• Advances in concrete construction
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• 제10권1호
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• pp.1-11
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• 2020

This study intends to produce an ultra-high performance fibre reinforced concrete (UHPFRC) made with hybrid fibres (i.e., steel and polypropylene). Compressive and tensile strength characteristics of the hybrid fibres UHPFRC are considered. A total of 14 fibre-reinforced composites (FRCs) with different fibre contents or types of fibres were prepared and tested in order to determine a suitable hybrid fibre combination. The compressive and tensile strengths of each concrete at 7 days were determined. The results showed that a hybrid mix of micro-polypropylene and steel fibres exhibited good compromising performances and is the ideal reinforcement mixture in a strong, cost-effective UHPFRC. In addition, maximum compressive strength of 167 MPa was achieved for UHPFRC using 1.5% steel fibres blended with 0.5% macro-polypropylene fibres.

• 소성∙가공
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• 제6권2호
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• pp.110-117
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• 1997

Sticking behavior under the hot rolling conditions for ferritic stainless steels have been studied. Sticking, which is a phenomenon that the naked metal exposed to the surface by scale breakaway during hot rolling sticks to the roll surface, was affected by both high temperature tensile strength and oxidation resistance of the steels. A steel having higher tensile strength and lower oxidation resistance exhibits better resistance to the sticking. It is due to that higher tensile strength increases localized deformation resistance and lower oxidation resistance creates lower friction between steel and roll by forming thicker scale as a lubricant during hot rolling. So, the sticking tends to occur more severely in the order of 430J1L, 436L, 430 and 409L. The most sensitive temperature to the sticking was found to be 90$0^{\circ}C$ for all grade of steels. It was also found that the high speed steel(HSS) roll compared to the Hi-Cr roll was more beneficial to prevent sticking. Because higher surface hardness of HSS roll compared to that of Hi-Cr roll provides less nucleation sites for sticking such as scratch on the roll surface.

• Corrosion Science and Technology
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• 제22권4호
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• pp.297-303
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• 2023

This study aimed to evaluate hydrogen permeation behaviors of pre-strained twinning-induced plasticity steel with or without Zn coating using electrochemical permeation technique. In contrast to un-strained and 30% strained samples, permeation current density was measured in the 60% strained sample. Tensile pre-straining at 60% involved microstructural modifications, including a high level of dislocation density and stacking fault with a semi-coherent twin boundary, which might provide a high diffusion path for hydrogen atoms. However, reproducibility of measurements of hydrogen permeation current was low due to non-uniform deformation and localized stress concentration. On the other hand, the permeation current was not measured in pre-strained TWIP steel with Zn coating. Instead, numerous blisters with some cracks were observed on the surface of the coating layer. In locally damaged Zn coating under tensile straining, hydrogen atoms could relatively easily permeate through the coating layer. However, they were trapped at the interface between the coating layer and the substrate, which might delay hydrogen penetration into the steel substrate.

• 한국자동차공학회논문집
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• 제13권2호
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• pp.127-134
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• 2005

This paper introduces a newly developed high speed material testing apparatus for tensile tests at the strain rate up to 500/sec. The tensile properties of sheet metals are indispensable for the accurate crashworthiness analysis of auto-bodies since the local strain rate reaches to 500/sec in the car crash. An appropriate experimental method has to be developed to acquire the tensile properties at the intermediate strain rate ranged from 0.003/sec to 200/sec. Tensile tests of various different steel sheets for an auto-body were perform ed to obtain the dynamic properties with respect to the strain rate. The dimensions of specimens that can provide the reasonable results were determined by the finite element analysis. A special jig fixture of a load cell is designed to reduce the load ringing phenomenon induced by unstable stress propagation at the high strain rate. Stress-strain curves were acquired for each steel sheet from the dynamic tensile test and utilized to obtain the relationship of the stress to the strain rate.

• 한국표면공학회지
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• 제36권5호
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• pp.398-405
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• 2003

The stainless steel wire requires good corrosion resistance and mechanical properties, such as drawing ability, combined with a high resistance to corrosion. For increasing drawing ability of stainless steel, Ni coating methods have been used in this study. However, there is no information on the electrochemical corrosion behavior of drawed wires after Ni coating. To investigate corrosion resistance and mechanical property of drawed wire, the characteristics of Ni coated wires have been determined by tensile strength tester, hardness tester, field emission scanning microscope, energy dispersive x-ray analysis and potentiodynamic method in 0.1 M HCl. The drawed stainless steel wires showed the strain-induced martensitic structure, whereas non-drawed stainless steel wire showed annealing twin in the matrix of austenitic structure. The hardness and tensile strength of drawed stainless steel wire were higer than that of non-drawed stainless steel wire. Electrochemical measurements showed that, in the case of drawed stainless steel o ire after Ni coating, the corrosion resistance and pitting potential increased compared with non-coated and drawed stainless steel wire due to decrease in the surface roughness.

• 한국자동차공학회논문집
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• 제13권5호
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• pp.42-49
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• 2005

In general, multi-lap spot weld joints are frequently present in automobile. Most research, however, has been focused on the single-lap spot weld joints until now. In this paper, tensile-shear strength tests are performed to examine the weldability of 3-lap spot joint welded by using the high strength steel sheet and the zinc coated steel sheet. The indentation depth and nugget diameter are used to propose the optimum welding conditions. The weldability is affected by the welding current and welding time for 3-lap spot joint. Meanwhile the expulsions is round to decrease with the increase of electrode force. The optimum welding conditions are presented for 3-lap spot joints of high strength steel sheet and zinc coated steel sheet.

• Journal of Welding and Joining
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• 제12권3호
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• pp.56-62
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• 1994

The spot weldability of high strength steel sheet and two stories galvannealed high strength steel sheet has been studied. 1) Tensile shear strength decreased inversely as welding current increased over 12KA in the case of two stories galvannealed high strength steel sheet. 2) When heat flux input over 12KA, hardening region become narrow in case of two stories galvannealed high strength steel sheet. 3) The size of hardening region affect the strength of nuggets.

• 소성∙가공
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• 제21권6호
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• pp.354-359
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• 2012

Effects of a nitriding treatment on the tensile and high cycle fatigue properties were investigated by conducting ion-nitriding and gas nitro-caburizing treatments on the spheroidized SCr430B medium-carbon steel and performing tensile and tension-tension high cycle fatigue tests. The nitrided samples showed much lower strength and ductility compared to those in the initial as-spheroidized state and premature fracture occurred at the hardened layers. The micro-voids in the compound layer caused fatigue crack initiation. Thus, the removal of the compound layer with micro-voids remarkably improved the fatigue resistance to even beyond that of the as-spheroidized sample.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.228-233
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• 2004

The characteristics of the probability distribution for mechanical properties, e.g. tensile strength, reduction of area ana elongation, for STS304 stainless steel in elevated temperature were investigated from tensile test performed by constant cross head speea controls with 1mm/min, Recently, in order to clarify the strengthening mechanisms at high temperature, a new scheme to improve high temperature mechanical properties is desired. Therefore, the test ,technique development of high temperature creep behaviors for this material is very important. In this paper, the creep praperties and creep life prediction by Larson-Miller parameter method for STS304 stainless steel to be used for other high temperature components were presented at the elevated temperatures of 600, 650 and $700^{\circ}C$.

• 한국강구조학회 논문집
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• 제14권2호
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• pp.385-394
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• 2002

현재, 국내에서 사용되고 있는 고강도강은 SM570 강재만이 극히 일부분 사용되고 있으며, 그 이상의 고강도강의 사용은 국내의 강교량에는 전무한 실정이다. 본 연구에서는 국내 장대교량 및 일반교량에서의 고강도강 적용의 활성화를 위해 고강도강재인 SM570 강재와 아직 교량에는 적용된 살계가 없는 POSTEN80 강재를 대상으로 횡방향 맞대기 용접연결부의 피로특성을 분석, 평가하였다. 이를 위해 소형시험편을 제작하여 일정진폭하중하에서의 인장 피로시험을 실시하였으며, 피로균열의 발생 및 진정양상, 기존의 연구결과와 비교, 분석하였다. 또한, 모재의 정적 인장강도와 판두께가 용접연결부의 피로강도에 미치는 영향을 분석하고 피로강도를 평가하므로서 고강도강인 SM570과 POSTEN80 강재의 피로특성과 에 따른 횡방향 맞대기 용접연결부에 대한 피로설계기준 제정을 위한 기초 자료를 제시하였다.