• 한국의류산업학회지
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• 제20권4호
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• pp.422-428
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• 2018

In this study, we developed honeycomb pads using foam and polymer gel and verified the impact protection performance of pads for the development of a fall protection pants for elderly women aged 65 and over who have a high risk of fracture due to falls. The results are as follows; In the first experiment, the impact protection performance was evaluated for four honeycomb pad samples (CR foam, EPDM foam, hardness 15 polymer gel, and hardness 30 polymer gel) manufactured to a thickness of 5 mm using a single material. When the force of about 10757N was applied to the specimens, all four pads reduced the impact force to 3100N or less. Polymer gels showed better protection than foam materials. In the second experiment, the thickness of the protective pad was set to 8 mm in order to improve the shock absorbing performance of the protective pad. As a result of evaluating the impact protection performance of the foam single pad and foam gel composite pad, the impact absorbing performance of the foam single pad was better. Finally, four kinds of protection pads were made by assigning the foam single pad and the foam gel composite pad to pants type and underwear type respectively. The pad thickness of the main protection area was set to 8 mm to enhance the protection, and gradually decreased to 5mm and 3mm toward the edge to improve the appearance and fit.

• 한국정밀공학회지
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• 제33권1호
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• pp.11-16
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• 2016

Lithography techniques are generally used to manufacture nano-patterns on silicon, however, it is difficult to make a V-shaped pattern using these techniques. Although silicon is a brittle material, it can be treated as a ductile material if mechanically machined at extremely low force scale. The manufacturing technique of nano-patterns on single crystal silicon using a mechanical method was developed in this study. First, the linear pattern was machined on the silicon with increasing thrust force. Then, the correlation between measured cutting force and machined pattern was analyzed. Based on the analysis, the critical thrust force was quantitatively determined, and then the silicon was machined at a force lower than the critical thrust force. The machined pattern was observed using SEM and AFM to check for the occurrence of brittle fractures. Finally, the sharp V-shaped nano-pattern was manufactured on the single crystal silicon.

• Archives of Plastic Surgery
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• 제44권1호
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• pp.53-58
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• 2017

Background Adequate fixation of replanted digits is essential not only for short-term healing but for long-term function. Various bony fixation methods using Kirschner (K-) and intraosseous wire are available in replantation. We examined clinical and radiographic outcomes of fixation methods on bone union after digital replantation. Methods A single institutional retrospective review identified 992 patients who had undergone 1,247 successful replantations between July 2009 and September 2015. Exclusion criteria included amputations of the distal phalanx, comminuted fractures, and intra-articular fractures. Patients were classified according to 5 categories of fixation methods: single K-wire, double longitudinal K-wires, cross K-wires, wire with, and wire without K-wire support. Bone union was evaluated by 5-month postoperative X-ray and fixation outcomes were compared across the 5 groups. Results The exclusion criteria were applied, and 88 patients with 103 replanted digits remained for analysis. Single K-wire fixation was used in 40 digits, double longitudinal K-wires in 30, and cross fixation in 14. Wire with and without K-wire support was required in 15 and 4 digits. Nonunion was observed in 32 digits (31.1%), of which 13 required additional operations such as bone graft or corrective osteotomy. The highest percent of nonunion was observed after cross fixation (35.7%) and the lowest after wire alone (25.0%). Conclusions In this study, contrary to general knowledge, we found that single K-wire fixation was not associated with poorer outcomes. Successful bone union outcomes may be achieved by careful selection of bone fixation methods. This study provides useful information for planning bone fixation in digital replantation.

• 대한치과의사협회지
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• 제58권2호
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• pp.83-92
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• 2020

In the anterior maxillary area, dental implants for tooth replacement are challenging due to the need to satisfy high esthetic level as well as functionality. Immediate implant placement and provisionalization can dramatically reduce the edentulous period, and then fulfill patient's demand for esthetics. The aim of present case report is to demonstrate two cases that successfully restored single tooth with immediate implant placement and provisionalization in the anterior maxillary area. A 47 years old female was scheduled to replace her maxillary right central incisor due to crown-root fracture by trauma. Another 54-year-old female was planned to place dental implant following tooth extraction of maxillary right lateral incisor owing to continuous pus discharge despite repetitive treatments including apicoectomy. In these two cases, surgical and prosthetic procedures progressed in a similar way. After minimal flap elevation, atraumatic tooth extraction was performed. Implant was placed in proper 3-dimensional position and angulation with primary stability. Bone graft or guided bone regeneration for peri-implant bone defect was conducted simultaneously. Provisionalization without occlusal loading was carried out at the same day. Each definitive crown was delivered at 7 and 5 months after the surgery. Two cases have been followed uneventfully for 2 to 5 years of loading time. In conclusion, Immediate implant placement and provisionalization could lead to esthetic outcome for single tooth replacement with dental implant under proper case selection.

• 대한두개안면성형외과학회지
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• 제19권3호
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• pp.190-193
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• 2018

Background: This study was conducted to determine the effect of the distributional relationship between dental roots and the mandibular bone on single mandibular bone fractures, which are common craniofacial fractures. Methods: This was a retrospective, single-center study in Seoul, Korea. Patients with single mandibular fractures in the symphysis, parasymphysis, body, and angle area, with tooth structure involvement were included. The control group included patients with simple, bone-level lacerations without fractures. In total, 94 patients (72 males and 22 females) were included in the treatment group, and 125 (71 males and 54 females) were included in the control group. The height of the mandibular bone and the dental root were measured with panoramic radiography. The central incisor represented the symphysis area, the canine represented the parasymphysis area, the first molar represented the body area, and the second molar represented the angle area. Results: In the treatment group, symphysis fractures occurred in 16 patients (17%), parasymphysis fractures in 36 patients (38%), body fractures in 17 patients (18%), and angle fractures in 25 patients (27%). The ratios of the dental roots to the total height of the mandibular bone in the treatment group were 30.35%, 39.75%, 39.53%, and 36.27% for symphysis, parasymphysis, body, and angle areas, respectively, whereas in the control group, they were 27.73%, 39.70%, 36.76%, and 35.48%. The ratios of the treatment group were significantly higher than those of the control group. Conclusion: The results show that the higher ratio of the dental root to the height of the mandibular bone increases the fracture risk.

• Structural Engineering and Mechanics
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• 제68권4호
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• pp.497-505
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• 2018

Three points bending flexural test was modeled numerically to study the crack propagation in the pre-cracked beams. The pre-existing edge cracks in the beam models were considered to investigate the crack propagation and coalescence paths within the modeled samples. The effects of particle size on the single edge-notched round bar in bending test were considered too. The results show that Failure pattern is constant by increasing the ball diameter. Tensile cracks are dominant mode of failure. These crack initiates from notch tip, propagate parallel to loading axis and coalescence with upper model boundary. Number of cracks increase by decreasing the ball diameter. Also, tensile fracture toughness was decreased with increasing the particle size. In the present study, the influences of particles sizes on the cracks propagations and coalescences in the brittle materials such as rocks and concretes are numerically analyzed by using a three dimensional particle flow code (PFC3D). These analyses improve the understanding of the stability of rocks and concretes structures such as rock slopes, tunnel constructions and underground openings.

• 한국항공우주학회지
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• 제38권2호
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• pp.111-118
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• 2010

복합재료 구조물에서 조인트 부위는 매우 취약한 부분이다. 본 논문에서는 후판 알루미늄-알루미늄 조인트 및 복합재-알루미늄 조인트를 접착제로 접합하여 제작한 다음, 인장실험을 수행하여 파손형태를 고찰하였다. 또한, 항복 변형률에 기초한 수정 파손영역 이론을 제안하였으며, 파괴모드별 파손하중과 상호 비교하였다. 후판 알루미늄-알루미늄 조인트와 복합재-알루미늄 조인트의 파손강도를 동일한 파손기준값을 적용하여 예측하였으며, 제작된 14종류의 시편에서는 최대 19.3% 오차범위 내에서 파손강도를 예측할 수 있었다.

• Nuclear Engineering and Technology
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• 제52권7호
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• pp.1579-1586
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• 2020

Dissimilar metal joints (DMJs) are more common in the application of piping system of many industries. A 2- D and 3-D finite element analysis (FEA) is carried out on dissimilar metal Single Edged Notch Bending (DMSENB) specimens fabricated from ferritic steel, austenitic steel and Inconel - 182 alloy to study the behavior of DMJs with constraints by using linear elastic fracture mechanics (LEFM) principles. Studies on DMSENB specimens are conducted with respect to (i) dissimilar metal joint width (DMJW) (geometrical constraints) (5 mm, 10 mm, 20 mm, 30 mm and 50 mm) (ii) strength mismatch (material constraints) and (iii) crack lengths (16 mm, 20 mm and 24 mm) to study the DMJ behavior. From the FEA investigation, it is observed that (i) SIF increases with increase of crack length and DMJWs (ii) significant constraint effect (geometry, crack tip and strength mismatch) is observed for DMJWs of 5 mm and 10 mm (iii) stress distribution at the interfaces of DMSENB specimen exhibits clear indication of strength mismatch (iv) 3-D FEA yields realistic behavior (v) constraint effect is found to be significant if DMJW is less than 20 mm and the ratio of specimen length to the DMJW is greater than 7.4.

• Advances in aircraft and spacecraft science
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• 제5권5호
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• pp.595-613
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• 2018

The objective of our study is to analyze the behavior of bonded, riveted and hybrid (bonded / riveted) steel / steel assemblies by tensile tests and to show the advantage of a hybrid assembly over other processes. the finite element method with the ABAQUS numerical code was used to model the fracture behavior of the different assemblies. Cohesive zone models (CZM) have been adopted to model crack propagation in bonded joints using a bilinear tensile separation law implemented in the ABAQUS finite element code. The riveted assemblies were modeled with the XFEM damage method identified in this ABAQUS numerical code. Both CZM and XFEM methods are combined to model hybrid assemblies. The results are consistent with the experimental results and make it possible to guarantee the validity of the applied numerical model. The use of a hybrid assembly shows a high resistance compared to other conventional methods, where the number of rivets has been highlighted. The use of the hybrid assembly improves mechanical strength and increases service life compared to a single lap joint and a riveted joint.

• Composites Research
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• 제23권4호
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• pp.21-27
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• 2010

대부분의 구조물 파괴는 피로에 의해서 발생한다. 따라서 지금까지 모드 혼합비가 피로 특성에 어떤 영향을 미치는지에 대한 수많은 연구가 수행되어 오고 있다. 하지만 대부분의 연구가 금속/금속 계면이나 복합재료 층간 분리에 관한 연구이다. 따라서 본 연구에서는 이종재료인 복합재료/금속 계면의 피로 특성에 대한 기초 자료를 얻고자 하였다. 이를 위하여 복합재료와 탄소강을 동시 경화법을 이용하여 접합한 SLB(single leg bending) 시편을 이용하여 피로 실험을 수행하였다. 특히, 피로 특성에 모드 혼합비$(G_{II}/G_T)$가 어떠한 영향을 미치는지에 대해 알아보고자 하였다. 전체적으로 모드 II 하중 성분 이 많을수록 균열진전속도가 빨라진다는 결과를 얻었다.