• Proceedings of the KSR Conference
• /
• 2004.10a
• /
• pp.733-738
• /
• 2004

Recently continuous welded rail is generally used to ensure running performances and to overcome the problems such as structural vulnerability and fastener damage at the rail expansion joint. Though the use of continuous welded rail on bridge has the advantage of decreasing the vibration and damage of rail, it still the risk of buckling and breaking of rail due to change of temperature, starting and/or breaking force, axial stress concentration and so on. So, VIC code and many methods has been developed by researchers considering rail-bridge interaction. Although there are many research concerning stability of continuous welded rail about temperature change on bridge and starting and/or breaking force, the study of continuous welded mil for earthquake load is still unsufficient. In this study, the nonlinear seismic response analysis of continuous welded rail on bridge considering soil-structure interaction, geotechnical characteristic of foundation and earthquake isolation equipment has been performed to examine the stability of continuous welded rail.

• The Journal of Korean Academy of Prosthodontics
• /
• v.41 no.4
• /
• pp.440-450
• /
• 2003

Statement of problem : The joints of removable partial denture alloys have failed frequently after routine usage. Purpose : The purpose of this study was to evaluate the mechanical properties of the laser welded Co-Cr alloys. Material and method : For this study 20 Co-Cr specimens were casted and 10 of them were seperated on the middle area and laser welded with Alpha laser welding machine(Siro Lasertec, Pforzheim, Germany). Rest of them which were as cast, were used as a control group. For the section of the experimental specimens, wire cutting machine was used to make a even gap of the all specimens. Laser welding was done with manufacturer's instrunction and tested each specimen by Instron Machine. Tensile strength, 0.2% yield strength and % elongations were recorded. Fractured surfaces were investigated with SEM. Results : The results were as follows : 1. The tensile strength of the laser welded group(617.7MPa) was about 75% of the as cast group(820.4MPa). It had stastically significant differences(p<0.05). 2. The % elongation of the experimental group was 6.6 which was lower than the control group(14.3). 3. Fracture of the experimental group occured in the welded surface and showed many voids. In contrast, the fracture surface of the control group was showed rough surfaces without any voids. Conclusion : The tensile strengths of the as-cast joints were higher than those for the laser welded joints, and the % elongation of the experimental group was lower than the control group. Porosity was found in laser-welded joints.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1998.06a
• /
• pp.110-120
• /
• 1998

Tailor-welded blanks are made of two or more different blanks in thickness or material. So car body with tailor-welded blanks need not reinforcement panels. However in order to make stamping tools for tailor-welded blanks, die engineers should know about the exact position of the welding line after the part is drawn. The necessity of knowledge about the position of welding line needs forming simulation methodology as a prior step in tooling. Therefor some parts of the simulation methodology are proposed and compared with the experimental results.

• Proceedings of the KSR Conference
• /
• 2007.11a
• /
• pp.1362-1369
• /
• 2007

Seoul Metro continuously converted the standard rail into continuous welded rail since the later part of 1990's, and currently, most of the sectors of the Seoul Metro are continuous welded rails. As the continuous welded rail is inhibited by the contraction and expansion force of the rail as well as rail-bed, this force is stored as the internal stress of the rail with the exception of portion of the both ends of the continuous welded rail. If the contraction and expansion of the rail is restricted, the internal stress, that is, the force in the direction of the axis, is proportional to the cross-sectional area of the rail. Therefore, with regards to the temperature changes, the internal stress changes in accordance with the type of rail, bolting apparatus, railroad tie and rail-bed. As such, the rail temperature becomes important data in securing the gap at the adjoining section of the rail in the standard rail section, and to determine the setting temperature for the continuous welded rail. In addition, it becomes basic data for maintenance of the track. Accordingly, this thesis introduces cases of installation of rail temperature detector in order to prevent and manage track defectiveness due to increase in rail temperature, and to utilize as basic data at the time of various construction and maintenance. Furthermore, this thesis aims to assist maintenance of track through systematic temperature management in the future by looking into means of its utilization.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.4
• /
• pp.467-474
• /
• 2010

Stainless steel sheets are widely used as the structural material for railroad cars and commercial vehicles. Structures made of stainless steel sheets are commonly fabricated by gas welding, For the fatigue design of gas welded joints such as fillet joints, it is necessary to obtain design information of the stress distribution at the weldment as well as the fatigue strength of the gas-welded joints. Further, the influence of the geometrical parameters of gas-welded joints on stress distribution and fatigue strength must be evaluated. in this study, ${\Delta}P-N_f$ curves were obtained by fatigue tests. and, the ${\Delta}P-N_f$ curves were rearranged on the basis of the ${\Delta}{\sigma}-N_f$ relation for the hot-spot stresses at the gas-welded joints. These results, were used for conducting an accelerated life test(ALT) From the experiment results, an acceleration model was derived and factors were estimated. The objective is to obtain the information required for the analysis of the fatigue lifetime of fillet welded joints and for data analysis by the statistic reliability method to save time and cost and to develop optimum accelerated life prediction plans.

• Journal of Power System Engineering
• /
• v.6 no.4
• /
• pp.68-72
• /
• 2002

For the evaluation of a flaw in a welded stainless steel by the Time of Flight Diffraction(TOFD) Method, we have made the reference specimen for experimentation. As a result, we could analyze a specific character and the inner state of the structure in a welded stainless steel and we came to the conclusion as followed. (1) For analyze the structure state of a section in a welded stainless steel through the optical microscope, we could have analyzed the generated shape and the location of a flaw and the inner parts of the structure state through the microscope of eighty magnification and two hundred magnification about the soundness, the heat affected zone(HAZ) and the welded part. (2) Through the comparison with the shape and the size of a flaw in the welded part about the conventional ultrasonic test and the TOFD Method, we could make an observation the special character of the TOFD Method and principles. (3) We analyzed and collected the merit of the TOFD Method on the basis of the experimental result by the shape and the size of a flaw in the inner welded parts. So, we made up a base that we could use as a basic data for a similar flaw like that. Through the study as mentioned above, we could make an observation the flaw detective method and principles used in the TOFD Method.

• Journal of the korean Society of Automotive Engineers
• /
• v.13 no.5
• /
• pp.42-50
• /
• 1991

According as the members and inner and outer plates 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. Therefore, it has been increasingly required to improve the fatigue strength of the spot welded structures. As one of the improving methods for such problem, the author had previously proposed the method of alleviating stress concentration at nugget edge of the spot weld part and improving its fatigue strength [1]. But, 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 estimation method of them. In this report, by considering nugget edge of the spot weld part of the spot welded lap joint subjected to tensile load to the ligament crack, fatigue strength of various spot welded lap joints was estimated with the stress intensity factor (S.I.F.) K which is fracture mechanical parameter. It is known that evaluation of fatigue strength of the spot welded lap joint by the stress intensity factor (S.I.F.) K is more effective than the maximum stress $(\sigma_{ymax}$) at edge of the spot weld part on the center line of width of the plate.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.5 no.2
• /
• pp.163-174
• /
• 2001

This paper is to study the characteristics of axial force behavior that operates to the part of turnout when it makes the turnout and the continuous welded rail unifying. The study is to model by using the 50kgN rail No. 15 turnout used in the domestic national railway and the UIC60 rail No. 18 turnout used in the rapid transit railway as the finite elements for analyzing the axial force behavior of the turnout by the continuous welded rail. It is to analyze the characteristics of behavior according to the change of creep resistance, ballast resistance and the change of parameter valuables of heel joint by the axial force simulation in making the continuous welded rail and then, it is to present the result. As the result of research on the parameter valuables through the analysis, it shows that the maximum axial force of turnout by the continuous welded rail are largely subordinated to the maximum resistance of heel joint and the fitting devices than the ballast resistance. Also it shows that the maximum axial force produced changes a lot according to the characteristics of creep resistance of the fitting part and the ballast resistance.

• Transactions of Materials Processing
• /
• v.12 no.5
• /
• pp.440-448
• /
• 2003

Sheet or plate bending is one of the most important industrial metal forming processes. Considerable attention has been focused on gaining a better understanding of bending characteristics. One of defaults in bending process is the springback. In this study, the springback characteristics of tailor-welded strips in U-bending process was investigated. Furthermore, effect of the process variables such as the geometry of the tools, thickness combination of workpiece, and welding prcoessing on springback were experimentally clarified. First, tailor-welded strips are joined by the laser welding process and consisted of two types of thickness combinations of the SCPl sheet, $0.8t{\times}1.2t$ and $0.8t{\times}1.6t$ to investigate the effect of different thickness combination on the springback. Secondly, two different directionly welded strips, one was welded along the centerline of the strip-width and the other was along the centerline of strip-length, were adopted to compare the effects of the location of weld line on the springback. Some cases of the experimental results were compared to the results simulated by using a commercial FEM code, PAM-STAMP and the theoretical results using the springback formula as well.

• Proceedings of the KWS Conference
• /
• 2002.10a
• /
• pp.121-126
• /
• 2002

The railroad cars or the commercial vehicles are generally manufactured by the spot welding. Among various kinds of spot welded lap joints, multi-lap joints are one of popular joints in manufacturing their body structures. But, fatigue strength of these joints are lower than that of base metal due to high stress concentration at the nugget edge of the spot weld and are known to considerably be influenced by welding conditions as well as the mechanical and geometrical factors. Thus, it is necessary to establish a reasonable and systematic fatigue design criterion for spot welded multi-lap joints. In this paper, the $\Delta$P-N$_{f}$ curves has been rearranged in the $\Delta$$\sigma$-N$_{f}$ relation with the maximum stress at the nugget edge of spot welded multi-lap joints subjected to tensile shear load. Consequently, the fatigue data were evaluated in terms of fracture mechanics by plotting on the $\Delta$OP-N$_{f}$ curves. From the results obtained, both of them have been revealed to be applicable to fatigue design of spot welded multi-lap joints. However, the fracture mechanical approach is found to be more effective than the maximum stress approach in the range on N$_{f}$$\geq$2x10$^{5}$ . .