• Structural Engineering and Mechanics
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• v.83 no.5
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• pp.693-707
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• 2022

Bonded joints have proven their performance against conventional joining processes such as welding, riveting and bolting. The single-lap joint is the most widely used to characterize adhesive joints in tensile-shear loadings. However, the high stress concentrations in the adhesive joint due to the non-linearity of the applied loads generate a bending moment in the joint, resulting in high stresses at the adhesive edges. Geometric optimization of the bonded joint to reduce this high stress concentration prompted various researchers to perform geometric modifications of the adhesive and adherends at their free edges. Modifying both edges of the adhesive (spew) and the adherends (bevel) has proven to be an effective solution to reduce stresses at both edges and improve stress transfer at the inner part of the adhesive layer. The majority of research aimed at improving the geometry of the plate and adhesive edges has not considered the effect of temperature and water absorption in evaluating the strength of the joint. The objective of this work is to analyze, by the finite element method, the stress distribution in an adhesive joint between two 2024-T3 aluminum plates. The effects of the adhesive fillet and adherend bevel on the bonded joint stresses were taken into account. On the other hand, degradation of the mechanical properties of the adhesive following its exposure to moisture and temperature was found. The results clearly showed that the modification of the edges of the adhesive and of the bonding agent have an important role in the durability of the bond. Although the modification of the adhesive and bonding edges significantly improves the joint strength, the simultaneous exposure of the joint to temperature and moisture generates high stress concentrations in the adhesive joint that, in most cases, can easily reach the failure point of the material even at low applied stresses.

• Korean Journal of Materials Research
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• v.33 no.11
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• pp.439-446
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• 2023

Changes in the microstructure and mechanical properties of as-roll-bonded AA6061/AA5052/AA1050 three-layered sheet with increasing annealing temperature were investigated in detail. The commercial AA6061, AA5052 and AA1050 sheets with 2 mm thickness were roll-bonded by multi-pass rolling at ambient temperature. The roll-bonded Al sheets were then annealed for 1 h at various temperatures from 200 to 400 ℃. The specimens annealed up to 250 ℃ showed a typical deformation structure where the grains are elongated in the rolling direction in all regions. However, after annealing at 300 ℃, while AA6061 and AA1050 regions still retained the deformation structure, but AA5052 region changed into complete recrystallization. For all the annealed materials, the fraction of high angle grain boundaries was lower than that of low angle grain boundaries. In addition, while the rolling texture of the {110}<112> and {123}<634> components strongly developed in the AA6061 and AA1050 regions, in the AA5052 region the recrystallization texture of the {100}<001> component developed. After annealing at 350 ℃ the recrystallization texture developed in all regions. The as-rolled material exhibited a relatively high tensile strength of 282 MPa and elongation of 18 %. However, the tensile strength decreased and the elongation increased gradually with the increase in annealing temperature. The changes in mechanical properties with increasing annealing temperature were compared with those of other three-layered Al sheets fabricated in previous studies.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.1
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• pp.34-41
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• 2017

In this study, the effect on the zinc nuclei crystallization caused by changes preprocessing of the zinc crystalline glaze preparation has been studied. The mechanism of the nuclei formation in the crystalline glaze and development of the nuclei by studying the preprocessing step was explained. The preprocessing step was improved by altering mixing process of the materials prior to sintering: number of sieving dispersion process and ultra-sonication prove tests with various duration of sonication. According to the result, the sieving and sonication of the starting materials facilitated the interface reactions of $ZnO-SiO_2$ from $680^{\circ}C$ where low temperature willemite is formulated, and altered Si bonding for the easier bonding between Zn-Si. In other words, solely sieving was enough to accelerate the formation of willemite in low temperature. When the particles were distributed evenly by sonication, the willemite formation was even more significant.

• Korean Journal of Materials Research
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• v.22 no.8
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• pp.403-408
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• 2012

A sample of ultra low carbon IF steel was processed by six-layer stack accumulative roll-bonding (ARB) and annealed. The ARB was conducted at ambient temperature after deforming the as-received material to a thickness of 0.5 mm by 50% cold rolling. The ARB was performed for a six-layer stacked, i.e. a 3 mm thick sheet, up to 3 cycles (an equivalent strain of ~7.0). In each ARB cycle, the stacked sheets were, first, deformed to 1.5 mm thickness by 50% rolling and then reduced to 0.5 mm thickness, as the starting thickness, by multi-pass rolling without lubrication. The specimen after 3 cycles was then annealed for 0.5 h at various temperatures ranging from 673 to 973 K. The microstructural evolution with the annealing temperature for the 3-cycle ARB processed IF steel was investigated in detail by transmission electron microscopy observation. The ARB processed IF steel exhibited mainly a dislocation cell lamella structure with relatively high dislocation density in which the subgrains were partially observed. The selected area diffraction (SAD) patterns suggested that the misorientation between neighboring cells or subgrains was very small. The thickness of the grains increased in a gradual way up to 873 K, but above 898 K it increased drastically. As a result, the grains came to have an equiaxed morphology at 898 K, in which the width and the thickness of the grains were almost identical. The grain growth occurred actively at temperatures above 923 K.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.236-236
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• 2011

Silicon oxynitride (SiON) was deposited for gas barrier film on polyethylene terephthalate (PET) using octamethylycyclodisiloxane (Si4O4C8H24, OMCTS) precursor by plasma enhanced chemical vapor deposition (PECVD) at low temperature. The ion flux and substrate temperature were measured by oscilloscope and thermometer. The chemical bonding structure and barrier property of films were characterized by Fourier transform infrared (FT-IR) spectroscopy and the water vapor transmission rate (WVTR), respectively. The deposition rate of films increases with RF bias and nitrogen dilution due to increase of dissociated precursor and nitrogen ion incident to the substrate. In addition, we confirmed that the increase of nitrogen dilution and RF bias reduced WVTR of films. Because, on the basis of FT-IR analysis, the increase of the nitrogen gas flow rate and RF bias caused the increase of the C=N stretching vibration resulting in the decrease of macro and nano defects.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.356-356
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• 2007

Plasma immersion ion beam deposition (PIIBD) technique is a cost-effective process for the deposition of diamond like carbon thin film, the possible solid lubricant on large surface and a complex shape. We used PIIB process for the preparation of DLC thin film on $Al_2O_3$ with deposition conditions of deposition temperature range $200^{\circ}C$, working gas pressure of 1.310-1Pa. DLC thin films were coated by $C_2H_2$ ion beam deposition on $Al_2O_3$ after the ion bombardment of SiH4 as the bonding layer. Energetic bombardment of $C_2H_2$ ions during the DLC deposition to ceramic materials generated mixed layers at the DLC-Si interface which enhanced the interface to be highly bonded. Wear test showed that the low coefficient of friction of around 0.05 with normal load 2.9N and proved the advantage of the low energy ion bombardment in PIIBD process which improved the tribological properties of DLC thin film coated alumina ceramic. Furthermore, PIIBD was recognized as a useful surface modification technique for the deposition of DLC thin film on the irregular shape components, such as molds, and for the improvement of wear and adhesion problems of the DLC thin film, high temperature solid lubricant.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.503-509
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• 2019

The demand for smaller, faster, and multi-functional mobile devices in increasing at a rapidly increasing rate. In response to these trends, Stacked Chip Scale Package (SCSP) is used widely in the assembly industry. A film type adhesive called die attach film (DAF) is used widely for bonding chips in SCSP. The DAF requires high flowability at high die attachment temperatures for bonding chips on organic substrates, where the DAF needs to feel the gap depth, or for bonding the same sized dies, where the DAF needs to penetrate bonding wires. In this study, the mixture design of experiment (DOE) was performed for three raw materials to obtain the optimized DAF recipe for low elastic modulus at high temperature. Three components are acrylic polymer (SG-P3) and two solid epoxy resins (YD011 and YDCN500-1P) with different softening points. According to the DOE results, the elastic modulus at high temperature was influenced greatly by SG-P3. The elastic modulus at $100^{\circ}C$ decreased from 1.0 MPa to 0.2 MPa as the amount of SG-P3 was decreased by 20%. In contrast, the elastic modulus at room temperature was dominated by YD011, an epoxy with a higher softening point. The optimized DAF recipe showed approximately 98.4% pickup performance when a UV dicing tape was used. A DAF crack that occurred in curing was effectively suppressed through optimization of the cure accelerator amount and two-step cure schedule. The imizadole type accelerator showed better performance than the amine type accelerator.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.11
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• pp.816-820
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• 2013

We investigated the characteristics of the silicon oxy-nitride and nitride films grown by plasma-enhanced chemical vapor deposition (PECVD) at the low temperature with a varying $NH_3/N_2O$ mixing ratio and a fixed $SiH_4$ flow rate. The deposition temperature was held at $150^{\circ}C$ which was the temperature compatible with the plastic substrate. The composition and bonding structure of the nitride films were investigated using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Nitrogen richness was confirmed with increasing optical band gap and increasing dielectric constant with the higher $NH_3$ fraction. The leakage current density of the nitride films with a high NH3 fraction decreased from $8{\times}10^{-9}$ to $9{\times}10^{-11}(A/cm^2$ at 1.5 MV/cm). This results showed that the films had improved electrical properties and could be acceptable as a gate insulator for thin film transistors by deposited with variable $NH_3/N_2O$ mixing ratio.

• Journal of the Korean Vacuum Society
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• v.7 no.2
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• pp.150-154
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• 1998

Photoluminescence(PL), XRD, TEM results $5\times1016/\textrm{cm}^2, 1\times10^{17}/\textrm{cm}^2, 3\times10^{17}/\textrm{cm}^2$ Si-implanted $SiO_2$ films on crystalline silicon are reported. At low dose implantation and low annealing temperature, visible PL are observed. The PL spectrum has 7400$\AA$ and 8360$\AA$ peaks. As annealing time increased, the PL intensity are increased and peak positions are changed. The PL spectrum are not observed at high dose implantation and high annealing temperature. For the samples of low dose and high annealing temperature, visible PL are observed at short annealing time (30 minutes) and disappear for more than 1 hour annealing. From XRD and TEM results, silicon cluster are related to nonradiative defects. It is concluded that the origin of visible PL in Si implanted SiO2 films are not nanocrystal but two kinds of radiative defects. The Si-O-O bonding related defects (O rich defects) and Si-Si-O bonding related defects (Si rich defects) are related to the PL spectrum and depend on concentraion of Si implantation, annealing temperature and time.

• The korean journal of orthodontics
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• v.22 no.1
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• pp.43-65
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• 1992

Bonding orthodontic adhesive resins to glazed porcelain surface is not attainable. The aim of this investigation was to examine, in vitro, the effect of three methods of porcelain surface pretreatment on the shear bond strength of orthodontic adhesives, and to compare the shear strength of orthodontic bracket bonding to porcelain surface by the best results that to human enamel. Porcelain disks ($Ceramco^{(TM)}$ and $Vita^{(TM)}$) baked in the laboratory were roughened by sandpapers, #320, #600, #800, #1000 and #1200, and were pretreated with silane and dried at the various temperatures, room temperature, $50^{\circ}C$, $70^{\circ}C$ and $90^{\circ}C$, and were etched by 3% hydrofluoric acid solution for 1, 3, 5, 7, and 9 minutes, orthodontic adhesives (System $1+^{(TM)}$ and $Unite^{(TM)}$) were applied on them, and shear bond strengths were measured by Instron. The best results of pretreatment of each method were determined by the shear bond strengths. Again, porcelain disks were pretreated by the determined best results and human enamel were etched by 37% hydrofluoric acid solution, orthodontic brackets were bonded on them by the orthodontic adhesives, and the shear bond strengths were measured and compared between them. 1. Roughening porcelain surfaces with coarse sandpaper (#300) showed higher shear bond strength than that with finer sandpapers, but it $(22.44Kgf/cm^2)$ was distinguishably low compared to that from etched human enamel $(144.11Kgf/cm^2)$. 2. There were disparities in shear bond strengths upon the orthodontic resins, which was presumably related to the contents of fillers in orthodontic adhesive resins. Also there were disparities in shear bond strength upon the porcelains which had different composition. 3. Silane enhanced the shear bond strength of orthodontic resins to porcelain surfaces ($25.20Kgf/cm^2$ at $50^{\circ}C$), which was markedly low compared to that from etched human enamel. 4. Etched porcelain surface with 3% hydrofluoric acid solution for 1 to 9 minutes showed no difference in shear bonding strength of orthodontic adhesive resins. Shear bond strength from etched porcelain $(97.43-120.72Kgf/cm^2)$ were as high as clinically available, but low compared to that from etched human enamel. 5. Roughening with #300 sandpaper and etching by 3% hydrofluoric acid followed silane application on porcelain surface showed lower shear bond strength than etched human enamel, but were as high as clinically useful. 6. The results suggest that etching porcelain surface by 3% hydrofluoric acid solution might provide comparatively high shear bond strength as much as clinically favorable.