• Journal of Welding and Joining
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• 제17권1호
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• pp.124-132
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• 1999

Thermal fatigue strength of the solder joints is the most critical issue for TSOP(Thin Small Outline Package) because the leads of this package are extremely short and thermal deformation cannot be absorbed by the deflection of the lead. And the TSOP body can be subject to early fatigue failures in thermal cycle environments. This paper was discussed distribution of thermal stresses at near the joint between silicon chip and die pad and investigated their reliability of solder joints of TSOP with 42 alloy clad lead frame on printed circuit board through FEM and 3 different thermal cycling tests. It has been found that the stress concentration around the encapsulated edge structure for internal crack between the silicon chip and Cu alloy die pad. And using 42 alloy clad, The reliability of TSOP body was improved. In case of using 42 alloy clad die pad(t=0.03mm). $$\sigma$_{VMmax}$ is 69Mpa. It is showed that 15% improvement of the strength in the TSOP body in comparison with using Cu alloy die pad $($\sigma$_{VMmax}$=81MPa). In solder joint of TSOP, the maximum equivalent plastic strain and Von Mises stress concentrate on the heel of solder fillet and crack was initiated in it's region and propagated through the interface between lead and solder. Finally, the modified Manson-Coffin equation and relationship of the ratio of $N_{f}$ to nest(η) and cumulative fracture probability(f) with respect to the deviations of the 50% fracture probability life $(N_{f 50%})$ were achieved.

• Structural Engineering and Mechanics
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• 제22권5호
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• pp.541-562
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• 2006

This paper compares the performance of axially loaded concrete filled steel tube (CFST) columns cast using a conventionally vibrated normal concrete (NC) and a novel self-consolidating concrete (SCC) made with a new viscosity modifying admixture (VMA). A total of sixteen columns with a standard compressive strength of about 50 MPa for both SCC and NC were tested by applying concentric axial load through the concrete core. Columns were fabricated without and with longitudinal and hoop reinforcement (Series I and Series II, respectively) in addition to the tube confinement. The slenderness of the columns expressed as height to diameter ratio (H/D) ranged between 4.8 and 9.5 for Series CI and between 3.1 and 6.5 for Series CII. The strength and ductility of SCC columns were found comparable to those of their NC counterparts as the maximum strength enhancement in NC columns ranged between 1.1% and 7.5% only. No significant difference in strain development was found due to the presence of SCC or NC or due to the presence of longitudinal and hoop reinforcement. Biaxial stress development in the steel tube as per von Mises yield criterion showed similar characteristics for both SCC and NC columns. The confined strength ($f^{\prime}_{cc}$) of SCC was found to be lower than that of NC and $f^{\prime}_{cc}$ also decreased with the increase of slenderness of the columns. Analytical models for the prediction of confined concrete strength and axial strength of CFST columns were developed and their performance was validated through test results. The proposed models were found to predict the axial strength of CFST columns better than existing models and Code based design procedures.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
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• pp.123-130
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• 2002

A general formulation for shape design sensitivity analysis over three dimensional beam structure is developed based on a variational formulation of the beam in linear elasticity. Sensitivity formula is derived based on variational equations in cartesian coordinates using the material derivative concept and adjoint variable method for the displacement and Von-Mises stress functionals. Shape variation is considered for the beam shape in general 3-dimensional direction as well as for the orientation angle of the beam cross section. In the sensitivity expression, the end points evaluation at each beam segment is added to the integral formula, which are summed over the entire structure. The sensitivity formula can be evaluated with generality and ease even by employing piecewise linear design velocity field despite the bending model is fourth order differential equation. For the numerical implementation, commercial software ANSYS is used as analysis tool for the primal and adjoint analysis. Once the design variable set is defined using ANSYS language, shape and orientation variation vector at each node is generated by making finite difference to the shape with respect to each design parameter, and is used for the computation of sensitivity formula. Several numerical examples are taken to show the advantage of the method, in which the accuracy of the sensitivity is evaluated. The results are found excellent even by employing a simple linear function for the design velocity evaluation. Shape optimization is carried out for the geometric design of an archgrid and tilted bridge, which is to minimize maximum stress over the structure while maintaining constant weight. In conclusion, the proposed formulation is a useful and easy tool in finding optimum shape in a variety of the spatial frame structures.

• 한국안전학회지
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• 제29권4호
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• pp.9-14
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• 2014

Self-piercing riveting(SPR) is a mechanical fastening technique which is put pressure on the rivet for joining the sheets. Unlike a spot welding, SPR joining does not make the harmful gas and $CO_2$ and needs less energy consumption. In this study, static and fatigue tests were conducted using tensile-shear specimens with Al-5052 plates for evaluation of fatigue strength of the SPR joints. During SPR joining process for the specimen, using the current sheet thickness and a rivet, the optimal applied punching force was found to be 21 kN. And, the maximum static strength of the specimen produced at the optimal punching force was 3430 N. During the fatigue tests for the specimens, interface failure mode occurred on the top substrate close to the rivet head in the most high-loading range region, but on the bottom substrate close to the rivet tail in the low -loading range region. There was a relationship between applied load amplitude $P_{amp}$ and lifetime of cycle N for the tensile-shear, $P_{amp}=3395.5{\times}N^{-0.078}$. Using the stress-strain curve of the Al-5052 from tensile test, the simulations for fatigue specimens have been carried out using the implicit finite element code ABAQUS. The relation between von-Mises equivalent stress amplitude and number of cycles was found to be ${\sigma}_{eq}=514.7{\times}N^{-0.033}$.

• 구강회복응용과학지
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• 제18권4호
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• pp.277-288
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• 2002

Seven finite element models were constructed in mandible having single screw-type implant fixture connected to the premolar superstructure, in order to evaluate how the length, diameter and platform shape of a screw-type fixture influence the stress in the supporting tissue around fixtures. Each finite element model was varied in terms of length, diameter, and platform shape of the fixture. In each model, 250N of vertical load was placed on the central pit of an occlusal plane and 250N of oblique load placed on the buccal cusp. The stress distribution in the supporting tissue and the other components was analysed using 2-dimensional finite element analysis and the maximum von Mises stress in each reference area was compared. Under lateral loading, the stress was larger at the abutment/fixture interface, and in the crestal bone, compared to the stress pattern under vertical loading. The amount of stress at the superstructure was similar regardless of the length, diameter and platform shape of a fixture. Around the longer fixture, the stress was decreased at the bone crest and subjacent cancellous bone and increased in the cancellous bone area apical to the fixture. Around the wider fixture, the stress was decreased at the abutment/fixture interface, and the bone crest and increased in the cancellous bone area apical to the fixture. Around the fixture having wider platform, less stress was produced at the abutment/fixture interface and the upper part of the cortical bone, compared to the fixture having standard platform. In conclusion, the stress distribution of the supporting tissue was affected by length, diameter, and platform shape of a fixture, and the fixture which was larger in diameter and length could reduce the stress in the supporting tissues at the bone-fixture interface and bone crest area.

• 구강회복응용과학지
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• 제28권2호
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• pp.147-161
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• 2012

본 연구에서는 유한요소해석 방법을 사용하여 임플란트 지지 3본 고정성 가공 의치에 수평적인 부적합이 존재할 때 그 정도가 임플란트 인접골 응력 발생에 미치는 영향에 대해 조사하였다. 3본 고정성 가공의치, 임플란트/악골 복합체로 구성된 해석 모델은 3차원으로 연구되었다. 3본 고정성 가공의치의 체결 간격은 하악 제2 소구치와 제2 대구치에 17.9mm 거리로 식립된 임플란트 간격에 비해 0.1mm 짧거나(17.8mm), 0.1mm 길게(18.0mm) 모델링하였다. 3본 고정성 가공의치와 임플란트 지대주 간의 체결은 총 6단계로 모사되었고 각 단계별로 가공의치가 하방으로 0.1mm 씩 변위되었다. 유한요소해석에는 PC용으로 출시된 DEFORM$^{TM}$ 3D 프로그램(ver 6.1, SFTC, Columbus, OH, USA)을 사용하였다. 3본 고정성 가공의치와 임플란트 사이의 응력은 von-Mises 응력, 최대 압축 응력, 필요한 경우 방사상 응력을 평가하였다. d=18.0mm인 모델에서는 가공의치와 지대주간의 체결이 이루어지지 않은 반면, d=17.8mm 인 모델에서는 성공적으로 체결이 가능했다. 체결 여부를 떠나 과도하게 높은 응력이 체결과정과 그 이후에 발생되었는데, 17.8mm 모델의 경우 체결완료 후에도 임플란트 주위 변연골에서 잔류하는 인장 및 압축 응력이 각각 최대 186.9MPa과 114.1MPa이었다. 이 경우 임플란트로부터 2mm 떨어진 부분까지 압축 응력이 골개조 장애 임계 응력인 55MPa($4,000{\mu}{\varepsilon}$과 같은 크기)보다 크게 측정되었다. 3본 고정성 가공의치의 0.1mm 크기의 수평적 부적합은 체결 과정뿐만 아니라 완료 후에도 인접 변연골에 높은 응력을 발생시킬 수 있다.

• 한국산학기술학회논문지
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• 제14권9호
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• pp.4142-4148
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• 2013

경사지 과수의 효율적인 재배 및 관리를 위해 과수원 전용 고소 작업차량 사용이 늘어나고 있다. 이러한 이유로 작업자 안전을 위해 고소 작업차의 안정성에 대해 연구가 요구되고 있다. 본 연구는 경사지 흙길을 주행할 수 있는 4개의 바퀴와 2개의 직교 좌표계 적재함을 가진 과수원 차량의 안정성 평가에 대한 연구이다. 차량 메커니즘에 대한 다물체 동역학(MBD) 해석을 통하여 19.2, $34.6^{\circ}$의 좌우 및 상하 방향의 전복각을 계산할 수 있었다. 바퀴들의 주행 저항과 소요 동력을 결정하였다. 그리고 적재함 프레임의 유한요소해석(FEA)를 통하여 최대응력 146 MPa로 구조적으로 안정하다. 따라서 적재함을 가진 바퀴형 과수원 차량은 정적 및 동적 안정성을 가짐을 알 수 있었다.

• 한국임상수의학회지
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• 제40권4호
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• pp.268-275
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• 2023

In this paper, we designed 3D-printed orthopedic splint models for patient-specific external coaptation on fracture healing and analyzed the stability of the models through finite element method (FEM) analysis under compressive load conditions. Polylactic acid (PLA) and acrylonitrile-butadiene-styrene (ABS) based 3D splint models of the thicknesses 1, 3, 5 and 7 mm were designed, and Peak von Mises stress (PVMS) and maximum displacement (MD) of the models were analyzed by FEM under compressive loads of 50, 100, 150, and 200 N. The FEM results indicated that PVMS and MD values, regardless of material, had a negative correlation with the thickness of the models and a positive correlation with the compressive load. There was a risk of splint deformation under conditions more extreme than 100 N with 5 mm thickness. For successful clinical application of 3D-printed orthopedic splints in veterinary medicine, it is recommended that the splint should be produced not less than 5 mm thickness. Also, it is expected to be stable when the splint is applied to situations with a compressive load of 100 N or less. There is an advantage of overcoming the limitations of the existing bandage method through 3D-printing technology as well as verifying the stability through 3D modeling before application. Such 3D printing technology will be widely used in veterinary medicine and various fields as well as orthopedics.

• 대한치과보철학회지
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• 제43권1호
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• pp.105-119
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• 2005

Statement of problem. As the effects of the various diameters of fixture and abutment screw on stress distribution was not yet examined, this study focused on the different design of single implant restoration using three dimensional finite element analysis. Purpose. This study was to compare five different fixture-abutment combinations for single implant supported restorations with different fixture and abutment screw diameters. Material of methods. The five kinds of finite element models were designed by 3 diameter fixtures ($\oslash$3.3, 3.75, 5.0 mm) with 3 different abutment screws $\oslash$1.5, 1.7, 2.0 mm). The crown for mandibular first molar was made using UCLA abutment according to Wheeler's anatomy. 244 N was applied at the central fossa with two different loading directions, vertically and obliquely (30$^{\circ}$) and at the buccal cusp vertically. Maximum von Mises stresses were recorded and compared in the supporting bone, crowns, fixtures, and abutment screws. Results. 1. The stresses in supporting bone and implant-abutment structure under oblique loading were greater than those under vertical or offset loading. The stresses under vertical loading were the least among 3 loading conditions regardless of the implant and abutment screw diameters. 2. The stresses in the narrow implants were greater than the wider implants. The narrow implant with narrow abutment screw showed highest stresses in the lingual crest, but the narrow implant with standard abutment screw showed highest stress in abutment screw. 3. The stresses of abutment screws were influenced by the diameter of fixtures and loading conditions. The wide implants showed least difference between two different abutment screw diameters. Conclusions. The wide implants showed lesser stresses than the narrow implants and affected least by the different abutment screw diameters. The narrow implants with standard abutment screw showed highest stresses in the lingual bony crest under oblique loading.

• Journal of Biosystems Engineering
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• 제32권6호
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• pp.430-439
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• 2007

This study was carried out to(1) visualize the installation effect of an anti-wind net; (2) evaluate structural stability of typical anti-wind nets in Jeju; and (3) present the optimal specification of pipes in an anti-wind net for maximum instant wind velocities of 40 m/s and 45 m/s. The analyses were done for anti-wind nets with a mesh of 4 mm and a height of 3 m by using CFX and ANSYS. The results showed that the wind went down due to flow resistance when passing through an. anti-wind net. The anti-wind net with the supporting pipe being installed every two main columns was certainly unstable because the main column not sustained by the supporting pipe became cantilever. With regard to the position of a fixing point of the supporting pipe, von Mises stress on pipes was certainly increased as vertical positions of the supporting pipe were changed to be too lower or higher than an adequate position but there was little difference according to horizontal positions. The adequate vertical position was $2{\sim}2.5\;m$ high from the ground. For a maximum instant wind velocity of 40 m/s, the optimal specification of pipes was a main column of ${\varphi}48.1{\times}2.1$ t@2,000, cross beams(bottom and top) of ${\varphi}26.7{\times}1.9\;t$, cross beams(center) of ${\varphi}33.5{\times}2.1$ t/2ea and a supporting pipe of ${\varphi}31.8{\times}1.5$ t@2,000. In case of a maximum instant wind velocity of 45 m/s, the optimal specification of pipes with structural stability was a main column of ${\varphi}48.6{\times}3.25$ t@2,000, cross beams(bottom and top) of ${\varphi}26.7{\times}1.9\;t$, cross beams(center) of ${\varphi}48.1{\times}2.1$ t/2ea and a supporting pipe of ${\varphi}31.8{\times}1.5$ t@2,000.