• Advances in concrete construction
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• 제2권1호
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• pp.13-27
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• 2014

The principal objective of this study is to deepen the characterization studies already led on sand concretes in previous works. Indeed, it consists in studying the effect of the sand type on the main properties of sand concrete: fracture and mechanical properties. We particularly insist on the determination of the fracture characteristics of this material which apparently have not been studied. To carry out this study, four different types of sand have been used: dune sand (DS), river sand (RS), crushed sand (CS) and river-dune sand (RDS). These sands differ in mineralogical nature, grain shape, angularity, particle size, proportion of fine elements, etc. The obtained results show that the particle size distribution of sand has marked its influence in all the studied properties of sand concrete since the sand having the highest diameter and the best particle size distribution has given the best fracture and mechanical properties. The grain shape, the angularity and the nature of sand have also marked their influence: thanks to its angularity and its limestone nature, crushed sand yielded good results compared to river and dune sands which are characterized by rounded shape and siliceous nature. Finally, it should further be noted that the sand concrete presents values of fracture and mechanical properties slightly lower than those of ordinary concrete. Compared to mortar, although the mechanical strength is lower, the fracture parameters are almost comparable. In all cases, the sand grains are debonded from the paste cement during the fracture which means that the crack goes through the paste-aggregate interface.

• 접착 및 계면
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• 제11권1호
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• pp.26-34
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• 2010

가열에 의해 해체가 가능한 열적특성을 갖는 폴리우레탄 접착제를 합성하였으며 열팽창비드를 혼합하여 해체성 접착제를 제조하였다. Dynamic mechanical thermal analyzer (DMA)를 사용하여 폴리우레탄의 열적특성을 확인하였고 접착강도와 열팽창비드의 함량, 가열 trigger의 종류와 처리조건에 따른 해체특성을 연구하였다. 열풍과 microwave 처리에 의해서 해체성 폴리우레탄 접착제의 부피팽창에 따른 접착된 시편의 해체가 가능하였으며, 열팽창비드의 함량이 증가될수록 접착된 피착재가 더 쉽게 분리되었다. 해체성 접착제에서 접착력과 해체특성 모두를 만족시킬 수 있는 가장 적합한 열팽창비드 사용량은 40%이였으며, 가열 trigger로 열풍을 사용한 경우에는 $160^{\circ}C$, 30 min의 조건에서, 가열 trigger로 microwave를 사용한 경우에는 조사시간 4 min의 조건에서 접착되어 있는 피착재가 완전히 해체되었다.

• The Journal of Advanced Prosthodontics
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• 제9권2호
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• pp.110-117
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• 2017

PURPOSE. This laboratory study assessed the effect of different dentin cleaning procedures on shear bond strength of resin cements for recementing prosthesis. MATERIALS AND METHODS. A $4{\times}4$ flat surface was prepared on the labial surface of 52 maxillary central incisors. Metal frames ($4{\times}4{\times}1.5mm$) were cast with nickel-chromium alloy. All specimens were randomly divided into 2 groups to be cemented with either Panavia F2.0 (P) or RelyX Ultimate (U) cement. The initial shear bond strength was recorded by Universal Testing Machine at a crosshead speed of 0.5 mm/min. Debonded specimens were randomly allocated into 2 subgroups (n = 13) according to the dentin cleaning procedures for recementation. The residual cement on bonded dentin surfaces was eliminated with either pumice slurry (p) or tungsten carbide bur (c). The restorations were rebonded with the same cement and were subjected to shear test. Data failed the normality test (P < .05), thus were analyzed with Mann Whitney U-test, Wilcoxon signed rank test, and two-way ANOVA after logarithmic transformation (${\alpha}=.05$). RESULTS. The initial shear bond strength of group P was significantly higher than group U (P = .001). Pc and Uc groups presented higher bond strength after recementation compared to the initial bond strength. However, it was significant only in Pc group (P = .034). CONCLUSION. The specimens recemented with Panavia F2.0 provided higher bond strength than RelyX Ultimate cement. Moreover, a tungsten carbide bur was a more efficient method in removing the residual resin cement and increased the bond strength of Panavia F2.0 cement after recementation.

• 콘크리트학회논문집
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• 제18권1호
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• pp.73-82
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• 2006

최근까지의 거푸집 공법은 거푸집의 설치 및 탈형공정에 따른 공기연장, 인건비 상승에 따른 추가적인 비용소모, 거푸집 탈형후 발생되는 건설 폐자재로 인한 환경문제 유발 등의 직 간접적인 문제를 발생시켜 왔다. 따라서 본 연구에서는 이와 같은 문제점을 해결하고자 스테인레스 강섬유를 이용한 고성능 영구거푸집 공법에 대한 재료 및 구조적 거동특성을 분석하였다. 재료적 거동특성의 경우, 고성능 영구거푸집의 휨 거동에 있어 안정적인 연성거동 특성을 나타내었으며 후타설 콘크리트와의 부착성능도 우수한 것으로 나타났다. 구조적 거동특성의 경우, 고성능 영구거푸집의 압축단 및 인장단 거동특성이 분석되었으며 실험결과, 추가적인 보강성능 이외에 충분한 구조거동 특성을 발휘한 것으로 분석되었다.

• 대한기계학회논문집A
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• 제21권11호
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• pp.1896-1911
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• 1997

Effects of fiber-matrix interphases on the micro-and macro-mechanical behaviors of unidirectionally fiber-reinforced composites subjected to transverse shear loading at remote distance have been studied. The interphases between fibers and matrix have been modeled by the spring-layer which accounts for continuity of tractions, but allows radial and circumferential displacement jumps across the interphase that are linearly related to the normal and tangential tractions. Numerical calculations for basic cells of the composites have been carried out using the boundary element method. For an undamaged composite the micro-level stresses at the matrix side of the interphase and effective shear stiffness have been computed as functions of fiber volume ratio $V_f$ and interphase stiffness k. Results are presented for various interphase stiffnesses from the perfect bonding to the case of total debonding. For a square array composite the results show that for a high interphase stiffness k>10, an increase of $V_f$ increases the effective transverse shear modulus G over bar of the composite. For a relatively low interphase stiffness k<1, it is shwon that an increase of $V_f$ slightly decreases the effective transverse shear modulus. For the perfect bonding case, G over bar for a hexagonal array composite is slightly larger than that for a square array composite. Also for a damaged composite partially debonded at the interphase, local stress fields and effective shear modulus are calculated and a decrease in G over bar has been observed.

• 대한치과교정학회지
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• 제46권6호
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• pp.364-371
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• 2016

Objective: With the introduction of third-generation light-emitting diodes (LEDs) in dental practice, it is necessary to compare their bracket-bonding effects, safety, and efficacy with those of the second-generation units. Methods: In this study, 80 extracted human premolars were randomly divided into eight groups of 10 samples each. Metal or polycrystalline ceramic brackets were bonded on the teeth using second- or third-generation LED light-curing units (LCUs), according to the manufacturers' instructions. The shear bond strengths were measured using the universal testing machine, and the adhesive remnant index (ARI) was scored by assessing the residual resin on the surfaces of debonded teeth using a scanning electron microscope. In addition, curing times were also measured. Results: The shear bond strengths in all experimental groups were higher than the acceptable clinical shear bond strengths, regardless of the curing unit used. In both LED LCU groups, all ceramic bracket groups showed significantly higher shear bond strengths than did the metal bracket groups except the plasma emulation group which showed no significant difference. When comparing units within the same bracket type, no differences in shear bond strength were observed between the second- and third-generation unit groups. Additionally, no significant differences were observed among the groups for the ARI. Conclusions: The bracket-bonding effects and ARIs of second- and third-generation LED LCUs showed few differences, and most were without statistical significance; however, the curing time was shorter for the second-generation unit.

• 마이크로전자및패키징학회지
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• 제16권4호
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• pp.23-28
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• 2009

Si 기판의 캐비티 형성이 불필요한 웨이퍼-레벨 MEMS capping 공정을 연구하였다. 4인치 Si 웨이퍼에 Ni 캡을 전기도금으로 형성하고 Ni 캡 rim을 Si 하부기판의 Cu rim에 에폭시 본딩한 후, SnBi debonding 층을 이용하여 상부기판을 Ni 캡 구조물로부터 debonding 하였다. 진공증착법으로 형성한 SnBi debonding 층은 Bi와 Sn 사이의 심한 증기압 차이에 의해 Bi/Sn의 2층 구조로 이루어져 있었다. SnBi 증착 층을 $150^{\circ}C$에서 15초 이상 유지시에는 Sn과 Bi 사이의 상호 확산에 의해 eutectic 상과 Bi-rich $\beta$상으로 이루어진 SnBi 합금이 형성되었다. $150^{\circ}C$에서 유지시 SnBi의 용융에 의해 Si 기판과 Ni 캡 구조물 사이의 debonding이 가능하였다.

• 대한치과보철학회지
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• 제27권2호
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• pp.101-121
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• 1989

This study investigated the effects of Silicoating procedure on the tensile bond strength of resin-bonded prostheses. The Rexillium III specimens were treated with electrochemical etching and Silicoating procedure, followed by thermocycling and the NNB, Pors-on 4, and Degudent-U specimens were treated with Silicoating procedure. The specimens were debonded in tension with a Tensilon machine. Also, all specimens were observed with SEM, concentration of Si elements was analyzed with EPMA, and the mode of failure was recorded. The results of this study were obtained as follows: 1. In the Rexillium III specimens, the tensile bond strength of the Silicoated specimens was higher than that of the electrochemically etched specimens, and significant differences were observed (P<0.05). 2. The tensile bond strength of electrochemically etched Rexillium III specimens, significant differences were observed between the thermocycled and nonthermocycled specimens (P<0.05), but no significant differences were observed in the Silicoated specimens (P>0.05). 3. The tensile bond strength of the Silicoated specimens decreased NNB, Pors-on 4, Rexillium III, and Degudent-U in that order named. 4. Unlike the electrochemically etched specimens, the Silicoated specimens showed gap-free metal-resin interfaces with SEM. 5. Compared to the electrochemically etched specimens, the Silicoated specimens showed higher concentration of Si elements at the metal-resin interfaces and resin cement. 6. Photographic evaluation (X2) of the fractured sites revealed mainly cohesive failures with the Silicoated specimens, and adhesive failures with the electrochemically etched specimens.

• Composites Research
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• 제16권2호
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• pp.68-73
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• 2003

Fragmentation 시험법과 전기저항 측정을 통하여 탄소 및 SiC 섬유강화 에폭시 복합재료의 계면물성과 섬유파단에 대한 전기적 감지능을 연구하였다. 섬유 함침 각이 증가함에 따라서 계면전단강도는 감소하였고, 섬유파단에 의한 전기저항도 값이 무한대로 증가하는 시간은 길어졌다. 높은 함침 각에서 전기저항도의 초기 기울기는 급격히 증가한 반면. 낮은 각에서는 점차적으로 증가하였다. 또한 낮은 함침각의 두 섬유 모두에서 stress whitening pattern을 뚜렷하게 관찰할 수 있었지만, 높은 함침 각에서는 그렇지 못했다. 섬유 함침 각이 감소함에 따라서 섬유 파단 간격과 debonding된 길이는 두 섬유 모두에서 증가하였다. 본 연구에서 사용한 electro-micromechanical 시험법은 전도성 섬유강화 복합재료의 섬유 함침 각에 따른 계면 감지능 측정을 위해서 비파괴적 평가방법으로 실행 가능하였다.

• The Journal of Advanced Prosthodontics
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• 제12권4호
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• pp.197-203
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• 2020

PURPOSE. The aim of this study was to evaluate the effect of multiple firings on the bond strength between yttriatetragonal zirconia polycrystals (Y-TZP) and 2 types of resin cements. MATERIALS AND METHODS. Sixty 3Y-TZP specimens (LAVA Frame Multi) were divided into 3 groups depending on the following firing procedures: (1) 2-firing cycles, (2) 5-firing cycles, (3) 10-firing cycles. Two samples from each group were investigated by using SEM to determine the morphological changes. All specimens were treated with 125 ㎛ airborne-particle abrasion and the surface roughness of each specimen was measured. The specimens from each firing group were then further divided into 2 subgroups (n = 9) to apply 2 types of resin cement (MDP-free resin cement: RelyX Unicem-RU, and MDP containing resin cement: Panavia F 2.0-PA). The shear bond strength (SBS) test was performed and failure types of all the debonded specimens were classified by using a stereomicroscope as adhesive, cohesive, and mixed. The statistical analysis of surface roughness and SBS data were performed by using 1-way ANOVA and 2-way ANOVA followed by Tukey-HSD tests (α=.05). Failure modes were calculated as a percentage for each group. RESULTS. The bond strength of RU and PA to the specimens obtained with 2 firings were not statistically different from each other (P=.1). However, the SBS values of PA were found to be significantly higher than RU for the specimens obtained with 5 and 10 firing cycles (P=.001 and P=.02, respectively). Surface roughness analysis revealed no statistical difference between groups (P=.2). The SEM analysis of samples fired 5- and 10- times showed irregularities and boundary loss in zirconia grains, and empty spaces between zirconia grains. CONCLUSION. The bond strength of PA cement was higher than that of RU to the zirconia subjected to repeated firings (5 and 10 firing cycles). When zirconia is subjected to multiple firings, using MDP-containing resin cement can be recommended.