Materials Science Forum Vols. 580-582

Abstract: The stability of plate structure is a very critical problem. The spot welding is practically designed by experiential decisions; so, it is inefficient and risks fatigue fracture. In real structure, multi-spot welded joints are more frequently used than single-spot welded joint. The fatigue behavior of multi-spot welded joints is different from that of single-spot welded joints. The fatigue lives of spot-welding specimen and multi points spot-welding structure are predicted using a FEMFAT 4.4e based on the linear finite element analysis. It is necessary to establish a reasonable and systematic design criterion for the long life design of the spot-welding body structure. In this study, relative location of spot welding was chosen as parameter and the stress distribution around the spot-welding joints’ subjected tensile load was numerically analyzed.

Abstract: The purpose of this study is to produce composite plates by explosive cladding process. This is a process in which the controlled energy of explosives is used to create a metallic bond between two similar or dissimilar materials. The welding conditions were tailored through parallel geometry route by using different explosive ratios to produce both wavy and straight interfaces. In this investigation, a two-pronged study was adopted to establish the conditions required for producing successful solid state welding: (a) Analytical calculations to determine the weldability window; (b) Metallurgical investigations of experiments carried out under different conditions. The required parameters in the experiments were selected through numerical simulations. The analytical calculations confirm the experimental results. Optical microscopy studies show that a transition from a smooth to wavy interface occurs with increase in explosive ratio. Scanning electron microscopy studies show the formation of intermetallic layer in the interface.

Abstract: The structural stress (SS) method developed by BATTELLE has been studied based on small or mid-size scale specimens. In order to apply the new method, such as SS, on an actual project, it should have application results on actual project. However, SS method didn’t have a lot of application data compared to class procedure using hot spot stress (HSS). In order to find out whether the SS method, for the evaluation of fatigue life, can give reasonable results when it is applied under the same loading suggested by classification societies, it was compared with fatigue lives derived by class. ABS & DNV’s simplified fatigue analysis method were adopted to check the validity of SS method. Before applying complicated loading of class, static loading case was applied, since the class method has their own correlation factor for wave loading. And then, simplified fatigue analysis was performed with more complicated loading cases. From the results of fatigue life calculation, it can be said that SS shows reasonable fatigue lives with respect to HSS or notch stress based fatigue lives.

Abstract: This study was aimed at evaluation of residual stress of steel pipe structures. The production process of pipes was complex (at first bending was done by roll forming or press forming and welding was final process of making of steel pipes). So there could be expected high residual stresses in steel pipes. In order to evaluate the changes of residual stress measurements of residual stress were done for the circular pipe (thickness 16 mm). For the evaluation of residual stress, holedrilling method (ASTM E837) was applied. The results showed that along the weld line high tensile stress were measured as expected, and high tensile stresses were measured where large plastic deformation developed. And in order to assist the experimental results, numerical method (finite element method) was applied. In finite element analysis, non-linear analysis of processes was considered. In welding (final case of pipe making), thermal-elastic-plastic analysis was done considering material properties according to temperature. The calculations showed there were good agreements with experimental results. And from results, experimental results could be more effectively assisted through numerical method in welded pipes production.

Abstract: In discussion on reduction of energy and an environmental issue on a global scale, the research project had been organized in Japan. In the project, a committee “Development of model for the high accurate prediction of welding distortion by computer simulation” was set up for the purpose of reduction of energy spent for correction of welding distortion. A lot of items were investigated. The research was carried out to find the dominant factor for the high accurate prediction of welding distortion generated by fillet welding in the committee. As the results, two dominant factors were found and welding distortion generated by fillet welding could be predicted with high accuracy by satisfying two dominant factors.

Abstract: There are two ways of conventional thermal distortion analysis. One is thermal elastoplastic analysis and the other is equivalent forces method based on inherent strain. The former needs exorbitant analysis time, while the latter cannot obtain stress results and requires more time with loads modeling on curved plates. To solve those time-consuming problems, a new kind of thermal distortion analysis method was developed. In this method, inherent strains are devised to be used as direct input factors as boundary conditions. Suggested analysis method was already adopted at welding distortion analysis of large hull block, which was considered as impossible.

Abstract: In recent years, the replacement repair welding, through which damaged bridges are repaired by replacing of the damaged sections with new steel plates through cutting and welding under in-service conditions, has been highlighted for its brilliant features i.e. it can be achieved without incurring traffic dislocation. However, the validity of the repair method is not fully verified because of its lack of safety and reliability. Moreover, repair method by welding inevitably involves cutting and welding process, and the weldability of the replacement repair welded joints has not yet been clarified. In this paper, the weldability of the replacement-repair-welded joints was investigated in order to improve reliability in the repair welded joints of the aged steel bridge. A Steel plate was extracted from the steel bridge after the period of prolonged service, and was welded with a new plate, using replacement repair welding technique, in order to construct a specimen. Flux Cored Arc Welding (FCAW) process was used to fabricate the double "V" butt joints. Welded joints were characterized on the basis of chemical composition analysis, hardness test and micro-structural analysis.

Abstract: We have developed non-equilibrium simulation model of GTA. In this paper, simulation results of plasma property of argon GTA at atmospheric pressure are presented and, furthermore, the reliability of the simulation model is evaluated. As a result, it was revealed that non-equilibrium characteristic appears in regions close to both electrodes and the fringe of the arc column where the temperatures decrease below approximately 10000K. It was also found that non-equilibrium region near the anode surface has thickness of 0.3mm. This result agrees with the simulation result predicted with one-dimensional electrical sheath model.

Abstract: The aim of this study is the development of a numerical technique applicable for the fatigue assessment based on the damage mechanics approach. The generalized elasto-visco-plastic constitutive equation, which can consider the internal damage evolution behavior, is developed in order to numerically evaluate the material fatigue responses. Explicit information of the relationships between the mechanical properties and material constants, which are required for the mechanical constitutive and damage evolution equations, are derived. The performance of the developed technique has been verified using the S-N relationship assessment for STS304 stainless steel.

Abstract: Different techniques are being studied to make the automotive electrical parts more compact and lightweight; along with improving their functionality for saving energy and protecting the environment. In the wake of this trend, the joints in these parts are required to have little distortion and a high degree of accuracy. Although laser welding, which yields low-distortion joints, was developed in response to this demand for high accuracy, it has been difficult to meet the needs of modern, high-accuracy automobile parts with conventional laser welding. In this research, in order to realize that degree of accuracy, a phenomenal and theoretical analysis of the melting solidification process was conducted and high-accuracy laser welding was investigated for controlling welding deformation.