• Journal of Conservation Science
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• v.32 no.4
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• pp.501-510
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• 2016

In this study, we investigated the degradation of adhesives when exposed to ultraviolet light irradiation using samples of lacquer (L), treated lacquer (TL), lacquer mixed with glue (LG), and urushiol mixed with glue (UG). Four types of film specimens were collected under the ultraviolet exposure time, and gloss test, tensile shear strength test, scanning electron microscope analysis, and infrared spectroscopic analysis were conducted for the specimens. LG and UG showed lowering rate of gloss is somewhat later than L. Also, it was observed that with increasing exposure time to ultraviolet irradiation, the surface of L began to show spherical pits and cracks when the polysaccharide layers started to be exposed, whereas the surfaces of LG and UG remained smooth. The Infrared spectra of L and TL showed that the intensity of the overall peak decreased with increasing ultraviolet irradiation time. There was no change in the peak intensity of LG, but for UG, the peaks at $3013cm^{-1}$, $1593cm^{-1}$ and so on disappeared and the overall intensity declined. The tensile shear strength of LG and UG was maintained or increased as compared to the initial test, whereas the tensile shear strength of L decreased sharply after 600 h. LG and UG exhibited fewer changes as a result of high temperature and humidity conditions, and they retained their strength under UV exposure. These results indicate that LG and UG are more durable than L when subjected to environmental change.

• Elastomers and Composites
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• v.41 no.3
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• pp.182-193
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• 2006

The retardation effects of a new polymeric UV stabilizer, DGEBA-HALS, on the UV degradation of SBR and NR were investigated in this study. The UV degradation behaviors of three different rubber compounds, without any photostabilizer and with commercial Cyabsorb UV-3529 and DGEBA-HALS, were compared. Also, the physical characteristics such as Young's modulus, tensile strength, blow-off deformation and crosslink density were examined. The Young's modulus was increased by UV irradiation for all samples, and the tensile strength, after UV irradiation, of the compound with UV stabilizer was better than that of the compound without stabilizer. Especially, the tensile strength of UV irradiated NR was improved by adding DGEBA-HALS. The results of blow-off deformation were in accord with those of Young's modulus. The degree of transmission of SBR compounds obtained from UV-vis transmission spectra was improved about 4% by adding the UV stabilizer. Commercial Cyabsorb UJV-3529 and DGEBA-HALS showed similar trends of transmission. The SEM photographs of SBR surface showed that the size of cracks created by UV irradiation became smaller by adding UV stabilizer. In particular, it is observed that the stabilization effect of DGEBA-HALS was better than that of commercial Cyabsorb UV-3529.

• The korean journal of orthodontics
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• v.30 no.5 s.82
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• pp.625-642
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• 2000

The purpose of this study is to evaluate the effects of mechanical and thermal fatigue stress on the shear, tensile and shear-tensile combined bond strengths(SBS, TBS, CBS) in various orthodontic brackets bonded to human premolars with chemically cured adhesive(Ortho-one, Bisco, USA). Five types of commercially available metal brackets with various bracket base configurations of Photoetched base(Tomy, Japan), Non-Etched Foil Mesh base(Dentaurum, Germany), Micro-Etched Foil Mesh base(Ortho Organizers, USA), Chessboard base(Daesung, Korea), and Integral base(3M Unitek, USA) were used. Samples were divided into 3 groups, the first group was acted with shear-tensile combined loads($45^{\circ}$) of 200g for 4 weeks(mechanical fatigue stress), the second group was subjected to the 5,000 thermocycles of 15 second dwell time each in $5^{\circ}C\;and\;55^{\circ}C$ baths(thermal fatigue stress), and the third group was the control. Bond strengths were measured at the crosshead speed of 0.5mm/min. The cross-section of bracket base/adhesive interface and the fracture surface were examined with the stereoscope and the scanning electron microscope. The resin remnant on bracket base surface was assessed by ART(Adhesive Remnant Index). The obtained results were summarized as follows, 1. In static bond strength, Photoetched base bracket showed the maximum bond strength and Integral base bracket showed the minimum bond strength(p<0.05). In all brackets, shear bond strength(SBS) was in the greatest value and shear-tensile combined strength(CBS) was in the least value(p<0.05). 2. After mechanical fatigue test, Photoetched base bracket showed the maximum bond strength and Integral base bracket showed the minimum bond strength(p<0.05). In Photoetched base bracket and Micro-Etched Foil Mesh base bracket, shear bond strength(SBS), tensile bond strength(TBS) and shear-tensile combined strength(CBS) were decreased after mechanical fatigue test(p

• Journal of Conservation Science
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• v.32 no.2
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• pp.167-178
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• 2016

Despite the size layer is an important part for conserving the artworks in the configuration of oil painting, the conservation scientific approaches of that have not been made yet. Therefore, this study produced standard samples on the basis of the analysis results of oil painting works, and carried out the evaluation of functions of the size layer materials. As a result of literature material, traditionally, animal glue was used for the size layer, whereas synthetic resin have been used in combination with animal glue since the modern age, in particular, it was identified that Polyvinyl Acetate(PVAc) was in general use. As a result of analysis of oil painting works, size layer was detected on the support and it was identified as animal glue. As a result of analysis based on Funaoka canvas for ground, it showed that the lead oxide and the titanium dioxide were the main constituents. On the basis of these results, standard samples were produced. As a result of evaluation on the functions of the size layer materials, in the case of the animal glue, stable result was observed in the shrinkag expansion rate, whereas slight weakness was observed in moisture proofing, color, and tensile strength, and dense cracks were found on surface. As for PVAc(A), moisture proofing, color, and the tensile strength exhibited stable results. Higher shrinkage rate was observed and the cracks with wide gaps were found on surface. As for PVAc(B), tensile strength, shrinkage expansion rate, and surface observation showed stable results, whereas moisture proofing property showed poor results. Different aspects were observed in each experiment, and this phenomena were considered to be due to the density and the adhesion properties between the hydrophilic and hydrophobic molecules in the size layer materials. The results are expected to be used as materials for the oil painting work conservation henceforth.

• Journal of the Korea Concrete Institute
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• v.25 no.4
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• pp.447-455
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• 2013

In this study, reinforced concrete slabs with steps were experimentally studied to analyze their structural performance and to suggest reinforcing details in the step. Because the stepped slabs may behave very poorly in terms of bending strength, stiffness, deflection, cracking, etc., the study is aimed to suggest proper reinforcing details such that the same bending strength is obtained as that without steps. The bending strengths of 12 test specimens with a variety of different reinforcing detail types or other parameters were compared with each other. The specimen without any additional reinforcement in the step had a very low bending strength and significant damage, and the specimens with diagonal reinforcements in the step showed substantial early cracks, experienced hinging of the step, and had a substantial loss of the bending strength. In contrast, the specimens with a combination of U-bars, reversed U-bars, L-bars, and reversed L-bars performed very well and almost reached to 100% of the slab bending strength. The U-bars and reversed U-bars were effective in controling the diagonal cracks, while the L-bars and reversed L-bars were effective in preventing from yielding of slab reinforcement near the step.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.134-140
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• 2017

In this study, the flexural behavior of high strength concrete members with different curing condition of 90 MPa of compressive strength was investigated. Experimental parameters included normal and low temperature curing conditions, tensile steel amount and concrete compressive strength. 8 beam members were fabricated and flexural tests were carried out. Crack spacing, load-deflection relation, load-strain relation and ductility index were determined. Experimental results show that as the amount of rebar increases, the number of cracks increases and the crack spacing decreases. The higher the concrete strength, the smaller the number of cracks, but the effect is significantly smaller than the amount of rebar. As a result of comparison with the proposed average crack spacing in the design criteria, the experimental results are slightly larger than the results of the proposed formula, but the proposed formula does not reflect the concrete strength and curing conditions. The ductility index of normal temperature cured members was 3.36~6.74 and the ductility index of low temperature cured members was 1.51~2.82. The behavior of low temperature cured members was found to be lower than that of normal temperature cured members. As a result of comparing the ductility index with the existing studies similar to the experimental members, the ductility index of the high strength concrete member was larger than the ductility index of the ordinary strength concrete of the previous study. Further research is needed to understand more specific results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.7
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• pp.635-643
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• 2017

The purpose of this study is to investigate the influence of the cold reduction rate and an ultrasonic fatigue test (UFT) on the fatigue behaviors of STS 304L. The tensile strength, yield strength, hardness value and fatigue limit in the UFT fatigue test linearly increased as thickness decreased from 1.5 mm to 1.1 mm, as the cold reduction rate of STS 304L increased. As a result of the UFT fatigue test (R = -1) of four specimens, the fatigue limit of the S-N curve formed a knee point in the region of $10^6$, and the 2nd fatigue limit caused by giga cycle fatigue did not appeared. In the case of t = 1.1 mm, the highest fatigue limit was 345 MPa, which was 64.3% higher than the original material (t = 1.5 mm). As a result of the UFT fatigue test of STS 304L, many small surface cracks occurred, grown, coalesced while tearing.

• Tunnel and Underground Space
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• v.26 no.3
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• pp.235-252
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• 2016

This study presents a methodology to reproduce the mechanical behavior of isotropic or transversely isotropic rock using the polygonal grain-based distinct element model. A numerical technique to monitor the evolution of micro-cracks during the simulation was developed in the present study, which enabled us to examine the contribution of tensile cracking and shear cracking to the progressive process of the failure. The numerical results demonstrated good agreement with general observations from rock specimens in terms of the behavior and the evolution of micro-cracks, suggesting the capability of the model to represent the mechanical behavior of rock. We also carried out a parametric study as a fundamental work to examine the relationships between the microscopic properties of the constituents and the macroscopic behavior of the model. Depending on the micro-properties, the model exhibited a variety of responses to the external load in terms of the strength and deformation characteristics. In addition, a numerical technique to reproduce the transversely isotropic rock was suggested and applied to Asan gneiss from Korea. The behavior of the numerical model was in good agreement with the results obtained in the laboratory-scale experiments of the rock.

• Journal of Welding and Joining
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• v.18 no.2
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• pp.213-213
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• 2000

This study was performed to investigate types and formation mechanism of cracks in two Al alloy welds, A5083 and A7NO1 spot-welded by pulse Nd: YAG laser, using SEM, EPMA and Micro-XRD. In the weld zone, three types of crack were observed: center line crack($C_{C}$), diagonal crack($C_{D}$), and U shape crack($C_{U}$). Also, HAZ crack($C_{H}$), was observed in the HAZ region, furthermore, mixing crack($C_{M}$), consisting of diagonal crack and HAZ crack was observed.White film was formed at the hot crack region in the fractured surface after it was immersed to 10%NaOH water. In the case of A5083 alloy, white films in C crack and $C_D crack region were composed of low melting phases, Fe₂Si$Al_8$ and eutectic phases, Mg₂Al₃ and Mg₂Si. Such films observed near HAZ crack were also consist of eutectic Mg₂Al₃. In the case of A7N01 alloy, eutectic phases of CuAl₂, $Mg_{32}$ (Al,Zn) ₃, MgZn₂, Al₂CuMg and Mg₂Si were observed in the whitely etched films near $C_{C}$ crack and $C_{D}$ crack regions. The formation of liquid films was due to the segregation of Mg, Si, Fe in the case of A5083 alloy and Zn, Mg, Cu, Si in the case of A7N01 aooly, respectively.The $C_{D}$ and $C_{C}$ cracks were regarded as a result of the occurrence of tensile strain during the welding process. The formation of $C_{M}$ crack is likely to be due to the presence of liquid film at the grain boundary near the fusion line in the base metal as well as in the weld fusion zone during solidification. The $C_{U}$ crack is considered a result of the collapsed keyhole through incomplete closure during rapid solidification. (Received October 7, 1999)

• The Journal of the Convergence on Culture Technology
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• v.5 no.3
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• pp.345-349
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• 2019

In Korea, the mountainous area occupies more than 70% of the whole country, cutting of earth slope that cuts a part of the ground surface is widely used when building infrastructures such as road, railroad, and industrial complex construction. In recent years, regulations on environmental damage have become more strict, and various methods have been developed and applied. Among them, Concrete-Panel Retaining Wall technique is actively applied. Concrete-Panel Retaining Wall is a method to resist horizontal earth pressure by forming a wall by attaching a precast retaining wall to the front of the support material and increasing the shear strength of the disk through reinforcement of the support material. Soil nailing, earth bolt, and ground anchor are used as support material. Among them, ground anchor is a more aggressive reinforcement type that introduces tensile load in advance to the steel wire, and a large concentrated load acts on the front panel. This concentrated load is a factor that creates cracks in the concrete panel and reduces the durability of the retaining wall itself. In this study, steel pipe sleeves and reinforcements were purchased at the anchorage of the panel to prevent cracks, and by applying bumpy shear keys to the end of the panel, the weakness of the individual behavior of the existing grout anchors was improved. The problem of degraded landscape by exposure to front concrete of retaining wall and protrusion of anchorage was solved by the production of natural stone patterns and the construction of sections that do not protrude the anchorage. In order to verify the effectiveness of anti-crack sleeves and reinforcements used in the null, indoor testing and three-dimensional numerical analysis have been performed, and the use of steel pipe sleeves and reinforcements has demonstrated the overall strength increase and crack suppression effect of panels.