• 한국강구조학회 논문집
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• 제9권2호통권31호
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• pp.237-248
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• 1997

크레인 주행거더에서 빈번히 발생되는3 종류의 균열을 재현하기 위해서 거더 길이 640 mm, 높이 600 mm, 폭 300 mm의 시험체 2기를 제작하여 피로실험을 수행하였다. 시험체의 균열은 재하점 부근과 가세트 단부 및 하부플랜지와 웨브의 모살용접부에서 발생하였다. 재하점 근방의 균열은 수직보강재가 위치한 상부플랜지와 웨브 사이의 모살용접부에서 발생해서 웨브의 대각선 방향으로 진전하였다. 또한 하부플랜지 종비드에서 발생된 균열은 주행거더방향에 수직으로 성장하였다. 크레인 주행거더의 각 부위의 피로등급은 JSSC 피로설계지침의 피로등급과 비교해 보면, 재하점 근방의 모살용접부는 E 등급, 가세트 단부는 G 또는 H 등급, 하부플랜지 종비드 부위는 D 등급 정도로 나타났다. 가세트 단부와 종비드 부위는 피로설계지침과 잘 일치하고 있음을 알 수 있다.

• Journal of Welding and Joining
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• 제17권6호
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• pp.53-61
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• 1999

The use of thick plate in increasing in recent years due to the rapid expansion of chemical plants, nuclear plants, ships and other industrial plants. Welding is the most popular joining techniques employed in manufacturing industrial machineries and structures. Normally, Groove shapes are prepared according to appropriate rules and regulations such as KS, JIS, AWS, LR, DNV and etc. for various thicknesses of plate. However those groove angles tend to be too large. As a result of large groove angle, residual stress, deformation of material and strength reduction is obtained. Therefore, the reliability and safety of structures and machinery tend to be decreasing. Therefore, in this paper, theoretical as well as experimental study are carried out to find optimum groove shapes for T-welded joint of mild steel. The test specimen are made in same condition with simulation model. Welding residual stresses measurement by sectional cutting method. ⅰ) The mechanical difference for change the thickness of plate and groove angle are not appeared. ⅱ) In a mechanical point of view minimum preparation angle(40°) is more suitable than maximum groove angle(60℃). ⅲ) The measurement value and distribution of welding residual stresses are not effected largely by groove angle. It is mechanical restraint that mainly affect welding residual stresses distribution. In mechanical point of view minimum groove angle is more suitable than maximum groove angle. Therefore, it is appropriate to minimize the size of groove shape in strength and safety.

• Steel and Composite Structures
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• 제46권2호
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• pp.211-220
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• 2023

Welded hollow spherical joints are commonly used joints in space grid structures. An internal stiffener is generally adopted to strengthen the joints when large hollow spheres are used. To further strengthen it, external stiffeners can be used at the same time. In this study, axial compression tests are conducted on four full-scale 550 mm spherical joints. The failure modes and strengths of the tested joints are investigated. It shows that the external stiffeners are able to increase the strength of the joint up to 25%. A numerical model for large spherical joints with stiffeners is established and verified against the experimental results. Parametric studies are executed considering six main design factors using the verified model. It is found that the strength of the spherical joint increases as the thickness, height and number of the external stiffeners increase, and the hollow sphere's diameter has a neglectable effect on the enhancement caused by the external stiffeners. Based on the experimental and numerical results, a practical formula for the compressive bearing capacity of large welded hollow spherical joints with both internal and external stiffeners is proposed. The proposed formula gives a conservative prediction on the compressive capacity of large welded hollow spherical joints with both internal and external stiffeners.

• 대한조선학회논문집
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• 제47권1호
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• pp.67-75
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• 2010

Submarine and deep sea diving structures are generally designed based on their ultimate strength. Fatigue strength at welded joint must be also taken into account because working stress is increased due to the increasing of diving depth and using high yield steel. The pressure hulls of submarine are subjected to fluctuating compressive loading. But in addition to the calculated stresses, high residual tensile stresses at welded part have to be considered. The state of stress level of pressure hull is tensile at surface and compressive at deep diving depth. This paper presents the results of an experimental investigation on the crack initiation and growth at the weld toe of T welded joints of HY-100 steel plate under constant amplitude loading. It is also investigated the phenomenon of the fatigue failure and test methods. Fatigue tests have been using real scaled local structural models of full penetration T-welded joint, which is a part of the cylindrical shell structures reinforced by ring stiffeners. Several load ratios under constant amplitude loading are considered in the tests. Crack initiation and growth characteristics are examined based on the beach marks of the cracked section of the test specimens. A design stress-life curve including the design formula is suggested according to tested data.

• Journal of Welding and Joining
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• 제20권2호
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• pp.95-101
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• 2002

After high power lasers are avaliable in the commercial market, the number of applications of the laser welding has been increased in manufacturing industries. Although the tailored blank laser welding of butt jointed steel sheets is well known recently in the automotive industries, the lap joint laser welding is a new technology to the automotive manufacturing people as well as the design people. But the deep penetration laser welding seems to be preferred to the partial penetration welding for the lap joint welding in the automotive manufacturers because the partial penetration is a serious deflect for the butt joint. In this study, the feasibility of partial penetration welding fur the lap joint $CO_2$ laser welding was studied fur the 1mm thick 390MPa high strength steel sheets for automotive bodies. The process window of the lap joint partial penetration welding was obtained from experiments with the gap size and the welding speed as process parameters. The partial penetration welding was found excellent on the basis of the tensile shear strength and sectional geometry. The bead width, input energy Per volume, tensile-shear strength, deformation energy and the sectional geometries after tensile-shear tests of partial penetration welded specimens are compared with those of full penetration welded specimens with a series of gaps and welding speeds.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1774-1779
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• 2005

Most of materials receive force in using, therefore, the characteristics of materials must be considered in system design not to occur deformation or destruction. Mechanical properties about materials can be expressed as responsible level of material itself under the exterior operation. Main mechanical properties is strength, hardness, ductility and stiffness etc. Currently, among major measure facilities to measure such mechanical properties, advanced indentation technique has focused in industrial areas as reason of nondestructive and easy applications for mechanical tensile properties and evaluation of residual stress of materials. This study is to find the optimum experimental condition about residual stress advanced indentation technique for accurate analysis of the welded joint of steel materials through indentation load-depth curve obtained from cruciform specimen experiment. Optimum selection was applied to the welded joint of real steel materials to give non-equi-biaxial stress state and compared with general residual stress analyzing method for verification.

• 한국강구조학회 논문집
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• 제28권4호
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• pp.281-292
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• 2016

본 연구에서는 HSA800 60mm 강재의 FCAW 용접성, 용접자세 및 이음성능을 확인하기 위해 용접자세 1G와 3G에 대한 FCAW 공시체를 제작하여 10종의 시험을 실시하였다. FCAW 1G 및 3G의 시험결과는 HSA800 강재의 KS 및 강도의 균질성에 대한 기준을 만족하며, 양호한 용접부로 나타났다. 그러나 용접부 평판 인장시험결과 FCAW 3G의 경우 용접기술 및 방법의 개선이 필요하다고 판단된다.

• 한국구조물진단유지관리공학회 논문집
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• 제22권1호
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• pp.129-136
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• 2018

대형 용접 구조물에 대한 피로설계 수명의 예측은 일반적으로 Palmgren Miner과 등가손상도 방법 또는 선형누적손상도 방법을 사용한다. 또한 용접 구조물에서 피로 균열이 발생되면 잔존 수명은 S-N 곡선과 선형 파괴역학에 기초하여 예측되고 있다. 본 연구에서는 면외거셋 용접이음의 3차원 피로균열 진전거동과 피로수명을 예측하기 위하여 피로 시험을 실시하였다. 면외거셋 용접이음의 3차원 피로균열진전해석은 NX NASTRAN 및 FRANC3D를 이용하여 유한요소 해석을 실시하였다. 면외거셋 용접이음의 균열 형상비, 초기균열 크기 및 응력비에 미치는 영향을 검토하기 위하여 피로균열진전 해석을 실시하였다. 또한 초기균열크기, 균열 형상비와 응력비의 변화에 따른 3차원 피로균열진전 해석 결과와 피로시험결과를 비교하였다. 피로균열진전 해석결과, 피로균열 진전속도와 응력확대계수와의 관계에서 피로시험과 유사하게 나타남을 확인하였으며, 면외거셋 용접이음의 피로수명을 추정할 수 있음을 확인하였다.

• 한국기계가공학회지
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• 제20권5호
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• pp.17-26
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• 2021

It is challenging to estimate the fatigue life of construction equipment consisting of a welded joint using field structure test owing to the uncertainty of the S-N curve. IIW recommends different S-N curves for various welded joint types. However, there is no way to define an appropriate curve considering complex design shape and strain gauge characteristics. This paper proposes an equivalent S-N curve method based on the relationship between IIW effective notch stress and virtual stress using finite element analysis. Moreover, a case study was conducted for the excavator fuel tank. The proposed method is expected to enhance accuracy and consistency in calculating the fatigue life for the welded structure of construction equipment.

• 한국산학기술학회논문지
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• 제19권5호
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• pp.570-576
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• 2018

철근콘크리트 구조물에서 철근의 이음은 철근을 겹쳐서 결속선으로 결속한 겹침이음과 커플러에 의한 기계적 이음이 일반적이다. 국내 설계기준(콘크리트구조기준)에서는 일반철근(비용접 철근)에 대해 용접 겹침이음을 제한하고 있으나, 해외기준(AWS D1.4)에서는 예열을 통한 일반철근의 용접 겹침이음을 허용하고 있다. 본 연구에서는 국내외 규격 및 설계기준을 조사하고, 건설현장에서 가장 많이 사용되는 SD400 강종의 일반철근을 대상으로 용접 겹침이음 인장실험을 수행하여 인장강도를 평가하였다. 용접 겹침이음 시험체의 용접길이는 KS규격(KS B ISO 17660-1)에 제시된 최소용접길이인 8d를 적용하고, 예열온도는 AWS D1.4에 따라 D19이하는 $150^{\circ}C$, D22이상은 $260^{\circ}C$로 설정하였다. 인장실험 결과, 용접 겹침이음된 일반철근은 콘크리트구조기준에서 요구하는 인장강도(항복강도의 125%)를 발현하였으며, 모두 철근 모재에서 파단이 발생되었다. 예열 유무에 따른 영향을 검토하기 위해, 일반철근을 예열한 후 용접한 것과 예열 등의 열처리하지 않은 것을 비교한 결과, 인장강도는 큰 차이를 보이지 않았다. 실험시 사용한 일반철근을 대상으로 화학성분을 분석하여 탄소당량(Ceq)을 확인한 결과, 0.45% 이하로 낮았다. AWS D1.4에 따르면, 탄소당량이 0.45% 이하면 예열이 필요하지 않은 조건이다. 결과적으로 예열의 영향이 미비한 것은 일반철근의 탄소당량이 낮았기 때문인 것으로 확인되었다.