성에 관한 연구

박영철(Young Chul Park),윤두표(Doo Pyo Yun),허선철(Sun Chul Hue),김순국(Soon Kook Kim),이준희(Jun Hee Lee) 한국자동차공학회 1999 한국 자동차공학회논문집 Vol.7 No.3

세라믹/금속접합재의 고온피로에 따른 접합계면의 응력분포

박영철(Young-Chul Park),허선철(Sun-Chul Hue),김현수(Hyun-Su Kim),윤두표(Doo-Pyo Yun),김광영(Kwang-Young Kim) 한국해양공학회 1996 韓國海洋工學會誌 Vol.10 No.2

The ceramic has various high mechanical properties such as heat, abrasion, corrosion resistance and high temperature strength compared with metal. It also has low specific weight, low thermal expansibility, low thermal conductivity. However, it could not be used as structural material since it is brittle and difficult for the machining. Therefore, there have been many researches to attempt to join ceramic with metal which is full of ductility in order to compensate the weakness of ceramic.<br/> The problem is that residual stress develops around the joint area while the ceramic/metal joint material is cooled from high joining temperature to room temperature due to remarkable difference of thermal expansion coefficients between ceramic and metal. Especially, the residual stress at both edges of the specimen reduces the strength of joint to a large amount by forming a singular stress field.<br/> In this study, two dimensional finite element method is attempted for the thermal elastic analysis. The joint residual stress of ceramic/metal developed in the cooling process is investigated and the change of joint residual stress resulted from the repetitive heat cycle is also examined.<br/> In addition, it is attempted to clarify the joint stress distribution of the case of tensile load and of the case of superposition of residual stress and actual loading stress.

Ti-Ni합금의 반복변형특성에 미치는 pre-strain의 효과

박영철(Young-Chul Park),조용배(Yong-Bae Cho),허선철(Sun-Chul Hue) 한국해양공학회 1995 韓國海洋工學會誌 Vol.9 No.1

In SMA(Shape Memory Alloy), the degradation by fatigue is one of the most important problems to be overcome, when SMA is used for robot-actuator materials.<br/> The actuator is operated repetitively for long time and its repeating operation develops the fatigue degradation of SMA. The fatigue degradation changes the transformation temperature and deformation behavior and results in inaccurate operation control of robot.<br/> Accordingly, the changing behavior of transformation temperature and deformation which results from repeating operation is to be investigated in advance and the scheme to resolve those problems have to be made for the design of actuator.<br/> In this paper, for the improvement of the fatigue degradation by repetive movement and better control of the correct movement by the stability of martensite transformation in the developement of Robots actuator, Pre-strain(0, 1.5, 5, 8%) are loaded in the specimens and fatigue testing were carried out by the method of heating and cooling in direct condition. From the results of these experiments, the effects on pre-strain which affect the transformation characteristic and fatigue degradation phenomena were correctly investigated

X-선 회절에 의한 SS41 불림재와 M.E.F. 복합 조직강의 피로 파단면 해석에 관한 연구

허선철,박영철,박수영,김득진,오세욱 韓國非破壞檢査學會 1996 한국비파괴검사학회지 Vol.16 No.1

본 연구에서는 SS41 불림재와 M.E.F. 복합 조직강에 대해서 파괴 역학 파라미터와 X-선 피라미터 사이의 관계를 규명하였다. 피로 균열 진전 실험이 수행되었고, X-선 회절 방법이 피로 파단면에 적용되었다. 피로 파단면을 순차적으로 전해 연마하면서 깊이에 따른 X-선 파라미터(잔류응력, 반가폭)의 변화를 관찰하였다. 최대 소성역 깊이 Wy는 SS41 불림재에서는 반가폭의 분포로, M.E.F. 복합 조직강에 대해서는 잔류 응력의 분포로 결정할 수 있었다. 피로 파단면의 깊이 방향에 따른 X-선 파라미터의 분포로부터 Kmax와 Wy의 관계식이 실험 데이터로부터 얻어지고, 이 식들로부터 Kmax은 Wy의 측정에 의하여 추정되어질 수 있다. This study verified the relationship between fracture mechanics parameters and X-ray parameters for normalized SS41 steel with homogeneous crystal structure and M.E.F. dual phase steel(martensite encapsulated islands of ferrite). The fatigue crack propagation test were carried out and X-ray diffraction technique was applied to fatigue fractured surface. The change in X-ray parameters(residual stress, half-value breadth) according to the depth of fatigue fractured surface were investigated. The depth of maximum plastic zone, Wy, were determined on the basis of the distribution of the half-value breadth for normalized SS41 steel and that of the residual stress for M.E.F. dual phase steel. Kmax could be estimated by the measurement of Wy.

세라믹/금속 접합재의 잔류응력 해석

박영철,허선철,김광영 韓國非破壞檢査學會 1994 한국비파괴검사학회지 Vol.14 No.1

동을 중간재로 하는 Si₃N₄/SUS304 접합재의 접합계면 근방의 잔류응력 분포를 유한요소법과 X선 응력측정법을 이용하여 해석을 하였다. 그 결과, 접합재의 세라믹부 계면 근방의 잔류응력 분포를 정량적으로 밝혀낼 수 있었다. 세라믹부에 발생되는 접합 잔류응력은 접합계면 근방에서 대단히 크게 나타났으며, 특히 최대인장 잔류응력 σx 는 단부에서 발생하였다. 한편, σx는 접합계면 근방에서 3차원분포를 하고 있기 때문에 2차원 유한요소 해석결과와는 대단히 다른 값을 나타내고 있으며, 특히 시험편 중앙부의 계면 근방에서는 X선 실측결과가 인장 잔류응력임에 반하여 2차원 유한요소 해석결과는 압축 잔류응력으로 계산되어짐을 알았다. 따라서, 이와같은 3차원 분포를 하고 있는 접합계면 근방의 잔류응력 σx보다 간편하고 정확하게 예측할 수 있는 유한요소 해석모델에 대하여 서로 검토하였다. The two-dimensional elastoplastic analysis was performed to reveal a detail residual stress distribution of ceramic/metal joint specimen using finite element method and X-ray method. The highest tensile residual stress, σx perpendicular to the interface appeared at the edge of the ceramic near the interface. In the vicinity of the interface, the high stress concentration occurs and residual stress distributes three-dimensionally. Therefore, the measured stress distribution differed remarkably from the result of the two-dimensional finite-element analysis. Especially at the center of the specimen near the interface, the residual stress, σx obtained from the finite element analysis was compressive, whereas X-ray measurement yielded tensile σx. Therefore, it is also attempted to investi gate the finite element model for the prediction of residual stree σx distributed nearly the interface of joint.

Ti-Ni합금의 반복변형특성에 미치는 pre-strain의 효과

박영철,조용배,허선철 東亞大學校 海洋資源硏究所 1995 硏究論文集 Vol.8 No.1

In SMA(Shape Memory Alloy), the degradation by fatigue is one of the most important problems tobe overcome, when SMA is used for robot-actuator materials. The actuator is operated repetitively for long time and its repeating operation develops the fatigue degradation of SMA. The fatigue degradation changes the transformation temperature and deformation behavior and results in inaccurate operation control of robot. Accordingly, the changing behavior of transformation temperature and deformation which results from repeating operation is to be investigated in advance and the scheme to resolve those problems have to be made for the design of actuator. In this paper, for the improvement of the fatigue degradation by repetive movement and better control of the correct movement by the stability of martensite transformation in the developement of Robots actuator, Pre-strain(0,1.5,5,8%) are loaded in the specimens and fatigue testing were carried out by the method of heating and cooling in direct condition. From the results of these experiments, the effects on pre-strain which affect the transformation characteristic and fatigue degradation phenomena were correctly investigated.