• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1996년도 추계학술대회
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• pp.337-346
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• 1996

Debonding of cement-femoral stem interface has been suggested as a initial focus of loosening mechanism in many previous studies of cemented total hip replacement. The purpose of this study was to investigate the effect of debonding of cement-femoral stem interface to the bone-cement interface by using three-dimensional non-liner finite element analysis. Three cases of partial debonded, full debonded, full bonded cement-bone interface were modelled with partial bonding of distal 70mm from the tip of femoral stem. Each situation was studied under loading stimulating one-leg stanced gait of 68kg patient. The results showed that under partial and full debonded cement-stem interface condition the peak von Mises stress(3.1 MPa) were observed at the cement of bone-cement interface just under the calcar of proximal medial of femur, and sudden high peak stresses(3.5MPa) were developed at the distal tip of femoral stem at the lateral bone-cement interface in all 3 cases of bonding. The stresses were transfered very little to the cement of upper lateral bone-cement interface in partial and full debonded cases. Thus, once partial or full debonded cement-femoral stem interface occured, 3 times higher stress concentration were developed on the cement of proximal medial bone-cement interface than full bonded interface, and these could cause loosening of cemented total hip replacement. Clinically, preservation of more rigid cement-femoral stem interface may be important factor to prevent loosening of femoral stem.

• 한국구조물진단유지관리공학회 논문집
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• 제6권1호
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• pp.95-102
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• 2002

The flexural behavior of the reinforced concrete (RC) structure upgraded by external reinforcements was examined in this study. It is well known that the incorporation of carbon fiber sheet (CFS) with concrete is one of the most effective ways to strengthen the RC structure. Complete bonding is required between CFS and concrete in order to make the RC structure provide its full function until the time the Re structures serve. Many studies have reported that construction deficiencies have caused the debonding of the CFS from concrete before the RC structure with CFS reaches its ultimate capacity. This research took a systematic look at the failure mechanism, macroscopic load-deformation characteristics, the maximum load applied, and maximum bending moment when construction deficiencies exist. The results of the experiment conducted were compared with theoretically derived values. In the future, the results of this investigation will help minimize the factors of construction deficiencies, which may occur when CFS is used to reinforce a RC structure. The experiment was manipulated with steel reinforcement ratio and piles of CFS on a total of 14 beams ($20cm{\times}30cm{\times}240cm$). The results showed that internal moment capacity increased even when construction deficiencies existed. However, RC structures with CFS in the field still contain a considerable level of potential risks.

• 한국구조물진단유지관리공학회 논문집
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• 제16권1호
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• pp.18-26
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• 2012

최근 FRP를 이용한 철근콘크리트 구조물의 보강방법으로서, 표면매입 보강 (Near-Surface-Mounted Retrofit, NSMR)방법의 연구가 활발히 진행되고 있다. 이 방법은 콘크리트에 홈을 형성하는 추가의 작업이 필요하지만 보강효과를 높일 수 있고 FRP가 표면에 노출되지 않기 때문에 환경의 영향을 저감시킬 수 있다. 본 연구에서는 이와 같은 표면매입 보강공법 즉, FRP판을 세워서 표면에 매입보강하는 공법의 보강효과를 실험적으로 규명하고자 하였다. 이를 위하여 철근콘크리트 보를 제작한 뒤 기존의 표면부착 보강과 표면매입 보강을 실시한 뒤 실험을 통하여 보강성능을 비교하였다. 또한 매입보강의 경우에는 중앙부를 부분적으로 비부착시켜 그 효과를 관찰하였다. 연구결과, FRP판을 이용한 철근콘크리트 부재의 휨보강방법으로서 FRP판을 세워서 표면에 매입하는 보강방법은 기존의 판 부착보강에 비하여 높은 보강성능을 발휘하는 것으로 나타났다. ACI 440-2R의 휨보강시 내력산정방법을 따르고 정착부분의 세가지 파괴형태를 고려함으로써 표면매입 보강된 부재의 내력을 평가할 수 있는 것으로 나타났다.

• Journal of Welding and Joining
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• 제23권6호
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• pp.99-105
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• 2005

The mixing ratio effect of the GTD-111(base metal) powder and the GNI-3 (Ni-l4Cr-9.5Co-3.5Al-2.5B) powder on TLP(Transient Liquid Phase) bonding phenomena and mechanism was investigated. At the mixing ratio of the base metal powder under $50wt\%$, the base metal powders fully melted at the initial time and a large amount of the base metal near the bonded interlayer was dissolved by liquid inter metal. Liquid insert metal was eliminated by isothermal solidification which was controlled by the diffusion of B into the base metal. The solid phases in the bonded interlayer grew epitaxially from the base metal near the bonded interlayer inward the insert metal during the isothermal solidification. The number of grain boundaries farmed at the bonded interlayer corresponded with those of base metal. At the mixing ratio above $60wt\%$, the base metal powder melted only at the surface of the powder and the amount of the base metal dissolution was also less at the initial time. Nuclear of solids firmed not only from the base metal near the bonded interlayer but also from the remained base metal powder in the bonded interlayer. Finally, the polycrystal in the bonded interlayer was formed when the isothermal solidification finished. When the isothermal solidification was finished, the contents of the elements in the boned interlayer were approximately equal to those of the base metal. Cr-W borides and Cr-W-Ta-Ti borides formed in the base metal near the bonded interlayer. And these borides decreased with the increasing of holding time.

• 대한금속재료학회지
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• 제47권10호
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• pp.675-680
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• 2009

Effects of $85^{\circ}C/85%$ Temperature/Humidity (T/H) treatment conditions on the peel strength of an electroless-plated Ni/polyimide system were investigated from a $180^{\circ}$ peel test. Peel strength between electroless-plated Ni and polyimide monotonically decreased from $37.4{\pm}5.6g/mm$ to $22.0{\pm}2.7g/mm$ for variation of T/H treatment time from 0 to 1000 hrs. The interfacial bonding mechanism between Ni and polyimide appears to be closely related to Ni-O bonding at the Ni/polyimide interface. The decrease in peel strength due to T/H treatment appears to be related to polyimide degradation due to moisture penetration through the interface and the bulk polyimide itself.

• Advances in nano research
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• 제15권1호
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• pp.49-57
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• 2023

As composite materials are used in many applications, the modern world looks forward to significant progress. An overview of the application of composite fiber materials in sports equipment is provided in this article, focusing primarily on the advantages of these materials when applied to sports equipment, as well as an Analysis of the influence of sports equipment of fiber-reinforced composite material on social sports development. The present study investigated surface morphology and physical and mechanical properties of S-glass fiber epoxy composites containing Al₂O₃ nanofillers (for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%). A mechanical stirrer and ultrasonication combined the Al₂O₃ nanofiller with the matrix in varying amounts. A compression molding method was used to produce sheet composites. A first physical observation is well done, which confirms that nanoparticles are deposited on the fiber, and adhesive bonds are formed. Al₂O₃ nanofiller crystalline structure was investigated by X-ray diffraction, and its surface morphology was examined by scanning electron microscope (SEM). In the experimental test, nanofiller content was added at a rate of 1, 2, and 3% by weight, which caused a gradual decrease in void fraction by 2.851, 2.533, and 1.724%, respectively, an increase from 2.7%. The atomic bonding mechanism shows molecular bonding between nanoparticles and fibers. At temperatures between 60 ℃ and 380 ℃, Thermogravimetric Analysis (TGA) analysis shows that NPs deposition improves the thermal properties of the fibers and causes negligible weight reduction (percentage). Thermal stability of the composites was therefore presented up to 380 ℃. The Fourier Transform Infrared Spectrometer (FTIR) spectrum confirms that nanoparticles have been deposited successfully on the fiber.

• The Journal of Advanced Prosthodontics
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• 제5권4호
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• pp.479-484
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• 2013

PURPOSE. The aim of this study was to evaluate the effects of additional acid etching and curing mechanism (light-curing or self-curing) of a composite resin on the dentin bond strength and compatibility of one-step self-etching adhesives. MATERIALS AND METHODS. Sixteen human permanent molars were randomly divided into eight groups according to the adhesives used (All-Bond Universal: ABU, Clearfil S3 Bond: CS3), additional acid etching (additional acid etching performed: EO, no additional acid etching performed: EX), and composite resins (Filtek Z-250: Z250, Clearfil FII New Bond: CFNB). Group 1: ABU-EO-Z250, Group 2: ABU-EO-CFNB, Group 3: ABU-EX-Z250, Group 4: ABU-EX-CFNB, Group 5: CS3-EO-Z250, Group 6: CS3-EO-CFNB, Group 7: CS3-EX-Z250, Group 8: CS3-EX-CFNB. After bonding procedures, composite resins were built up on dentin surfaces. After 24-hour water storage, the teeth were sectioned to make 10 specimens for each group. The microtensile bond strength test was performed using a microtensile testing machine. The failure mode of the fractured specimens was examined by means of an optical microscope at ${\times}20$ magnification. The data was analyzed using a one-way ANOVA and Scheffe's post-hoc test (${\alpha}$=.05). RESULTS. Additional etching groups showed significantly higher values than the no additional etching group when using All-Bond Universal. The light-cured composite resin groups showed significantly higher values than the self-cured composite resin groups in the Clearfil S3 Bond. CONCLUSION. The additional acid etching is beneficial for the dentin bond strength when using low acidic one-step self-etch adhesives, and low acidic one-step self-etch adhesives are compatible with self-cured composite resin. The acidity of the one-step self-etch adhesives is an influencing factor in terms of the dentin bonding strength and incompatibility with a self-cured composite resin.

• 대한치과재료학회지
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• 제42권2호
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• pp.95-106
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• 2015

Hardening mechanism associated with post-firing heat treatment of softening heat treated and then firing simulated Pd-Ag-Au alloy for bonding porcelain was examined by observing the change in hardness, crystal structure and microstructure. By post-firing heat treatment of as-cast, solution treated and pre-firing heat treated specimens at $650^{\circ}C$ after casting, the hardness value increased within 10 minutes. Then, hardness consistently increased until 30 minutes, and gap of hardness value among the specimens was reduced. The increase in hardness after post-firing heat treatment was caused by grain interior precipitation in the matrix. The softening heat treatment did not affect the increase in hardness by post-firing heat treatment. The precipitated phase from the parent Pd-Ag-Au-rich ${\alpha}$ phase with face-centered cubic structure by post-firing heat treatment was $Pd_3$(Sn, In) phase with face-centered tetragonal structure, which has lattice parameters of $a_{200}=4.0907{\AA}$, $c_{002}=3.745{\AA}$. From above results, appropriate post-firing heat treatment in order to support the hardness of Pd-Ag-Au metal substructure was expected to bring positive effects to durability of the prosthesis.

• Composites Research
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• 제35권2호
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• pp.93-97
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• 2022

열가소성 복합재의 핫프레스 성형공정에서 근적외선 가열의 적용은 소재를 성형온도까지 고속가열함으로써 공정 전체의 생산성을 확보할 수 있으나, 고에너지, 높은 성형온도, 고속가열에 의해 소재의 열화가 발생하여 재용융 성능 등의 소재 특성이 저하될 수 있다. 이에 본 연구는 고성능 항공소재로 활발히 연구개발되고 있는 Carbon fiber reinforced Polyetherketoneketone(CF/PEKK) 복합재에 적합한 핫프레스 성형공정의 최적화된 공정조건을 확립하기 위하여 근적외선 고속가열을 적용하였을 때, CF/PEKK 복합재에서 발생할 수 있는 열화 메커니즘과 그 특성을 형태학적, 열적 특성 및 기계적 성능 시험을 통해 평가하였다. 열화 반응에 따른 메커니즘 규명은 광학현미경을 활용하여 PEKK의 결정구조의 형태학적 조사를 기반으로 분석하였다. 그 결과, 열화가 진행됨에 따라 구결정의 크기가 감소하며 최종적으로 완전 열화 시 구결정이 소멸되는 것을 확인하였다. 열적 특성은 용융온도, 결정화온도, 발열량이 열화가 진행됨에 따라 감소하는 경향이 관찰되며, 460℃ 장시간 노출에서 결정구조가 소멸된 것을 확인하였다. 랩전단강도(Lap shear strength)시험 결과, 열화된 표면에서는 낮은 접합강도가 관찰되며, 접합면 분석에서 특정 면에서는 열에 의한 용융 특성이 나타나지 않았다. 결론적으로 CF/PEKK 복합재의 근적외선 고속가열 적용에 있어 특정 온도에서 열화 진행되며, 이에 구결정의 형태학적 변화와 열가소성 소재의 재용융 특성의 저하를 확인하였다.

• 콘크리트학회논문집
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• 제20권1호
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• pp.23-33
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• 2008

철근콘크리트 연속보에서 모멘트재분배는 철근콘크리트 부재 설계의 효율성과 경제성을 높일 수 있는 매우 유익한 현상이다. 그러나 모멘트재분배 현상에 의한 구조적 거동을 이해하기 위해서는 인장증강 효과, 모멘트재분배와 보 처짐 관계, 균열과 유효 강성 등이 고려된 모멘트재분배 현상에 대해 실험적인 검증이 요구된다. 따라서 이번 연구에서는 인장증강 효과가 모멘트재분배 현상에 미치는 영향을 실험을 통해 검증하기 위해 실제 사용되는 보의 크기를 고려하여 폭 250 mm, 높이 350 mm, 길이 7,000 mm로 하고, 인장증강 효과와 관련있는 철근과 콘크리트의 비부착 구간의 위치를 변수로 하여 총 6개의 철근콘크리트 연속보를 제작하였다. 실험 결과 철근 비부착 구간의 위치에 따라 시험체의 모멘트재분배율이 다르게 측정되었으며, 특히 부모멘트와 정모멘트 발생 지점에 모두 비부착 구간이 있는 경우에는 모멘트재분배 현상이 생기지 않는 것으로 관찰되었다.