• 한국자동차공학회논문집
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• 제12권1호
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• pp.91-98
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• 2004

This paper is concerned with crash analysis for an auto-body member with the forming effect. Auto-body members such as a front frame assembly are fabricated with sheet metal forming processes that induce forming histories such as the plastic work hardening and non-uniform thickness distribution. Numerical simulation is carried out with LS-DYNA3D in order to identify the forming effect on the crashworthiness. The crash analysis of the front frame assembly with the forming effect leads to a different result from that without the forming effect. Crashworthiness such as the load-carrying capacity, the crash mode and the energy absorption are calculated to investigate and identify the forming effect. It is fully demonstrated that the design of auto-body members needs to consider the forming effect for accurate assessment of the load-carrying capacity and the deformation mechanism of the formed members.

• 한국군사과학기술학회지
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• 제11권4호
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• pp.83-91
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• 2008

The development of the equal channel angular pressing(ECAP) process in metals has recently provided a feasible solution to produce ultra-fine or nano-grained bulk materials with tailored material properties. However, ECAP process is difficult to scale up commercially due to requirements of an excessive load. In this paper, a new Hybrid-ECAP process with torsional die is considered to obtain materials of ultra-fine grain structure under low forming load. An upper bound analysis and numerical simulation (DEFORM 3D, a commercial FEM code) are carried out on the torsional die. By the upper bound analysis, analytical expression for the compression force and rotation speed are obtained. By the FEM analysis, the distribution of strain, stress and deformation are obtained. These results show that the Hybrid-ECAP is a useful process because this process can obtain the homogeneous deformations with relatively low forming load. Additionally, due to decreased forming load, die life can be improve.

• Nuclear Engineering and Technology
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• 제48권6호
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• pp.1387-1395
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• 2016

To investigate the dynamic strain aging (DSA) behavior of Alloy 617, high-temperature tensile tests were carried out with strain rates variations of $10^{-3}/s$, $10^{-4}/s$, and $10^{-5}/s$ from $24^{\circ}C$ to $950^{\circ}C$. Five flow relationships, Hollomon, Ludwik, Swift, Ludwigson, and Voce, were applied to describe the tensile true stress-strain curves, and the DSA region was defined. In describing the tensile curves, Ludwigson's equation was superior to the other equations, and the DSA region was adequately defined by this equation as plateaus at intermediate temperatures from $200^{\circ}C$ to $700^{\circ}C$. It was identified that Alloy 617 is dominated by three types of serrations, known as Types D, A+B, and C. The activation energy values for each serration type were obtained by the Arrhenius equation. By using the obtained activation energy values, the serrated yielding map and the DSA mechanism were drawn and manifested. In addition, the relationship between the tensile strength and strain rate at higher temperatures above $700^{\circ}C$ was found to be closely related to the amounts of slip lines. In the scanning electron microscope (SEM) fractographs, there was a significant difference at the low, intermediate, and high temperatures, but almost the same to the three strain rates.

• 소성∙가공
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• 제21권1호
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• pp.58-66
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• 2012

The work roll surface temperature rises and falls repetitively during hot slab rolling because the work roll surface is cooled continuously by water. This study focused on Std. No. 7 to determine a cooling method which significantly reduces the tangential tensile stresses on the work roll surface of the hot slab mill at Hyundai Steel Co. in Korea. A series of finite element analyses were performed to compute the temperature distribution and the tensile stresses in the circumferential direction of the work roll. The virtual slab model was used to reduce the run time considerably by assigning a high temperature to the virtual slab. Except for the heat generated by plastic deformation, this is equivalent to the hot rolling condition that a high temperature slab (material) would experience when in contact with the work rolls. Results showed that when the virtual slab model was coupled with FE analysis, the run time was found to be reduced from 2000 hours to 70 hours. When the work roll surface cooled with a certain on-off patter of water spray, the magnitude of the tangential stresses on the work rolls were decreased by 54.1%, in comparison with those cooled by continuous water spraying. Savings of up to 83.3% in water usage are possible if the proposed water cooling method is adopted.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.926-929
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• 2005

Recently, laser interferometer is widely used as a measuring system in many fields because of its high resolution and its ability to measure a board area in real-time ail at once. In conventional laser interferometer, for examples Out of plane ESPI, In plane ESPI, Shearography and Holography, it uses PZT or other components as a phase shift instrumentation to extract 3-D deformation data, vibration mode and others. However, in most cases PZT has some disadvantages, which include noli-linear errors and limited time of use. In present study, a new type of laser interferometer using a laser diode(LD) is proposed. Using Laser Diode Sinusoidal Phase Modulating(LD-SPM) interferometer, the phase modulation can be directly modulated by controlling the LD injection current thereby eliminating the need for PZT components.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2006년도 학술발표회 논문집
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• pp.445-452
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• 2006

A new Energy-Dissipating Sacrificial Device(EDSD) is proposed, which can effectively dissipate the energy stored in the structures during seismic actions. A mathematical 3-D bridge models and analysis techniques are developed to represent the non-linear behavior of the EDSD, various seismic responses of a sample bridge with the EDSD are analyzed in terms of energy, member forces and deformation using the developed analysis method. And the EDSD is tested and certified it's behavior and stability to apply on exiting bridges. The EDSD can be able to dissipate a large amount of energy and therefore it can prevent the pier's excessive forces under seismic excitations and EDSD and its connected members are also stable. Additionally, the method and guidelines of an optimum EDSD design are proposed in terms of installation method and decision of number of EDSD. The Proposed EDSD under seismic excitations can significantly decrease the excessive storing energy in the bridge structures and reduce the relative displacements of each superstructure to the ground. The EDSD is also found to function as a structural fuse under strong ground motions, sacrificing itself to absorb the excessive energy. Consequently, economical enhancement of the seismic performance of bridges can be achieved by employing the newly developed energy dissipation sacrificial device(EDSD).

• Steel and Composite Structures
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• 제25권6호
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• pp.649-661
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• 2017

This paper is motivated by the lack of studies in the technical literature concerning to the influence of carbon nanotubes (CNTs) waviness and aspect ratio on the vibrational behavior of functionally graded nanocomposite annular sector plates resting on two-parameter elastic foundations. The carbon nanotube-reinforced (CNTR) plate has smooth variation of CNT fraction based on the power-law distribution in the thickness direction, and the material properties are also estimated by the extended rule of mixture. In this study, the classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. Parametric studies are carried out to highlight the influence of CNTs volume fraction, waviness and aspect ratio, boundary conditions and elastic foundation on vibrational behavior of FG-CNT thick sectorial plates. The study is carried out based on three-dimensional theory of elasticity and in contrary to two-dimensional theories, such as classical, the first- and the higher-order shear deformation plate theories, this approach does not neglect transverse normal deformations. The annular sector plate is assumed to be simply supported in the radial edges while any arbitrary boundary conditions are applied to the other two circular edges including simply supported, clamped and free. For an overall comprehension on 3-D vibration of annular sector plates, some mode shape contour plots are reported in this research work.

• Bulletin of the Korean Chemical Society
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• 제20권12호
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• pp.1413-1417
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• 1999

Chemical poisoning of Ni/MgO catalyst was induced by hot alkali carbonate vapor in molten carbonate fuel cell (MCFC), and the poisoned (or contaminated) catalyst was characterized by TPR/TPO, FTIR, and XRD analysis. Carbonate electrolytes such as K and Li were transferred to the catalyst during DIR-MCFC operation at 650 ℃. The deposition of alkali species on the catalyst consequently led to physical blocking on catalytic active sites and structural deformation by chemical poisoning. TPR/TPO analysis indicated that K species enhanced the reducibility of NiO thin film over Ni as co-catalyst, and Li species lessened the reducibility of metallic Ni by chemical reaction with MgO. FTIR analysis of the poisoned catalyst did not exhibit the characteristic ${\vector}_1$$(D_{3h})$ peaks (1055 $cm^{-1},\;1085\;cm{-1})$ for pure crystalline carbonates, instead a new peak (1120 $cm^{-1})$ was observed proportionally with deformed alkali carbonates. From XRD analysis, the oxidation of metallic Ni into $Ni_xMg_{1-x}O$ was confirmed by the peak shift of MgO with shrinking of Ni particles. Conclusively, hot alkali species induced both chemical poisoning and physical deposition on Ni/MgO catalyst in DIR-MCFC at 650 ℃.

• Safety and Health at Work
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• 제1권1호
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• pp.43-50
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• 2010

Objectives: The objective of this study was to investigate the effect of chain installation condition on stress distribution that could eventually cause disastrous failure from sudden deformation and geometric rupture. Methods: Fractographic method used for the failed chain indicates that over-stress was considered as the root cause of failure. 3D modeling and finite element analysis for the chain, used in a crane hook, were performed with a three-dimensional interactive application program, CATIA, commercial finite element analysis and computational fluid dynamic software, ANSYS. Results: The results showed that the state of stress was changed depending on the initial position of the chain that was installed in the hook. Especially, the magnitude of the stress was strongly affected by the bending forces, which are 2.5 times greater (under the simulation condition currently investigated) than that from the plain tensile load. Also, it was noted that the change of load state is strongly related to the failure of parts. The chain can hold an ultimate load of about 8 tons with only the tensile load acting on it. Conclusion: The conclusions of this research clearly showed that a reduction of the loss from similar incidents can be achieved when an operator properly handles the installation of the chain.

• Steel and Composite Structures
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• 제39권2호
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• pp.149-158
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• 2021

In this research paper, the free vibrational response of laminated composite plates is investigated using a non-polynomial refined shear deformation theory (NP-RSDT). The most interesting feature of this theory is the parabolic distribution of transverse shear deformations while ensuring the conditions of nullity of shear stresses at the free surfaces of the plate without requiring the Shear correction factor "Ks". A fourth-nodded isoparametric element with four degrees of freedom per node is employed for laminated composite plates. The numerical analysis of simply supported square anti-symmetric cross-ply and angle-ply laminated plate is carried out using a special discretization based on four-node finite element method which four degrees of freedom per node. Several numerical results are presented to show the effect of the coupling parameters of the plate such as the modulus ratios, the thickness ratio and the plate layers number on adimensional eigen frequencies. All numerical results presented using the current finite element method (FEM) is presented in 3D curve form.