•The analysis code to simulate the 3D multipass welding process quickly was improved.•The improved analysis code provides the same analysis accuracy as a well-known commercial code.•Assumption of ...annealing effect and the isotropic hardening rule improve simulation accuracy.•The improved analysis code can solve welding problems faster than a well-known commercial code.
An iterative substructure method has been proposed as a technique to calculate thermal elastic–plastic problems quickly and efficiently. Based on the iterative substructure method, an analysis code for the multipass welding was developed so as to realize accurate residual stress computation using a 3D precise model within a practical time. In the present study, the fast computation performance of the iterative substructure method was considered as a means to improve the original code. Then analysis accuracy and speed of the improved code were investigated. The proper analysis accuracy of the improved code was demonstrated by comparing with residual stress measurements of a multipass butt-welded pipe joint. The analysis speed of the improved code was clarified to be faster than a well-known commercial code in comparison between their computation times.
The joint of oxide dispersion strengthened (ODS) ferritic steel and martensitic steel was produced by friction stir welding. The thermo-mechanical process during welding causes recrystallization in ...the ODS steel and phase transformation in the martensitic steel. In stir zones of both steels, low-angle boundaries significantly convert to high-angle boundaries. The recrystallization in ODS steel is characterized by the increase in the Σ3 twin boundary with an almost constant fraction of Σ5–Σ29 boundaries, while the martensitic steel shows an opposite trend.
A data-base of the advanced multi-material joint performance has to be prepared for designing a future multi-material car body in order to select both the advanced materials and the joining methods ...appropriately. In this research, as one of the most important joint performances, the tensile fatigue properties of dissimilar lap joints were studied. Various advanced multi-material dissimilar lap joint using an ultra-high strength steel (UHHS), a carbon fiber reinforced thermo-plastic (CFRTP) and an aluminum alloy of A5083P-O were fabricated by the resistance spot welding (RSW), refill friction stir spot welding (RFSSW), friction stir spot welding (FSSW) and laser irradiation assistance plastic welding (LIAPW). Regardless of the types of dissimilar materials, it is found that the number of cycle achieving to the fracture decreases almost monotonically with increasing the applied load. In addition, the shear fatigue properties of UHHS & A5083P-O joint joined by RFSSW is found to be similar to that of aluminum alloy joint joined by RSW. Moreover, the fatigue properties of UHHS & CFRTP and A5083P-O & CFRTP joints made by FSSW are revealed to be governed by the interfacial strength between the metals and CFRTP and to be predicted by the tensile shear strength of the dissimilar lap joint.
In order to design a future multi-material car body, both an appropriate selection of the advanced materials and a suitable assignment of joining methods are essential technologies, where the ...data-base of the advanced multi-material joint performance has to be prepared. In this research various advanced multi-material dissimilar lap joints were fabricated and the tensile shear strength of those joints was evaluated. The materials used were an ultra-high strength steel (UHHS), a carbon fiber reinforced thermo-plastic (CFRTP) and an aluminum alloy of A5083P-O. The resistance spot welding (RSW) and refill friction stir spot welding (RFSSW) were employed for joining UHHS and A5083P-O, while UHHS & CFRTP and A5083P-O & CFRTP lap joints were fabricated by the friction stir spot welding (FSSW) and laser irradiation assistance plastic welding (LIAPW). The tensile shear strength of UHHS & A5083P-O joint joined by RFSSW was found to be almost two times of that produced by RSW, and this difference seems to be mainly caused by the difference of joint area. The difference of joint area also affects the tensile shear strength of UHHS & CFRTP or A5083P-O &CFRTP lap joints made by FSSW and LIAPW, and the joint strength of LIAPW was larger than that of FSSW. Moreover, all the tensile shear tests suggest that the total heat input during joining process might not influence the tensile shear strength proportionally and the relationship between the joining conditions and tensile shear strength has be evaluated by using the artificial intelligence technologies in order to contribute the data-base of the advanced multi-material joint performance.
The friction stir welding (FSW) method was used to form joints in an oxide dispersion strengthened (ODS) steel with tool rotation speeds ranging from 250rpm to 400rpm to investigate the effect of ...rotation speed of the tool on the mechanical properties and microstructure of the joints. The hardness of the stirred zone (SZ) of the ODS steel joints was reduced after welding at all rotation speeds because of recrystallization induced by the heat generated during the FSW process. The recrystallization was accompanied by a change in the grain morphology from elongated grains to isotropic grains. The sizes of recrystallized grains increased with increasing rotation speed of the tool. Oxide particles, however, were slightly coarsened by the FSW process, and there was no systematic relationship between the particle size and the rotation speed. The hardness of the SZ of ODS steel joints followed the Hall–Petch relationship. Tensile tests of the FSW ODS steel joints revealed that the change in the ultimate tensile strength is similar to the change in the hardness, suggesting that the joint strength was reduced by grain growth but not by degradation of the fracture strength.
In this study, the possibility of using adhesive for friction stir spot welding was investigated with the aim of improving the strength and rigidity of aluminum and CFRP dissimilar material joining ...members and improving galvanic corrosion resistance. As a result, it was found that there is a trade-off relationship between the friction stir spot welding, which improves the joint strength in proportion to the frictional heat, and the weld bond, in which the adhesive is thermally decomposed by the frictional heat. When using adhesive together, it is necessary to consider the selection of adhesive and the optimization of frictional heat according to the application and required strength level.
The weldability of oxide dispersion strengthened (ODS) ferritic steels is a critical obstructive in the development and use of these steels. Friction stir welding has been considered to be a ...promising way to solve this problem. The main purpose of this work was to reveal the effects of mechanical force on grain structures of friction stir welded ODS ferritic steel. The grain appearances and the misorientation angles of grain boundaries in different welded zones were investigated by the electron backscatter diffraction (EBSD). Results showed that the mechanical force imposed by the stir tool can activate and promote the recrystallization characterized by the transformation of boundaries from LABs to HABs, and contribute to the grain refinement. The type of recrystallization in the stir zone can be classified as the continuous dynamic recrystallization (CDRX).
The paper investigates the inherent deformations of thin plate bead-on-plate welding with varying plate thicknesses for eight different materials. Firstly, three-dimensional (3D) thermal ...elastic–plastic finite element (FE) model based on interactive substructure method (ISM) is used to compute welding deformations within practical time. Computed results are compared with experimental results. Very good correlation is obtained for temperature as well as deformation predictions between experimental and ISM. The effectiveness of ISM is validated. Then, welding inherent deformations are evaluated by inverse analysis using the computational results of ISM. Using inherent deformations, weld deformation can be estimated within shorter time by elastic-shell model. Finally, a database of inherent deformations for eight different materials including 144 computational cases is developed. In addition, the relationship between welding heat input parameter and inherent deformations is discussed.
Oxide dispersion strengthened （ODS） steels can be used as the structural materials in the future fusion reactors and the fuel cladding materials in the advanced fission reactors. However, the ...weldability of ODS steels is a severe problem. In the present study, defect-free joints of the 15Cr-ODS ferritic steel were achieved by friction stir welding at different rotation speeds. The recrystallization, hardness and tensile properties are highly related with the rotation speed of the stir tool. The higher rotation speed results in coarser grains in the top SZ, while the grain size exhibits more complicated relation with the rotation speed in the SZ center. The joint welded at 250 rpm exhibits a maximum tensile strength of 974 MPa that reaches about 84% of that of the base metal.
