Key Engineering Materials Vols. 345-346

Abstract: Pre-produced triplate transition joint assemblies are widely used in shipbuilding industry to make welds between aluminum and steel for a number of years now. The straight-shaped transition joint assemblies are bent during shipbuilding. So it is necessary to study the residual stresses created by punch forming, which would have heavy effects on the quality of structural parts. ABAQUS is a suite of powerful engineering simulation programs, based on the finite element method. In this paper, ABAQUS was used as the main tool to simulate the residual stresses in a triplate transition joint after unloading. Punch-pressing was carried to simulate bending moment in ABAQUS. The triplate is consisted of baselayer (steel: Lloyd’s Shipplate Gr. A), interlayer (pure aluminum: Al99.5) and superlayer (Al-Mg alloy: AlMg4.5Mn). Results from the ABAQUS analysis showed that increasing the radius of punch significantly reduced the von Mises residual stresses in steel. Changes of von Mises residual stresses in interlayer (Al99.5) and superlayer (AlMg4.5Mn) were negligible.

Abstract: This present work investigated the influence of welding conditions, such as welding current, diameter of welding wire on the microstructural change, and mechanical properties of TIG welded joint in extruded AZ31B Mg plate. It was found that a good and sound welded joint was achieved in all welding conditions. The grain size decreased with increasing welding current and decreasing diameter of welding wire. In addition, the second phases were homogeneously distributed in the grain and grain boundary as the welding current and the diameter of the welding wire were decreased. β discontinuous precipitates were observed in the welded joint; this microstructure has not been reported by previous researches investigating AZ31B Mg alloy. The hardness value was affected by the existence state of the second phase and the hardness of the welded joint region was lower than the other regions in welded AZ31B Mg alloy. The strength of the welded joint region was influenced by the grain size and had more than 90 %, compared to that of ASTM standard specification.

Abstract: Dissimilar metal welding (DMW) are used widely in various industrial applications due to the practical importance from the technical and economic aspect. However, DMW have several fabricative and metallurgical drawbacks that can often lead to in-service failures. For example, the most pronounced fabrication faults are hot cracks. Recently, DMW have used the several of heat source to decrease such as faults. Laser welding process has, in recent years, attracted more attention due to its special features: a small heat-affected zone and narrow weld bead due to the low heat input; welding at high speed; welding can be carried out in areas of difficult access; contactless energy transfer; welding in an exact and reproducible manner; possibilities for automation and robotization, and welding performed in various atmospheres. In this paper, the weldability on dissimilar metal welding of austenite stainless steel and carbon steel using Nd:YAG laser with a continuous wave was experimentally investigated.

Abstract: The microstructure and bonding strength of the wide-gap region brazed with different filler metal powder (BNi-3 and DF 4B) and various powder mixing ratios of additive powder to filler metal powder were investigated. The microstructure characterization showed that Cr borides with a blocky morphology were existed in the brazed region in both filler metal powder. The bonding strength of the wide-gap region brazed with 60 wt.% IN738 additive and 40 wt.% DF 4B powder exhibited 92% tensile strength of IN738 superalloy at room temperature. The Cracks in the wide-gap brazed region initiated at the intermetallic compound and eutectic structure, and then propagated through them.

Abstract: The fatigue characteristic of triple spot welded SPCC plates with the variation of the thickness and the geometry under tensile-shear loading is studied by finite element analysis (FEA) and the obtained data is compared with experimental data. Using 3-D solid element model and 3-D beam-shell model, the maximum equivalent stress and the beam deformation angle (BDA) for various thickness and geometry is studied. The linear relation between crack opening angle (COA) from experiment and the BDA from FEA for beam-shell model is represented, and the empirical prediction of fatigue lifetime is proposed using the relation between COA and BDA.

Abstract: Al bonding in air by inserted A5056 was investigated in this study. Heating rate in thermal history of bonding process may have the relation with the growth of Al oxide film and the deformation of bonding surface by softening. Both of phenomena affect the joinability and the mechanical properties of bond. Al bonding in air was carried out by several heating rate. Growth of Al oxide film significantly suppressed the progress of bonding in air by low heating rate, 1K/s. Decrease of deformation of bonding surface suppressed also the progress of bonding by high heating rate, 10K/s. In case of medium heating rate, 5K/s, good joinabilty of Al bonding in air was obtained by the medium growth of oxide film and the deformation of bonding surface.

Abstract: Laser welding process is widely used in the industrial area due to its less affects to base metal than general welding. Laser welding has characteristics that highly affect ratio, deeply penetration depth and small heat affected zone(HAZ) due to its in a short time melting and then solidification by a high energy absorption rate. The objective of this research work is to investigate the optimum conditions of a cold rolled carbon steel(SCP1) in a laser welding process using a Nd:YAG laser with a continuous wave(CW). The determination of optimum conditions were performed to change the laser power, beam speed, focus length and then carry out an butt welding. From the results of the investigation, it has been shown that the optimal welding condition without defects in the vicinity of the welded area and with a good welding quality is 1325W of the laser power, 1.4m/min of laser welding speed and 0mm of focus position.

Abstract: During manufacturing the welded joint of steel structures, residual stress is produced and weld metal is used inevitably. And residual stress and weld metal influence on the static and dynamic mechanical behavior of steel structures. Therefore, to predict the mechanical behavior of steel pile with a welded joint during static and dynamic deformation, the research on the influence of the welded joints on the static and dynamic behavior of steel pile is clarified. In this paper, the residual stress distribution in a welded joint of steel piles was investigated by using three-dimensional welding analysis. The static and dynamic mechanical behavior of steel piles with a welded joint is investigated by three-dimensional elastic-plastic finite element analysis using a proposed dynamic hysteresis model. Numerical analyses of the steel pile with a welded joint were compared to that without a welded joint with respect to load carrying capacity and residual stress distribution. The influence of the welded joint on the mechanical behavior of steel piles during static and dynamic deformation was clarified by comparing analytical results

Abstract: In this paper, stress distribution in a double lap joint subjected to a tensile load is investigated using the boundary element method. The adhesive used in this study is a commercial epoxy system which can be cured at room temperature. The adhesive is assumed to be linearly viscoelastic. The order of the singularity is obtained numerically for a given viscoelastic model. The numerical results show that interface stresses are large enough to initiate local yielding or edge cracks. Since the exceedingly large stresses cannot be borne by the adhesive layer, edge cracks can occur at the interface corner.