• Structural Engineering and Mechanics
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• 제82권1호
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• pp.17-30
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• 2022

The use of composite patches for the reduction of stresses at the level of the damaged zone in aeronautical structures has experienced rapid expansion given its advantages over conventional mechanical processes (riveting, bolting, etc.). Initially, The research axes in this field were aimed at choosing suitable mechanical properties for the composite and the adhesive, then to optimize the shape of the composite patch in order to ensure good load transfer and avoid having a debonding at the level of the edges essentially for the case of a repair by single side where the bending moment is present due to the non-symmetry of the structure. Our work falls within this context; the objective is to analyze by the finite element method the fracture behavior of a damaged plate repaired by composite patch. Stress reduction at the edge is accomplished by creating a variable angle chamfer on the composite patch. The effects of the crack length, the laminate sequence and the nature of the patch as well as the use of a hybrid patch were investigated. The results show clearly that a beveled patch reduces the stress concentrations in the damaged area and even at its edges. The hybrid patch also ensures good durability of the repair by optimizing its stacking sequence and the location of the different layers according to the fibers orientations.

• 대한치과보철학회지
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• 제42권2호
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• pp.133-141
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• 2004

Statement of problem : Porcelain restorations are widely used in restorative dentistry with a high degree of general success. However, porcelain is brittle and may fracture intraorally. Sometimes a repair may be attempted using composite resin and bonding system available. Color stability of porcelain repair resins affects esthetics and prognosis of prosthesis, so that provides important criteria for the choice of porcelain repair resins. Purpose : The purpose of this study was to investigate the color stability of composite resins used widely as porcelain repair system. Materials and method : Composite resins used for this study were Carisma(Kulzer, Germany), Tetric ceram(Ivoclar, Liechtenstein), Filtek Z250(3M, USA), and Arabesk Top(VOCO, Germany). Thirty disc-shaped specimens($10{\times}2mm$) were fabricated from each composite resin. Color changes of specimens after treatment using thermocycling system(KD-TCS30, Kwang-duk F.A. Korea) and after immersion in methylene blue(0.05% by Wt) were measured with colorimeter(Model Tc-6Fx, Tokyo Denshoku Co.) and obtained data were analyzed. Results and Conclusion: The results obtained from this study were as fo11ows. 1. The color change of Filtek Z250 was lesser than those of Tetric ceram and Arabesk Top after thermocycling (12000 times). 2. All of the composite resins in this study showed increase of color change according to increase of thermocycling frequency. 3. After treatment with methylene blue, the color change of Arabesk Top was greater than those of Carisma and Tetric ceram, and Tetric ceram was more stable than others.

• The Journal of Advanced Prosthodontics
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• 제5권3호
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• pp.248-255
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• 2013

PURPOSE. This study compared the effect of three intraoral repair systems on the bond strength between composite resin and zirconia core. MATERIALS AND METHODS. Thirty zirconia specimens were divided into three groups according to the repair method: Group I-CoJet$^{TM}$ Repair System (3M ESPE) [chairside silica coating with $30{\mu}m$ $SiO_2$ + silanization + adhesive]; Group II-Ceramic Repair System (Ivoclar Vivadent) [etching with 37% phosphoric acid + Zirconia primer + adhesive]; Group III-Signum Zirconia Bond (Heraus) [Signum Zirconia Bond I + Signum Zirconia Bond II]. Composite resin was polymerized on each conditioned specimen. The shear bond strength was tested using a universal testing machine, and fracture sites were examined with FE-SEM. Surface morphology and wettability after surface treatments were examined additionally. The data of bond strengths were statistically analyzed with one-way ANOVA and Tamhane post hoc test (${\alpha}$=.05). RESULTS. Increased surface roughness and the highest wettability value were observed in the CoJet sand treated specimens. The specimens treated with 37% phosphoric acid and Signum Zirconia Bond I did not show any improvement of surface irregularity, and the lowest wettability value were found in 37% phosphoric acid treated specimens. There was no significant difference in the bond strengths between Group I ($7.80{\pm}0.76$ MPa) and III ($8.98{\pm}1.39$ MPa). Group II ($3.21{\pm}0.78$ MPa) showed a significant difference from other groups (P<.05). CONCLUSION. The use of Intraoral silica coating system and the application of Signum Zirconia Bond are effective for increasing the bond strength of composite resin to zirconia.

• Steel and Composite Structures
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• 제32권1호
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• pp.127-139
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• 2019

Bridges, offshore oil platforms and other infrastructures usually require at some point in their service life rehabilitation for reasons such as aging and corrosion. This study explores the application of adhesively bonded CFRP patches in repair of corroded circular hollow sectional (CHS) steel beams. An experimental program involving three-point bending tests was conducted on intact, corroded, and repaired CHS beams. Meso-scale finite element (FE) models of the tested beams were developed and validated by the experimental results. A parametric study using the validated FE models was performed to examine the effects of different CFRP patch parameters, including patch dimensions, number of plies and stacking sequence, on efficiency of the repair system. Results indicates that the corrosion reduced elastic stiffness and flexural strength of the undamaged beam by 8.9 and 15.1%, respectively, and composite repair recovered 10.7 and 18.9% of those, respectively, compared to undamaged beam. These findings demonstrated the ability of CFRP patch repair to restore full bending capacity of the corroded CHS steel beam. The parametric study revealed that strength and stiffness of the repaired CHS beam can be enhanced by changing the fiber orientations of wet composite patch without increasing the quantity of repair materials.

• 한국세라믹학회지
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• 제56권6호
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• pp.521-525
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• 2019

A study was conducted to investigate the possibility of a composite material containing a composite resin as a matrix and hydroxyapatite (HAp) powder as a substitute material for tooth repair. As the content of HAp increased, hardness value (111.9 HV at 9%) increased and flexural strength (73.3 MPa at 9%) decreased. Observation of the microstructure after immersion in a simulated body fluid (SBF) solution confirmed a dense structure due to mutual coagulation and curing. It was thought that fine HAp recrystals were formed with the lapse of time, and they were entangled to form a condensation structure and had a dense structure. In addition, since the activity was shown by the ion migration on the surface of a tooth, it was highly likely that a biocompatible bond occurred during tooth contact. Therefore, it could be used as a substitute material for tooth repair.

• Structural Engineering and Mechanics
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• 제59권1호
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• pp.123-132
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• 2016

Many military and commercial aging aircrafts flying beyond their design life may experience severe crack and corrosion damage, and thus lead to catastrophic failures. In this paper, were used in a finite element model to evaluate the effect of corrosion on the adhesive damage in bonded composite repair of aircraft structures. The damage zone theory was implemented in the finite element code in order to achieve this objective. In addition, the effect of the corrosion, on the repair efficiency. Four different patch shapes were chosen to analyze the adhesive damage: rectangular, trapezoidal, circular and elliptical. The modified damage zone theory was implemented in the FE code to evaluate the adhesive damage. The obtained results show that the adhesive damage localized on the level of corrosion and in the sides of patch, and the rectangular patch offers high safety it reduces considerably the risk of the adhesive failure.

• Composites Research
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• 제36권2호
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• pp.108-116
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• 2023

본 논문에서는 복합재료로 제작된 구조물의 유지보수 자동화를 위한 소형 매니퓰레이터 플랫폼 개발을 위해 기구학적 설계와 다물체 동역학 해석을 수행하였다. 매니퓰레이터의 기구학적 설계를 수행하기 위해 기존복합재 보수 공정을 고려하였다. 보수용 패치 적층 공정을 고려하여 매니퓰레이터와 엔드 이펙터의 기본 제원을 선정한 뒤 3-D 설계를 수행하였다. 이후 보수공정을 고려한 역기구학 해석을 통해 시뮬레이션 및 제어에 필요한 변수를 MATLAB에서 생성하였다. 플랫폼의 구조안정성 평가를 위해 Altair Inspire와 Optistruct를 통한 다물체 동역학 해석을 수행하였다. Inspire에서 진행된 시뮬레이션을 기반으로 Optistruct에서 다물체 동역학 해석을 수행한 뒤 시간에 따른 최대 변위와 Von-Mises 응력 결과를 통해 구조안정성을 검증하였다. 설계검증을 위해 플랫폼의 실제 제작 및 제어를 수행하여 시뮬레이션과 비교한 결과, 실제 보수과정 경로와 시뮬레이션이 잘 일치하는 것을 확인하였다.

• 구강회복응용과학지
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• 제34권2호
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• pp.89-96
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• 2018

목적: 본 연구의 목적은 비스 아크릴 복합 레진의 수리 시 지연시간, 표면처리, 수리재료가 미치는 영향을 전단 결합강도 비교를 통해 알아보고, 폴리메틸 메타크릴레이트 레진을 이용한 비스 아크릴 복합 레진 수리의 효용성을 평가하고자 하는 것이다. 연구 재료 및 방법: 총 90개의 비스 아크릴 복합 레진 시편을 제작하였고, 지연시간, 표면처리, 수리재료에 따라 10개씩 9개의 실험군으로 분류하였다. 각각의 시편들은 제작 직후 만능시험기를 사용하여 전단 결합강도를 측정하였고, 통계분석 프로그램(IBM SPSS statistics 20)을 이용하여 분석하였다. 전단 결합강도 측정 후 시편의 파절 단면을 관찰하였다. 결과: 시편 제작 직후, 접착제(bonding agent)를 이용하여 광중합형 유동성 복합 레진을 접착한 실험군에서 가장 높은 전단 결합강도를 보였다($17.54{\pm}3.14MPa$). 결론: 비스 아크릴 복합 레진을 수리할 때 경과시간에 따라 재제작 여부를 고려해야 하며, 효과적인 수리를 위해 사용부위나 목적에 따라 알맞은 재료와 표면처리 방법을 고려하는 것이 바람직할 것이다.

• 구강회복응용과학지
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• 제26권3호
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• pp.339-347
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• 2010

이전에 존재하던 컴포지트와 새로운 컴포지트 사이의 결합강도의 강화는 미세 기계적 유지를 증진하기 위한 표면 거칠기의 증가가 필요하다. 이 연구는 시효처리 후의 레진 컴포지트의 repair 결합강도에 다른 표면처리의 효과를 평가하는 것이다. 알루미늄 옥사이드를 이용한 air abrasion, chair-side silica coating한 그룹들에서 대조군과 불산 적용에 비하여 유의하게 높은 결합강도를 보였다. 레진 수복물의 repair시에 air abrasion의 사용은 필요한 것으로 보이며 부가적으로 silane의 적용은 결합강도에 긍정적 영향을 미치는 것으로 보인다.

• Structural Engineering and Mechanics
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• 제82권3호
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• pp.343-354
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• 2022

An understanding of the mechanism of concrete girders repaired with CFRP plates and its influence on the dynamic parameters is presented in this paper. Dynamic parameters are governed by the relationship with the physical properties of concrete girders and CFRP plates as well as the adhesive layer between them. A brief explanation of the mechanism of the composite action of concrete girders repaired with CFRP is also given in this paper. Experimental work was carried out to validate the theory of the composite action. The results show a decrease in the modal parameters of CFRP repaired girders that were turned over during the repair procedure, which contrasts with the proven static-based results that CFRP plates increase the stiffness of repaired girders. The composite action theory has explained the results based on the tension and compression forces' growth at the adhesive layer between the CFRP plates and girder surface during the repair procedure. Other girders were prepared and repaired without turning over in order to avoid tension and compression forces at the adhesive layer. The experimental results show an increase in the dynamic parameters of CFRP repaired girders that were not turned over during the repair procedure, which aligns with the static-based results. The study concludes that the dynamic parameters are excellent indicators for the assessment of CFRP repaired concrete girders. The study also suggests that researchers should not turn over damaged concrete girders to repair them with CFRP plates if they intend to study the dynamic parameters, in order to avoid the proposed composite action effect on modal parameters.