• Steel and Composite Structures
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• v.29 no.4
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• pp.509-526
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• 2018

The direct strength method adopted by the AISI Standard and AS/NZS 4600 is an advanced design method meant to substitute the effective width method for the design of cold-formed steel structural members accounting for local instability of thin plate elements. It was proven that the design strength formula for the direct strength method could predict the ultimate strength of medium strength steel welded section compressive and flexural members with local buckling reasonably. This paper focuses on the modification of the direct strength formula for the application to high strength and high performance steel welded section columns which have the nominal yield stress higher than 460 MPa and undergo local buckling, overall buckling or their interaction. The resistance of high strength steel welded H and Box section columns calculated by the proposed direct strength formulae were validated by comparison with various compression test results, FE results, and predictions by existing specifications.

• Steel and Composite Structures
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• v.11 no.3
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• pp.225-232
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• 2011

In this study, the deflection and deformation behaviours of IPN80 steel beam and column were investigated under the different industrial loads. Single-sided welds were applied to IPN80 steel beams using shielded metal arc (SMAW) and metal inert gas welding (MIG) method in the form of T-type. After that, the performance of SMAW and MIG welded joints were identified using beam bending test under 500 and 3000 N loads. SMAW and MIG methods were compared with each other to understand the deflection and deformation behaviours of the welded steel structures. Lower deformation and deflection were obtained in MIG welded steel beams. The results show that, steel beams welded MIG method has higher load capacity than SMAW welded ones. MIG welding method is more reliable than the SMAW method for the combining performance and load capacity.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.401-407
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• 2004

This study is on the constant-current stress corrosion test related to the load stress in welded zone and non-welded zone of high tensile strength steel for natural gas transmission. The surface corrosion pattern of the welded zone of API 5L-X65 specimens for natural gas transmission showed global corrosion and narrow pitting, and the pitting was increased by increasing the load stress. Initially, the average relative electrode potential and the average relative current of the high tensile strength steel for natural gas transmission specimens was decreased suddenly, and the average relative electrode potential was higher and the average relative current was lower in welded zone than base metal. and the average relative electrode potential was decreased by increasing the load stress, and the average relative current was somewhat increased by increasing the load stress. The corrosion rate was less in welded zone than base metal, and the corrosion rate was decreased by increasing the load stress.

• Journal of Industrial Technology
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• v.21 no.B
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• pp.213-222
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• 2001

In the study, the fatigue strength improvement and mechanism have been estimated by the Spot-Heating treatment on welded bead toes. For this, web-gusset specimens were made without residual stresses and the others with residual stresses imposed by Spot-Heating. The 4-point bending tests were performed in order to estimate the effect of spot-heating on fatigue strength and fatigue characteristics quantitatively for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue test, fatigue strength of As-Welded specimen for non load-carrying fillet welded joints subjected to pure bending has satisfied the grade of fatigue prescribed in specifications of korea, AASHTO and JSSC. As compare with As-Welded specimen and Spot-Heating specimen have increased about 20% for the fatigue strength at $7.7{\times}10^6$ cycles. The Spot-Heating by reformation of the residual stress on welded bead toes has greatly affected the fatigue crack propagation life, but has slightly affected the fatigue crack initiation life.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.5
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• pp.20-27
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• 1998

According as the member of the automobile body structure have been thinned their thickness and have become high strength, each part of the body structure has been put more severe stress condition. And, because fatigue strength of the spot welded lap joint is influenced by its geometrical and mechanical factors, welding condition and etc., there needs a quantitative and systematic evaluation method for them. In this study, by considering nugget edge of the spot weld part of the IB-type spot welded lap joint under tension-shear load to the ligament crack. fatigue strength of various IB-type spot welded lap joints was estimated with the stress intensity factor(S.I.F.) KIII which is fracture mechanical parameter. We could find that fatigue strength evaluation of the IB-type spot welded lap joints by KIII is more effective than the maximum principal stress ($\sigma$1max) at edge of the spot weld obtained from FEM analysis.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.05a
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• pp.125-129
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• 2002

Authors had developed the model for the fatigue life assessment of welded details considering residual stress and its relaxation. The model consists of three ingredients; a hot-spot stress approach, a residual stress relaxation, and an equivalent stress. The equivalent stress is induced by stress ranges and the ratios between the applied mean stresses and the ultimate stress of material. Once being tuned with two specific fatigue tests by using load carrying cruciform joint, this model can be applied to many kinds of welded details which structural stress concentration factors are different from each other. This paper reports the application of the proposed model for various welded details including cover plate, longitudinal stiffener, gusset and side attachment. From the investigation of predicted results by using the proposed model it was shown that the ambiguous fatigue characteristics of the various details influenced widely by the welding residual stress are clarified, and also the model could be applied to assess fatigue life of general welded structures.

• Journal of the Korean Society for Precision Engineering
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• v.3 no.3
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• pp.13-21
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• 1986

Turning property of metal is affected by the cutting condition, tool geome- try and cutting material. But the turning property of welded material is not welknown. Welded structures usually contain nonhomogeneity, defects and resi- dual stresses due to differential contraction between welded metal and base metal. In this paper, authors conducted the experimental test on the turning property, by changing turning condition and welding electrodes of the welded specimens. The results obtained in these experimental tests are as follows; (1) Within the limit of this experimental test, the cutting force of the weld zone is bigger than that of base metal, and this phenomena is caused by the different mechanical property of the weld zone. The range of the variation of cutting force in the weld zone is caused by the nonhomogeneity of the weld zone, respectively. (2) The surface roughness follows the general characteristic of the effect of cutting condition on the surface roughness and the surface roughness of the weld zone shows coarse surface comparing with that of the base metal. (3) The specimen welded by the electrode E4301, shows worse cutting property than that of E4361 and E4313.

• Nuclear Engineering and Technology
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• v.38 no.3
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• pp.277-284
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• 2006

In order to ensure the structural integrity of nuclear welded structures during design life, the fatigue life has to be evaluated by fatigue analysis procedures presented in technical codes such as ASME B&PV Code Section III. However, existing fatigue analysis procedures do not explicitly consider the presence of welded joints. A new fatigue analysis procedure based on a structural stress/fracture mechanics approach has been recently developed in order to reduce conservatism by erasing uncertainty in the analysis procedure. A recent review of fatigue crack growth data under various mean loading conditions using the structural stress/fracture mechanics approach, does not consider the mean loading effect, revealed some significant discrepancies in fatigue crack growth curves according to the mean loading conditions. In this paper, we propose the use of the stress intensity factor range ${\Delta}K$ characterized with loading ratio R effects in terms of the structural stress. We demonstrate the effectiveness in characterizing fatigue crack growth and S-N behavior using the well-known data. It was identified that the S-N data under high mean loading could be consolidated in a master S-N curve for welded joints.

• Journal of Welding and Joining
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• v.27 no.3
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• pp.52-59
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• 2009

Flash butt welding is applied in many industries. New technology was developed recently for joining billets which called "EBROS (Endless Bar Rolling System)". After reheating billets in furnace, two billets were joined using flash butt welding. The objective of this study was to investigate the effect of alloying elements on mechanical properties of flash butt welded zone of hot rolled steel bar. The tensile properties on welded zone of Fe-Mn steel and Fe-Mn-V steel were dropped as compared with non-welded zone. Fe-Mn-Nb steel was opposed to the former. It was found that the white band at the welded zone had high ferrite volume fraction and large ferrite grain size. The vertical white band between flash butt welded billets was transformed into an arrowhead it of steel bar. According to this band, softening has been appeared. There was a interesting phenomenon with HAZ of Fe-Mn-Nb Steel, 40nm scale of particles were observed and hardness of HAZ was higher than non-welded zone.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.2
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• pp.157-165
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• 1997

The strength level of welded joint in room temperature and elevated temperature up to $600^{\circ}C$ was investigated in 250 and 300 grade 18% Ni maraging steel sheet welded with electron beam. The results obtained in this study are as follows; 1. Optimum welding heat input was 600J/cm in 1.0mm thickness and the room temperature tensile strength, joint efficiency of welded joint treated with optimum aging condition were found to be about 166kg/$mm^2$, 95% in 250 grade, 189kg/$mm^2$, 92% in 300 grade maraging steel sheet, respectively. 2. Tensile strength of welded joint in room temperature increased slightly by aging after repeated solution heat treatment, but the fracture mode showed a shear. 3. Joint efficiency at a temperature between $540^{\circ}C$and $600^{\circ}C$ found to be about 72% to 55%, but the joint efficiency exceeded about 90% below $300^{\circ}C$. 4. The fracture occurred in most weld metal, and the fracture surface showed a shallow dimple.