• Journal of the Korean GEO-environmental Society
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• v.22 no.2
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• pp.5-13
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• 2021

In this study, as the production of high-strength steel pipes due to the development of steel materials, the stability and applicability of the soil nailing method using high-strength steel pipes were evaluated. Rebars used as reinforcement in the soil nailing method are the same in order to determine the behavioral characteristics and the effect of increasing the reinforcement when replacing it with a high-strength steel pipe of a diameter, a field test were conducted to confirm the stability. As a result of the tensile test, the measured strain is smaller than the strain in the theoretical equation, so it can be seen that the behavior is similar to that of the soil nailing method using rebars. As a result of the displacement measurement, the displacement of the high-strength steel pipe is larger than that of the rebars is considered to be the effect of the internal grouting effect of the steel pipe and the decrease in the cross-sectional area. In the case of using high-strength steel pipes for the soil nailing method, it is judged that the field applicability is good by improving stability and workability through member performance and weight reduction.

• Korean Journal of Materials Research
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• v.15 no.4
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• pp.240-245
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• 2005

An oxygen free copper was severely deformed by accumulative roll-bonding (ARB) process for improvement of its mechanical properties. Two copper sheets 1 m thick, 30 mm wide and 300 m long are first degreased and wire-brushed for sound bonding. The sheets are then stacked to each other, and roll-bonded by about $50\%$ reduction rolling without lubrication at ambient temperature. The bonded sheet is then cut to the two pieces of same dimensions and the same procedure was repeated to the sheets up to eight cycles $(\varepsilon-6.4)$. TEM observation revealed that ultrafine grains were developed after the third cycle, and their size was slightly increased at higher cycles. Tensile strength of the copper increased with the strain at low strain levels, but it hardly increased from 3 cycles $(\varepsilon>2.4)$ due to occurrence of dynamic recovery, even if the imposed strain increased.

• Journal of Welding and Joining
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• v.34 no.3
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• pp.6-11
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• 2016

Joining Al/Fe dissimilar metals is becoming a subject of special interest in the assembly of automotive parts as a trade-off between the weight lightening and the cost reduction. Although various studies have been introduced to join Al alloy with the steel sheet by fusion welding, weak joint strength and galvanic corrosion still remained as problems to be solved. As a solid state welding, friction stir welding has been preferred to fusion welding processes in the dissimilar metal joints. This study investigated friction stir spot welding (FSSW) of Al alloy to the thin steel sheet with a thickness of 0.65 mm. The conventional FSSW is a stationary spot welding process but new approach adopted an additional circumferential movement in company with high speed tool rotation. A full factorial experimental design was implemented, and the main and interaction effects of parameters were analysed on the failure load in the tensile shear test. The direction and radius of rotation were statistically significant parameters and these two parameters affected the joint width and the shape of the hook.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.5
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• pp.5-12
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• 2014

Weatherstrip coatings of urethane and silicon type which are fit to EPDM and thermoplastic materials are used in sealing systems for automotive applications for noise reduction and high slip characteristics for external applications, respectively. Polyurethane binder was successfully synthesized from poly(butyladiphate)diol (PBAD), poly(tetramethylene)glycol (PTMG) and isocyanate as starting materials. Then, polyurethane coating agents were prepared by using various additives. To investigate effects of segment types on the abrasion resistance of polyurethane coating agents, thin films based on polyurethane coating materials were fabricated. With increasing the amount of hard segment in the coating agent, abrasion resistance, modulus and tensile strength of the coating films were improved, but the elongation of the coating films was decreased.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.2
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• pp.58-66
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• 1997

Ti alloys, with the advantageous tensile strength/density ratio and the chemical stability, have been used widely in the aerospace and chemical engineering industries and their usages are still expanding in various industrial areas. In the automotive industry, because of their superior merits of weight reduction and fuel saving, Ti alloys are expected to be used as various part materials including connecting rods, engine valves, springs and retainers, which are all subjected to the fatigue loads. In this study, using Ti-3A1-2.5V, the effects of temperature and microstructure change on fatigue crack propagation has been investigated. Five different microstructures were tested at the temperatures of room temperature, 20$0^{\circ}C$, 30$0^{\circ}C$ and 40$0^{\circ}C$ under the same frequency 20Hz. Some of the conclusions obtained are as follows: (1)Microstructurally, the morphology of less $\alpha$-phase and finer lamellar structure of $\alpha$ and $\beta$-Ti showed better registance to the fatigue crack propagation. (2)Fatigue crack growth rate increased with test temperature.

• Journal of the Korean Society of Clothing and Textiles
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• v.19 no.1
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• pp.51-56
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• 1995

Cotton fabric was treated with acrylonitrile in t-butyl alcohol and then aminized by reduction of the resultant cyanoethyl cellulose with LiAIH4, under various temperatures and times. Aminized cotton fabric toras dyed with acid and reactive dye. Dyeability as to temperatures, pH, and color fastness were compared to the amiRe group content of treated cotton fabrics. The results of this study were as follow: 1. D.S of cyanoethyl cellulose has been increased by increasing treating temperatures and times. Maximum D.S of cyanoethyl cellulose was 1.45. By SEM and the tensile strength, the damage of the treated cotton was not observed. 2. Since aminized cotton has greater affinity on acid dye than untreated cotton, dyeability increased with the increase of amino group content, and the lower pH, $60^{\circ}C$. 3. Since amino group in aminized cotton changes surface charge of cotton, dyeability for reactive dye increased by increasing the amino group content. Optimum dyeability was obtained at pH 5-7, $40^{\circ}C$. And dyeability of the amine treated cotton increased with the NaCl conc. 4. Color fastness to washing & light of the amine treated cotton was very low except for the wash fastness of the reactive dye.

• Journal of Powder Materials
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• v.10 no.2
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• pp.97-102
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• 2003

The powder-in sheath rolling was applied to the fabrication of $Al/Al_2O_3$ composite. A stainless steel tube with outer diameter of 12 mm and wall thickness of 1 mm was used as a sheath. Mixture of aluminum powder and $Al/Al_2O_3$ particles of which volume content was varied from 5 to 20 vol.% was filled in the tube by tap filling and then rolled to 75% reduction at ambient temperature. The re]]ed specimen was sintered at 56$0^{\circ}C$ for 0.5 hr. The $Al/Al_2O_3$ composite fabricated by the sheath rolling and subsequent sintering showed the relative density higher than 0.96. The tensile strength of the composite increased with the volume content of $Al_2O_3$ particles, and it reached a maximum of 90 MPa which is 1.5 times higher than unreinforced material. The elongation decreased with the volume content of $Al_2O_3$ particles. It is concluded that the powder-in sheath rolling is an effective method for fabrication of $Al/Al_2O_3$ composite.

• Korean Journal of Materials Research
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• v.16 no.9
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• pp.592-597
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• 2006

A deoxidized low-phosphorous (DLP) copper was processed by accumulative roll-bonding (ARB) for ultra grain refinement and high strengthening. Two copper sheets 1 mm thick, 30 mm wide and 300 mm long are first degreased and wire-brushed for sound bonding. The sheets are then stacked to each other, and roll-bonded by about 50% reduction rolling without lubrication at ambient temperature. The bonded sheet is then cut to the two pieces of same dimensions and the same procedure was repeated to the sheets up to eight cycles (${\varepsilon}{\sim}6.3$). TEM observation revealed that ultrafine grains were developed after the 4th cycle, and their size decreased at higher cycles. Tensile strength of the copper increased with the equivalent strain, and it reached 547 MPa which was 3 times higher than that of the initial material. It is concluded that the ARB process is an effective method for high strengthening of the DLP copper.

• Transactions of Materials Processing
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• v.23 no.8
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• pp.495-500
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• 2014

Magnesium alloys are currently expected to be widely used for weight reduction of cars and as high efficient materials in the automotive and electronics industries. Although the specific strength of magnesium is excellent, it cannot be easily formed at room temperature due to its HCP structure. However in order to improve the formability of magnesium, it is necessary to investigate its formability in the warm temperature range. In the current study, the aim was to add to the magnesium property database so that the mass production of a magnesium car body can be accomplished. Warm tensile tests were conducted and the forming limit diagram was determined to confirm formability characteristics of magnesium AZ31B alloy sheet. In addition the bending formability and the magnesium damping capacity were evaluated for AZ31B and compared to SPRC440E which is a sheet steel used for car bodies.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.31-36
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• 2008

Architectural membrane are now used in the roof of large span structures throughout the world with the merits of free shape and lightness. Some membrane have some problems of structural capacity by the wind or snow load conditions, large span structures was shown to the tearing of the membrane. This paper is the experimental test on the stress strain curve of cycling load for the glass fiber membrane. In the result of stress strain relationship curve by the cycling load, glass fiber membrane was reduced the tensile strength, the polyester membrane was shown to occur the increase of displacement without load reduction in each load step.