• Journal of Biomedical Engineering Research
• /
• v.21 no.6
• /
• pp.599-606
• /
• 2000

고정체 나사산 형상이 식립된 고정체를 둘러싸고 있는 턱 뼈에서 발생된 응력분포에 미치는 영향과 효과적인 나사산 형상을 결정하기 위해서 다양한 치아 고정체 형상에 대해서 응력해석을 수행하였다. 나사산 골 한쪽 부위에 라운딩이 된 형상의 고정체에서 발생된 응력분포는 다른 나사산 형상의 고정체에서 발생된 응력분포보다 더 효과적으로 나타났다. 이 해석 결과를 근거로 최적의 고정체 치수를 결정하기 위해서 나사산 끝단의 폭, 나사산 높이, 그리고 가해지는 하중의 방향 등과 같은 설계 변수의 변화에 따른 응력해석이 수행되었다. 최대 응력 집중은 고정체 나사산의 첫단 부위에서 발생하였으며, 100 N의 15도 경사하중이 가해졌을 때 발생된 최대 등가응력은 동일 크기의 수식하중보다 2배 정도 더 높게 나타났다. 그리고 나사산 끝단의 폭과 나사산 높이 사이의 연관성에 관련된 해석결과에서 나사산 끝단의 폭과 나사산 높이 사이의 연관성 효과는 무시할 만큼 작다는 것을 알았다. 고정체의 나사산 피치에 대한 나사산 끝단의 폭의 비와 나사산 높이의 비가 각각 0.5와 0.46일 때 다른 고정체의 치수들보다 더 효과적인 응력분포가 나타났다

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.3A
• /
• pp.189-198
• /
• 2011

Although high strength bolts with tensile strength of 1,000 MPa are mainly used in steel structure construction sites throughout the world, new high strength bolts are required owing to the installation of continuous long-span bridges resulting from the development and distribution of high strength steel and ultra-thick steel plates. Currently, high strength bolts with tensile strength of 1,300 MPa are being used. However, as they tend to place a large load on a small section of space, a high strength bolt of high structural performance and screw thread shape with less stress concentration is thought to be more effective. This study conducted analyses in order to develop an improved screw thread shape relative to the KS screw thread shape. A new screw thread shape with less stress concentration and effective load distribution at the time of fastening bolts and nuts was provided upon analysis of the characteristics of screw thread shape. Additionally, in an experimental study, the structural performance of high strength bolts with tensile strength of 1,300 MPa was investigated. The results revealed that the new screw thread shape was more effective than the existing screw thread shape in terms of structural performance and mitigating the stress concentration.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.11
• /
• pp.971-978
• /
• 2016

Recent trends in miniaturization and lightness in portable electronics parts have driven developments in subminiature screws. This study aims to investigate the thread rolling process of a subminiature screw with an outer diameter and pitch of 1.0 and 0.25 mm, respectively. Finite element (FE) analyses were performed for the thread rolling process of symmetric and asymmetric screw threads. Through FE analyses, various process parameters, such as the horizontal and vertical die gap and the rolling stroke, were investigated in terms of the forming accuracy. The material flow characteristics in the thread rolling process of the symmetric and asymmetric screws were also discussed, and the relevant process parameters were determined accordingly. These simulation results were then reflected on real thread rolling processes, from which the symmetric and asymmetric screws could be formed successfully with allowable dimensional accuracy.

• The Journal of Korean Academy of Prosthodontics
• /
• v.52 no.4
• /
• pp.279-286
• /
• 2014

Purpose: The aim of this study was to investigate the effect of implant thread profile on the marginal bone stresses which develop during implant insertion. Materials and methods: Four experimental implants were created by placing four different thread systems on the body ($4.1mm{\times}10mm$) of the ITI standard implant. The thread types studied in this study included the buttress, v-shape, reverse buttress, and square shape threads. In order to examine the insertion stress generation, 3D dynamic finite element analysis was performed which simulated the insertion process of implants into a 1.2 mm thick cortical bone plate (containing 3.5 mm pilot hole) using a PC-based DEFORM 3D (ver 6.1, SFTC, Columbus, OH, USA) program. Results: Insertion stresses higher than human cortical bone developed around the implants. The level of insertion stresses was much different depending on the thread. Stress level was lowest near the v-shape thread, and highest near the square shaped thread. Difference in the interfacial bone stress level was more noticeable near the valley than the tip of the threads. Conclusion: Among the four threads, the v-shape thread was turned out to minimize the insertion stress level and thereby create better conditions for implant osseointegration.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.10
• /
• pp.1549-1554
• /
• 2010

Recently, plastic screws have replaced metal screws because of the former's light weight, thermal and electrical insulating properties, and anticorrosion characteristics. Plastic screws are usually produced by injection molding, which involves material shrinkage during the solidification of the polymer. This shrinkage results in the degeneration of the dimensional accuracy. In the present study, the effect of injection-molding conditions on the dimensional accuracy of plastic screws was investigated through a numerical simulation of injection molding; on the basis of this simulation, we could determine the mold-design parameters. The design of experiment was applied in accordance with the numerical analysis in order to optimize the injection-molding conditions with a view to improving the dimensional accuracy of the precision plastic screw.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.6
• /
• pp.3692-3697
• /
• 2015

A screw is a type of fastener characterized by a helical ridge known as thread. The demands for screws with the miniaturization and weight reduction are increasing for the trend of small size of mobile devices. The successful designs of mold and process are very important to obtain screws with good mechanical properties and high precision. In this study, the design of cold forging process of micro screw was carried out by using finite element method. In particular, in order to investigate the effects of die geometries and friction, design of experiment method was adopted and it was revealed that the friction was the dominant factor of folding defects. From these results, the design of die was modified and experiments were carried out with the modified die. From the experimental results, it was found that the folding defects disappeared.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.11 no.6
• /
• pp.62-68
• /
• 2012

Geometry of a screw fabricated by a turning process determined by the shape of the tool, feed rate of the tool and rotation speed of the spindle. Therefore, computing the exact geometry of the screw is very important to perform a simulation on machining or an evaluation of the workpice quality. In this paper, a new mathematical geometry model of the 3 dimensional screw is fabricated by turning process introduced for the exact geometry computation. Becasue model has a parametric formulation, it is easy to process for a CAD geometry or apply for a machining simulation. Also, it can be applied to process planning because it gives precise machined geometry on whole the 3 dimensional surface of the screw. This paper introduces a new parametric model of a geometry for screw fabricated by turning process. As an application, a simulation software for the 3 dimensional screw surface is developed and evaluated for several manufacturing parameters.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2005.11a
• /
• pp.318-322
• /
• 2005

In this study the regression rate of hybrid rocket fuel has been investigated by swirl injectors and helical grains. Tests have been done with two kinds of injector and helical grain. In this paper the swirl injector and helical grain were varied to find the optimal condition to obtain the max regression rate for a given operational condition.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.4
• /
• pp.375-382
• /
• 2015

The dome and neck part of a vessel is generally formed by a hot spinning process with a seamless tube. However, as studies on and design data from the hot spinning process are insufficient, this process has been performed based on trial and error and the experiences of field engineers. Changes in the inner diameter from the bottom to the top of the neck have occurred mainly because of the characteristics of the hot spinning process due to the high-speed rotation of the rollers. In this study, a theoretical and finite element analysis of the vessel is conducted with different material(Cr-13)-supplemented screw threads for tapping and to reduce shape errors. Based on the results, tne structural safety under the operating conditions is evaluated.

• The Journal of Korean Academy of Prosthodontics
• /
• v.48 no.3
• /
• pp.224-231
• /
• 2010

Purpose: This study was to investigate how the crestal module design could affect the level of marginal bone stress around dental implant. Materials and methods: A submerged implant of 4.1 mm in diameter and 10 mm in length was selected as baseline model (Dentis Co., Daegu,Korea).A total of 5 experimental implants of different crestal modules were designed (Type I model : with microthread at the cervical 3 mm, Type II model : the same thread pattern as Type I but with a trans-gingival module, Type III model: the same thread pattern as the control model but with a trans-gingival module, Type IV model: one piece system with concave transgingival part, Type V model: equipped with beveled platform). Stress analysis was conducted with the use of axisy mmetric finite element modeling scheme. A force of 100 N was applied at 30 degrees from the implant axis. Results: Stress analysis has shown no stress concentration around the marginal bone for the control model. As compared to the control model, the stress levels of 0.2 mm areas away from the recorded implant were slightly lower in Type I and Type IV models, but higher in Type II, Type III and Type V models. As compared to 15.09 MPa around for the control model, the stress levels were 14.78 MPa, 18.39 MPa, 21.11 MPa, 14.63 MPa, 17.88 MPa in the cases of Type I, II, III, IV and V models. Conclusion: From these results, the conclusion was drawn that the microthread and the concavity with either crestal or trans-gingival modules maybe used in standard size dental implants to reduce marginal bone stress.