• International Journal of Highway Engineering
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• v.4 no.3 s.13
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• pp.35-42
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• 2002

Many temperature-related problems are created in asphalt pavement due to the low temperature. In particular, loss of tensile strength due to low temperature is known to be responsible for thermal failure of pavements in cold regions under $-20^{\circ}C$. The objective of this study is to evaluate characteristics of resistance against low-temperature cracking of polymer asphalt concrete mixtures modified with LDPE and SBS. The test results showed that the mixtures had the maximum indirect tensile strength(ITS) at low temperature ranging from $-10^{\circ}C. It was proved through ITS test that the stress due to differential thermal contraction over the tensile strength did generate internal damage at the temperature below $-20^{\circ}C$. It was shown that the asphalt mixtures modified with polymer had better ITS than the normal asphalt mixture at the temperature below $-20^{\circ}C$. Thus the effect of modification was revealed as tensile strength improvement. From the results of this study, it was recommended that polymer-modified asphalt should be used in order to prevent low-temperature cracking in cold region.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.42-48
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• 2017

When concrete structures expose to fire, the structures were damaged accompanied with degradation of material properties of concrete. In order to determine the reuse of fire-damaged concrete structures, it is needed a careful determination considering conditions of fire damage, such as exposure temperature and exposure time, and also potential to restore fire damage. This study investigates on the evaluation of residual material properties of fire-damaged concrete under different post-fire curing regimes. An experimental study was performed on concrete samples to measure the dynamic elastic modulus by the impact resonance vibration method. Upon the experimental results, the evidence of restoration of material properties was confirmed on specific post-fire curing regimes, higher humidity conditions. Additionally, a correlation analysis was performed on the dynamic elastic modulus with the tensile strength for identifying the effects of post-fire curing regimes on both material properties of fire-damaged concrete.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3277-3283
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• 2010

In this study, in order to find effects of collagen manipulation on hair in permanent wave treatment, it was conducted measurement and analysis on hair curl formation, thickness, tensile strength, methylene blue absorbance, and moisture loss after manipulating concentration proportion of collagen in permanent wave treatment on normal hair. As a result, it was found that by contrast with applying the reductant, hair thickness, tensile strength, methylene blue absorbance, and moisture loss were decreased when applied collagen in permanent wave treatment the higher concentration proportion of collagen was applied, the less damage was occurred on hair However curl formation capacity was decreased in permanent wave treatment as concentration proportion of collagen was increased. Therefore, the appropriate concentration proportion of collagen was 2% in order to reduce hair damage in permanent wave treatment.

• Journal of the Korea Convergence Society
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• v.5 no.1
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• pp.1-8
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• 2014

The purpose of this paper was to evaluate the fatigue life to apply the vibration fatigue analysis considering the stiffness change of the spot welding due to fatigue damage accumulation. For this, the mechanical and fatigue properties of base and spot welded standard specimens were obtained through the tensile and constant amplitude fatigue test. The transfer function of the spot-welded structure was obtained from the frequency response analysis and fatigue analyisis was performed under the condition of PSD=0.11. A vibration fatigue analysis that considered changes in the frequency response due to the fatigue damage that is, failure of some wleding point was conducted on spot-welded structure. The fatigue life of the spot-welded structure was determined by combining the transfer function, the S-N curve of the tensile-shear spot-welded joint and the input PSD.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.2
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• pp.167-173
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• 2016

This paper proposes ductile failure simulation under high strain rate conditions using finite element (FE) analyses. In order to simulate a cracked component under a high strain rate condition, this paper applies the stress-modified fracture strain model combined with the Johnson/Cook model. The stress-modified fracture strain model determines the incremental damage in terms of stress triaxiality (${\sigma}_m/{\sigma}_e$) and fracture strain (${\varepsilon}_f$) for a dimple fracture using the tensile test results. To validate the stress-modified fracture strain model under dynamic loading conditions, the parameters are calibrated using the tensile test results under various strain rates and the fracture toughness test results under quasi-static conditions. The calibrated damage model predicts the CT test results under a high strain rate. The simulated results were then compared with the experimental data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.12
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• pp.1619-1625
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• 2012

An electrical steel strip is commonly used as a core material in all types of electric transformers and motors. It is produced by a cold rolling process. In this paper, a damage-mechanics-based approach that predicts the edge fracture of an electrical steel strip during cold rolling is presented. We adopted the normal tensile stress criterion and the fracture energy method as a damage initiation criterion and a damage evolution scheme, respectively. We employed finite element analysis (FEA) to simulate crack initiation and propagation at the initial notch located at the edges of the strip. The material constants required in FEA were experimentally obtained by tensile tests using a standard and a notched sheet-type specimen. The results reveal that the edge crack was initiated at the entrance of the roll bite and that it rapidly evolved at the exit. The evolution length of the edge crack increased as the length of the initial notch as well as the front tension reel force of the strip increased.

• Journal of Fashion Business
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• v.12 no.6
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• pp.1-10
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• 2008

Public interest in healthy hairs gets growing as damaged hairs are seen more frequently with the generalization of heat permanent waves. For this study, experiments have been conducted to understand the influences on the changes in physical and morphological features of wave forms and damaged hairs, by collecting virgin hairs from the women in their mid-20's, who had not experienced chemical applications, and by dividing the applications of heat perm hair treatments, PPT(for pre-treatment) and LPP(for post-treatment), into the pre-treatment, the post-treatment, the pre & post-treatment, and the non-treatment. For the wave formations, curl waves were investigated by the bare eyes using the pictures taken by a digital camera. For the comparison of physical features, the experiments of tensile strength and elongation were done and their mean values were found. For the observations of morphological features, the pictures were taken by SEM for comparison. As for the findings, regarding the curl wave shapes of hairs, the most even and elastic S curl was formed in the case of non-treatment. In the physical features, both of the tensile strength and elongation showed a decreasing tendency in line with the hair damage levels, and the case of the pre & post-treatment indicated the tendency most similar to the control group. In the morphological features of the cuticle, observed with an SEM, the pre-treatment showed the higher possibility of reducing the cuticle damages than the post-treatment did. LPP was found to play the role of protective membrane for the post-treatment, and the pre & post-treatment turned out to reduce most effectively the cuticle damages.

• Journal of the Korean Society of Clothing and Textiles
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• v.33 no.3
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• pp.391-400
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• 2009

The purpose of this study is to investigate the efficacy of safflower yellow colorant as a natural dye for hair coloring. The dyeing properties of safflower yellow colorant on hair were explored to obtain optimum conditions. Also, the effect of mordant was studied in terms of dye uptake, colorfastness, and hair damage to better understand the characteristics of the colorant. Tensile strength measurement and SEM analysis were carried out for investigating hair damage to light exposure and washing. On the basis of obtained results considering possible hair damage, optimum dyeing conditions were set 100%(o.w.h.) colorant concentration, pH 5, $40^{\circ}C$, and 20min. Dye uptake was improved more effectively by repeated dyeing rather than by increasing concentration. Pre-mordanting method improved dye uptake slightly, irrespective of mordant type. The safflower yellow colorant produced Y colors on hair. Cu and Fe mordants improved washing and light fastness slightly. Better strength retention was obtained with the mordanted-dyed hair than the unmordanted-dyed hair after light irradiation for 40 hours and 10 repeated washing. The hair was more damaged by light exposure than by washing. It was concluded that the safflower yellow colorant can be used as a natural semi-permanent hair dye producing Y color without mordanting.

• Advances in concrete construction
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• v.6 no.6
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• pp.645-658
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• 2018

Despite being one of the most abundantly used construction materials because of its exceptional properties, concrete is susceptible to deterioration and damage due to various factors particularly corrosion, improper loading, poor workmanship and design discrepancies, and as a result concrete structures require retrofitting and strengthening. In recent times, Fiber Reinforced Polymer (FRP) composites have substituted the conventional techniques of retrofitting and strengthening of damaged concrete. Most of the research studies related to concrete strengthening using FRP have been performed on undamaged test specimens. This contribution presents the results of an experimental study in which concrete specimens were damaged by mechanical loading and elevated temperature in laboratory prior to application of Carbon Fiber Reinforced Polymer (CFRP) sheets for strengthening. The test specimens prepared using concrete of target compressive strength of 28 MPa at 28 days were subjected to compressive and splitting tensile testing up to failure and the intact pieces of the failed specimens were collected for the purpose of repair. In order to induce damage as a result of elevated temperature, the concrete cylinders were subjected to $400^{\circ}C$ and $800^{\circ}C$ temperature for two hours duration. Concrete cylinders damaged under compressive and split tensile loads were re-cast using concrete and rich cement-sand mortar, respectively and then strengthened using CFRP wrap. Concrete cylinders damaged due to elevated temperature were also strengthened using CFRP wrap. Re-cast and strengthened concrete cylinders were tested in compression and splitting tension. The obtained results revealed that re-casting of specimens damaged by mechanical loadings using concrete & mortar, and then strengthened by single layer CFRP wrap exhibited strength even higher than their original values. In case of specimens damaged by elevated temperature, the results indicated that concrete strength is significantly dropped and strengthening using CFRP wrap made it possible to not only recover the lost strength but also resulted in concrete strength greater than the original value.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.2
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• pp.51-59
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• 2019

There is increasingly more research focusing on the application of FRP reinforcing bars as an alternative material for steel reinforcing bars, but most such research look at short term behavior of FRP reinforced structures. In this study, the microscopic analysis and tensile behavior of Basalt and Glass FRP bars under freezing-thawing and alkaline conditions were experimentally evaluated. After 100 cycles of the freezing and thawing, the tensile strength and elastic modulus of FRP bars decreased by about 5%. In the case of microstructure of FRP bars during the initial 20 days, no significant damages of FRP bar sections were found under $20^{\circ}C$ alkaline solution; however, the specimens immersed in $60^{\circ}C$ alkaline solution were found to experience resin dissolution, fiber damage and the separation of the resin-fiber interface. In the alkaline environment, the strength decrease of about 10% occurred in the environment at $20^{\circ}C$ for 100 days, but the tensile strength of FRPs exposed for 500 days decreased by 50%. At temperature of $40^{\circ}C$ and $60^{\circ}C$, an abrupt decrease in the strength was observed at 50 and 100 days. Especially, the tensile strength decrease of Basalt fiber Reinforced Polymer bars showed more severe degradation due to the damage caused by dissolution of resin matrix and fiber swelling in alkaline solution. Therefore, in order to improve the long-term performance of the surface braided FRPr reinforcing bars, surface treatment is required to ensure alkali resistance.