In this study, the effect of flow rate ratio (R) and total flow rate (Q) on the surface temperature of thermal barrier coatings (TBC) was investigated using a newly developed small-scale methane-oxygen burner rig. Subsequently, the failure mode of electron beam physical vapor deposition (EB-PVD) TBC was examined, and the relationship between surface temperature and coating life was established. The surface temperature of the TBC was found to be strongly dependent on both the flow rate ratio and the total flow rate. Specifically, surface temperature exhibited a proportional relationship with total flow rate, while it showed an inverse relationship with flow rate ratio. The failure mode of the EB-PVD TBC involved a gradual increase in delamination from the rim to the center of the coin-shaped specimen, and this failure mode was found to be independent of surface temperature. Additionally, it was determined that the surface temperature of EB-PVD TBC has a perfectly inverse linear relationship with coating life. This finding implies that the derived linear regression line from the burner rig test can be directly used to predict coating life for any untested surface .temperature.
In this study, we developed a new vertical thermal gradient rig that uses methane-oxygen fuel. We conducted thermal gradient testing on a thermal barrier coating system, with a flame temperature of 1,900℃. Our results showed that the maximum surface temperature reached 1,065℃, while the temperature difference between the surface temperature and the temperature of the middle substrate (ΔT) was 70oC. Using the same torch as in this study, our finding suggest that the total flow rate of the flame should be above 12.4 LPM, and the gun distance should be less than 8 cm, to simulate a surface temperature of 1,300℃, while keeping the substrate temperature below 1,000℃. This will ensure that the flame is wide enough to cover the entire surface area of the thermal barrier coating.
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Thermal Fatigue Life Evaluation of EB-PVD TBC Using Newly Developed Small-scale Burner Rig Soo Park, Dae-Jin Kim, Jun-Young Kim, Seoung-Ju Kim, Chang-Sung Seok Journal of the Korean Society for Precision Engineering.2025; 42(1): 65. CrossRef
With the development of various 3D printing technologies, many studies are being conducted in the field of food printing. In particular, chocolate printing is widely used for decoration. As a result, there is a growing demand for color printing, which goes beyond conventional monochrome chocolate 3D printing. Therefore, in this study, we tried to confirm the possibility of printing a new color gradation by mixing two types of chocolates with different colors using a static mixer. For this purpose, extrusion type printer equipment consisting of extrusion parts with dual syringe, heater, and mixer, and transport parts with motors and linear guide were manufactured. Proper process conditions were achieved by changing the chocolate temperature and extrusion quantity. Through this process, the color-mixed structure was successfully printed, and it was confirmed through color-code analysis that proper mixing was achieved. Further, through the production of multi-mixed color chocolate printing structures with various shapes, structural and visual diversity was acquired.
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Since most commercialized DLP 3D printers fabricate 3D structures by sinking materials to Vat using a bottom-up method, it is difficult to use various materials simultaneously and there are many restrictions on printing composite materials. Especially, composite resin mixed with various functional powders in photo curable resin generally has high viscosity, causing difficult material flow in the bottom-up method when using Vat. Additionally, most of the previously presented methods for fabricating multi-material structure use individual curing for each material, so the adhesion force at the contact surface is less than 50% compared to single material. Thus, in this paper, we propose a new type of DLP 3D printer that combines Material Extrusion and the DLP system. The proposed equipment can supply high viscosity composite material resins to a specific area to cure various materials simultaneously. This method will enable fabrication of multiple composite material structures with sufficient adhesion force. The tensile test will be performed to verify suitability of the proposed method.
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The necessity for printing multi-materials has increased as the importance of 3D printing grew in various industries. Many studies have undertaken for printing multi-materials simultaneously. In ME (Material Extrusion) type 3D printers, the method of printing different materials using multi nozzles is generally commercialized. Polymers with different composition are hardto-mix with each other, making it difficult to maintain the structural strength of printer parts. So the MJ type 3D printer uses a unique method that mixes multi-materials in a liquid state before printing. In the ME type 3D printer, there were also efforts to mix materials in a melted state, but they were mainly demonstrated for multi-colored parts. In this study, the effect of multi-material mixing on structural strength changes was tested. Multi-Materials were printed with the ME type 3D printer by using one nozzle with a multiple filament feeding system. The bending and tensile tests were conducted to verify the structural characteristics.
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A guided missile is a weapon system used in the interception of a ballistic missile using kinetic energy of a kill vehicle. The DACS (Divert and Attitude Control System) is a quick reaction propulsion system and subsystem of a kill vehicle that provides control over positions of a kill vehicle. The DACS allows for the interception of its target with greater accuracy and reliability. A Kill vehicle needs to move at high speed in a bid to intercept a ballistic missile after detecting a target. Thus, the weight reduction design of DACs system is required. The DACS operates under high temperature and pressure environment. In this study, one-way FSI (Fluid and Structure Interaction) analysis were conducted for various types of weight reduction valve model to validate its robustness. Through this process, we suggest an optimized weight reduction valve model
Elastomeric O-ring seals are widely used in static and dynamic applications due to their excellent sealing capacity, and availability in various costs and sizes. One of the critical applications of O-ring seals is solid rocket motor joint seal. In this, the operating hot gas must be sealed during the combustion time. In this study, we analyzed the behavior of O-ring compressed and highly pressurized by using the finite element method. The numerical analysis technique was verified through the comparison of analytical model and FE results. By using the verified FE method, the contact stress profiles at the sealing surfaces were investigated. It was found out that the contact stress profiles and deformation behaviors of the Oring are affected by friction coefficient, extrusion gap and stress relaxation considerably.
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Injection molding is the most effective process for the mass production of plastic parts. However, there are various plastic part surface defects which occur during the injection molding process. Sink marks are among the most difficult surface defects to improve. The sink marks usually appear as depressions on the surface of a molded part. These depressions are typically very small; however, they are often quite visible because they reflect light in different directions to the part. In this paper, we conducted experimental studies in order to minimize sink marks that occurred on the in-mold type PAB door seam line by using the Mucell injection process. The results of the study indicate this method can be used to eliminate sink marks using the Mucell injection molding process.
Laser beam machining has been known as efficient for glass micromachining. It is usually used the ultra-short pulsed laser which is time-consuming and uneconomic process. In order to use economic and powerful long pulsed laser, indirect processing called laser-induced backside wet etching (LIBWE) is good alternative method. In this paper, micromachining of glass using Nd:YAG laser with nanosecond pulsed beam has been attempted. In order to improve shape accuracy, combined processing with magnetic stirrer has been widely used. Magnetic stirrer acts to circulate the solution and remove the bubble but it is not suitable for deep hole machining. To get better effect, ultrasonic vibration was applied for improving shape accuracy
Laser beam machining (LBM) is fast, contactless and able to machine various materials. So it is used to cut metal, drill holes, weld or pattern the imprinted surface. However, after LBM, there still leave burrs and recast layers around the machined area. In order to remove these unwanted parts, LBM process often uses electrochemical etching (ECE). But, the total thickness of workpiece is reduced because the etching process removes not only burrs and recast layers, but also the entire surface. In this paper, surface coating was performed using enamel after LBM on metal. The recast layer can be selectively removed without decreasing total thickness. Comparing with LBM process only, the surface quality of enamel coating process was better than that. And edge shape was also maintained after ECE.
The purpose of this paper is to compare with estimation of equivalent fatigue load in time domain and frequency domain and estimate the fatigue life of structure with multi-axial vibration loading. The fatigue analysis with two methods is implemented with various signals like random, sinusoidal signals. Also an equivalent fatigue life estimated by rainflow cycle counting in time domain is compared with results estimated with probability density function of each signal in frequency domain. In case of frequency domain, equivalent fatigue life can estimate through Dirlik’s method with probability density function. And the work proposed in this paper compared the fatigue damage accumulated under uni-axial loading to that induced by multi-axial loading. The comparison is preformed for a simple cantilever beam, which is exposed to vibrations of several directions. For verification of estimation performance of fatigue life, results are compared to those of FEM analysis (ANSYS).
In micro electrochemical machining (micro ECM), machining conditions have been determined to maintain a small side gap and to machine a workpiece stably. However, machining speed is slow. To improve machining speed while maintaining the form accuracy, the paper investigates machining parameters such as pulse amplitude, duty ratio, pulse on-time, and the electrolyte’s temperature and concentration. The experiment in this study shows that the electrolyte’s concentration is the key factor that can reduce machining time while maintaining the form accuracy. Micro square columns were fabricated to confirm the machining parameters’ effects.
Electrical discharge drilling (ED-drilling) is a widespread machining method used to bore small holes with a high aspect ratio. This paper presents additional methods by which ED-drilling can improve machining speed, tool wear, and machined surface quality. Firstly, for high machining speed, and low tool wear, a new-type electrode that was ground on one side or both sides of the cylindrical electrodes was suggested to expel debris. The debris which is generated during the machining process can cause sludge deposition and secondary discharge problems: major reasons to decrease machining speed. This new-type electrode also reduced tool wear that was due to the decrease of unstable discharge in a machining gap by helping to expel waste water and debris from the gap. Secondly, to improve the machined surface roughness, an electrolyzation process was included after drilling. This process made the machined surface smooth by means of an electrochemical reaction between an electrode and a workpiece. In this study, the machining speed, electrode wear, and surface roughness were improved by the newtype electrode and the electrolytic process.
The repeated unit cell structure is applied to the composite, the carbon nano tube and sandwich panel. In this paper, a study on the stiffness of unit cell structure has been performed with the tube support plate of the steam generator. For this, repeated unit cell structure’s equivalent elastic constant and poisson’s ratio was evaluated through FEA and tests under the elastic range load. Also we evaluated the effect on the specimen size from results.
A straight pipe is used after complicated bending work in a mechanical system. In this work process, the plastic deformation of the pipe produces residual stress in the pipe. This residual stress significantly affects the behavior of pipe fracture. For this reason, residual stress must be evaluated. Measuring the residual stress of a U-shaped pipe is difficult with existing destructive and nondestructive measurement methods. In this paper, the residual stress of a U-shaped aluminum pipe (99.7% pure aluminum) was evaluated from the Raman shift by Raman spectroscopy and FEM(Finite Element Method, FEM) analysis. The results of the stiffness test by FEM analysis are compared with those by experiments. The analyzed results of the Raman spectra showed a similar tendency with the results of the FEM analysis with respect to the residual stress distributions in U-shaped pipes. Also, the results of the bending tests showed resemblance to each other.
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