• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.307-310
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• 2009

Nowadays, the usage of high strength steel has been growing in automobile industry mainly as structural parts since for its lightweight and high strength properties the oil crisis happened. Owing to poor formability, complex-shaped high-strength steel components are invariably produced through hot press forming. The high-strength steel sheets are in so me instances used with an Al-Si-coating with a view to prevent scaling of components during hot press forming. How ever, friction and fracture characteristics of Al-Si-coated high-strength steel during hot press forming process have not yet been investigated. In this paper, the formed parts which were formed in hot bending process were investigated by using EDS. SEM and nano indenter in order to analysis the coating layer behavior.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.840-843
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• 2005

For an analysis of nonlinear dynamic behavior in carbon nanotube(CNT) an electrostatic force of CNT was investigated. The boundary condition in the CNT was assumed to clamped-clamped case at both ends. This type of CNT is widely used as micro and nano-sensors. For larger gaps in between sensor and electrode the van der Waals force can be ignored. The electrostatic force can be expressed as linear form using Taylor series. However, the first term of the series expansion was investigated here. The electrostatic force From this study we can conclude that for larger gaps the electrostatic force play an important role in determining the deflections as well as the pull-in voltage of simply supported switches.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.04a
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• pp.97-99
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• 2004

To understand the geochemical processes controlling the distribution of nitrate and other agricultural constituents in an alluvial aquifer, hydrogeological and hydro geochemical studies were carried out in an agricultural area within Cheonan. In this selected field, nitrate concentrations were very wide in range but was locally attenuated significantly down to very low levels (<1.0 mg/L). Abrupt removal of nitrate coincided with the pattern of redox change and thus indicated that geochemical processes occurring during and after recharge events control the behavior and distribution of nitrate and other redox-sensitive chemical species.

• Transactions of Materials Processing
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• v.31 no.2
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• pp.64-72
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• 2022

Since aluminum alloys experience both tensile and compression deformation modes during forming process, it is important to understand the role of deformation mode on the hot formability of metallic alloys. In the present work, the hot formability of Al7050 alloy was investigated by conducting both tensile and Gleeble tests at various temperatures and strain rates. Processing maps representing low efficiency regions were observed at low temperature and high strain rate in both tensile and compressive deformation modes while the maximum efficiency regions depended on different deformation modes. Moreover, samples tested at stable processing conditions presented a smaller pore fraction than those at instable conditions that resulted in crack initiation during plastic deformation. This result shows that different deformation modes during plastic forming can affect formability changes of metallic alloys. Understanding of tension-compression behaviors will help us solve this problem.

• Korean Journal of Environment and Ecology
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• v.6 no.2
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• pp.218-228
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• 1993

Visitors to Sobaekson National Park were surveyed from August 6 to 9 and from October 16 to 18. During this time. 773 visitors were contacted. Of those individuals, 61.7% were males. 40.8% of respondents reported that they had gone beyond high school. and almost one-half (46.9% ) had gone as far as college. 52.8% were 20 years of age. Over one-half (55.8% ) of the survey respondents were making their first trip to Sobaeksan National Park. The largest percentage of respondents were reported that they visited Sobaeksan Nat'l Park for enjoying natural landscape. In group type, 62% were traveling with their asociates or friends. In activity characteristics. 62.9% were day-time visitors, and 37.8% mentioned carrying in their own food. The majority of visitors perceived that landscape interpretation boards were useful to understand Sobaeksan Nat'1 Park. Most respondents were not likely to intervene to stop other visitors' depreciative behavior.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.529-535
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• 2013

A new thin sandwich panel composed of an aluminum expanded metal core adhesively jointed with stainless steel face sheets is introduced, and its mechanical behavior under three-point bending is investigated. The strength and stiffness are analyzed theoretically, and the press-formability and strength enhancement are evaluated experimentally. The specimens with the specific configurations exhibit face yielding well before face-core separation, which means that the sandwich panel can be formed by a press without failure. The measured load levels corresponding to the face yielding and the face-core separation agree fairly well with the theoretical estimations. For a given weight, the sandwich panel is superior to a solid panel in terms of strength, stiffness, and press-formability.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.6
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• pp.389-395
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• 2017

This study was performed to provide the information of the soot formation behavior of octane single fuel droplet under the identical combustion conditions. To achieve this, this experimental study provide the results of the soot formation characteristics of octane droplet in accordance with different initial droplet diameter($d_0$), at the same time, experiment was conducted under the same combustion conditions which are 1.0atm of ambient pressure($P_{amb}$), 21% of oxygen concentration($O_2$) and 79% of nitrogen concentration($N_2$). Visualization of octane droplet combustion was performed by visualization system with high speed camera. The results of maximum soot volume fraction($f_{vmax}$) was almost the same under the equivalent ambient conditions regardless of initial droplet diameter. Furthermore, maximum soot volume fraction was showed the higher value in the measuring direction between $135^{\circ}$ and $315^{\circ}$ since the soot-tail is generated during two opposing igniters movement process.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.2
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• pp.161-168
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• 2015

An experimental study was conducted to scrutinize the influence of the frequency of an ultrasonic standing wave on the variation in the behavior of a methane-air premixed flame. The evolutionary features of the propagating flame were captured by a high-speed camera, and the macroscopic flame behavior, including the flame structure and local velocities, was investigated in detail using a post-processing analysis of the high-speed images. It was found that a structural variation and propagation-velocity augmentation of the methane-air premixed flame were caused by the intervention of the ultrasonic standing wave, which enhanced the combustion reaction. Conclusive evidence for the dependency of the flame behaviors on the driving frequency of the ultrasonic standing wave and equivalence ratio of the reactants is presented.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.3
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• pp.243-250
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• 2014

Fiber-optic cables towed by underwater vehicles have an important role in enhancing the mission capability of a mother ship. In general, fiber optic cables are unwound in water for securing unwinding stability and preventing unwinding-related problems. Therefore, in this study, the numerically simulated result is verified against the experimental result in water, and the cable-unwinding motion is predicted based on the increase in unwinding velocity. The experimental apparatus is composed of a water tank and a winder, and a high-speed camera is used for photographing the cable-unwinding motion. The numerical result defined in the Cartesian coordinate system is solved using a transient-state unwinding equation of motion. The numerical result agrees well with the experimental result, and it can predict cable-unwinding behaviors in according to an increase in the unwinding velocity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.10
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• pp.1377-1384
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• 2010

The objective of this study is to determine the best material model that represents the deformation behavior of the Sn37Pb solder alloy accurately. First, a specimen is fabricated and subjected to a thermal cycle with temperatures ranging from the room temperature to $125^{\circ}C$. An experiment is conducted to examine deformation by Moire interferometry. Three different constitutive equation models are used in the finite element analysis (FEA) of the thermal cycle. In order to minimize the difference between the FEA results and the experimental results, the material parameters of the solder alloy are considered to be unknown and are determined by conducting optimization. As a result of the study, the Anand model is found to represent the deformation behavior of the solder most accurately.