• Tribology and Lubricants
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• v.36 no.3
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• pp.147-152
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• 2020

This paper is within the framework of an adhered complete contact problem wherein the contact between a half plane and sharp edged indenter, both of which are elastic in character, is constituted. The eigensolutions of the contact shear and normal stresses, σ_rq and σ_q, respectively, are evaluated via asymptotic analysis. The ratio of σ_rq/σ_qq is investigated and compared with the coefficient of friction, μ, of the contact surface to observe the propensity to slip on the contact surface. Interestingly, there exists a region of |σ_rθ/σ_θθ| ≥ |μ|. Thus, slipping can occur, although the problem is solved under the condition of an adhered contact without slipping. Given that a tribological failure potentially occurs at the slipping region, it is important to determine the size of the slipping region. This aspect is also factored in the paper. A simple example of the adhered contact between two elastically dissimilar squares is considered. Finite element analysis is used to evaluate generalized stress intensity factors. Furthermore, it is repeatedly observed that slipping occurs on the contact surface although the size of it is extremely small compared with that of the contacting squares. Therefore, as a contribution to the field of contact mechanics, this problem must be further explained logically.

• Progress in Superconductivity and Cryogenics
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• v.13 no.1
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• pp.17-21
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• 2011

A hybrid superconducting fault current limiter (SFCL) with fast switch had been previously suggested by our research group. To make a hybrid SFCL, different superconducting wires were wound two pancake coils so that two pancake coils had asymmetric configuration. The impedance of the asymmetric non-inductive coils are zero with applied normal current. However during the fault. currents were distributed unequally into the two pancake coils because each superconducting wires have different electrical characteristics. This unequal distribution of current causes effective magnetic flux which generate repulsive force. Fast switch was thus opened by the force applied to the aluminum plate which consists of SFCL. In this paper, the AC loss characteristics of the asymmetric non-inductive coils with combinations of superconducting wires were studied and calculated by related experiments and finite element method (FEM) simulation. From these results, we suggested the appropriate combination of two superconducting wires to be used for the asymmetric non-inductive coils.

• The Journal of the Acoustical Society of Korea
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• v.19 no.2
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• pp.3-7
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• 2000

This paper is on the sensitivity characteristics of a concentric composite mandrel type fiber optic acoustic sensor with inclusion of an air cavity With the finite element method, we have analyzed sensitivity variation of the sensor in relation to its geometrical factors such as thickness of the air cavity, thickness of the foaming layer, and the ratio of inner diameter/outer diameter of the mandrel. Results of the analysis suggest a thicker air cavity, a thinner foaming layer, and a smaller ratio of the inner diameter/outer diameter of the mandrel to be desirable for higher sensitivity. The sensor structure designed with the above rules provides the sensitivity of about 0.8dB higher than that of a normal concentric composite mandrel sensor without the inherent air cavity.

• Journal of Ocean Engineering and Technology
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• v.8 no.1
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• pp.33-40
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• 1994

Welding of structure produces welding residual stresses which influence buckling strength, brittle fracture strength and cold crack on the weld parts. Therefore, it is very important to accurately analyze the residual stress before welding in order to guarantee the safety of weldment. If the weld length is long enough compared to the thickness and the breadth of plate, thermal and mechanical behaviors in the middle portion of the plate are assumed to be uniform along the thickness direction(z-axis). Thus, the following conditions(so-called plane deformation) can be assumed for the plate except near its end;1) distributions of stress and strain are independent on the z-axis;2) plane normal to z-axis before deformation remains plane during and after deformation. In this paper, plane-deformation thermal elasto-plastic problem is formulated by being based on the finite element method. Moreover special regards and paid to the fact that material properties in elastic and plastic region are temperature-dependence. And the method to solve the plane-deformation thermal elasto-plastic problem is shown by using the incremental technique. From the results of analysis, the characterisics of distribution of welding residual stress and plastic strain with the production mechanism are clarified.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.2140_2141
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• 2009

We used the eddy current sensor for a 22.9kV distribution power line insulation cable diagnosis. The insulation cable which is used in the 22.9kV distribution power line is having element wire from 6 to 18. Consequently, currently to ECT applications it has a limit in the distribution power line. We about under producing to apply in pick-up coil forms and the differential total coil form where becomes sum of zero in order to have. From measurement result, partial broken cable was confirmed 500 mV~980 mV changes from normal state.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.5 no.1
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• pp.26-32
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• 2012

This paper presents a metamaterial absorber unit sell structure with four-element electric-LC resonators (ELC). In order to enhance the operating bandwidth of the proposed absorber unit cell two pairs of ELC resonators with a different size are used. The proposed unit cell shows negative permittivity and permeability when the electric field is parallel to the capacitive gap and the magnetic field is normal to the plane of ELC resonator. The simulated results show peak absorbance over 90% at two frequencies of 8.53 and 9.08 GHz, respectively.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.9
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• pp.1352-1358
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• 2004

The mechanical spring is one of widely used machine elements. Among various kinds, flat-type spring loaded by a rotating pin was studied. A flat spring was simplified to a cantilever beam, and numerical analysis was attempted. Since the loading pin rotates about a separate axis from the fixed spring or vice versa, the location, direction, and magnitude of the contact force including normal contact and friction loads vary accordingly. Meanwhile, the spring is deformed substantially as the relative motion progresses. Therefore, this problem needs to be formulated taking the follower loading characteristics and geometrical non-linearity into account. Derived nonlinear differential equation was solved to yield the spring deflection, contact force and the torque to rotate the pin, and the result was compared with a finite element solution. Also, the influences of principal design parameters were studied. The proposed methodology is expected to be useful for the design of pin-loaded flat spring and the prevention of mechanical failures in the form of yielding or fatigue failure of spring or severe wear of the components.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.3
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• pp.333-340
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• 2011

We evaluated the stress-reduction effect for different shapes of a composite adherend with or without a spew fillet. Six different single-lap joint specimens were modeled and assessed using nonlinear finite element analysis. Moreover, we investigated the effect of the stiffness ratio of the adherend and adhesive. The single-lap joint with normal tapering had the highest stress values, and the single-lap joint with reverse tapering and a spew fillet had the lowest stress values. The composite adherends with higher stiffness had lower stress values, and the adhesives with lower stiffness had lower stress values.

• International Journal of Precision Engineering and Manufacturing
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• v.4 no.1
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• pp.56-62
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• 2003

The objective of this study is to adjust the roll gap for the dimension accuracy of bar in hot bar rolling process considering roll wear. In this study hot bar rolling processes for round and oval passes have been investigated. In order to predict the roll wear, the wear model is reformulated as an incremental form and then wear depth of roll is calculated at each deformation step on contact area using the results of finite element analysis, such as relative sliding velocity and normal pressure at contact area. Archard's wear model was applied to predict the roll wear. To know the effects of thermal softening of DCI (Ductile Cast Iron) roll material according to operating conditions, high temperature micro hardness test is executed and a new wear model has been proposed by considering the thermal softening of DCI roll expressed in terms of the main tempering curve. The new technique developed in this study for adjusting roll gap can give more systematically and economically feasible means to improve the dimension accuracy of bar with full usefulness and generality.

• Journal of Mechanical Science and Technology
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• v.19 no.3
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• pp.887-893
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• 2005

The aggregability of red blood cells (RBCs) was determined by laser backscattering light analysis in a microfluidic channel. Available techniques for RBC aggregation often adopt a rotational Couette-flow using a bob-and-cup system for disaggregating RBCs, which causes the system to be complex and expensive. A disposable microfluidic channel and vibration generating mechanism were used in the proposed new detection system for RBC aggregation. Prior to measurement, RBC aggregates in a blood sample were completely disaggregated by the application of vibration-induced shear. With the present apparatus, the aggregation indexes of RBCs can be measured easily with small quantities of a blood sample. The measurements with the present aggregometer were compared with those of LORCA and the results showed a strong correlation between them. The aggregability of the defibrinogenated blood RBCs is markedly lower than that of the normal RBCs. The noble feature of this design is the vibration-induced disaggregation mechanism, which can incorporate the disposable element that holds the blood sample.