• Transactions of Materials Processing
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• v.30 no.3
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• pp.134-141
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• 2021

In order to improve excessive spring-back behavior as a result of the roll forming process using ultra high strength steel (UHSS) sheet, local softening in region of a partial area expected to be deformed on an initial blank is considered in this study. With SPFC1470 UHSS sheet with initial blank thickness of 1.20mm, the local softening is performed with the following conditions: temperatures of 500℃, 550℃, 600℃ and 650℃, and holding time of 20s, 40s, 80s and 160s. Mechanical properties, such as yield stress and tensile strength, as well as elongation, are evaluated through uniaxial tensile tests, while the microstructural characteristics as a result of local softening are also investigated using the heat-treated specimens. As a result, it is shown that the spring-back behavior of the roll-formed prototype was reduced about by 78.9%, when the local softening at about 500℃ was performed for 160s considering the practical manufacturing condition.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.781-784
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• 2004

Method of Steel plate reinforced by fiber sheet is advantageous in the secure loading facility. For this method are a light weight and a high strength, the thickness of steel can be reduced Effects of composite system are depreciated when the thickness of steel is thin. This is the result of the difference of ductility ratio with steel plate. Steel plate reinforced by fiber sheets confirms the ability of transformation. This is the result of the property of steel materials Steel plate reinforced by fiber sheet didn't display an enough performance when theadhesives are epoxy rosin. This is the result of the slide of the surface of stee1. The adhesive ability is varied by the number and span of anchor bolts. There wasn't happening the separation between steel and epoxy. Thus the method used in combination with anchor and epoxy is best excellent. This is the result of the upward of accumulation effects Shearing force is in proportion to the number of bolts. But the ability of shearing force per one bolt is reducing. Thickness of steel plate reinforced by fiber sheet must be designed so that steel is endure before concrete is wreck.

• Proceedings of the KWS Conference
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• 2001.05a
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• pp.201-204
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• 2001

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.146.2-146.2
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• 2005

• Journal of Welding and Joining
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• v.26 no.5
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• pp.79-89
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• 2008

With the increased use of surface textured steel sheet in body-in-white assembly, resistance spot weldability of these steels is considered to be an important subject. This study evaluated nugget formation and weldability by measuring dynamic resistance with various weld pressure, current, and weld time for steel sheet with two different surface roughnesses. The surface roughness for T-H steel ($R_{a}=1.70\;{\mu}m$) was higher than that for T-L steel ($R_{a}=1.33\;{\mu}m$), and resulted in increased contact resistance and heating for T-H steel spot welding. Therefore, at low weld current and weld cycle ranges, the T-H steel showed better weldability over the T-L steel. The evaluations of weld interface showed that the fusion zone in the T-H steel sheet was continuous in contrast to discontinuous fusion zone for T-L steel sheet at the same welding conditions. A comparison of dynamic resistance and tensile-shear strength (TSS) between T-H and T-L steel sheet suggested that high surface roughness provided larger heating at early cycle of welding and larger TSS.

• Transactions of Materials Processing
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• v.26 no.2
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• pp.121-126
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• 2017

The hot stamping process is an innovative forming method that could prevent the cracking of high strength steel sheets. The formability test of boron steel sheet using forming limit diagrams at elevated temperature is very complicated and time consuming job. In this paper, an alternative test method to evaluate the formability of boron steel in hot stamping has proposed. It measured the FLD0 instead of whole strain combinations of FLD with the tensile test machine and specially designed test rig. Test results shows that the proposed test method can simulate the plain strain condition fracture and can make the FLD of boron steel sheet at elevated temperature with less effort.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.491-496
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• 2001

In recent years, the research and development about the new material proceed rapidly and actively in the building industry. As building structures become bigger, higher and more specialized, so does the demand for material with higher strength. In the future, we will need to research repair and rehabilitation to make high strength concrete mixed steel fibrous building safe. The carbon fiber reinforced plastic bonding method is widely used in reinforcing the existing concrete structure among the various methods. The repair of initiate loaded reinforced high-strength concrete beams mixed steel fibrous with epoxy bonded Carbon Fiber Sheets(CFS) was investigated experimentally. The CFS thickness and length were varied to assess the peel failure at the curtailment of CFS, The behaviour of the repaired beams was represented by load-longitudinal steel strain relation and failure modes were discussed. The test results indicate that CFS is very effective for strengthening the demand beams and controlling deflections of reinforced high strength concrete beams mixed steel fibrous happen diagonal crack, the increase in the number of CFS layers over two layers didn't effect the increase in the strength of beams.

• Journal of the Korea institute for structural maintenance and inspection
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• v.2 no.4
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• pp.201-208
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• 1998

To observe the confinement effects of Carbon Fiber Sheet(CFS) on the high-strength R/C short columns, Fifteen specimens with CFS were manufactured and tested under uni-axial compressive load. Major variables of this study are amount, spacing, type of CFS and amount of transverse steel. Increasing the amount of transverse steel and CFS, compressive strength and axial rigidity is improved. R/C columns with transverse steel and CFS exhibited less axial stress than columns with only CFS. From the test results, it is shown that the area confined with transverse steel and CFS is considerably important to evaluate axial stress of R/C short columns.

• Transactions of Materials Processing
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• v.12 no.8
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• pp.718-723
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• 2003

Tn order to develop springback control technology for high-strength steel sheets, several studies have been conducted: dome stretching test, stepped s-rail forming and springback measurement, and optimally shaped initial blank design. First, to find out the formability of TRIP60, dome stretching test was performed. Next, the stepped s-rail die, which was designed to form a channel type panel with large twist and wall curl, was manufactured and used to evaluate the effect of controlling forming variables, such as blank holding force and flange amount on the springback. Furthermore, new measurement method of the springback was introduced to define wall curl and twist in geometrically complex panels. Finally, the optimally shaped initial blank was employed to verify one of the best ways to control the springback in channel type. high-strength sheet panels.

• Textile Coloration and Finishing
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• v.34 no.3
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• pp.157-164
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• 2022

This study tried to analyze the heat resistance properties by blending epoxy and phenolic resin in a certain ratio, and to analyze the adhesive properties at the time of metal-polymer hetero-adhesion by applying Epoxy-phenolic resin between a silicon steel sheet and m-aramid sheet, the viscosity, adhesive peel strength, and adhesive cross section were measured using a rotational rheometer, a tensile tester(UTM), and a field emission scanning electron microscopy(FE-SEM). The thermal stability and heat resistance were confirmed by measuring the mass loss according to the temperature increase using Thermogravimetric analysis(TGA). After blending with epoxy and Phenolic resin(1:0.25 ratio) curing at 110℃ for 10 min, high adhesive strength was improved more than 40% compared to the adhesive strength using epoxy alone. When the space between the silicon steel sheet and m-aramid sheet, which is created during curing of the E-P blend, is cured with a slight weight, it is possible to control the empty space and improve adhesion.