• 대한기계학회논문집A
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• 제32권6호
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• pp.488-495
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• 2008

In order to achieve long fatigue lifetimes for cyclically pressurized thick cylinders, multi-layered compound cylinder has been proposed. Such compound cylinder involves a shrink-fit procedure incorporating a monobloc tube which has previously undergone autofrettage. The basic autofrettage theory assumes elastic-perfectly plastic behaviour. Because of the Bauschinger effect and strain-hardening, most materials do not display elastic-perfectly plastic properties and consequently various autofrettage mo dels are based on different simplified material strain-hardening models, which is assumed that combination of linear strain-hardenig and power strain-hardening model. This approach gives a more accurate prediction than the elastic-perfectly plastic model and is suitable for different strain-hardening materials. In this paper, a general autofrettage model that incorporates the material strain-hardening relationship and the Bauschinger effect, based upon the actual tensile-compressive stress-strain curve of a material was proposed. The model was obtained using the von Mises yield criterion and plane strain condition. The tensile-compressive stress-strain curve was obtained by experiment. The parameters needed in the model were determined by fitting the actual tensile-compressive curve of the material. Finally, strain- hardening model was compared with elastic-perfectly plastic model.

• 대한기계학회논문집A
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• 제40권10호
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• pp.879-886
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• 2016

CNG 압력용기 제조를 위한 딥드로잉 공정에 사용되는 트랙트릭스 다이는 블랭크 홀더 없이 성형을 가능하게 한다. 기존의 연구에서는 D.D.I. 공정의 1차 딥드로잉 공정에 트랙트릭스 곡선을 다이에 적용하였을 뿐, 다이의 수명향상 및 제조원가 절감을 위한 형상 최적화에 관한 연구는 전무한 실정이다. 이에 본 논문에서는 트랙트릭스 곡선의 점근선 이동을 통하여 다이의 높이에 따른 딥드로잉 공정의 유한요소해석을 수행하였다. 또한 펀치의 성형하중에 따른 다이 응력집중부의 Von-Mises 응력을 분석하여 최적의 트랙트릭스 다이 형상을 제시하였다.

• 구강회복응용과학지
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• 제21권2호
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• pp.153-167
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• 2005

The purpose of this study was to compare the v-shape thread with the square shape thread of fixture in the view of stress distribution pattern using finite element stress analysis. The finite element model was designed with the parallel placement of two standard fixtures(4.0 mm diameter ${\times}$ 11.5 mm length) on the region of mandibular 1st and 2nd molars. Three dimensional finite element model was created with the components of the implant and surrounding bone. This study simulated loads of 200 N at the central fossa in a axial direction (load A), 200 N at the buccal offset load that is 2 mm apart from central fossa in a axial direction (load B), 200 N at the buccal offset load that was 4 mm apart from central fossa in a axial direction (load C). These forces of load A',B',C' were applied to a $15^{\circ}$ inward oblique direction at that same site with 200 N. Von Mises stress values were recorded and compared in the supporting bone, fixture, and abutment screw. The following results have been made based on this study : 1. The highest stress concentration occurred at the cervical region of the implant fixture. 2. Von Mises stress value of off-site region was higher than that of central fossa region. 3. Square shape thread type showed more even stress distribution in the vertical and oblique force than V-shape thread type. 4. Stress distribution was the most effective in the case of buccal offset load (2, 4 mm distance from central fossa) in the square shape thread type. 5. V-shape thread type revealed higher von Mises stress value than square shape thread type in all environmental condition. The results from numerical analyses concluded that square shape thread type had the lower destructive stress and more stress distribution between the fixture and bone interface than V-shape thread type. Therefore, square shape thread type was regarded as optimal thread configuration in biomechanical concepts.

• Journal of the Korean Data and Information Science Society
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• 제7권1호
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• pp.37-46
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• 1996

계단충격가속수명시험에서 얻은 자료를 토대로 통계적 추론을 위해 가정하는 수명분포에 대한 적합도 검정을 Kolmogorov-Smirnov, Cramer-von Mises, Anderson-Darling과 같은 비모수적 검정통계량들을 이용한 검정절차를 제안하고, 각 통계량들을 검정력 측면에서 비교하고자 한다.

• 한국정밀공학회지
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• 제21권1호
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• pp.173-180
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• 2004

This paper presents the effect of varying boundary conditions such as ground subsidence, internal pressure and temperature variation for buried pipelines on failure prediction by using a failure probability model. The first order Taylor series expansion of the limit state function incorporating with von-Mises failure criteria is used in order to estimate the probability of failure mainly associated with three cases of ground subsidence. Using stresses on the buried pipelines, we estimate the probability of pipelines with von-Mises failure criterion. The effects of varying random variables such as pipe diameter, internal pressure, temperature, settlement width, load for unit length of pipelines, material yield stress and pipe thickness on the failure probability of the buried pipelines are systematically studied by using a failure probability model for the pipeline crossing ground subsidence regions which have different soil properties.

• Structural Engineering and Mechanics
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• 제9권1호
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• pp.51-68
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• 2000

The paper presents theoretical and experimental investigations on three varying thickness circular cylinders, which were tested to destruction under external hydrostatic pressure. The five buckling theories that were presented were based on inelastic shell instability. Three of these inelastic buckling theories adopted the finite element method and the other two theories were based on a modified version of the much simpler von Mises theory. Comparison between experiment and theory showed that one of the inelastic buckling theories that was based on the von Mises buckling pressure gave very good results while the two finite element solutions, obtained by dividing the theoretical elastic instability pressures by experimentally determined plastic knockdown factors gave poor results. The third finite element solution which was based on material and geometrical non-linearity gave excellent results. Electrical resistance strain gauges were used to monitor the collapse mechanisms and these revealed that collapse occurred in the regions of the highest values of hoop stress, where considerable deformation took place.

• Structural Engineering and Mechanics
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• 제62권4호
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• pp.487-496
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• 2017

The focus of this study were to investigate patterns between wall pressures and stresses with grain moisture of soybean and rice varieties widespread cultivated in Turkey in order to determine needed designing parameters for structure analysis in silos at filling and discharge. In this study, the wall pressures and stresses were evaluated as a function of moisture contents in the range of 8-14% and 10-14% d.b. The pressures and von Mises stresses affected as significant by the change of grain moisture content. The main cause of pressure and stress drops is changed in bulk density. Therefore is extremely important bulk density and moisture content of the product at the structural design of the silos. 4 mm wall thickness, were determined to be safe for von Mises stresses in both soybean and rice silos is smaller than 188000 kPa.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제28권3호
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• pp.196-204
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• 2002

For the study of its stability when the screw has been fixed after sagittal split ramus osteotomy(SSRO) of the mandible, the methods of screw arrangement are classified into two types, triangular and straight. The angles of screws to the bone surface are classified as perpendicular arrangements, the $60^{\circ}$ anterioinferior screw, known as triangular, and the most posterior screw, called straight arrangement, thus there are four types. The finite element method model has been made by using a three dimensional calculator and a supercomputer. The load directions are to the anterior teeth, premolar region, and molar region, and the bite force is 1 Kgf to each region. The distribution of stress, the von-Mises yield strength, and safety of margin refer to the total sum of transformed energy have been studied by comparison with each other. The following conclusion has been researched : 1. When shear stress is compared, in the triangular arrangement in the form of "ㄱ", the anterosuperior screw is seen at contributing to the support of the bone fragment. In the straight arrangement, substantial stress is seen to be concentrated on the most posterior angled screw. 2. When the von-Mises yield strength is compared, it seemed that the stress concentration on the angled anteroinferior screw is higher, it shows a higher possibility of fracture than any other screw. In the straight arrangement, stress appeared to be concentrated on the most posteriorly angled screw. 3. When the safety margins of the transfomed energy are compared, the energy conduction is much greater in the case of the angled screw than in the case of the perpendicular screw. The triangular arrangement in the form of "ㄱ" shows a superior clinical sign to that of the straight arrangement. Judging from the above results, when the screw fixation is made after SSRO in practical clinical cases, two screws should be inserted in the superior border of mandibular ramus and a third screw of mandibular inferior border should be inserted in the form of triangular. All screws on the bony surface should be placed perpendicularly-$90^{\circ}$ angles apparently best promote bony support and stability.

• Journal of Korean Dental Science
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• 제5권1호
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• pp.13-20
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• 2012

Purpose: The purpose of this study was to investigate the effect of patterning on the stress distribution in the bone tissue using the finite element analysis (FEA) model. Materials and Methods: For optimal comparison, it was assumed that the implant was axisymmetric and infinitely long. The implant was assumed to be completely embedded in the infinitely long cortical bone and to have 100% bone apposition. The implant-bone interface had completely fixed boundary conditions and received an infinitely big axial load. von Mises stress and maximal principal stress were analyzed. Conventional thread and 2 or 3 patterns on the upper and lower flank of the thread were compared. Result: The surface areas of patterned implants were increased up to 106~115%. The thread with patterns distributed stress better than conventional thread. Patterning in threads may produce more stress in the implant itself, but reduce stress in the surrounding bone. Stress patterns of von Mises stress were favorable with patterns, while the maximal principal stress was increased with patterns. Patterns in the lower flank showed favorable stress distribution. Conclusion: The patterns in implant thread reduce the stress generated in surrounding bone, but the number and position of patterns were crucial factors in stress distribution.

• 대한치과기공학회지
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• 제40권1호
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• pp.41-47
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• 2018

Purpose: The purpose of this study was to analyze the biomechanical properties of the dental implants on the supporting bone using three-dimensional finite element method when three different abutment materials were applied to the implant system. Methods: Three different dental implant models were fabricated by applying Ti, PEEK, and CRE-PEEK (60% carbon-reinforced PEEK) to abutment material. The abutment and connecting screw from the fixture was applied with a tightening torque of 20 Ncm. And then, total loads of 150 N were applied in an $30^{\circ}oblique$ direction (to the vertical). The structural stability of dental implants on the supporting bone was analyzed using Von Mises stress and principal stress values. Results: The maximum tensile stress of the cortical bone was highest at 12.6 MPa in the PEEK abutment (Model-B). Ti abutment (Model-A) and CRE-PEEK abutment (Model-C) showed similar stress distributions (10.6 and 10.3 MPa, respectively). And the maximum compressive principal stress was similar in all models. The Von Mises stress value delivered to the bone around the implant was highest at 16.5 MPa in Model-B. On the other hand, Model-A and C showed similar stress distributions (14.0 and 13.8 MPa, respectively). In addition, the maximum equivalent stress applied to the abutment was highest at 629.8 MPa in Model-A. The stress distribution in Model-C was 573.9 MPa. Whereas, Model-B showed the lowest value at 165.6 MPa. Conclusion : The dental implant supporting bone system using PEEK material seems to have the possibility of supporting bone fracture. It was found that the CRE-PEEK abutment can reduce the elastic deformation and reduce the stress value of the interfacial bone.