The deformation process of metal foils is usually under a complex stress status, and the size effect has an obvious influence on the microforming process. To study the effect of grain orientation and grain size distribution on the yield loci evolution of SUS304 stainless steel foils, three representative volume element (RVE) models were built based on the open source tools NEPER and MTEX In addition, the yield loci with different grain sizes are obtained by simulation with Duisseldorf Advanced Material Simulation Kit (DAMASK) under different proportional loading conditions. The initial yield loci show a remarkable difference in shape and size, mainly caused by the distinct texture characteristics. By comparing the crystal plasticity simulation with the experimental results, the model with normal grain size distribution and initial texture based on Electron Back-scattered Diffraction (EBSD) data can more accurately describe the influence of the size effect on the shape and size of yield loci, which is the result of the interaction of grain size distribution and texture. However, the enhancement of grain deformation coordination will weaken the impact of the size effect on yield loci shape if the grain size distribution is more uniform.
Earings appear easily during deep drawing of cylindrical parts owing to the anisotropic properties of materials. However, current methods cannot fully utilize the mechanical properties of material, and the number of earings obtained differ with the simulation methods. In order to predict the eight-earing problem in the cylindrical deep drawing of 5754O aluminum alloy sheet, a new method of combining the yield stress and anisotropy index (r-value) to solve the parameters of the Hill48 yield function is proposed. The general formula for the yield stress and r-value in any direction is presented. Taking a 5754O aluminum alloy sheet as an example in this study, the deformation area in deep drawing is divided into several equal sectorial regions based on the anisotropy. The parameters of the Hill48 yield function are solved based on the yield stress and r-value simultaneously for the corresponding deformation area. Finite element simulations of deep drawing based on new and existing methods are carried out for comparison with experimental results. This study provides a convenient and reliable way to predict the formation of eight earings in the deep drawing process, which is expected to be useful in industrial applications. The results of this study lay the foundation for the optimization of the cylindrical deep drawing process, including the optimization of the blank shape to eliminate earing defects on the final product, which is of great importance in the actual production process.
The filling quality of micro-feature structures has a significant impact on the forming quality of micro-channels. The electrical-assisted forming technology can effectively improve the formability of difficult-to-deform materials. In this research, the electrically driven micro-compression constitutive model of SUS304 stainless steels was established to assign grain boundary and grain interior with different material properties. An electrical–thermal–mechanical coupling model was constructed to simulate the filling process considering the effect of grain boundary and grain size. Compared to the experimental results, the simulation indicated a good agreement in microstructure characteristics and higher filling height for the fine-grained material. The increase in grain boundary density makes the resistivity of the fine grain material larger, causing the current destiny and temperature of the specimen to increase with the decrease in grain size. An ellipsoidal gradient temperature distribution is observed due to the uneven current density. Because of the high geometric dislocation density near the grain boundary, a significant dislocation pile-up causes stress to concentrate. It is observed that the deformation coordination is enhanced between the grain boundary and grain core with the decrease in grain size, thus improving the material formability and forming quality.
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