• Journal of Welding and Joining
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• 제28권3호
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• pp.36-41
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• 2010

High Mn steel has been developed for automotive applications since the steel has an excellent combination of strength and ductility. However, from the viewpoint of welding, high Mn steel has a few problems related to its chemical composition. This paper describes characteristics of dissimilar $CO_2$ laser welding for expanding application of high Mn steel. From this work it was cleared that dissimilar laser welded joint between high Mn steel and carbon steel had poor formability due to the formation of martensite within weld metal. In order to improve ductility of welded joint, the method of controlling the dilution ratio of high Mn steel was suggested.

• 대한조선학회지
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• 제13권2호
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• pp.45-51
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• 1976

• 대한기계학회논문집
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• 제12권4호
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• pp.747-754
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• 1988

본 연구에서는 우리나라 자동차업계에서 널리 사용되는 복합조직인 고장력 강 판(high strength steel sheet, HS)과 아연도금강판(galvanized steel sheet, GA)을 선택하여 각 강판간의 점용접 피로특성을 규명하기 위하여 아래와 같은 4가지 조건하 의 단점 점용접 시험편을 제작하였다.

• 한국레이저가공학회지
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• 제18권2호
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• pp.5-10
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• 2015

A tailor welded blank (TWB) is a welded blank comprised of two or more sheets with different properties - thickness, strengths or formabilities. TWBs are applied to the body panels to reduce weight and cost of the part. In this research, ultra high strength steel and high ductility steel were joined and laser tailor welded blanks were implemented. Yb:YAG laser welding tests were conducted with various welding conditions, and mechanical and geometrical characteristics of weldments were evaluated.

• Structural Engineering and Mechanics
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• 제81권5호
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• pp.551-563
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• 2022

Bolted connector could be an alternative to replace the conventional welded headed stud in steel-ultra high performance concrete (UHPC) lightweight composite structures. In this paper, a novel demountable bolted shear connector, consisting of a high-strength bolt (HSB) and a specially-designed nut which is pre-embedded in a thin UHPC slab, is proposed, which may result in the quick installation and disassembly, due to the mountable, demountable and reusable features. In order to study the shear behavior of the new type of bolted shear connector, static push-out tests were conducted on five groups of the novel demountable bolted shear connector specimens and one group of conventional welded headed stud specimen for comparison. The effect of the bolt shank diameter and aspect ratio of bolt on failure mode, shear stiffness, peak slip at the steel-UHPC interface, shear strength and ductility of novel bolted connectors is investigated. Additionally, design formula for the shear strength is proposed to check the suitability for assessment of the novel demountable bolted shear connectors.

• Steel and Composite Structures
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• 제31권4호
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• pp.361-372
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• 2019

In recent years, considerable attention has been paid to the research and development of high-strength steel plates, with particular emphasis on the enhancement of the seismic resistance of buildings and bridges. Many efforts have also been undertaken to improve the properties of high-strength bolts and weld materials. However, there are still different opinions on steel joints that combine high-strength bolts and fillet welds. Therefore, it is necessary to verify the design specifications and guidelines, especially for newly developed 1,400-MPa high-strength bolts, 570-MPa steel plates, and weld materials. This paper presents the results of literature reviews and experimental investigations. Test parameters include bolt strengths, weld orientations, and their combinations. The results show that advances in steel materials have increased the plastic deformation capacities of steel welds. That allows combination joints to gain their maximum strength before the welds have fracture failures. When in combination with longitudinal welds, high-strength bolts slip, come in contact with cover plates, and develop greater bearing strength before the joints reach their maximum strength. However, in the case of combinations with transverse welds, changes in crack angles cause the welds to provide additional strength. The combination joints can therefore develop strength greater than estimated by adding the strength of bolted joints in proportion to those of welded joints. Consequently, using the slip resistance as the available strength of high-strength bolts is recommended. That ensures a margin of safety in the strength design of combination joints.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 추계학술발표대회 개요집
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• pp.79-81
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• 2005

Bridges constructed recently are preferred to have long spans and simple structure details considering not only the function as bridge but scenic beauty, maintenance, construction term and life cycle cost, etc. Therefore, they require high performance steels like extra-thick plate steels and TMCP steels. A TMCP steel produced by themo-mechanical control process is now spot lighted due to the weldability for less carbon equivalent. It improved at strength and toughness in microstructure. Recently, the SM570-TMC steel which is a high strength TMCP steel whose tensile strength is 600MPa has been developed and applied to steel structures. But, for the application of this steel to steel structures, it is necessary to elucidate not only the material characteristics but also the mechanical characteristic of welded joints. In this study, the characteristics of residual stresses in welded joints of SM570-TMC steel were studied through the three-dimensional thermal elastic-plastic analyses on the basis of mechanical properties at high temperatures obtained from the elevated temperature tensile test.

• Steel and Composite Structures
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• 제27권2호
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• pp.229-242
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• 2018

High strength steel is widely used in industrial applications to improve the load-bearing capacity and reduce the overall weight and cost. To take advantage of the benefits of this type of steel in construction, an innovative hybrid fabricated member consisting of high strength steel tubes welded to mild steel plates has recently been developed. Component-scale uniaxial and multiaxial cyclic experiments have been conducted with simultaneous constant or varying axial compression loads using a multi-axial substructure testing facility. The structural interaction of high strength steel tubes with mild steel plates is investigated in terms of member capacity, strength and stiffness deterioration and the development of plastic hinges. The deterioration parameters of hybrid specimens are calibrated and compared against those of conventional steel specimens. Effect of varying axial force and loading direction on the hysteretic deterioration model, failure modes and axial shortening is also studied. Plate and tube elements in hybrid members interact such that the high strength steel is kept within its ultimate strain range to prevent sudden fracture due to its low ultimate to yield strain ratio while the ductile performance of plate governs the global failure mechanism. High strength material also significantly reduces the axial shortening in columns which prevents undesirable frame deformations.

• 국제강구조저널
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• 제18권5호
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• pp.1589-1597
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• 2018

Fatigue tests and numerical analysis were carried out to evaluate the fatigue performance at the U-rib to deck welded joint in steel box girder. Twenty specimens were tested corresponding to different penetration rates (80 and 100%) under fatigue bending load, and the fatigue strength was investigated based on hot spot stress (HSS) method. The detailed stress distribution at U-rib to deck welded joint was analyzed by the finite element method, as well as the stress intensity factor of weld root. The test results show that the specimens with fully penetration rate have longer crack propagation life due to the welding geometry, resulting in higher fatigue failure strength. The classification of FAT-90 is reasonable for evaluating fatigue strength by HSS method. The penetration rate has effect on crack propagation angle near the surface, and the 1-mm stress below weld toe and root approves to be more suitable for fatigue stress assessment, because of its high sensitivity to weld geometry than HSS.

• Steel and Composite Structures
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• 제33권3호
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• pp.445-461
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• 2019

The ultrasonic guided wave-based technique has become one of the most promising methods in non-destructive evaluation and structural health monitoring, because of its advantages of large area inspection, evaluating inaccessible areas on the structure and high sensitivity to small damage. To further advance the development of damage detection technologies using ultrasonic guided waves for the inspection of welded components in structures, the transmission characteristics of the ultrasonic guided waves propagating through welded joints with various types of defects or damage in steel plates are studied and presented in this paper. A three-dimensional (3D) finite element (FE) model considering the different material properties of the mild steel, high strength steel and austenitic stainless steel plates and their corresponding welded joints as well as the interaction condition of the steel plate and welded joint, is developed. The FE model is validated against analytical solutions and experimental results reported in the literature and is demonstrated to be capable of providing a reliable prediction on the features of ultrasonic guided wave propagating through steel plates with welded joints and interacting with defects. Mode conversion and scattering analysis of guided waves transmitted through the different types of weld defects in steel plates are performed by using the validated FE model. Parametric studies are undertaken to elucidate the effects of several basic parameters for various types of weld defects on the transmission performance of guided waves. The findings of this research can provide a better understanding of the transmission behaviour of ultrasonic guided waves propagating through welded joints with defects. The method could be used for improving the performance of guided wave damage detection methods.