The nanoleakage patterns of experimental hydrophobic adhesives after load cycling

Sohn, Suh-Jin,Chang, Ju-Hae,Kang, Suk-Ho,Yoo, Hyun-Mi,Cho, Byeong-Hoon,Son, Ho-Hyun 大韓齒科保存學會 2008 Restorative Dentistry & Endodontics Vol.33 No.1

본 연구의 목적은 두 가지 실험용 소수성 상아질 접착제와 전통적인 3-step 상아질 접착제의 nanoleakage양상을 load cycling 전, 후에 비교하여 상아질 접착제의 내구성을 예측해 보고자 하는 것이다. 두 가지 실험용 소수성 상아질 접착제 즉, 에탄올 포함 상아질 접착제, 메탄올 포함 상아질 접착제를 만들었다. 대구치 30개의 치관부 3분의 1을 절단하고 임의로 3군으로 나누어 각각 Scotchbond Multi-Purpose (3M ESPE, St. Paul, MN, USA), 에탄올 포항 상아질 접착제 및 메탄올 포함 상아질 접착제를 사용하여 상아질 접착 후, 복합레진으로 치관부를 수복하였다. 각각의 접착 시스템을 Load cycling 여부에 따라 두 군으로 나누고 각각의 치아를 접착 계면에 수직으로, 약 2.0 mm의 두께가 되도록 절단하여 치아 마다 2개의 시편을 얻어 각 군 당 10개의 시편을 얻었다. 시편을 50 % ammoniacal silver nitrate를 이용하여 염색한 후 주사전자현미경을 이용하여 혼성층의 nanoleakage를 관찰하였다. 은 침착의 분포는 image analysis software (Scion Image Beta 4.03, Scion Corp., Frederick, MD, USA)를 이용하여 gray value로 계산하였고 이원분산분석법으로 통계처리하였다. 3종의 상아질 접착제에서 모두 nanoleakage가 관찰되었으나. 에탄올 포함 상아질 접착제와 메탄올 포함 상아질 접착제에서 Scotchbond Multi-Purpose보다 적은 양의 nanoleakage가 관찰되었다 (p < .0001). 각각의 상아질 접착제에서 load cycling에 따른 nanoleakage 양상의 변화는 관찰되지 않았다. 이상의 결과에서 친수성기를 줄이고 소수성기를 극대화한 실험용 상아질 접착제가 접착 계면의 내구성 향상에 도움을 줄 수 있을 것으로 사료된다. The purpose of this study was : (1) to compare nanoleakage patterns of a conventional 3-step etch and rinse adhesive system and two experimental hydrophobic adhesive systems and (2) to investigate the change of the nanoleakage patterns after load cycling. Two kinds of hydrophobic experimental adhesives, ethanol containing adhesive (EA) and methanol containing adhesive (MA), were prepared. Thirty extracted human molars were embedded in resin blocks and occlusal thirds of the crowns were removed. The polished dentin surfaces were etched with a 35 % phosphoric acid etching gel and rinsed with water. Scotchbond Multi-Purpose (MP), EA and MA were used for bonding procedure. Z-250 composite resin was built-up on the adhesive-treated surfaces. Five teeth of each dentin adhesive group were subjected to mechanical load cycling. The teeth were sectioned into 2 mm thick slabs and then stained with 50 % ammoniacal silver nitrate. Ten specimens for each group were examined under scanning electron microscope in backscattering electron mode. All photographs were analyzed using image analysis software. Three regions of each specimen were used for evaluation of the silver uptake within the hybrid layer. The area of silver deposition was calculated and expressed in gray value. Data were statistically analyzed by two-way ANOVA and post-hoc testing of multiple comparisons was done with the Scheffe's test. Silver particles were observed in all the groups. However, silver particles were more sparsely distributed in the EA group and the MA group than in the MP group (p < .0001). There were no changes in nanoleakage patterns after load cycling.

Flowable 및 microfill 복합레진으로 충전된 제 5급와동에서 load cycling 전,후의 미세변연누출 비교

강석호,김오영,오명환,조병훈,엄정문,권혁춘,손호현 大韓齒科保存學會 2002 Restorative Dentistry & Endodontics Vol.27 No.2

Low-viscosity composite resins may produce better sealed margins than stiffer compositions (KempScholte and Davidson, 1988; Crim, 1989). Flowable composites have been recommended for use in Class V cavities but it is also controversial because of its high rates of shrinkage. On the other hand, in the study comparing elastic moduli and leakage, the microfil had the least leakage (Rundle et al. 1997). Furthermore, in the 1996 survey of the Reality Editorial Team, microfills were the clear choice for abfraction lesions. The purpose of this study was to evaluate the microleakage of 6 composite resins (2 hybrids, 2 microfills, and 2 flowable composites) with and without load cycling. Notch-shaped Class V cavities were prepared on buccal surface of 180 extracted human upper premolars on cementum margin. The teeth were randomly divided into non-load cycling group (group 1) and load cycling group(group 2) of 90 teeth each. The experimental teeth of each group were randomly divided into 6 subgroups of 15 samples. All preparations were etched, and Single bond was applied. Preparations were restored with the following materials (n=15) : hybrid composite resin [Z250(3M Dental Products Inc. St.Paul, USA), Denfil(Vericom, Ahnyang, Korea)], microfil [Heliomolar RO(Vivadent, Schaan, Liechtenstein), Micronew(Bisco Inc. Schaumburg, IL, USA)], and flowable composite[AeliteFlo(Bisco Inc. Schaumburg, IL, USA), Revolution(Kerr Corp. Orange, CA, USA)]. Teeth of group 2 were subjected to occlusal load (100N for 50,000 cycles) using chewing simulator(MTS 858 Mini Bionix Ⅱ system, MTS Systems Corp., Minn, USA). All samples were coated with nail polish 1mm short of the restoration, placed in 2% methylene blue for 24 hours, and sectioned with a diamond wheel. Enamel and dentin/cementum margins were analyzed for microleakage on a sclale of 0 (no leakage) to 3 (3/3 of wall). Results were statistically analyzed by Kruskal-Wallis One way analysis, Mann-Whitney U-test, and Student-Newmann-Keuls method. (p=0.05) Results: 1. There was significantly less microleage in enamel margins than dentinal margins of all groups. (p<0.05) 2. There was no significant difference between six composite resin in enamel margin of group 1. 3. In dentin margin of group 1, flowable composite had more microleakage than others but not of significant differences. 4. There was no significant difference between six composite resin in enamel margin of group 2. 5. In dentin margin of group 2, the microleakage were R>A=H=M>D>Z. But there was no significant differences. 6. In enamel margins, load cycling did not affect the marginal microleakage in significant degree. 7. In dentin margins, load cycling did affect the marginal microleakage only in Revolution. (p<0.05)

Nonlinear Dynamic Responses of Shear-Deformable Composite Panels under Combined Supersonic Aerodynamic, Thermal, and Random Acoustic Loads

이홍범,김영남,최인준,박재상,김인걸 한국항공우주학회 2020 International Journal of Aeronautical and Space Sc Vol.21 No.3

The skin panel structures of vehicles in supersonic flights are subjected to combined thermal, acoustic, and aerodynamic loads. These combined loads may cause a nonlinear dynamic response of the high-speed flight vehicle’s panel structures. Among these nonlinear dynamic responses, the snapthrough and limit cycle oscillation response seriously affect the fatigue failure of the panel structures. This work investigates the nonlinear dynamic responses using the numerical method, when combined supersonic aerodynamic, thermal, and random acoustic loads are applied to the panel structures simultaneously. To consider the thin and thick composite panels, the first-order shear deformation plate theory (FSDT) and the von Karman nonlinear displacement–strain relationship are applied. The aerodynamic load in the supersonic flow is modeled using the first-order piston theory. The thermal load distribution is assumed constant in the thickness direction of the composite panel. The random acoustic load is represented as stationary white-Gaussian random pressure with zero mean and uniform magnitude over the panels. The nonlinear equations of motion of the composite panel under combined loads are derived using the principle of virtual work and the finite element method. The static displacement, which is the solution of the nonlinear static equation, is calculated using the Newton–Raphson method, and the nonlinear dynamic equation is solved using the Newmark-β time integration method. Using these numerical methods, the nonlinear dynamic analyses are conducted under various loading conditions such as thermal–random acoustic loads, thermal–supersonic aerodynamic loads, and supersonic aerodynamic–thermal–random acoustic loads. Numerical results show the nonlinear dynamic response of the composite thin and thick panels such as snapthrough and limit cycle oscillation responses. Particularly, the snapthrough response is caused when the random acoustic load is applied appropriately to the thermally buckled composite plate when the aerodynamic load is not applied or applied with the relatively small magnitude of the dynamic pressure.

Influence of different fatigue loads and coating thicknesses on service performance of RC beam specimens with epoxy-coated reinforcement

Xiao-Hui Wang,Yang Gao,Run-Dong Gao,Jing Wang,Xi-La Liu 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.19 No.3

Epoxy-coated reinforcing bars are widely used to protect the corrosion of the reinforcing bars in the RC elements under their in-service environments and external loads. In most field surveys, it was reported that the corrosion resistance of the epoxy-coated reinforcing bars is typically better than the uncoated bars. However, from the experimental tests conducted in the labs, it was reported that, under the same loads, the RC elements with epoxy-coated reinforcing bars had wider cracks than the elements reinforced with the ordinary bars. Although this conclusion may be true considering the bond reduction of the reinforcing bar due to the epoxy coating, the maximum service loads used in the experimental research may be a main reason. To answer these two phenomena, service performance of 15 RC beam specimens with uncoated and epoxy-coated reinforcements under different fatigue loads was experimentally studied. Influences of different coating thicknesses of the reinforcing bars, the fatigue load range and load upper limit as well as fatigue load cycles on the mechanical performance of RC test specimens are discussed. It is concluded that, for the test specimens subjected to the comparatively lower load range and load upper limit, adverse effect on the service performance of test specimens with thicker epoxy-coated reinforcing bars is negligible. With the increments of the coating thickness and the in-service loading level, i.e., fatigue load range, load upper limit and fatigue cycles, the adverse factor resulting from the thicker coating becomes noticeable.

부하순환 하에서 제V급 복합레진 수복물의 미세변연누출에 대한 재접착제의 효과에 관한 연구

윤연희,김영재,김정욱,장기택,이상훈,김종철,한세현 大韓小兒齒科學會 2004 大韓小兒齒科學會誌 Vol.31 No.3

저점도의 레진을 복합레진 수복물 위에 도포하는 것은 미세누출방지와 변연 완전성(integrity) 유지를 위한 한 방법이다. 하지만 장기간 관찰하면, 수복물은 저작압에 의한 영향을 받게 되는데, 저점도의 레진으로 수복물 변연부를 재접착(rebonding)하였을 때 저작압에 의한 응력에 견디면서 계속하여 수복물에 긍정적인 영향을 주는지에 대한 연구는 미흡한 실정이다. 본 연구는 부하순환(load cycling) 하에서 제Ⅴ급 수복물의 미세변연누출에 대한 재접착제 (rebonding agent)의 효과를 알아보고자 하였다. 40개의 건전한 소구치의 협면에 제Ⅴ급 와동을 형성하고 제조사의 지시대로 광중합복합레진으로 수복하였다. 20개씩 무작위로 나누어 표면전색을 하지 않는 Ⅰ군과 표면을 산부식 후 재접착한 Ⅱ군으로 설정하였다. 열순환 후 각 군에서 10개씩의 하위군 (A군=No load cycling군, B군=Load cycling군)으로 나누어 이중 B군의 시편에 1 Hz의 속도로 수직력이 4-100까지 100,000회의 부하순환을 가하였다. methylene blue용액에 침윤시켜 변연의 미세누출릉도를 평가하여 다음과 같은 결과를 얻었다. 1. 교합변연에서는 재접착과 무관하게 유의한 차이가 없었다(ⅠA-ⅡA군, ⅠB-ⅡB군) (p>0.05). 2. 치은변연의 경우는 부하순환을 하지 않은 군의 경우 재접착을 한 군(ⅡA군)이 재접착을 하지 않은 군 (ⅠA군)에 비해 더 적은 미세누출결과를 보였다(p<0.05). 3. 치은 변연에서 부하순환을 시행한 군의 경우에는 재접착을 한 군(ⅡB군)과 재접착을 하지 않은 군 (ⅠB군)과 유의차가 없는 비슷한 미세누출의 결과를 보였다(p>0.05). One clinical technique recommended f3r improving marginal integrity is "rebonding" or application of unfilled resins to the surface of composite restoration. But continuously the restorations are affected with occlusal load. There is room for doubt that the rebonding agent has the positive effect on microleakage in spite of the stress generated by the occlusal load. This study determined the effect of rebonding on microleakage of Class Ⅴ resin composite restorations under load cycling. Class Ⅴ cavities were prepared on the buccal surface of 40 sound extracted premolars and restored with a hybrid light-cured resin composite according to manufacturers' directions. They wert randomly divided into two groups consisting of 20 samples a control(group Ⅰ), without surface sealing, and the other group (group Ⅱ) in which margins were etched and rebonded. After thermocycling, each of groups was divided into subgroups (group A, B), and load cycling(total 100,000 cycles with 4-100N load at a rate of 1 Hz) were applied on the group B. Assessment of microleakage utilized methylene blue dye penetration. The following results were obtained : 1. In the occlusal region, no significant difference was noted in the scores regardless of whether or not the rebonding agent was used (group ⅠA-ⅡA, ⅠB-ⅡB) (p>0.05). 2. In the cervical region, the control group with rebonding (group ⅡA) showed the better result than the group without rebonding (group ⅠA) (p<0.05). 3. In the cervical region, the rebonded group with load cycling(group ⅡB) showed similar results to the groupf·ithout rebonding(group ⅠB) and no significant difference was noted(p>0.05).

Effect of GDC interlayer on the degradation of solid oxide fuel cell cathode during accelerated current load cycling

Khan, M.Z.,Song, R.H.,Lee, S.B.,Lee, J.W.,Lim, T.H.,Park, S.J. Pergamon Press 2014 International journal of hydrogen energy Vol.39 No.35

The effect of gadolinium-doped ceria (GDC) interlayer on the cathode degradation of solid oxide fuel cell (SOFC) during accelerated current load cycling was investigated. The SOFC half-cells with and without GDC interlayer were prepared and tested under 400 rapid current load cycles. The half-cells consisted of lanthanum strontium cobalt ferrite (LSCF)-GDC composite cathode, GDC interlayer, scandia ceria stabilized zirconia (ScCeSZ) electrolyte, and platinum anode as a counter electrode. The area specific resistance (ASR) of the half-cell was measured every 10 current load cycles. The ASR of the half-cell without GDC interlayer greatly increased with current load cycling, which is attributed to the delamination of the cathode/electrolyte interface due to SrZrO<SUB>3</SUB> formation during sintering. On the other hand, the half-cell with GDC interlayer showed a minute increase in ASR during current load cycling due to very small elemental diffusion across the GDC interlayer/electrolyte interface. These results mean that the GDC interlayer produced high resistance to cathode degradation under the current load cycling due to effective suppression of Sr diffusion across the interface.

Model tests on bearing capacity and accumulated settlement of a single pile in simulated soft rock under axial cyclic loading

Zhang, Benjiao,Mei, Can,Huang, Bin,Fu, Xudong,Luo, Gang,Lv, Bu Techno-Press 2017 Geomechanics & engineering Vol.12 No.4

The research reported herein is concerned with the model testing of piles socketed in soft rock which was simulated by cement, plaster, sand, water and concrete hardening accelerator. Model tests on a single pile socketed in simulated soft rock under axial cyclic loading were conducted and the bearing capacity and accumulated deformation characteristics under different static, and cyclic loads were studied by using a device which combined oneself-designed test apparatus with a dynamic triaxial system. The accumulated deformation of the pile head, and the axial force, were measured by LVDT and strain gauges, respectively. Test results show that the static load ratio (SLR), cyclic load ratio (CLR), and the number of cycles affect the accumulated deformation, cyclic secant modulus of pile head, and ultimate bearing capacity. The accumulated deformation increases with increasing numbers of cycles, however, its rate of growth decreases and is asymptotic to zero. The cyclic secant modulus of pile head increases and then decreases with the growth in the number of cycles, and finally remains stable after 50 cycles. The ultimate bearing capacity of the pile is increased by about 30% because of the cyclic loading thereon, and the axial force is changed due to the applied cyclic shear stress. According to the test results, the development of accumulated settlement is analysed. Finally, an empirical formula for accumulated settlement, considering the effects of the number of cycles, the static load ratio, the cyclic load ratio and the uniaxial compressive strength, is proposed which can be used for feasibility studies or preliminary design of pile foundations on soft rock subjected to cyclic loading.

Analysis of Design and Part Load Performance of Micro Gas Turbine/Organic Rankine Cycle Combined Systems

Joon Hee Lee,Tong Seop Kim 대한기계학회 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.9

This study analyzes the design and part load performance of a power generation system combining a micro gas turbine (MGT) and an organic Rankine cycle (ORC). Design performances of cycles adopting several different organic fluids are analyzed and compared with performance of the steam based cycle. All of the organic fluids recover greater MOT exhaust heat than the steam cycle (much lower stack temperature), but their bottoming cycle efficiencies are lower. R123 provides higher combined cycle efficiency than steam does. The efficiencies of the combined cycle with organic fluids are maximized when the turbine exhaust heat of the MGT is fully recovered at the MGT recuperator, whereas the efficiency of the combined cycle with steam shows an almost reverse trend. Since organic fluids have much higher density than steam, they allow more compact systems. The efficiency of the combined cycle, based on a MGT with 30 percent efficiency, can reach almost 40 percent. Also, the part load operation of the combined system is analyzed. Two representative power control methods are considered and their performances are compared. The variable speed control of the MGT exhibits far better combined cycle part load efficiency than the fuel only control despite slightly lower bottoming cycle performance.

Flexural Properties of Lithium Slag Concrete Beams Subjected to Loading and Thermal-Cold Cycles

Liuzhuo Chen,Jitao Yao,Guangtai Zhang 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.2

This paper presents the flexural test results of 10 lithium slag reinforced concrete beams (120 × 200 × 1,100 mm3) subjected to the combined effect of loading and Thermal-Cold (TC) cycles. The parameters include the polypropylene (PP) fibers, number of TC cycles and level of flexural loading. The results show that the cracking load, ultimate load, maximum crack width and deflection improve significantly after 100 TC cycles and deteriorate slightly after 300 TC cycles. As the percentage of the peak moment, which is an experimental value, increases from 0.20 to 0.35, the deflection decreases, the cracking load increases, and there is no noticeable change in the ultimate load. Further, the addition of PP fibers to the concrete beams enhances both the cracking load and the ultimate load, reduces the maximum crack width, and improves the resistance to erosion.

Energy and exergy analysis of gas turbine combined cycle with exhaust gas recirculation under part-load conditions

Keying Li,Jinling Chi,Shijie Zhang 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.5

This paper presents the energy and exergy analysis of the gas turbine combined cycle during part-load operation under the exhaust gas recirculation - inlet/variable guide vane control (EGR-IGVC) strategy. The exergy destruction across each component and the energy and exergy efficiency of the topping, bottoming, and combined cycle are determined. Results show that EGR-IGVC and IGVC both effectively enhance the part-load efficiency of the combined cycle compared to fuel flow control (FFC) because higher turbine exhaust temperature allows more exergy to enter the bottoming cycle and increases bottoming cycle power output. However, EGR-IGVC decreases the bottoming cycle energy and exergy efficiency compared with IGVC. Even so, EGR-IGVC increases the topping cycle energy and exergy efficiency and can obtain a higher bottoming cycle power output. The combined cycle efficiency is enhanced by 0.97-1.21 percentage points over IGVC at 40 %-90 % loads. Exergy analysis has important guiding significance for further improving the part-load performance of the combined cycle.