A hybrid cladding technology was developed by combining direct energy deposition (DED) and ultrasonic nanocrystal surface modification (UNSM). This is an effective process to control the mechanical properties inside the metal-clad layer, but the scope to improve the internal properties is low. Therefore, in this study, the UNSM process was applied while heating at 300 and 600℃ to increase the effectiveness of this hybrid additive process. To validate the characteristics of this method, a study on the cross-sectional properties upon application of heating was conducted. Hybrid cladding at 300 degrees produced improvements- over a 40% larger area than the results at room temperature. At 600 degrees, the hybrid cladding improved mechanical properties over a larger area by nearly 2 times. In this study, the characteristics of the roomtemperature and the high-temperature hybrid cladding process were analyzed. The proposed method shows a high improvement effect and is a promising method to improve the internal mechanical properties of the cladded layer.
Soft robots, known for their flexible and gentle movements, have gained prominence in precision tasks and handling delicate objects. Most soft grippers developed thus far have relied on molding processes using high-elasticity rubber, which requires additional molds to produce new shapes, limiting design flexibility. To address this constraint, we present a novel approach of fabricating pneumatic soft grippers using thermoplastic polyurethanes (TPU) through the Fused Filament Fabrication (FFF) technique. The FFF technique enables the creation of various gripper shapes without the need for additional molds, allowing for enhanced design freedom. The soft grippers were designed to respond to applied air pressure, enabling controlled bending actions. To evaluate their performance, we conducted quantitative measurements of the gripper’s shape deformation under different air pressure conditions. Moreover, force measurements were performed during gripper operation by varying the applied air pressure and adjusting the mounting angle. The results of this study provide valuable insights into the design and control of soft grippers fabricated using TPU and the FFF process. This approach offers promising opportunities for employing soft robots in various fields and paves the way for further advancements in robotics technology.
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In this study, based on directed energy deposition (DED) technology, one of the additive manufacturing technologies, a porous material fabricated by mixing various aluminum alloys and foaming agent was manufactured. First, the foaming agent formed pores inside the deposited materials and differences in foaming characteristics were observed depending on the type of aluminum. Also, the foaming characteristics according to the laser power, which is a representative process variable, were analyzed. As a result, a closed-cell porous material with a maximum porosity at a laser power of 1,100 W was manufactured. Results of the compression test showed that the porous material made by the pores generated therein collapses to absorb energy, and the internal pores disappear to become high density. Therefore, Young’s modulus and yield stress were reduced by the pores inside the sample of pure aluminum and Al6063. However, it was found that the specific energy absorption, which is an advantage of the foamed materials, increased compared to non-porous materials. The findings of this study confirmed that it was possible to manufacture DED-applied foam materials using aluminum powder and a foaming agent.
In this study, we present the fabrication of dual-morphing vascular stents using an additive-lathe printing method and two different shape-memory polymers. Traditional additive manufacturing techniques confront significant challenges in producing vascular stents with complex, hollow, mesh-like structures due to limitations such as a flat printing bed and the placement of supports. To overcome these obstacles, we employed a lathe-type additive manufacturing system with a rotatable base substrate, enabling precise fabrication of cylindrical-shaped stents. To achieve shape transformability, we used shapememory polymers as the stent materials, offering the advantage of minimally invasive surgery. Two distinct shape-memory polymers, with different transition temperatures (35 and 55oC), were printed using the additive-lathe method. The printed stents consisted of two distinct parts that underwent dual-stage morphological changes at the different temperatures. By manipulating the printing paths, the dual-morphing properties of the stents could be adjusted in both longitudinal and circumferential directions. This innovative approach could be a solution to several limitations associated with the application of stents in diseased vascular tissues with complex shapes, facilitating minimal invasion during surgical procedures.
Recently, the demand for lightweight open-pore lattice structures with specific stiffness is increasing in many fields, such as the aeronautical, automotive, mechanical and bone tissue engineering sectors. For each concrete application, there is a need to predict its mechanical properties precisely and efficiently. There are several methods used to analyze the mechanical properties of lattice structures. Among them, the asymptotic expansion homogenization method is a more advantageous approach over the experimental, theoretical, and finite element methods, because it handles some of their limitations such as the time-consuming process, size effect, and the high amount of computational resources needed. Therefore, in this work, we use the asymptotic expansion homogenization method to perform a systematic parametric study to calculate the effective stiffness of different open-pore lattice structures. In addition, the designed models were fabricated using an SLA 3D printer, and the effective stiffness of the fabricated specimens was tested via UTM experiment to validate the numerical results computed by the asymptotic expansion homogenization method. Consequently, it was proved that this method is precise and effective for predicting the mechanical properties of lattice structures.
With the increasing interest in research on the development of next-generation technologies such as flexible smartphones, displays, and wearable devices, interest in the development of materials and processes for transparent electrodes constituting them is also increasing. The most widely used material for manufacturing transparent devices is indium tin oxide (ITO). However, ITO is scarce, expensive, and brittle, making it is essential to replace it with new materials. In this study, we successfully fabricated a transparent electrode by electrospinning polyvinylpyrrolidone (PVP) and copper electroless deposition on the polyimide film. Especially, this study suggests a new combined heat treatment that uses both the hot plate and the convection oven. Through the combined heat treatment, the junctions between the nanofibers overlapped removed consequently reducing contact resistance. The mechanical stability of the fabricated electrode was evaluated by using a highly repeated bending test. Also, through the tape-peeling test, we confirmed that the adhesive strength of the electrode was high. This method can be applied to various polymer-based, substrate which are vulnerable to annealing process.
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This study aimed to characterize the mechanism of thermal runaway phenomenon in lithium-ion batteries, which represent secondary cells among energy storage devices. Thermal runaway reaction was induced by heating 18650 cells with 5%, 40%, and 80% state of charge (SOC). We divided the thermal runaway of the battery into three stages and discussed the physical measurements that distinguish each stage. We also provided a visual comparison and thermal image of the characterized exhaust gases in all stages. The state of charge and the amount of heat generated by thermal runaway were proportional, and in the third stage of thermal runaway, where the highest mass transfer occurred, 40% of SOC released gas for 13 seconds and 80% of SOC emitted gas and flame for 3 seconds. In addition, a temperature and voltage measurement method that can predict the thermal runaway phenomenon of a battery is presented.
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When a narrow gap was formed under appropriate welding conditions in the steel pipe manufacturing process using highfrequency resistance welding, temperature distribution was analyzed to predict the length of the gap. Assuming the length of the gap from the apex point to the welding point at an applied voltage, and calculating the temperature distribution around the gap, the length of the gap with an appropriate fusion width at the welding point could be estimated. Along with this, the current density and magnetic flux density distributions that appeared in the narrow gap were obtained according to the change in the applied voltage, and the distribution shape and size of the electromagnetic force acting on the gap were also predicted. The current density, magnetic flux density, and electromagnetic force gradually increased along the narrow gap, showing the maximum value at the welding point. In the temperature distribution in the narrow gap, the surface of the front end began to melt at an appropriate applied voltage, and the melting width was the largest at the welding point. As the applied voltage increased, the narrow gap became longer, and the appropriate gap length appeared in proportion to the applied voltage.
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Analysis of Stress Distribution around the Weld Zone in High Frequency Resistance Welding of Steel Pipe Young-Soo Yang, Kang-Yul Bae Journal of the Korean Society of Manufacturing Process Engineers.2024; 23(6): 21. CrossRef
Advanced engineering ceramics have been highlighted mainly owing to their superior hardness, corrosion/wear resistance, and thermal insulation performances. However, they are usually very difficult-to-cut because of their high brittleness. In light of this, ultra-precision machining has been studied to perform ductile-regime cutting in the machining of ceramics. Ductile-regime cutting can feature a smoother surface, and lower subsurface damage as the dominant material response during cutting showed ductile behavior. Researchers have investigated promoting ductileregime cutting to improve the machinability of ceramics. In this study, various coating materials were applied to the workpiece surface, and their effects on machinability improvements were explored. A total of 6 surface coatings and lubricants were applied to soda-lime glass. The critical depth of cut (CDC), the depth where the ductile-brittle transition (DBT) occurred, was increased in all coatings and lubricants, with an improved ductile cutting regime. Experimental results showed that solid coatings were more effective than liquid lubricants in enhancing the ductile cutting regime. It was thought that solid coatings induced an additional downward force by resisting material deformation and chip evacuation, thus contributing to suppression of crack opening. It is expected that this research can contribute to the machinability improvements of brittle materials.
Polymer electrolyte membrane fuel cells (PEMFC) require activation to maximize their performance. Thus, an appropriate activation process is essential for the performance of the fuel cell. In this study, the performance of the fuel cell was investigated by changing the voltage range during the activation process. There were three voltage ranges: 0.3-0.9 V, 0.3-0.6 V, and 0.6-0.9 V. When the fuel cell was activated in the low voltage region, the highest performance was output. On the other hand, it showed the lowest performance at high voltage. The results suggest that it is advantageous to activate the fuel cell with a high current. On the other hand, if activation is performed while outputting at a low current, the generation of water and the electrochemical reaction are insufficient, resulting in a load on the fuel cell. Through this experiment, it was confirmed that the control method greatly affects fuel cell performance when activated.
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