• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.626-629
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• 2004

Recently, the self-healing technique is being investigated to repair the damaged polymeric composites by the use of microcapsules with the healing agent. This technique can obtains both the damage detection and the damage repair simultaneously over the converntional repairing techniques. In this study, the effects of the catalyst ratio to the healing agent and thermal characteristics to the mixtures of healing agent are investigated through single lap shear tests and DSC. The Healing agents such as DCPD, ENB, and their mixtures are considered and Grubb's catalyst is used as a catalst.

• The Journal of Advanced Prosthodontics
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• 제12권5호
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• pp.273-282
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• 2020

PURPOSE. To assess shear bond strengths (SBS) of resin composites on aged and non-aged prosthetic materials with various surface treatments. MATERIALS AND METHODS. Cerasmart (CE), Vita Enamic (VE), Vita Mark II (VM), and IPS e.max CAD (EC) blocks were sliced, and rectangular-shaped specimens (14 × 12 × 1.5 mm; N = 352) were obtained. Half of the specimens were aged (5000 thermal cycles) for each material. Non-aged and aged specimens were divided into 4 groups according to the surface treatments (control, air abrasion, etching, and laser irradiation; n = 11) and processed for scanning electron microscopy (SEM). The repair procedure was performed after the surface treatments. SBS values and failure types were determined. Obtained data were statistically analyzed (P≤.05). RESULTS. The material type, surface treatment type, and their interactions were found significant with regard to SBS (P<.001). Aging also had a significant effect on prosthetic material-resin composite bonding (P<.001). SBS values of non-aged specimens ranged from 12.16 to 17.91 MPa, while SBS values of aged specimens ranged from 9.46 to 15.61 MPa. Non-aged VM in combination with acid etching presented the highest score while the control group of aged CE showed the lowest. CONCLUSION. Etching was more effective in achieving durable SBS for VM and EC. Laser irradiation could be considered as an alternative surface treatment method to air abrasion for all tested materials. Aging had significant effect on SBS values generated between tested materials and resin composite.

• Structural Engineering and Mechanics
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• 제82권1호
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• pp.121-131
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• 2022

The main goal of this study is to prepare a program for analyzing High Strength Steel Fibrous Reinforced Concrete (HSSFRC) slabs and predict the response and strength of the slab instead of preparing a prototype and testing it in the laboratory. For this purpose, new equations are proposed to represent the material properties of High Strength Steel Fibrous Reinforced Concrete. The proposed equations obtained from performing regression analysis on many experimental results using statistical programs. The finite element method is adopted for non-linear analysis of the slabs. The eight-node "Serendipity element" (3 DoF) is chosen to represent the concrete. The layered approach is adopted for concrete elements and the steel reinforcement is represented by a smeared layer. The compression properties of the concrete are modeled by a work hardening plasticity approach and the yield condition is determined depending on the first two stress invariants. A tensile strength criterion is adopted in order to estimate the cracks propagation. many experimental results for testing slabs are compared with the numerical results of the present study and a good agreement is achieved regarding load-deflection curves and crack pattern. The response of the load deflection curve is slightly stiff at the beginning because the creep effect is not considered in this study and for assuming perfect bond between the steel reinforcement and the concrete, however, a great agreement is achieved between the ultimate load from the present study and experimental results. For the models of the tension stiffening and cracked shear modulus, the value of Bg and Bt (Where Bg and Bt are the curvature factor for the cracked shear modulus and tension stiffening models respectively) equal to 0.005 give good results compared with experimental result.

• Structural Engineering and Mechanics
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• 제85권3호
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• pp.337-351
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• 2023

In this paper, the shear behavior of soft filling in rectangular-hollow concrete specimens was simulated using the 2D particle flow code (PFC2D). The laboratory-measured properties were used to calibrate some PFC2D micro-properties for modeling the behavior of geo-materials. The dimensions of prepared and modeled samples were 100 mm×100 mm. Some disc type narrow bands were removed from the central part of the model and different lengths of bridge areas (i.e., the distance between internal tips of two joints) with lengths of 30 mm, 50 mm, and 70 mm were produced. Then, the middle of the rectangular hollow was filled with cement material. Three filling sizes with dimensions of 5 mm×5 mm, 10 mm×5 mm, and 15 mm×5 mm were provided for different modeled samples. The parallel bond model was used to calibrate and re-produce these modeled specimens. Therefore, totally, 9 different types of samples were designed for the shear tests in PFC2D. The shear load was gradually applied to the model under a constant loading condition of 3 MPa (σc/3). The loading was continued till shear failure occur in the modeled concrete specimens. It has been shown that both tensile and shear cracks may occur in the fillings. The shear cracks mainly initiated from the crack (joint) tips and coalesced with another one. The shear displacements and shear strengths were both increased as the filling dimensions increased (for the case of a bridge area with a particular fixed length).

• 한국구조물진단유지관리공학회 논문집
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• 제10권1호
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• pp.197-204
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• 2006

본 연구는 전단연결재 없이 부착면적을 확대한 요철 단면SC보의 휨 거동을 실험하여 이론 해석 및 상용 구조해석 프로그림인 ANSYS해석 결과와 비교 강판과 콘크리트의 부착성능과 초기강성 등을 분석하였고 이를 통해 효율적인 SC보의 실용화를 위한 기초 연구 자료를 제공하고자 한다. 실험결과는 이론값의 88%-98% 정도의 내력을 발휘한 것으로 나타났으며, 합성율은 분석결과 30-70%로 완전합성에 이르지 못한 것으로 나타나 완전합성을 발휘할 수 있는 접합방법의 필요성을 확인할 수 있었다.

• 대한치과교정학회지
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• 제42권1호
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• pp.32-38
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• 2012

Objective: The aim of this study was to compare the effects of different enamel conditioning techniques for bracket bonding. Methods: Ninety-one human premolars were randomly divided in six groups of 15 specimens each. The enamel surfaces of the teeth were etched with 35% orthophosphoric acid in Group 1, with a self-etching primer in Group 2, sandblasted in Group 3, sandblasted and etched with 35% orthophosphoric acid in Group 4, conditioned by Er:YAG laser in Group 5 and conditioned by Er:YAG laser and etched with 35% phosphoric acid gel respectively in Group 6. After enamel conditioning procedures, brackets were bonded and shear bonding test was performed. After debonding, adhesive remnant index scores were calculated for all groups. One tooth from each group were inspected by scanning electron microscope for evaluating the enamel surface characteristics. Results: The laser and acid etched group showed the highest mean shear bond strength (SBS) value ($13.61{\pm}1.14$ MPa) while sandblasted group yielded the lowest value ($3.12{\pm}0.61$ MPa). Conclusions: Although the SBS values were higher, the teeth in laser conditioned groups were highly damaged. Therefore, acid etching and self-etching techniques were found to be safer for orthodontic bracket bonding. Sandblasting method was found to generate inadequate bonding strength.

• 한국도로학회논문집
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• 제16권4호
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• pp.21-33
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• 2014

PURPOSES: The purpose of this study was to break away from the workforce method using cold-mix asphalt mixtures and has a constant quality and has develop repair materials of pre-production asphalt-precast types. METHODS: The selection of the repair material was determined as the results obtained through physical properties of materials and the field applicability. In case of repair materials, values obtained through Marshall stability test & the dynamic stability test & retained stability test as well as the site conditions was considered. In case of adhesive, test results were obtained through examination of the bond strength(tensile, shear) and the field applicability of the adhesive was examined through combined specimens to simulate field applications. RESULTS : According to the results of laboratory tests, in the case of repair materials, Marshall stability and dynamic stability, retained stability of cold-mix reaction type asphalt mixture is the highest. In the case of adhesive, two-component epoxy-urea has a very high bonding strength(tensile, shear) was most excellent. According to the results of field tests, when epoxy-urea was excellent workability. Also, the repair body through actual mock-up test did not occur large deformation and fracture after 12 months. CONCLUSIONS : A suitable repair material is cold-mix reaction type mixture of asphalt-precast, a suitable adhesive is a two-component epoxy-urea.

• 구강회복응용과학지
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• 제36권1호
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• pp.1-11
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• 2020

목적: 본 연구의 목적은 polyetherketoneketone (PEKK)의 표면 처리 방식에 따른 세가지 종류의 임시 보철물 제작용 레진과의 전단결합강도를 비교하는 것이다. 연구 재료 및 방법: 60개의 PEKK 시편을 110 ㎛의 산화알루미늄 입자(Cobra, Renfert GmbH, Hilzinge, Germany)로 분사 처리하고 시편에 Visio.link (Bredent, Senden, Germany)를 도포하지 않은 군(U)과 도포한 군(P)으로 30개씩 나누었다. 이후 한 변이 3.2 mm인 정사각형의 모양으로 polymethylmethacrylate (PMMA), polyethylmethacrylate (PEMA), bis-acryl composite resin을 PEKK에 각각 20개씩 접착하여 총 6개의 군(UM, UE, UC, PM, PE, PC)으로 분류하였다. 완성된 시편은 37℃의 증류수에 24시간 보관하였다. 만능재료시험기의 크로스헤드의 속도를 2 mm/min로 설정하고 전단결합강도를 측정하였다. 각 군간의 전단결합강도 값의 유의차를 확인하기 위하여 일원배치분산분석(one-way ANOVA)과 Tukey HSD test를 시행하였다. 결과:UM, UE군은 UC군과 유의한 전단결합강도의 차이를 나타내었다(P < 0.05). PC군이 UC군보다 높은 전단결합강도를 나타내었다(P < 0.05). 결론: 임상적으로 PEKK에 PMMA와 PEMA를 접착하는 경우에 Visio.link의 적용이 필요하지 않으나, bis-acryl composite resin을 접착하는 경우에는 Visio.link의 적용이 추천된다.

• Journal of the Korean Wood Science and Technology
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• 제11권1호
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• pp.12-17
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• 1983

본(本) 실험(實驗)에서는 합판(合板) 및 파티클보드 공장(工場)에서 폐기물(廢棄物)로 버려지고 있는 Douglas-fir 수피분말(樹皮粉末)과 particle-board sander dust(PSD)를 요소수지접착제(尿素樹脂接着劑)의 증량재료(增量材料)로 이용(利用)하여 제조(製造)한 합판(合板)과 밀가루를 증량재료(增量材料)로 이용(利用)하여 제조(製造)한 합판(合板)과의 상태(常態) 및 내수접착력(耐水接着力)을 비교(比較)하였다. 또한 접착제(接着劑)의 증량비율(增量比率)을 수지액(樹脂液)의 중량(重量)에 대(對)하여 5, 10, 20, 30% 순(順)으로 증가(增加)시켜서 각(各) 증량재료(增量材料)의 적정증량조건(適定增量條件)을 찾고자 하였다. 실험(實驗) 결과(結果), 실험(實驗)에 이용(利用)된 증량재료(增量材料) 모두가 증량비율(增量比率) 5 %일 때 상태접착력(常態接着力)이 가장 높았으며, 내수접착력(耐水接着力)은 무증량(無增量)과 증량비율(增量比率) 5%일 때 가장 높았다. Douglas-fir 수피분말(樹皮粉末)은 증량비율(增量比率) 10%까지, PSD는 증량비율(增量比率) 20%까지 밀가루와 비슷한 상태(常態) 및 내수접착력(耐水接着力)을 보였으나 증량비율(增量比率) 30%에서는 밀가루의 상태(常態) 및 내수접착력(耐水接着力)이 높았다. Douglas-fir 수피분말(樹皮粉末)과 PSD는 도포작업성(塗布作業性)을 개선(改善)하고 접착시(接着尸)의 두께를 가능한 얇게하여 접착력(接着力)을 높이기 위해서는 매우 고운 분말(粉末)로 만들어져야 하다고 생각된다.(325 mesh screen 통과(通過)) 그러나, 본(本) 실험(實驗)에서는 100 mesh screen을 통과(通過)하는 것을 사용(使用)하였다.

• Structural Engineering and Mechanics
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• 제18권5호
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• pp.645-669
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• 2004

In seismic analysis of moment-resisting frames, beam-column connections are often modeled with rigid joint zones. However, it has been demonstrated that, in ductile reinforced concrete (RC) moment-resisting frames designed based on current codes (to say nothing of older non-ductile frames), the joint zones are in fact not rigid, but rather undergo significant shear deformations that contribute greatly to global drift. Therefore, the "rigid joint" assumption may result in misinterpretation of the global performance characteristics of frames and could consequently lead to miscalculation of strength and ductility demands on constituent frame members. The primary objective of this paper is to propose a rational method for estimating the hysteretic joint shear behavior of RC connections and for incorporating this behavior into frame analysis. The authors tested four RC edge beam-column-slab connection subassemblies subjected to earthquake-type lateral loading; hysteretic joint shear behavior is investigated based on these tests and other laboratory tests reported in the literature. An analytical scheme employing the modified compression field theory (MCFT) is developed to approximate joint shear stress vs. joint shear strain response. A connection model capable of explicitly considering hysteretic joint shear behavior is then formulated for nonlinear structural analysis. In the model, a joint is represented by rigid elements located along the joint edges and nonlinear rotational springs embedded in one of the four hinges linking adjacent rigid elements. The connection model is able to well represent the experimental hysteretic joint shear behavior and overall load-displacement response of connection subassemblies.