• 구강회복응용과학지
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• 제25권2호
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• pp.109-123
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• 2009

임플란트 골유착의 성공과 임플란트 안정성에서 가장 중요한 것은 골의 양과 질이며 안정성을 평가하는 방법 중 하나인 주입회전력도 골질에 영향을 받는다. 임플란트를 식립할 때 모터에서 생긴 힘이 임플란트에 전달되면 임플란트는 회전력(moment)과 축력(axial force)을 갖게 되고 임플란트와 접촉한 골에서는 절삭과 압박 그리고 마찰이 일어나 응력이 생기는데 이 때 측정되는 주입회전력(insertion torque)은 골질에 따라 다양하게 나타난다. 본 연구에서는 임플란트를 하악 소구치 부위 골에 식립하는 것을 가정하여 골질을 치밀골의 두께와 망상골의 밀도 그리고 하방 치밀골 존재 시로 나누고, 골의 응력과 변위를 소탄성 범위의 유한요소법으로 분석하고 유효응력(von Mises stress)과 회전력 그리고 축력을 비교 연구하여 골질이 주입 회전력에 미치는 영향을 평가하였다. 임플란트($Br{\aa}nemark$ MKIII.RP, ${\phi}3.75{\times}10.0mm$, Nobel Biocare, $G{\ddot{o}}teborg$, Sweden) 와 원통형 골모형(${\phi}9.5{\times}12.0mm$)의 유한요소 모형을 설계하고 변수로 상부 치밀골의 두께(0.5 mm, 1.5 mm, 2.5 mm)와 치밀골 하부에 망상골의 밀도($0.85g/cm^3$, $1.11g/cm^3$, $1.25g/cm^3$) 그리고 골모형 하부에 1 mm 두께의 치밀골 유무에 따라 총 7개의 모형을 만들었으며, 임플란트가 식립될 때 발생하는 유효응력과 축력 그리고 회전력을 시간대 별로 비교하였다. 임플란트 플랜지 하연이 골의 상부를 파고드는 300 msec, 중간 정도 들어간 550 msec, 완전히 들어가 플랜지 상면이 골 표면과 일치한 800 msec로 나누어 관찰하였을 때 축력은 500 msec 전후에서, 회전력은 800 msec 전후에서 최대값를 보였으며 유효응력 분포는 서로 비슷하였다. 이 같은 실험 결과를 바탕으로 축력을 영역 별로 비교하여 다음과 같은 결과를 얻었다. 1. $Br{\aa}nemark$ MKIII 임플란트는 플랜지가 골을 파고들 때 축력이 치밀 골에서 가장 높았고, 회전력은 플랜지가 골상부에 걸리어 축력이 급격히 감소한 이후에 최대 회전력을 보였으며, 이 때 유효응력 분포는 플랜지와 접촉하는 골 상부에 집중되었다. 2. 임플란트 식립 시 치밀골의 두께가 두꺼울수록 축력과 회전력이 높게 나타났으며 치밀골의 두께가 축력과 회전력에 가장 큰 영향을 주었다. 3. 치밀골의 두께가 1.5 mm 이상인 경우 망상 골의 밀도가 축력에 미치는 영향은 작았고, 치밀골의 두께가 0.5 mm인 경우 망상골의 밀도가 축력과 회전력에 영향이 있을 것으로 사료되었다. 4. 양측 피질골 존재 시 축력의 합은 상부 피질골의 두께가 같은 다른 경우와 비슷하였으나 부위별 촉력은 골하부에서 양측 피질골 모형이 가장 높았고, 회전력은 하방 피질골과 접촉할 때는 피질골 두께가 같은 다른 모형보다 다소 높으나 최대 회전력은 비슷하였다. 위 결과를 토대로 하악 소구치 부위에 $Br{\aa}nemark$ MKIII 임플란트 식립 시 골질과 관련된 요소 중에 치밀골의 두께가 주입회전력에 가장 큰 영향을 주며 망상골의 밀도를 높이는 술식도 일차적 안정성 증가에 유용할 것으로 사료되는 바이다.

• Communications for Statistical Applications and Methods
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• 제30권2호
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• pp.191-213
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• 2023

Unit distributions are frequently used in probability theory and statistics to depict meaningful variables having values between zero and one. Using convenient transformation, the unit inverse exponentiated weibull (UIEW) distribution, which is equally useful for modelling data on the unit interval, is proposed in this study. Quantile function, moments, incomplete moments, uncertainty measures, stochastic ordering, and stress-strength reliability are among the statistical properties provided for this distribution. To estimate the parameters associated to the recommended distribution, well-known estimation techniques including maximum likelihood, maximum product of spacings, least squares, weighted least squares, Cramer von Mises, Anderson-Darling, and Bayesian are utilised. Using simulated data, we compare how well the various estimators perform. According to the simulated outputs, the maximum product of spacing estimates has lower values of accuracy measures than alternative estimates in majority of situations. For two real datasets, the proposed model outperforms the beta, Kumaraswamy, unit Gompartz, unit Lomax and complementary unit weibull distributions based on various comparative indicators.

• 한국정밀공학회지
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• 제23권10호
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• pp.121-125
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• 2006

In this paper, results are presented by nonlinear finite element simulations in order to analy the interactions between the stent and artery or plaque. Maximum of von Mises stress was calculated in the contacting areas between the stent and the artery. The simulated results show that the distal end of stent, which tilts after expansion, may injure the artery wall. In conclusion, this study may help designing new stents.

• 대한치과보철학회지
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• 제51권1호
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• pp.1-10
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• 2013

연구 목적: 임플란트 나사선 경사각이 치조골의 응력분포에 미치는 영향을 검토하여 어떤 임플란트가 응력분산에 유리한 지 알아보고자 하였다. 연구 재료 및 방법: 피치는 0.8 mm로 일정하게 하고 나사선의 줄(thread) 수를 다르게 하여 나사선 경사각의 변화를 준 1줄 나사선 임플란트(single thread type: 경사각 $3.8^{\circ}$)와 2줄 나사선 임플란트(double thread type: 경사각 $7.7^{\circ}$) 그리고 3줄 나사선 임플란트(triple thread type: 경사각 $11.5^{\circ}$)의 세 가지 모델을 통해 3차원 유한요소 응력분석을 시행하였다. 임플란트가 치조골의 치아 장축에 대하여 $0^{\circ}$, $10^{\circ}$, $15^{\circ}$ 경사지게 식립된 것으로 가정하여 9 가지 모델을 만들었다. 200 N의 수직 방향의 하중과, 200 N의 임의의 $15^{\circ}$ 경사 하중을 가한 경우에 임플란트와 치조골에서 발생된 응력분포를 3차원 유한요소법으로 분석하였다. 결과:1. 임플란트의 경사 식립 각도가 클수록 치조골과 임플란트의 등가응력(von-Mises stress)과 최대주응력이 높게 나타났다. 2. 수직하중보다 경사하중을 가할 경우 치조골과 임플란트의 등가응력과 최대주응력이 높게 나타났다. 3. 임플란트의 나사선 줄 수가 증가할수록 응력분산 효과가 커서 등가응력과 최대주응력의 크기가 감소되었다. 4. 치조골에 작용하는 최대주응력의 크기는 수직하중 시에나 경사하중 시에 3줄 나사선을 가진 임플란트가 가장 작고 다음으로 2줄 또는 1줄 나사선의 순으로 나타나 3줄 나사선의 경우가 가장 우수한 결과를 보였다. 결론: 이상의 결과는 3줄 나사선 임플란트가 1줄 및 2줄 나사선 임틀란트보다 응력분산 효과 면에서 우수하며, $10^{\circ}$ 이상 경사지게 식립된 경우에라도 나사선 경사각이 커지면서 줄 수가 증가할수록 치조골에서 발생하는 최대 주응력 값이 감소하므로 임플란트 나사선 줄 수와 경사각을 최적화함으로써 임플란트 응력분산에 도움이 될 수 있음을 시사하였다.

• 한국안전학회지
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• 제28권5호
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• pp.5-9
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• 2013

Recently, eco-friendly sources of energy by fuel cells that use hydrogen as an energy source has emerged as the next generation of energy to solve the problem of environmental issues and exhaustion of energy. A solid oxide fuel cell(SOFC) classified based on the type of ion transfer mediator electrolyte has actively being researched. However, the reliability according to the thermal cycle is low during the operation of the fuel cell, and deformation problem comes from the difference in thermal expansion coefficient between the electrode material, the components made of ceramic material is also brittle, which means disadvantages in terms of the strength. Therefore, in this study, considering the states of the manufacturing and operating of SOFC single cells, the stress analyses in the each of the interfacial layer between the anode, electrolyte and the cathode were performed to get the basic data for reliability assessment of SOFC. The obtained results show that von Mises stress according to the thickness direction on operating state occurred maximum stress value in the electrolyte layer. And also the stresses inside the active area on a distance of 1 ${\mu}m$ from the electrode interface were estimated. Futhermore the evaluation was done for the variation of the stress according to the stage of the operation divided into three stages of manufacturing, stack, and operating.

• 대한치과보철학회지
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• 제43권4호
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• pp.544-561
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• 2005

Purpose : This study was to assess the loading distributing characteristics of implant systems with internal connection or external connection under vertical and inclined loading using finite element analysis. Materials and methods : Two finite element models were designed according to type of internal connection or external connection The crown for mandibular first molar was made using cemented abutment. Each three-dimensional finite element model was created with the physical properties of the implant and surrounding bone This study simulated loads of 200N at the central fossa in a vertical direction (loading condition A), 200N at the centric cusp tip in a 15$^{\circ}$ inward inclined direction (loading condition B), or 200N at the centric cusp tip in a 30$^{\circ}$ outward inclined direction (loading condition C) respectively. Von Mises stresses were recorded and compared in the supporting bone, fixture, abutment and abutment screw. Results : 1. In comparison with the whole stress or the model 1 and model 2, the stress pattern was shown through th contact of the abutment and the implant fixture in the model 1, while the stress pattern was shown through the abutment screw mainly in the model 2. 2. Without regard to the loading condition, greater stress was taken at the cortical bone, and lower stress was taken at the cancellous bone. The stress taken at the cortical bone was greater at the model 1 than at the model 2, but the stress taken at the cortical bone was much less than the stress taken at the abutment, the implant fixture, and the abutment screw in case of both model 1 and model 2. 3. Without regard to the loading condition, the stress pattern of the abutment was greater at the model 1 than at the model 2. 4. In comparison with the stress distribution of model 1 and model 2, the maximum stress was taken at the abutment in the model 1. while the maximum stress was taken at the abutment screw in the model 2. 5. The magnitude of the maximum stress taken at the supporting bone, the implant fixture, the abutment, and the abutment screw was greater in the order of loading condition A, B and C. Conclusion : The stress distribution pattern of the internal connection system was mostly distributed widely to the lower part along the inner surface of the implant fixture contacting the abutment core through its contact portion because of the intimate contact of the abutment and the implant fixture and so the less stress was taken at the abutment screw, while the abutment screw can be the weakest portion clinically because the greater stress was taken at the abutment screw in case of the external connection system, and therefore the further clinical study about this problem is needed.

• 한국안전학회지
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• 제20권1호
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• pp.7-12
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• 2005

In heavy industrial fields such as power plant and chemical plant, it is often necessary to restore a damaged part of large machinery or structure which is installed in the hazard working place. In this paper, to evaluate the safety of plastic deformed cylindrical beam a finite element technique has been used. The variations of residual stresses on the process of damaging and restoring for surfaces and cross-sections have been examined. The results show that the maximum von Mises stresses occur outer cylinder surfaces of boundary between cylindrical beam support md cylindrical beam when deformation procedure and restoring force is applied. The maximum residual stress remains 158.6MPa in the inner wall and this value correspond to $53\%$ of yield stress then restoration procedure is finished.

• Smart Structures and Systems
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• 제26권3호
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• pp.311-318
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• 2020

The goal of this study is to analytically and non-stochastically generate structural uncertainty behaviors of isotropic beams and laminated composite plates under plane stress conditions by using an interval finite element method. Uncertainty parameters of structural properties considering resistance and load effect are formulated by interval arithmetic and then linked to the finite element method. Under plane stress state, the isotropic cantilever beam is modeled and the laminated composite plate is cross-ply lay-up [0/90]. Triangular shape with a clamped-free boundary condition is given as geometry. Through uncertainties of both Young's modulus for resistance and applied forces for load effect, the change of structural maximum deflection and maximum von-Mises stress are analyzed. Numerical applications verify the effective generation of structural behavior uncertainties through the non-stochastic approach using interval arithmetic and immediately the feasibility of the present method.

• Structural Engineering and Mechanics
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• 제88권4호
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• pp.369-377
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• 2023

In this study, previously developed algorithm is used for Optimization of hybrid composite plates using Tsai-Wu criteria. For the stress-based Design Optimization problems, Von-Mises stress uses as design variable for isotropic materials. Maximum stress, maximum strain, Tsai Hill, and Tsai-Wu criteria are generally used to determine failure of composite materials. In this study, failure index value is used as design variable in the optimization algorithm and Tsai-Wu criteria is utilized to calculate this value. In the analyses, commonly used design domains according to different hybrid orientations are optimized and results are presented. When the optimization algorithm was applied, 50% material reduction was obtained without exceeding allowable failure index value.

• 대한치과보철학회지
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• 제43권2호
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• pp.204-217
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• 2005

Purpose. The purpose of this study was to analyze stress distribution of all ceramic posterior fixed partial denture using a three dimensional finite element method. Material and method. A three dimensional finite element model was created to demonstrate all-ceramic posterior fixed partial denture and then this computer model measured the stress distribution of the all ceramic bridges which has a ceramic core materials such as Zirconia, IPS Empress. 2. In-Ceram zirconia, Metal-Ceramic. Also the stress distribution was examined according to loading sites when force was applied to sites such as the central area of second premolar the mesial connector of pontic, the central fossa of pontic, the distal connector of pontic, and the central fossa of second molar. Results. 1. In all the materials of the core in this study, von Mises stress indicated that the stress increased as force was applied to loaded sites, just at those points, on the connector, and the margin in the area adjacent to the connectors. 2. The maximum principal stress was much higher in the lower part of the connectors than in any other region. 3. As the load was applied to the different locations, the research showed a consistent increase of stress in the lower connectors. The maximum value of the von Mises stress was two or three times greater when the load was applied directly to the connectors rather than indirectly through another stressed region. 4. In the case of In-Ceram zirconia, the stress in lower connectors was the highest of all the reference points, the stress showed 75% of all the maximum stress. Ziconia showed 72%, Metal Ceramic 67% and IPS Empress 2 50%. 5. In the case of Ziconia, the stress was well dispersed in each reference point that the stress differences were smaller when compared to In-Cream ziconia.