• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.2
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• pp.121-143
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• 2010

To investigate the effect of implant types and bone resorption on the fracture characteristics. 4 types of Osstem$^{(R)}$Implant were chosen and classified into external parallel, internal parallel, external taper, internal taper groups. Finite elements analysis was conducted with ANSYS Multi Physics software. Fatigue fracture test was performed by connecting the mold to the dynamic load fatigue testing machine with maximum load of 600N and minimum load of 60N. The entire fatigue test was performed with frequency of 14Hz and fractured specimens were observed with Hitachi S-3000 H scanning electron microscope. The results were as follows: 1. In the fatigue test of 2 mm exposed implants group, Tapered type and external connected type had higher fatigue life. 2. In the fatigue test of 4 mm exposed implants group, Parallel type and external connected types had higher fatigue life. 3. The fracture patterns of all 4 mm exposed implant system appeared transversely near the dead space of the fixture. With a exposing level of 2 mm, all internally connected implant systems were fractured transversely at the platform of fixture facing the abutment. but externally connected ones were fractured at the fillet of abutment body and hexa of fixture or near the dead space of the fixture. 4. Many fatigue striations were observed near the crack initiation and propagation sites. The cleavage with facet or dimple fractures appeared at the final fracture sites. 5. Effective stress of buccal site with compressive stress is higher than that of lingual site with tensile stress, and effective stress acting on the fixture is higher than that of the abutment screw. Also, maximum effective stress acting on the parallel type fixtures is higher. It is careful to use the internal type implant system in posterior area.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.9
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• pp.1043-1048
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• 2014

As micro screws feature reduced screw lengths and pitches, the resulting clamping force diminishes because of the reduced length of the actual joints. The elements of the clamping force are material, geometry, and friction. We studied the shrinking size of the screw and the methods to improve the clamping force by changing the material. We developed a micro screw using SWCH18A and SUS XM7 materials, and obtained the precision and thickness of the pitch through three-dimensional measurement. We also measured the external resistance of the micro screw by applying the Vicker's hardness test and conducted a break surface analysis using a break torque test and SEM for obtaining the break characteristics.

• Journal of Korean Society of Steel Construction
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• v.12 no.3 s.46
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• pp.259-268
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• 2000

In the friction-type joints the external applied load is transmitted by frictional force acting on the contact area of the plates fastened by the high strength bolts. This frictional force is proportional to the product of the bolt clamping force and slip coefficient of the faying surface. But the bolt clamping force is dependent on many factors when the turn-of-nut method is used. The preserved thread length and length-to-diameter ratios are one of the major factors governing the bolt clamping force. This paper presents the correct method of high strength bolt tightening through the experiment on the mechanical properties on sets of high strength bolts in accordance with preserved thread length and length-to-diameter ratios.

• The Journal of Korean Academy of Prosthodontics
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• v.49 no.4
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• pp.316-323
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• 2011

Purpose: The purpose of this study was to investigate the effect of different thread designs on the marginal bone stresses around dental implant. Materials and methods: Standard ITI implant(ITI Dental Implant System; Straumann AG, Waldenburg, Switzerland), 4.1 mm in diameter and 10 mm in length, was selected as control. Test implants of four different thread patterns were created based on control implant, i.e. maintaining all geometrical design of control implant except thread pattern. Four thread designs used in test implants include (1) small V-shape screw (model A), (2) large V-shape screw (model B), (3) buttress screw (model C), and (4) trapezoid screw (model D). Surface area for unit length of implant was 14.4 $mm^2$ (control), 21.7 (small V-shape screw), 20.6 (large V-shape screw), 17.0 (buttress screw) and 28.7 $mm^2$ (trapezoid screw). Finite element models of implant/bone complex were created using an axisymmetric scheme with the use of NISA II/DISPLAY III (Engineering Mechanics Research Corporation, Troy, MI, USA). A load of 100 N applied to the central node on the crown top either in parallel direction or at 30 degree to the implant axis (in order to apply non-axial load to the implant NKTP type 34 element was employed). Quantification and comparison of the peak stress in the marginal bone of each implant model was made using a series of regression analyses based on the stress data calculated at the 5 reference points which were set at 0.2, 0.4, 0.6, 0.8 and 1.0 mm from implant wall on the marginal bone surface. Results: Results showed that although severe stress concentration on the marginal bone cannot be avoided a substantial reduction in the peak stress is achievable using different thread design. The peak marginal bone stresses under vertical loading condition were 7.84, 6.45, 5.96, 6.85, 5.39 MPa for control and model A, B, C and D, respectively. And 29.18, 26.45, 25.12, 27.37, 23.58 MPa when subject to inclined loading. Conclusion: It was concluded that the thread design is an important influential factor to the marginal bone stresses.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.232-236
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• 2006

하이브리드 로켓에서 그레인 전체 부분에서 고른 연소율 향상을 이룰 수 있는 방법으로 스월 유동과 나사산 그레인을 동시에 적용하여 실험을 실시하였다. 그 결과 입구부분과 연료 후반부에 집중된 연소현상을 확인하였다. 스월 유동은 스월 유동의 종류에 상관없이 일정한 감소율을 나타낸다. 그리고 연소율 향상은 연료 벽면에서의 회전 유동 강도에 비례한다고 가정 할 수 있다. 따라서 입구부분의 집중된 연소현상을 해소하고 일정한 연소율 향상을 이룰 수 있는 스월 유동 조건에 대해 연구하였다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.341-344
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• 2006

Finite element analysis and verification experiments were performed in order to find cause of defects such as folding and improper radius around the root area of the thread rolled stud bolts. Thread rolling experiments under several conditions were also carried out to understand the effect of process parameters, such as the rotation speed of the dies and the hardness of the work pieces, on the product quality. Folding defects at the top of thread are attributed to the higher hardness of the work piece and higher rotation speed of the rolling die. It was also found that the radius of screw mainly determined by the radius of the die.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.794-799
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• 2001

For the development of an electric molding machine with low energy, high performance, and high reliability, characterization, finite element analysis and fatigue strength analyses were performed. Strain was measured by strain gages bonded on electric molding machine and compared with stress analysis results using I-DEAS. The analyses showed good agreement with test results. By means of the comparison, we could draw an adequate boundary condition for the stress analysis of the components of electric molding machine. Additionally, we could verify the load distribution mechanism among the parts. The life prediction results for tie bar and thread zone showed infinite life.

• Journal of the Korean Arthroscopy Society
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• v.13 no.3
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• pp.280-284
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• 2009

Purpose: The authors introduce a new technique of arthroscopic reduction of subluxed medial meniscus using suture anchor for the restoration of hoop stress. Operative Technique: Anterolateral, anteromedial, and medial midpatellar arthroscopic portal are used. Arthroscope was inserted through anterolateral portal. Through the scope, we confirmed subluxation of medial meniscus. Transection of menisci including radial and root tear were excluded. We released the anterior horn of medial meniscus through anteromedial and burred the future insertion site of suture anchor. After inserting suture anchor through medial midpatellar portal, we used 90 degree suture hook and no.2 Nylon to retrieve the suture of inserted anchor. We tied the suture by sliding knot-tying method. Weight bearing was limited for 6 weeks postoperatively. Conclusion: Arthroscopic retightening of medial meniscus is less invasive, conserving and progressed method for subluxed meniscus.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.8
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• pp.917-923
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• 2014

Subminiature joining bolts are required for the electronic parts of gadgets such as mobile phones and watch phones. During the miniaturization of bolt heads, it is difficult to obtain sufficient joining force owing to the risk of shear fracture of the bolt head or severe plastic deformation on the bit region. In this study, the maximum joining torque for the bit depth was predicted using finite element analysis. A shear fracture test was conducted on a wire used in bolt forming. The results of this test were subjected to finite element analysis and a fracture criterion was obtained by comparing the experimental and analysis results. The shear fracture of the bolt head during joining was predicted based on the obtained criterion. Furthermore, the maximum joining torque was predicted for various bit depths. Fracture on the boundary between the bolt head and thread was found to occur in lower joining torque as bit depth increases.

• Journal of Dental Rehabilitation and Applied Science
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• v.24 no.3
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• pp.269-281
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• 2008

Fatigue or overload can result in mechanical problems of implant components. The mechanical strength in the implant system is dependent on several factors, such as screw and fixture diameters, material, and design of the fixture-abutment connection and abutment. In these factors, the last rules the strength and stability of the fixture-abutment assembly. There have been some previous reports on the mechanical strength of the fixture-abutment assembly with the compressive bending test or short-term cyclic loading test. However, it is restrictive to predict the long-term stability of the implant system with them. The purpose of this study was to evaluate the influence of the design of the fixture-abutment connection and abutment on the mechanical strength and failure mode by conducting the endurance limit test as well as the compressive bending strength test. Tests were performed according to a specified test(ISO/FDIS 14801) in 4 fixture-abutment assemblies of the Osstem implant system: an external butt joint with Cemented abutment (group BJT), an external butt joint with Safe abutment (group BJS), an internal conical joint with Solid abutment (group CJO), and an internal conical joint with ComOcta abutment (group CJT). The following conclusions were drawn within the limitation of this study. Compressive bending strengths were decreased in order of group BJS(1392.0N), group CJO(1261.8N), group BJT(1153.2N), and group CJT(1110.2N). There were no significant differences in compressive bending strengths between group BJT and group CJT(P>.05). Endurance limits were decreased in order of group CJO(600N), group CJT(453N), group BJS(360N), and group BJT(300N). 3. Compressive bending strengths were influenced by the connection and abutment design of the implant system, however endurance limits were affected more considerably by the connection design.