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Spacer grid springs support fuel rods so that the rods keep the position laterally and axially in pressurized water reactor fuel assemblies. The spring load-deflection characteristic, i.e. spring force and stiffness, is needed to evaluate the rod support conditions in the case of fuel assembly manufacturing, shipping and handling. In general, the load-deflection characteristic of grid spring is obtained by mechanical test, but it takes long time to get the new designed grid specimen because the grid manufacturing process comprises strip material manufacturing, stamping die and punch preparation, heat treatment and welding, etc. Therefore the analytic method such as finite element method (FEM) is tried to predict the nonlinear load-deflection characteristic of new designed grid. The spring characteristic mechanical test is simulated with unit cell model and analyzed by FEM tool. Comparing the results between test and analysis shows that more details are needed in the modeling because the boundary conditions of the spring are very complicated and the spring material thickness is changed by the stamping process. The analysis of modified model including expanded cells and thickness changed springs is performed. Using the analytic method of the work to obtain the load-deflection characteristic of spacer grid spring is expected to be useful in the prediction of the characteristic of new designed grids.

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Hemming is used to connect two sheet metal components by folding the edge of an outer panel around an inner panel to create a smooth edge. The minimization of hemming defects is critical to the final quality of automobile products because hemming is one of the last operations during fabrication. Designing the hemmed part is not easy and is influenced by the geometry of the bent part. Therefore, the main problem for automotive parts is dimensional accuracy since formed products often deviate geometrically due to large springback. Few numerical approaches using 3-dimensional finite element model have been applied to hemming due to the small element size which is needed to properly capture the bending behavior of the sheet around small die corner and the comparatively big size of automotive opening parts, such as doors, hoods and deck lids. The current study concentrates on the 3-dimensional numerical simulation of hemming for an automotive door. The relationship between the design parameters of the hemming operation and the height difference defect is shown. Quality improvement of the automotive door can be increased through the study of model parameters.