• Geomechanics and Engineering
• /
• 제10권6호
• /
• pp.775-791
• /
• 2016

The indirect tensile strengths (ITSs) of different cemented paste backfill mixes with different curing times were determined by considering crack initiation and fracture toughness concepts under different loading conditions of steel loading arcs with various contact angles, flat platens and the standard Brazilian test jaw. Because contact area of the ITS test discs developes rapidly and varies in accordance with the deformability, ITSs of curing materials were not found convenient to determine under the loading apparatus with indefinite contact angle. ITS values increasing with an increase in contact angle can be measured to be excessively high because of the high contact angles resulted from the deformable characteristics of the soft paste backfill materials. As a result of the change of deformation characteristics with the change of curing time, discs have different contact conditions causing an important disadvantage to reflect the strength change due to the curing reactions. In addition to the experimental study, finite element analyses were performed on several types of disc models under various loading conditions. As a result, a comparison between all loading conditions was made to determine the best ITSs of the cemented paste backfill materials. Both experimental and numerical analyses concluded that loading arcs with definite contact angles gives better results than those obtained with the other loading apparatus without a definite contact angle. Loading arcs with the contact angle of $15^{\circ}$ was found the most convenient loading apparatus for the typical cemented paste backfill materials, although it should be used carefully considering the failure cracks for a valid test.

• Journal of Mechanical Science and Technology
• /
• 제17권12호
• /
• pp.1928-1937
• /
• 2003

Effect of elastic modulus mismatch on the contact crack initiation is investigated to find major parameters in designing desirable surface-coated system. Silicon nitride coated soft materials with various elastic modulus mismatch, E$\_$c//E$\_$s/＝1.06∼356 are prepared for the analysis. Hertzian contact test is conducted for producing contact cracks and the acoustic emission detecting technique for measuring the critical load of crack initiation. The implication is that coating thickness and material strength are controllable parameters to prevent the initiation of contact cracks resulted from the elastic modulus mismatch in the hard ceramic coating layer on the soft materials.

• ETRI Journal
• /
• 제35권4호
• /
• pp.571-577
• /
• 2013

The fabrication of a thin-film transistor backplane and a liquid-crystal display using printing processes can eliminate the need for photolithography and offers the potential to reduce the manufacturing costs. In this study, we prepare contact via structures through a poly(methyl methacrylate) polymer insulator layer using inkjet printing. When droplets of silver ink composed of a polymer solvent are placed onto the polymer insulator and annealed at high temperatures, the silver ink penetrates the interior of the polymer and generates conducting paths between the top and bottom metal lines through the partial dissolution and swelling of the polymer. The electrical property of various contact via-hole interconnections is investigated using a semiconductor characterization system.

• 소성∙가공
• /
• 제4권1호
• /
• pp.48-58
• /
• 1995

In this study, a contact algorithm for the finite element analysis of free surface contact problem in materials forming is presented. The proposed contact algorithm consists of two parts. The first is the contact searching part, and the second, the constraint part. The contact searching algorithm does not require any a priori knowledge of the pairs of contact nodes or segments and the impenetrability constraint is satisfied using the penalty function scheme. void colsure in open-die forging was simulated to verify the accuracy and capability of the currently developed contact algorithm. The simulation results, obtained from ABAQUS simulation, were compared well to the experimental data available in the literature.

• 대한금속재료학회지
• /
• 제50권10호
• /
• pp.785-792
• /
• 2012

A new flip chip structure consisting of interlocking joints locally surrounded by non-conductive adhesive was investigated in order to improve the contact resistance characteristics and prevent the parasitic capacitance increase. The average contact resistance of the interlocking joints was substantially reduced from $135m{\Omega}$ to $79m{\Omega}$ by increasing the flip chip bonding pressure from 85 MPa to 185 MPa. Improvement of the contact resistance characteristics at higher bonding pressure was attributed not only to the increased contact area between Cu chip bumps and Sn pads, but also to the severe plastic deformation of Sn pads caused during formation of the interlocking-joint structure. The parasitic capacitance increase due to the non-conductive adhesive locally surrounding the flip chip joints was estimated to be as small as 12.5%.

• The Journal of Advanced Prosthodontics
• /
• 제1권1호
• /
• pp.1-5
• /
• 2009

STATEMENT OF PROBLEM. Poor wettability of denture relining materials may lead to retention problems and patient discomfort. PURPOSE. Purpose of this study is to compare and evaluate wettability of nine denture relining materials using contact angle measurements under air and water storage over time. MATERIAL AND METHODS. Nine denture relining materials were investigated in this study. Two heat-curing polymethyl-methacrylate(PMMA) denture base materials: Vertex RS, Lang, one self-curing polyethyl-methacrylate(PEMA) chairside reline resin: Rebase II, six silicone relining materials: Mucopren soft, Mucosoft, $Mollosil^{{R}}$ plus, Sofreliner Touch, GC $Reline^{TM}$ Ultrasoft, Silagum automix comfort were used in this experiment. Contact angles were measured using high-resolution drop shape analysis system(DSA 10-MK2, KRUESS, Germany) under three conditions(in air after setting, 1 hour water storage, and 24 hours water storage). Nine materials were classified into three groups according to material composition(Group 1: PMMA, Group 2: PEMA, Group 3: Silicone). Mean values of contact angles were compared using independent samples t-test and one-way ANOVA, followed by a Scheffe's post hoc analysis($\alpha$=0.01). RESULTS. Contact angles of materials tested after air and water storage increased in the following order: Group 1(PMMA), Group 2(PEMA), Group 3(Silicone). Heat-cured acrylic denture base resins had more wettability than silicone relining materials. Lang had the highest wettability after 24 hours of water storage. Silicone relining materials had lower wettability due to their hydrophobicity. Wettability of all denture relining materials, except Rebase II and $Mollosil^{{R}}$ plus, increased after 24 hours of water storage. CONCLUSIONS. Conventional heat-cured resin showed the highest wettability, therefore, it can be suggested that heat-cured acrylic resin is material of choice for denture relining materials.

• 생명과학회지
• /
• 제19권4호
• /
• pp.538-542
• /
• 2009

본 연구는 itaconic acid로부터 합성한 새로운 soft contact lens 소재의 함수율과 산소투과도를 확인 하였다. Soft contact lens의 새로운 polymer소재 개발을 위하여 기본 monomer인 HEMA (2-hydroxyethyl methacrylate)와 가교제로서 EGDMA (ethylene glycol dimethacrylate) 그리고 A. itaconicus의 발효에 의해 생산된 itaconic acid로부터 얻어진 mono-ester 1과 di-ester 2를 새로운 첨가제로 사용하여 중합반응을 시도하였다. Soft contact lens의 새로운 폴리머 소재들은 HEMA와 mono-ester 1 또는 di-ester 2를 서로 다른 비율로 합성하여 함수율(water content)과 산소투과도(oxygen permeability)를 분석하였다. Polymer 형성을 위한 HEMA와 additive의 혼합에서 HEMA/mono-ester 1의 혼합물은 HEMA/di-ester 2 보다 함수율과 산소투과도가 뛰어 났으며 HEMA와 첨가제 mono-ester 1 (15%)를 이용한 중합의 경우, 제작된 soft contact lens의 함수율과 산소투과도는 각각 57.7%와 28.6 Dk로 좋은 값을 나타냈다. 새로운 소재를 사용하여 만든 soft contact lens의 함수율과 산소투과도는 우수하게 나타났다.

• 한국미생물·생명공학회지
• /
• 제37권1호
• /
• pp.75-79
• /
• 2009

In this study, we polymerized new materials for soft contact lens using HEMA (2-hydroxyethyl methacrylate) which is the based-monomer of soft contact lens, EGDMA (ethylene glycol dimethacrylate) as cross linkage agent, and the new additives of monoester or di-ester derived from itaconic acid commercially produced by the fermentation of Asp. itaconicus. New polymer materials for soft contact lens were synthesized with the mixture of HEMA and mono- or diester at different ratios and presented to a good water content and oxygen transmissibility (Dk/L) values. In case of polymerization with HEMA and mono-ester (15%), the water content and oxygen transmissibility of contact lens were found to be good values at 57.6% and 28.5 Dk respectively. The mixture of HEMA and mono-ester is more excellent than HEMA/di-ester in the water content and oxygen transmissibility. The toxicity of new contact lens materials were confirmed in the fibroblast L-929 cell line using a agar overlay test and a growth inhibition test with the extract solution of contact lens.

• 대한금속재료학회지
• /
• 제48권6호
• /
• pp.565-569
• /
• 2010

We report on the characteristics of indium-oxide-doped ZnO (IZO) ohmic contact to p-GaN. The IZO ohmic contact layer was deposited on p-GaN by a Roll-to-Roll (RTR) sputter method. IZO contact film with a thickness of 360, 230 and 100 nm yielded an ohmic contact resistance of $4.70{\times}10^{-4}$, $5.95{\times}10^{-2}$, $4.85{\times}10^{-1}\;{\Omega}cm^{2}$ on p-GaN when annealed at $600{^{\circ}C}$ for 1 min under a nitrogen ambient, respectively. While the transmittance of IZO film with a thickness of 360 nm slightly increased in the wavelength range of 380-800 nm after annealing, the transmittance rapidly increased up to 80% after annealing at $600{^{\circ}C}$ in the wavelength range of 380~430 nm because the crystallization of IZO film and created Ga vacancies near the p-GaN surface region were affected by the annealing. These results indicate that ohmic contact resistance and transmittance of the IZO films improved.

• 한국재료학회지
• /
• 제19권8호
• /
• pp.417-420
• /
• 2009

This study develops a highly transparent ohmic contact using phosphorus doped ZnO with current spreading for p-GaN to increase the optical output power of nitride-based light-emitting diodes (LEDs). The phosphorus doped ZnO transparent ohmic contact layer was prepared by radio frequency magnetron sputtering with post-deposition annealing. The transmittance of the phosphorus doped ZnO exceeds 90% in the region of 440 nm to 500 nm. The specific contact resistance of the phosphorus doped ZnO on p-GaN was determined to be $7.82{\times}10^{-3}{\Omega}{\cdot}cm^2$ after annealing at $700^{\circ}C$. GaN LED chips with dimensions of $300\times300{\mu}m$ fabricated with the phosphorus doped ZnO transparent ohmic contact were developed and produced a 2.7 V increase in forward voltage under a nominal forward current of 20 mA compared to GaN LED with Ni/Au Ohmic contact. However, the output power increased by 25% at the injection current of 20 mA compared to GaN LED with the Ni/Au contact scheme.