• Journal of Korean Society of Steel Construction
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• v.10 no.4 s.37
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• pp.721-730
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• 1998

In this paper, an experimental study have been many studies on the joints of steel structure, for it has great influences on the safety of structures. Research on block shear rupture of the joint receiving pure tension have been done in foreign countries, but not in Korea. This study focuses on the propriety of block shear design code, according to limited state design criteria of steel structures recently established in Korea, by an experiment on the joint of angle tension members. The methods of this study were to compare other study results on block shear rupture mode and ultimate capacity, and to evaluate the propriety of the criteria design code. The result is that tension yield shear ruptures and shear yield tension ruptures happened at the joint, and the experimental rupture load was 15% higher than the capacity entered in the criteria design code. We conclude that it is necessary to revaluate the block shear design code presented by many studies on the limited state design criteria of steel structures.

• Journal of Korean Society of Steel Construction
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• v.11 no.3 s.40
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• pp.291-299
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• 1999

In this paper, an experimental study have been many studies on the propriety of block shear design code. according to limited state design criteria of steel structures recently established in Korea, by an experiment on the joint of H-Beam Flange tension members. The objects of this study were to compare with the results of other studies on block shear rupture mode and ultimate capacity, and to evaluate the propriety of the design criteria. The result is that the joint happened, two types, tension yield-shear ruptures and shear yield-tension ruptures, and the experimental rupture load was 23% higher than the capacity entered in the criteria design code In this criteria, it was found that ultimate strength of block shear of H-Beam Flange was lowly estimated. Therefore, we emphasize the need of estimates on the block shear rupture by carrying out many studies in this field.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.10
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• pp.1054-1064
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• 2009

In this work, we predict a true fracture strain using load-displacement curves from tensile test and finite element analysis (FEA), and suggest a method for acquiring true stress-strain (SS) curves by predicted fracture strain. We first derived the true SS curve up to necking point from load-displacement curve. As the beginning, the posterior necking part of true SS curve is linearly extrapolated with the slope at necking point. The whole SS curve is then adopted for FE simulation of tensile test. The Bridgman factor or suitable plate correction factors are applied to pre and post FEA. In the load-true strain curve from FEA, the true fracture strain is determined as the matching point to test fracture load. The determined true strain is validated by comparing with test fracture strain. Finally, we complete the true SS curve by combining the prior necking part and linear part, the latter of which connects necking and predicted fracture points.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.45-45
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• 2009

원가 측면에서 유리한 저항점용접(Resistance Spot Welding)이 차체 용접에 80%이상으로 가장 많이 적용되고 있다. 첨단고강도강(Advanced High Strength Steel)의 저항점용접성 및 용접부 특성에 미치는 공정 변수의 영향에 대한 연구결과는 많으나, 합금원소의 영향에 대해서는 전무하다. 특히, Si는 DP(Dual Phase)강에 첨가 시 균일한 마르텐사이트의 분포를 촉진하는 원소로 저항 점용접성 및 용접부 특성에 영향을 미칠 것으로 예상되며, 이에 대한 연구는 보고된바 없다. 본 연구에서는 냉연 DP강의 저항 점용접시 중요한 인자 중 하나인 너깃경과 전단인장강도에 미치는 Si함유량의 영향을 검토하였다. 사용된 강재 및 용접기는 1.2mm 두께의 Si함유량(0, 0.5, 1.0, 1.5wt%)이 다른 인장강도 780~1000MPa급 냉연 DP강과 단상 AC용접기를 사용하였다. 용접조건은 ISO 18278-2규격에 따라 가압력 4kA, 초기가압시간 40cycle, 유지시간 17cycle로 고정하고, 용접전류만 변화하여 용접을 실시하였다. 너깃경은 용접부 단면을 컷팅 후 폴리싱 하여, 광학현미경과 Image Pro plus를 이용하여 측정했으며, 인장시편규격은 JIS Z 3137를 이용하였다. Si함유량이 증가에 따라 스패터 발생 전류는 감소했고, 너깃경은 직선적으로 증가했다. Si함유량 증가에 따른 너깃경 증가 이유는 저항(R) 측정결과, Si함유량 증가에 따라 모재의 저항이 높아져, 따라서 입열량($Q=I^2Rt$)이 많아지기 때문으로 판단되었다. 인정전단강도는 Si함유량 증가에 따라 직선적으로 증가했다. 이러한 이유는 Si함유량 증가에 따라 너깃경이 증가되기 때문으로 판단되었고, 너깃경과 인장전단강도 사이에 직선적 관계(PL(kN)=$3.2N_{dia.}$-0.81, $R^2$=0.93)를 가지고 있었다. 파단양상은 Si함유량에 상관없이 5.4kA이하에서는 계면파단이 일어났고, 6.0kA이상에서는 풀 아웃 파단이 일어났다. 계면파단주원인은 용접부 가장자리에 지름이 약 $5{\mu}m$이하의 예리한 노치가 존재하여 노치응력집중과 HAZ계면 근처에 미접합부가 존재하기 때문으로 판단되었다. 6.0kA이상에서는 예리한 노치가 없었고, HAZ부가 완전히 접합되어 있기 때문에 풀 아웃 파단이 일어난 것으로 판단되었다. 따라서, Si함유량 증가에 따라 적정용접전류 구간은 감소했고, 너깃경은 직선적으로 증가했다. 또한, Si함유량 증가에 따라 인장전간강도는 증가 했으며, 너깃경과 인장전단강도 사이에 직선적 관계를 가지고 있었다. 파단 양상은 Si함유량에 상관없이 5.2kA이하에서는 계면파단이, 6.0kA이상에서는 풀 아웃 파단이 일어났다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.81-85
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• 2006

Through-the-thickness properties of thick-walled cylindrical composites are required to determine structural performances because interlaminar tensile stress is primarily responsible for structural failure of the composites during their curing process. It is necessary for evaluating the tensile properties to find individual test methods to find appropriate methods because there are no recognised international standards(test methods and test specifications) available for generating reliable tensile properties in the direction. This paper has performed an experimental Study to measure that properties of carbon fabric/phenolic composites are produced by domestic company. Several test methods using an aluminum specimen were compared and evaluated. The best method, found out, was adopted to measure transverse through-the-thickness properties of composite materials. The results show that strain trends on four faces of composite specimen are the same.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.3
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• pp.48-52
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• 2006

Through-the-thickness properties of thick-walled cylindrical composites are required to determine structural performances because interlaminar tensile stress is primarily responsible for structural failure of the composites during their curing process. It is necessary for evaluating the tensile properties to find individual test methods to find appropriate methods because there are no recognised international standards(test methods and test specifications) available for generating reliable tensile properties in the direction. This paper has performed an experimental study to measure that properties of carbon fabric/phenolic composites which are produced by domestic company. Several test methods using an aluminum specimen were compared and evaluated. The best test method to measure transverse through-the-thickness properties of composite materials was developed by the experimental results that strain trends on all faces of composite specimen are the same.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.81-89
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• 2018

Austenitic stainless steels have excellent corrosion resistance, durability and fire resistance. Especially, since STS304L among austenitic types is a low-carbon variation of STS304 and has excellent intergranular corrosion resistance, it can often be used under the welded condition without heat treatment after field welding. This paper investigated ultimate behaviors such as ultimate strength and weld metal fracture mechanism of STS304L fillet-welded connections with TIG(tungsten inert gas) welding through test results. Main variables of specimens are weld length and welding direction against loading. Fracture of specimens are classified into three modes(tensile fracture, shear fracture and block shear fracture). Ultimate strengths were compared according to the welding direction and weld length and TFW series with transverse fillet weld had the highest strength compared with other types(LFW series with longitudinal fillet weld and FW series with all round weld). It is known that current design specifications such as KBC 2016 and AISC2010 underestimated the strength of TFW and LFW specimens and provided unconservative estimates for FW specimens. Finally, strength equations were proposed considering material properties of STS 304L material.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1172-1182
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• 1993

In orthogonal machining a quantitative model for burr formation process and fracture when tool exits workpiece is proposed. When no fracture during burr formation burr formation process is divided by three parts; Initiation, Development and Final burr formation. According to the properties of workpiece fracture will happen or not after initiation of burr formation. Considering the fact that fracture depends on the ductility of workpiece, the fracture strain obtained from ductile fracture criterion is used for prediction. It is verified that the fracture strain from tension test can be used as fracture criterion in burr formation without large error. For detailed observation of burr formation an experimental stage for micro orthogonal cutting inside SEM (Scanning Electron Microscope) is built. Through the comparison between model prediction and experimental result from orthogonal machining in milling machine the model is verified.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.3
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• pp.157-165
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• 2003

The paper deals with the rupture strain estimation of fiber sheets. The experimental study involved tensile testing of 120 fiber sheet specimens and bending testing of 72 concrete beams strengthened with various types of fiber sheets(carbon, glass, and aramid fiber). Concrete beams have 3 types of reinforcement ratios. Rupture strains of fiber sheet specimens are determined by tensile tests to be a little less than the tensile failure strain by the catalog, independently on the number of fiber sheet layers. It is shown that the rupture strain of fiber sheet bonded to reinforced concrete beam is not constant, but decreases as the fiber sheet layer increases. Based on these results, the rupture fiber sheet strain is estimated.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.14 no.4
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• pp.269-275
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• 1981

The fishing hooks were tested for breaking and unbending due to plastic deformation of the material. Study of tensile test is not complicated, but has not even worked out fully enough, especially when the test specimen is subjected to plastic deformation. The fishing hook is subjected to unbending stress and the critical section is a Point which is furthest from the line of action of the forces. The dynamic force of fish during jerks depends on their speed of movement and body weight, the kinetic energy corresponding to it and also on the rlastic displacement of the rigging which absorb the energy. Six kinds of hook were tested by the dynamometer under tensile speed 290mm/min (subscript s) and 780mm/min (subscript f). According to their results, the breaking load(B: kg) can be induced with the formula $B={\alpha}wd^2+\beta$ where w(mm) is the distance between the barb base and the lower shank and d(mm) is diameter. The coefficients of the formula for the round hooks(R) and the angular hooks(A) are approximately as follows: $$R:\;\alpha_{s}=0.5,\;\beta_{s}=1.6,\;\alpha_{f}=0.4,\;\beta_{f}=1.4$$ $$A:\;\alpha_{s}=1.1,\;\beta_{s}=2.0,\;\alpha_{f}=1.0,\;\beta_{f}=0.9$$ The ratio of $B_{f}\;to\;B_{s}$ is corresponding to 0.8. The ratio of deformation(X) that is moved distance of barb base at break to the distance(H) between head base and barb base is about $50\%$. Further study should be carried out on the subject of impact and fatigue test under the same condition which is exerted force by the hooked fish.