The development of vehicle body parts using dissimilar materials is increasing to achieve weight reduction of body components. Dissimilar materials are often employed in lightweighting research because they can provide performance that is difficult to achieve with a single material. Dissimilar materials are primarily joined using mechanical joining methods such as Flow Drill Screw(FDS) and Self-Piercing Rivet(SPR). However, if the joints fail due to external forces, the body components cannot perform their intended function. Therefore, the performance of dissimilar material components is determined by the fastening performance of the joints. If the fracture behavior of the joints due to external forces can be predicted, it can lead to the development of body components with deformation modes that protect the driver. In this paper, various modeling techniques were compared to simulate the behavior of FDS joints, and the optimal modeling technique was selected. Based on this, finite element analysis was conducted to predict the fastening strength of FDS joints using the constructed finite element model.

Lightweight design has always been a critical concern in the automotive and aerospace industries, prompting extensive research. Recently, Fiber Metal Laminate (FML) has gained recognition as a promising solution for achieving both reduced weight and high strength in crashworthiness designs. This study introduces a method for fabricating FML using localized heating and multi-point dieless forming (MDF) technology. Rectangular specimens were fabricated using aluminum (Al 5052-h32) as the outer layer and carbon fiber-epoxy prepreg (USN150A) as the inner material. To enhance adhesion, adhesive films and sanding processes were employed in combination. A simplified FML manufacturing apparatus capable of heating up to 300℃ was developed, with the curing process completed in just 5 minutes, significantly shorter than conventional autoclave conditions. Tensile tests conducted on the fabricated FML specimens revealed tensile strengths exceeding those of aluminum by over 50%. This research validates the feasibility of using localized heating MDF technology for FML fabrication and highlights the need for further studies on interfacial bonding strength and microstructural analysis to ensure the technology's reliability.

The microstructure and room temperature tensile properties of ultra-thin sheet superalloys (Co based Elgiloy and Ni based Hastelloy C22) were investigated. Elgiloy exhibited FCC and HCP phases and Hastelloy C22 showed an FCC structure with observed twin boundaries. Both alloys exhibited deformation bands inside the grains during tensile deformation. Elgiloy showed intermediate tensile properties between as-rolled and heat-treated states, whereas Hastelloy C22 exhibited higher tensile and yield strengths than conventional materials. Fracture surface analysis of Elgiloy revealed shallow dimples and striated fracture patterns along weak interfaces between FCC and band-shaped HCP phases, indicative of crack propagation. In contrast, Hastelloy C22 showed brittle fracture characteristics, such as river patterns concentrated at the center and cleavage features near the edges. Elgiloy exhibited strain hardening from TRIP effects during tensile deformation, showed higher tensile strength after yielding than Hastelloy C22. The 60° shear fracture angle is Elgiloy was caused by high strain concentration and microcracks at FCC/HCP interfaces. Hastelloy C22 displayed higher yield strength due to deformation twins and increased dislocation density. Fracture initiation in Hastelloy C22 occurred at twin boundary cross-sections, and its higher atomic bond energy and twin-induced strengthening resulted in a higher elastic modulus compared to Elgiloy.

The application of coil springs with various coil diameters and pitches is required to improve steering performance and ride comfort. Meanwhile, high strength spring is primarily manufactured by hot coiling process to ensure formability. But hot coiling process has limits in producing coil springs due to high energy consumption, low efficiency, and the need for mandrel. Therefore, this study considers the cold coiling process, which allows for degrees of freedom in forming, to manufacture high-strength coil springs. However, the cold coiling process is difficult to implement the complex shape, so accurate shape prediction and dimensional control are essential during the cold coiling process. This study proposes a method to simulate the cold coiling process through finite element(FE) simulation to predict shape and dimensional changes that occur during the forming of coil springs. First, uniaxial tensile test was conducted to evaluate the mechanical properties of the high-strength material. Next, FE-simulation was performed to predict the shape changes occurring during the forming process. Finally, comparison was performed with coil springs produced through actual cold coiling process. As a result, the effectiveness of the simulation proposed in this study for cold coiling process was verified.

The ASTM E9 standard provides specifications for metallic compression testing using specimens categorized as short, medium, or long specimens on their length-to-diameter ratios. For strong materials such as bearing metals, the standard specifies short specimens (length-to-diameter ratios of 0.8 or 2.0), while medium specimens (length-to-diameter ratio of 3.0) are commonly used for general metallic specimens. However, the metal additive manufacturing processes, which involve melting and rapid solidification, result in even traditional metals exhibiting high-strength properties. Consequently, for metal additive manufacturing specimens, consider using lower length-to-diameter ratios compared to the standard evaluation of general metallic samples, which typically use a length-to-diameter ratio of 3.0. Based on the experimental data, an ANOVA test was conducted to examine changes in compressive strength across various L/D ratios (length-to-diameter of 2.0, 2.5, 3.0, 3.5). The results indicated a statistically significant difference in compressive strength for ratios of 3.0 and above. Notably, L/D ratios of 2.0 and 2.5 yielded reliable compressive strength values, suggesting their optimal applicability in compression performance evaluations. The results of this study are expected to be used as important guideline for establishing standards and integrating specifications for reliable performance evaluation of metal additive manufacturing.

This study deals with multi-stage cold and warm forging for fabricating a tripod housing used as a torque member of inner constant velocity (CV) joint. The multi-stage cold and warm forging process is composed of warm forging operations such as primary forward extrusion, forward extrusion, upsetting, backward extrusion, and of cold sizing. C48P medium carbon steel round bar with a diameter of 55.0mm is selected as initial billet workpiece, and uni-axial compression tests are performed to evaluate the compressive strength under various temperature conditions. In order to consider a series of thermal effects during warm forging operations, each forging stage is subdivided into feeding, forging, and ejection. Numerical simulations based on elasto-plastic finite element method are sequentially carried out to verify process flow designed for the multi-stage cold and warm forging process. As a result, the primary designed process flow is shown to be applicable itself to fabricate the tripod housing, but to be necessary minor modification for realizing the near net-shape forged tripod housing.