• Journal of Mechanical Science and Technology
• /
• v.20 no.3
• /
• pp.335-344
• /
• 2006

A comprehensive review of through thickness transverse residual stress distributions in a range of as-welded and mechanically bent components made up of a range of steels has been carried out, and simplified generic transverse residual stress profiles for a plate and pipe components have been proposed. The geometries consisted of welded pipe butt joints, T-plate joints, tubular T-joints, tubular Y-joints and a pipe on plate joints as well as cold bent tubes and pipes. The collected data covered a range of engineering steels including ferritic, austenitic, C-Mn and Cr-Mo steels. Measured residual stress data, normalised with respect to the parent material yield stress, has shown a good linear correlation versus the normalised depth of the region containing the residual stress resulting from the welding or cold-bending process. The proposed simplified generic residual stress profiles based on the mean statistical linear fit of all the data provides a reasonably conservative prediction of the stress intensity factors. Whereas the profiles for the assessment procedures are fixed and case specific, the simple bilinear profiles for the residual stresses obtained by shifting the mean and bending stress from the mean regression line have been proposed and validated.

• Korean Journal of Materials Research
• /
• v.9 no.2
• /
• pp.217-225
• /
• 1999

The effect on the pitting corrosion resistance of laser welding and surface treatment developed as a repair method of stream generator tubing material that was a major component of primary system at nuclear power plant was observed. Some heat-treated Alloy 600 tubing materials used at domestic nuclear power plants were laser-surface observed. Some heat-treated Alloy 600 tubing materials used at domestic nuclear power plants were laser-surface melted and the microstructural characteristics were examined. The pitting corrosion resistance was examined through Ep(pitting potential) and degree of pit generation by means of the electrochemical tests and the immersion tests respectively. The pit formation characteristics were investigated through microstructural changes and the pit initiation site and pit morphology. The test results showed that the pitting corrosion resistances was increased in the order of the followings; sensitized Alloy 600, solution annealed alloy600, and laser surface melted Alloy 600. Pits were initiated preferably at Ti-containing inclusions and their surroundings in all tested specimens and it is believed that higher pitting resistance of laser-surface treated Alloy 600 was caused by fine, homogeneous distribution of non-soluble inclusions, the disappearance of grain boundary, and the formation of dense, stable oxide film. The major element of corrosion products filled in the pit was Cr. On the other hand, Fe was enriched in the deposit formed on the pit.

• Journal of the Korean Society for Precision Engineering
• /
• v.26 no.4
• /
• pp.134-140
• /
• 2009

The feasibility of electrochemical drilling and milling on stainless steel are investigated using tungsten microelectrode with $10{\mu}m$ in diameter. For the development of environmentally friendly and safe electrochemical process, citric acid solution is used as electrolyte. A few hundred nanoseconds duration pulses are applied between the microelectrode and work material for dissolution localization. Tool fracture by Joule heating, micro welding, capillary phenomenon, tool wandering by the generated bubbles are observed and their effects on micro ECM are discussed. Occasionally, complex textures including micro pitting corrosion marks appeared on the hole inner surface. Metal growth is also observed under the weak electric conditions and it hinders further dissolutions for workpiece penetration. By adjusting appropriate pulse and chemical conditions, micro holes of $37{\mu}m$ in diameter with $100{\mu}m$ in depth and 26Jim in diameter with $50{\mu}m$ in depth are drilled on stainless steel 304. Also, micro grooves with $18{\mu}m$ width and complex micro hand pattern are machined by electrochemical milling.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2004.10a
• /
• pp.120-123
• /
• 2004

The bending phenomenon has been known to be occurred by the difference of velocity at the die exit. The difference of velocity at the die exit section can be obtained by the different velocity of billets inside die chamber after passing the multi-hole container. The curvature can be controlled by the two variables, the one of them is the different velocity of billets through the multi-hole container, the other is the difference of hole diameter. The bending phenomenon during extruding using four billets can be obtained by the difference of hole diameters in the multi-hole container or by the difference of relative velocity of billet inserted in the container. As results of DEFORM-3D analysis, it can be shown that bending can be obtained during extruding by the difference of relative velocity of two billets or by the difference of hole diameter, and the amount of curvature is increased by the difference of velocity and diameter. According to the shape of products, the curvature of rectangular section is bigger than the curvature of regular square section. And, it is estimated that, because the stress on the welding line is much higher than yield stress of material, the bonding of four billets can be obtained.

• Journal of the Korean Society for Precision Engineering
• /
• v.28 no.10
• /
• pp.1204-1209
• /
• 2011

In this study, fatigue life is evaluated by comparing with lighter car body through the experiment on SPR joints. An experimental activity on sheet metal samples of Aluminum 5J32 and Steel SPRC440 has been conducted to achieve better understanding of the process. In addition, SPR joint used less than the existing Spot Welding improves joint strength and fatigue life is evaluated by using SPR and adhesive joining Hybrid. Joining(bonding) strength and fatigue life on SPR and Hybrid (SPR + adhesive) are evaluated throughout the experiment. With joining strength than 20 % of the aluminum material, dissimilar materials has improved over 2 times as large as the strength In case of dissimilar materials, the fatigue life of aluminum is increased by 1.6 to 2.5 times as large as the life.

• Transactions of Materials Processing
• /
• v.26 no.4
• /
• pp.222-227
• /
• 2017

In order to respond to environmental regulations and increased demand for fuel economy, the demand for lightweight car bodies has grown. Hydroforming of aluminum is one possible solution as it eliminates the need for additional welding to develop closed cross-sectional parts. However, the low formability of aluminum is a limitation of its application. On the other hand, the ductility of materials can be improved at higher temperatures, and hot metal gas forming has been widely applied in the production of lightweight vehicle parts. In this study, aluminum alloy for pipe extrusion was developed by controlling the Mg:Cr:Mn ratio based on AA5083. Mechanical properties of the developed material were examined by tensile test and were applied to a forming simulation. Cold forming simulation for preforming and non-isothermal hot forming simulation for hot metal gas forming were carried out to validate process conditions. A prototype of the sidemember was manufactured under the given process condition. Finally, thickness distribution was compared with finite element analysis results.

• Proceedings of the KWS Conference
• /
• 2005.11a
• /
• pp.79-81
• /
• 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.

• Nuclear Engineering and Technology
• /
• v.50 no.1
• /
• pp.107-115
• /
• 2018

To ensure the structural integrity of nuclear power plants, it is essential to predict the lifetime of Alloy 182 weld, which is used for welding in nuclear reactors. The lifetime of Alloy 182 weld is directly related to the crack initiation time. Owing to the large time scatter in most crack initiation tests, a probabilistic model, such as the Weibull distribution, has mainly been adopted for prediction. However, since statistically more advanced methods than current typical methods may be applied, we suggest a statistical procedure for parameter estimation of the crack initiation time of Alloy 182 weld, considering right-censored data and the covariate effect. Furthermore, we suggest a procedure for uncertainty evaluation of the estimators based on the bootstrap method. The suggested statistical procedure can be applied not only to Alloy 182 weld but also to any material degradation data set including right-censored data with covariate effect.

• Corrosion Science and Technology
• /
• v.19 no.2
• /
• pp.57-65
• /
• 2020

As competition among global automakers intensifies, demand for materials that are better in price and performance is increasing. While steel and plastic materials compete for automotive fuel tanks, plastic materials have advantages such as light weight for automobiles. However, they have high prices. Accordingly, in this paper, four types of Zn-X plated steel sheets, electroplating (X = none, Sn) and galvannealed (X = Fe, Fe-Mg), were manufactured and their applicability as a fuel tank material was evaluated. Nano-composite coating solution with good conductivity was treated on the surface of plated steels using a roll coater and then cured through induction furnace to improve corrosion resistance. Quality characteristics such as corrosion resistance, fuel resistance to diverse gasoline and diesel fuels, and seam weldability were evaluated for the above plated steels. Their properties were compared and analyzed with conventional Zn-Ni electroplating steels. Among the above plated steels, Zn-Fe-Mg galvannealed steels coated with nano-composite coating exhibited better properties than other steels. Detailed experimental results suggest that evenly distributed Mg elements on the coating layer play a key role in the enhanced quality performance.

• Journal of the Society of Naval Architects of Korea
• /
• v.48 no.2
• /
• pp.178-182
• /
• 2011

Generally in order to reduce the steel weight of stiffened plate, stiffener spaces tend to be narrow and the plate gets thin. However, it will involve more fabrication cost because it can lead to the increase of welding length and the number of structural members. In the yard, the design which is able to reduce the total fabrication cost is needed, although it requires more steel weight. The purpose of this study is to find optimum stiffener spaces to minimize the fabrication cost for the cargo tank of LPG Carriers. Global optimization methods such as ES(Evolution Strategy) and GA(Genetic Algorithm) are introduced to find a global optimum solution and the sum of steel material cost and labor cost is selected as main objective function. Convergence degree of both methods in according to the size of searching population is examined and an efficient size is investigated. In order to verify the necessity of the optimum design based on the cost, minimum weight design and minimum cost design are carried out.