• Journal of Power System Engineering
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• v.3 no.2
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• pp.89-97
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• 1999

In this paper the forming simulations of ellipse bulge have been researched by using $PAM-STAMP_{TM}$ to estimate the sheet metal forming and the plastic deformation characteristic of ellipse bulge. Thin elliptical diaphragms of brass, copper, aluminum, and mild steel are bulged in elliptical dies having aspect ratios of 1.33 and 2. In order to compare the simulation results with the experiment and ellipse bulge's theory derived by using Johnson and Duncan's theory, the relations of hydraulic pressure and polar height, polar thickness strain and polar height, were compared. According to this study, the results of simulation and ellipse bulge's theory derived by using Johnson and Duncan's theory, and the bursting pressure and the bursting polar height are good agreement to the experiment. So, the results of simulation by using $PAM-STAMP_{TM}$ and the ellipse bulge's theory will give engineers good information to make assessment the formability and plastic deformation characteristic of hydraulic ellipse bulge test.

• Composites Research
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• v.34 no.4
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• pp.257-263
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• 2021

Composite materials have been widely applied for fabricating pressure vessels used for storing gaseous and liquid fuel because of their high specific stiffness and specific strength. Accordingly, the accurate measurement of their mechanical property, particularly the burst pressure or fracture strain, is essential prior to the commercial release. However, verification of the safety of composite pressure vessels using conventional test methods poses some limitations because it may lead to the deformation of the load transferring media or provoke an additional energy loss that cannot be ignored. Therefore, in this study, the segment-type ring burst test device was designed considering the theoretical load transferring ratio and applicable displacement of the vertical column. Moreover, to verifying the uniform distribution of pressure of the segment type ring burst test device, the hoop stress and strain distribution of ring specimens were compared with that of the hydraulic pressure test method via FEM. To conduct a simulation of the fracture behavior of the composite pressure vessel, a Hashin failure criterion was applied to the ring specimen. Furthermore, the fracture strain was also measured from the experiment and compared with that of the result from the FEM.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.16 no.1
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• pp.49-55
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• 2020

Creep rupture data for Alloy 690 steam generator tubes in a pressurized water reactor are essentially needed to demonstrate a severe accident scenario on thermally-induced tube failures caused by hot gases in a damaged reactor core. The rupture data were obtained using the tube specimens under different applied-stress levels at 650℃, 700℃, 750℃, 800℃, and 850℃. Important creep constants were proposed using various creep laws in terms of Norton power law, Monkman-Grant (M-G) relation, damage tolerance factor (λ), and Zener-Hollomon parameter (Z). In addition, a creep activation energy (Q) value for Alloy 690 tube was reasonably determined using experimental data. Creep behaviors such as creep strength, creep rates, rupture elongation showed the results of temperature dependence well. Modified M-G plot improved a correlation of the creep rate and rupture life. Damage tolerance factor for Alloy 690 tubes was found to be λ =2.20 in an average value. Creep activation energy for Alloy 690 tube was optimized for Q=350 (kJ/mol). A plot of Z parameter obeyed a good linearity, and the same creep mechanism was inferred to be operative in the present test conditions.

• Journal of the Korea Convergence Society
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• v.5 no.3
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• pp.17-22
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• 2014

The stress between work piece and end mill at the use of end mill at machining and the structural deformation due to the and the pressure are investigated by simulation analysis of three end mill models in this study. These results are achieved with structural and fatigue analyses. Model 1 has the deformation less than model 2 or model 3. As the maximum equivalent stress of model 1 is shown to become the least among all models, model 1 can endure the highest load by comparing with other models. It is useful to estimate the damage prevention and the durability by applying this study result into the design of end mill.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.5
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• pp.363-372
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• 2020

Dynamic compressive material properties at high strain rates is essential for improving the reliability of finite element analysis in dynamic environments, such as high-speed collisions and high-speed forming. In general, the dynamic compressive material properties for high strain rates can be obtained through SHPB equipment. In this study, SHPB equipment was used to acquire the dynamic compressive material properties to cope with the collision analysis of Woven tpye CFRP material, which is being recently applied to unmanned aerial vehicles. It is also used as a pulse shaper to secure a constant strain rate for materials with elastic-brittle properties and to improve the reliability of experimental data. In the case of CFRP material, since the anisotropic material has different mechanical properties for each direction, experiments were carried out by fabricating thickness and in-plane specimens. As a result of the SHPB test, in-plane specimens had difficulty in securing data reproducibility and reliability due to fracture of the specimens before reaching a constant strain rate region, whereas in the thickness specimens, the stress consistency of the specimens was excellent. The data reliability is high and a constant strain rate range can be obtained. Through finite element analysis using LS-dyna, it was confirmed that the data measured from the pressure rod were excessively predicted by the deformation of the specimen and the pressure rod.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.5
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• pp.429-435
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• 2016

Cold stretching(CS) pressure vessels from ASS304 (austenitic stainless steel 304) are used for the transportation and storage of liquefied natural gas(LNG). CS pressure vessels are manufactured by pressurizing the finished vessels to a specific pressure to produce the required stress ${\sigma}_k$. After CS, there is some degree of plastic deformation. Therefore, CS vessels have a higher strength and lighter weight compared to conventional vessels. In this study, we investigate the tensile and fatigue behavior of ASS304 sampled by CS pressure vessels in accordance with the ASME code at cryogenic temperature. From the fatigue test results, we show S-N curves using a statistical method recommended by JSEM-S002. We carried out the fractography of fractured specimens using scanning electron microscopy (SEM).

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.529-535
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• 2011

In this study, evaluation of acoustic emission signals characteristics for the post weld heat treated (PWHT) multi-pass weldment and weldment was dealt. Charpy standard specimens were taken from the lowest, middle and highest regions of the weld block. Pre-crack was made using the repeated load. Four point bend and AE tests were conducted simultaneously. Regardless of the specimens, AE signals were absent within elastic region and produced in the process of plastic deformation. AE signals for all specimens were not emitted after the maximum load. Value of signal strength for the all PWHT specimens was lower than that of the weldment. Besides, relations of plastic deformation zone size and accumulated AE counts for the PWHT specimens were more simple compared with the weldment. In case of the PWHT specimen, particles on the fractured surface decreased prominently compared with the weldment due.to PWHT. From these results, it can be concluded that PWHT was effective in reducing the AE sources for the weldment.

• Journal of the Korean Wood Science and Technology
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• v.42 no.3
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• pp.282-289
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• 2014

After being laminated with a combination of glass fiber reinforced plastic and plywood, the GFRP laminated plate was densificated for 1 hour at $150^{\circ}C$ with pressure of $1.96N/mm^2$. A partial reinforced beam was produced by attaching the 5 GFRP laminated plates to the joint of glulam and the column. In addition, the column to beam joint was produced by using reinforced laminated wooden pin which was made of GFRP sheet and plywood, fiber glass reinforced cylindrical-LVL column. The joint was made of round log, glulam and drift pin as the reference specimen, and its moment resistance was evaluated. As a result, the strength performance of specimens with partial reinforced beams were 1.8 times stronger than the reference specimen on average. Furthermore, rupture was neither occurred on partial reinforced beam nor column. Toughness and stiffness of joints were also fine. The GFRP sheet reinforced laminated plate showed better reinforcement effect than GFRP textile reinforced one. GFRP sheet was inserted into each layer of laminate, and it showed good condition in rotation-angle and strength, therefore it is the most appropriate to reinforce the part of the beam.