• 소성∙가공
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• 제3권4호
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• pp.415-426
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• 1994

Multistage deformation behavior of Nb-microalloyed steel and carbon steel was studied by torsion test with declining temperature T, constant pass strain $\varepsilon_i$, interrupt time $(t_i)$, and varying strain rate $(\.{\varepsilon})$. In the range of $1000^{\circ}C~790^{\circ}C$ and 4.00/sec~0.38/sec, the flow stress at each pass was correlated to the deformation variables. As the finished deformation temperatures are decreased to the range of $790^{\circ}C~900^{\circ}C$, Nb precipitates play an important role on the grain refinement of Nb-microalloyed steel. the flow stress of Nb-microalloyed steel was higher than the carbon steel's while the grain size of Nb-microalloyed steel was smaller than carbon steel below the temperature of $900^{\circ}C$.

• Structural Engineering and Mechanics
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• 제53권2호
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• pp.311-324
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• 2015

The purpose of this study was to investigate experimentally the fatigue performance of reinforced concrete (RC) beams with hot-rolled ribbed fine-grained steel bars of yielding strength 500MPa (HRBF500). Three rectangular and three T-section RC beams with HRBF500 bars were constructed and tested under static and constant-amplitude cyclic loading. Prior to the application of repeated loading, all beams were initially cracked under static loading. The major test variables were the steel ratio, cross-sectional shape and stress range. The stress evolution of HRBF500 bars, the information about crack growth and the deflection developments of test beams were presented and analyzed. Rapid increases in deflections and tension steel stress occured in the early stages of fatigue loading, and were followed by a relatively stable period. Test results indicate that, the concrete beams reinforced with appropriate amount of HRBF500 bars can survive 2.5 million cycles of constant-amplitude cyclic loading with no apparent signs of damage, on condition that the initial extreme tensile stress in HRBF500 steel bars was controlled less than 150 MPa. It was also found that, the initial extreme tension steel stress, stress range, and steel ratio were the main factors that affected the fatigue properties of RC beams with HRBF500 bars, whose effects on fatigue properties were fully discussed in this paper, while the cross-sectional shape had no significant influence in fatigue properties. The results provide important guidance for the fatigue design of concrete beams reinforced with HRBF500 steel bars.

• 한국강구조학회 논문집
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• 제8권3호통권28호
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• pp.3-11
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• 1996

To investigate the effect of fatigue crack growth due to the surface residual stress, it is measured the residual stress distribution by x-ray diffraction at the crack tip each constant crack growth in the notch specimens, and quantitively assessed the effect of crack closure caused to the distribution of compressive stress at the crack tip from evaluating crack openning stress using the finite element analysis. It is concluded that the degree of the residual stress distribution at the crack tip is decreased with increasing the crack length. From the fact that it is similar to the crack openning stress ratio, it is found that the compressive residual stress distribution and size is related to the crack closure effect and surface residual stress field with propagating crack in the notch specimens depends on the stress intensity factor range at the crack tip.

• 국제초고층학회논문집
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• 제9권4호
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• pp.325-334
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• 2020

This paper aims to evaluate the interfacial stress concentrations on connection between vertical through-plate and H-beam in CFT column. Full-scale experiments were performed on three specimens with varying thickness of the vertical through-plate to investigate the interfacial stress concentration factor in the connections. The specimens underwent brittle failure at the location where the steel beam is connected to the vertical through-plate before the steel beam reached its plastic moment. The strain data of the part were analyzed, and the sectional analyses were conducted to determine appropriate residual stress models. In addition, the stress concentration factor was quantified by comparing the analytical local behavior in which the stress concentration is not reflected and the experimental data reflecting the stress concentration. The results showed that the maximum reduction of the stress concentration factor due to an increase in the thickness of the vertical through-plate is 50.3%.

• Steel and Composite Structures
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• 제26권6호
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• pp.693-703
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• 2018

To better understand the influence of hollow ratio on the hollow concrete-filled circular steel tubular (H-CFT) stub columns under axial compression and to propose the design formula of ultimate bearing capacity for H-CFT stub columns, 3D finite element analysis and laboratory experiments were completed to obtain the load-deformation curves and the failure modes of H-CFT stub columns. The changes of the confinement effect between core concrete and steel tube with different hollow ratios were discussed based on the finite element results. The result shows that the axial stress of concrete and hoop stress of steel tube in H-CFT stub columns are decreased with the increase of hollow ratio. AfteGr the yield of steel, the reduction rate of longitudinal stress and the increase rate of circumferential stress for the steel tube slowed down. The confinement effect from steel tube on concrete also weakened slowly with the increase of hollow ratio. Based on the limit equilibrium method, a simplified formula of ultimate bearing capacity for the axially loaded H-CFT stub columns was proposed. The predicted results showed satisfactory agreement with the experimental and numerical results.

• 한국해양공학회지
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• 제12권1호
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• pp.39-49
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• 1998

In this work, fatigue tests by axial loading were carried out to investigate the effect of stress ratio on the growth behaviors of surface fatigue crack for SM45C steel and Al 2024-T4 alloy. The growth behaviors of surface crack have been monitored during fatigue process by measuring system attached CCTV and monitor. When the growth rates of surface crack were investigate by the concept of LEFM based on Newman-Raju's .DELTA.K, the dependence of stress ratio appears both SM45C steel and Al 2024-T4 alloy. Therefore, modified stress intensity factor range, .DELTA.K' [=(1+R)/sup n/.DELTA.K] are intorduced to eliminate the dependence of stress ratio. Using .DELTA.K', it is found that the dependence of stress ratio disappears both SM45C steel and Al 2024-T4 alloy.

• 대한조선학회지
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• 제20권4호
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• pp.17-24
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• 1983

In this study, it was investigated the distribution of residual stress in the direction of loading between the root and toe the load fillet welds for thick steel plate. Residual stress distributions are measured by sectioning method which is one of stress-relaxation technique in welded joint, and analyzed by two dimensional finite element method on thermo-elasto-plastic theory under plane stress condition. These are compared the results of F.E.M analysis with the experimental result by stress-relaxation techniques. As a results, the following conclusion were obtained. (1) In the no penetration fillet welded joint specimen using mild steel plate with 25mm in thickness, the residual stress of loading direction near the root was about $10kg/mm^2$ tensile. (2) The tensile residual stress has been observed in fillet region of the fillet joint by F.E.M. analysis method. (3) The range of compressive residual stress distribution from the root was largest in the case of 5mm root penetration.

• Journal of Welding and Joining
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• 제16권5호
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• pp.67-75
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• 1998

This study aimed at he experimental and finite element analytic investigation of the effect of preheating on he residual stress of weldment. In this study, an autogenous arc welding was used on type 304 stainless steel and MARC as F.E.M. common code was utilized in analysis The analyses include transient and moving heat source and thermal properties as function of temperature. During welding, the thermal cycles of four locations in the weldment were recorded to investigate of the behavior of thermal stress and residual stress. The experimental and analytic results had good coincidence and show that there are two factors influencing the formation of welding residual stress in preheat process. One is the elevation of welding equilibrium temperature and the other is the increase of amount of heat input. The former decrease welding residual stress and the latter increase welding residual stress. Therefore, the cumulative effects result in the welding residual stress not being improved significantly with preheating in 304 stainless steel.

• 대한기계학회논문집A
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• 제25권3호
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• pp.390-398
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• 2001

Welding process generates distortion and residual stress in the weldment due to rapid heating and cooling. Welding distortion and residual stress in the welded structure result in many troubles such as dimensional inaccuracies in assembling and safety problem during service. The accurate prediction of welding residual stress is thus very important to improve the quality of weldment and find the way to reduce itself. This paper suggests new analysis method to predict welding residual stress by considering solid phase transformation during welding process. Using the method, analysis is performed for medium and low carbon steel. The analysis result for medium carbon steel reveals that case considering phase transformation has compressive residual stress in contrast with the case neglecting phase transformation because of martensite formation. However, for the case of low carbon steel, residual stress shows little difference between the case considering phase transformation and the other case, because it has small transformation strain and recovers rapidly stress after phase transformation.

• 한국안전학회지
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• 제28권5호
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• pp.61-65
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• 2013

Occupational stresses of steel manufacturing workers have been investigated using an organized questionnaire composed of 40 items. Three hypothesizes were developed based on the literature review of related researches. Empirical data surveyed from ones working in steel manufacturing jobs were collected and the in-depth statistical analyses using Statistical Package for the Social Sciences(SPSS) software were performed. These statistical results indicate that the existence of occupational stress may cause to take place industrial accidents. Consequentially, the prevention of occupational stress helps to promote the will to work, following by increasing job satisfaction in working circumstance of steel manufacturing.