In this study, we performed molecular static simulations to investigate the enhanced elastic modulus of multiply twinned nanowires (MTNs) that had fivefold twin planes. MTNs have the same size-dependent elastic behavior as twin-free nanowires (TFNs), however, the simulation results reveal stiffer elastic behavior of MTNs when compared with that of TFNs of the same size. This is because atomic rearrangement occurs inside MTNs through the intrinsic elastic deformation as a result of their unique geometry. These results are supported by the elastic-modulus distribution on the cross-sectional area—the elastic modulus increases close to the central part of MTNs—and the intrinsically strained structure that has a highly compressed central portion in the radial direction.

A multi-stage cold forging process was developed and complemented with finite element analysis (FEA) to manufacture a high-strength one-body input shaft with a long length body and no separate parts. FEA showed that the one-body input shaft was manufactured without any defects or fractures. Experiments, such as tensile, hardness, torsion, and fatigue tests, and microstructural characterization, were performed to compare the properties of the input shaft produced by the proposed method with those produced using the machining process. The ultimate tensile strength showed a 50% increase and the torque showed a 100 Nm increase, confirming that the input shaft manufactured using the proposed process is superior to that processed using the machining process. Thus, this study provides a proof-of-concept for the design and development of a multi-stage cold forging process to manufacture a one-body input shaft with improved mechanical properties and material recovery rate.

In order to prevent the surface defect in the magnesium alloy extrusion process, it is important to set an appropriate process condition. The extrusion limit diagram is very useful to achieve the maximum extrusion speed without surface defect. In this study, the extrusion limit diagram for the magnesium alloy extrusion is constructed by using extrusion experiment and finite element analysis. For finite element analysis hot compression test is carried out to obtain the effective stress and stain curves according to the various strain rates and temperatures. The effectiveness of the constructed extrusion limit diagram is verified through the porthole extrusion experiment for producing the magnesium alloy bumper beam.

Adapters are a component of the output system in the internally geared hub for a bicycle. Originally, adapter parts were produced by a machining process with low productivity and material usage rate. In this study, the metal powder injection molding (MIM) process has been applied as an alternative manufacturing method to the machining process. Microstructure analysis and mechanical property testing has been conducted in order to select the material for the adapter with changes in the nickel content. The geometrical precision of the adapter is measured by using three-dimensional scanner with various mixing ratios of the powder and the binder. The developed alternative process for the adapter results in increased productivity and material usage rate. Previously, this process was only used for small parts less than 10 mm in diameter. With this development, the MIM process may be used more widely than before.

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