• Composites Research
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• v.27 no.2
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• pp.72-76
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• 2014

This study is investigated by experiments and analyses at rates of 2.5m/s, 7.5m/s and 12.5m/s on the impact of tapered double cantilever beam specimens with aluminium alloy. It aims to examine the mechanical property of aluminum alloy by evaluating energy release rate and equivalent stress happened at the bonded part of specimen. Because bonding force remains after the separation of specimen, the energy release rate at the bonded part becomes highest. As crack propagates and the high stress happens at the end of the bonded part, the maximum equivalent stress becomes higher at the last stage, regardless of impact rate. These results of experiments and analyses are the data necessary to develop the safe design of composite material to prevent crack propagation due to impact.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.4
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• pp.244-249
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• 2014

In this research, it have developed a sensor that could diagnose inner deterioration of covered wires. With this sensor it observed results from simulation, and the attribute required for realization. For simulation it have used FLUX, it have considered all of geometric and electromagnetic information from coil and base metal that influences eddy current sensor's property in order to predict the final result. It assumed there is no mutual inductance in the coil with N number of turns, because equivalent current flows in coil that is continuously connected in eddy current sensor. It assumed circular coil loop draws a circle, always have self inductance, and they are connected in series and overlapped according number of turns (N) in coil, and bobbin configuration. Actual sensor was produced with consideration of inductance and number of turns (N). In conclusion, it were able to test the dependency through results from simulation, actual measurement, and modeling of simulation. It is considered that attributes of respective base metal and structure can be predicted by simulating in advance.

• Structural Monitoring and Maintenance
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• v.3 no.2
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• pp.175-194
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• 2016

Based on the change of traditional viscoelastic damper structure, a brand-new damper is designed to control simultaneously the translational vibration and the rotational vibration for platforms. Experimental study has been carried out on the mechanical properties of viscoelastic material and on its multi-dimensional seismic response control effect of viscoelastic damper. Three types of viscoelastic dampers with different shapes of viscoelastic material are designed to test the influence of excited frequency, strain amplitude and ambient temperature on the mechanical property parameters such as circular dissipation per unit, equivalent stiffness, loss factor and storage shear modulus. Then, shaking table tests are done on a group of single-storey platform systems containing one symmetric platform and three asymmetric platforms with different eccentric forms. Experimental results show that the simulation precision of the restoring force model is rather good for the shear deformation of viscoelastic damper and is also satisfied for the torsion deformation and combined deformations of viscoelastic damper. The shaking table tests have verified that the new-type viscoelastic damper is capable of mitigating the multi-dimensional seismic response of offshore platform.

• Journal of the Korean Ceramic Society
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• v.48 no.6
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• pp.549-558
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• 2011

Application of a generalized equivalent circuit including the electrode condition for the Hebb-Wagner polarization in the frequency domain proposed by Jamnik and Maier can provide a consistent set of material parameters, such as the geometric capacitance, partial conductivities, chemical capacitance or diffusivity, as well as electrode characteristics. Generalization of the shunt capacitors for the chemical capacitance by the constant phase elements (CPEs) was applied to a model mixed conducting system, $Ag_2S$, with electron-blocking AgI electrodes and ion-blocking Pt electrodes. While little difference resulted for the electron-blocking cell with almost ideal Warburg behavior, severely non-ideal behavior in the case of Pt electrodes not only necessitates a generalized transmission line model with shunt CPEs but also requires modelling of the leakage in the cell approximately proportional to the cell conductance, which then leads to partial conductivity values consistent with the electron-blocking case. Chemical capacitance was found to be closer to the true material property in the electron-blocking cell while excessively high chemical capacitance without expected silver activity dependence resulted in the electron-blocking cell. A chemical storage effect at internal boundaries is suggested to explain the anomalies in the respective blocking configurations.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1013-1019
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• 2016

CFRP is the composite material manufactured by the hybrid resin on the basis of carbon fiber. As this material has the high specific strength and the light weight, it has been widely used at various fields. Particularly, the unidirectional carbon fiber can be applied with the layer angle. CFRP made with layer angle has the strength higher than with no layer angle. In this paper, the property of crack growth due to each layer angle was investigated on the crack propagation and fracture behavior of the CFRP compact tension specimen due to the change of layer angle. The value of maximum stress is shown to be decreased and the crack propagation is slowed down as the layer angle is increased. But the limit according to the layer angle is shown as the stress is increased again from the base point of the layer angle of $60^{\circ}$. This study result is thought to be utilized with the data which verify the probability of fatigue fracture when the defect inside the structure at using CFRP of mechanical structure happens.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.7
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• pp.773-778
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• 2011

Accelerometers are widely used to measure the lateral vibrations of pipe-like structures such as a gun tube under impulse loads. Stress waves that precede the lateral vibrations due to the explosion within a gun contribute little to the vibrations, but saturate the accelerometer input. A mechanical filter eliminates this high-frequency stress wave and only transmits the signal corresponding to the lateral vibrations. The mechanical filter consists of a mechanical structure for mounting the accelerometers and a damping material. The low-pass filter characteristics are determined from the equivalent damping and stiffness property of this damping material. In this paper, we tested nine commercially available damping materials for their vibration characteristics by using a test rig. We also observed the change in the vibration characteristics while compressing the material. We designed and manufactured a mechanical filter and verified its filtering performance.

• Applied Chemistry for Engineering
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• v.8 no.2
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• pp.197-203
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• 1997

The effect of additives on the mechanical properties of polyurethane foam were investigated. The resin used in this study was prepared by adding catalyst, surfactant and cross-linker to both KONIX FA-703 polyether polyol(80%) and KONIX FA-733 polyether polyol(20%). The polyurethane was foamed by adding equivalent amount of isocyanate(TDI-80, prepolymer M-200, pure MDI) to the resin and was used in property measurements after 72 hours hardening. The physical properties of polyurethane foam were investigated in terms of density, tensile strength, tear strength, elongation, sound absorption coefficient and gel profile measurements. The effects of surfactant on the cell size was investigated by scanning electron microscopy(SEM). The sound absorption coefficient was directly related to the cell size. The physical properties were improved with increasing amount of surfactant(L-5309) until 1.0 part per hundred polyol(1.0pphp).

• Geotechnical Engineering
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• v.13 no.6
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• pp.147-164
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• 1997

This study has the assumption that scale effects in rock mass properties are atrributed to the discontinuous and inhomogeneous nature of rock masses. In order to escape the general equivalent material approach applied to the concept of representative volume element, this study presents the new method considering irregular i oink geometry and arbitrary numbers of i oink and arbitrary joint orientations. Based on the theoretical approach, this theory is applied to a real engineering project. Showing the property variations with size of rock mass element, various numerical experiments about scale effect are conducted. Particularly, to prove the adequacy of the verification process in scale effect with nomerical method, and to investigate the detailed source of scale effect, 4 models with increas ins number of joints are tested. On the basis of the experimental results, the test results of scale effects in 3-D rock mass are presented. From these experiments the effects of the mechanical properties of rock joints on the scale effects in rock mass strength and elastic constants are discussed. To verify the mechanism of scale effects in jointed rock mass, two models with different j oink geometries are studied.

• Structural Engineering and Mechanics
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• v.80 no.6
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• pp.701-709
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• 2021

The paper aims at improving the understanding and mitigating the effects of tunnel fires that may breakout due to the burning fuel and/or explosion within the tunnel. This study particularly focuses on the behavior of the commonly used horse shoe geometry of tunnel systems. The problem has been obtained using an adequate well-established program incorporating the Lagrangian approach. A transient-thermo-coupled static structural analysis is carried out. The effects of radiation and convection to the outer walls of the tunnel is studied. The paper also presents the impact of the hazard on the structural integrity of the tunnel. A methodology is proposed to study the tunnel fire using a model which uses equivalent steel sheet to represent the presence of reinforcements to improve the computational efficiency with adequate validation. A parametric study has been carried out and the effect of suitable lining property for mitigating the fire hazard is arrived at. Detailed analysis is done for the threshold limits of the properties of the lining material to check if it is acceptable in all aspects for the integrity of the tunnel. The study may prove useful for developing insights for ensuring tunnel fire safety. To conduct such studies experimentally are tremendously costly but are required to gain confidence. But, scaled models, as well as loading and testing conditions, cannot be studied by many trials experimentally as the cost will shoot up sharply. In this context, the results obtained from such computational studies with a feasible variation of various combinations of parameters may act as a set of guidelines to freeze the adequate combination of various parameters to conduct one or two costly experiments for confidence building.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.139-144
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• 2015

Recently, to realize sound-absorbing structures, we have to insert sound-absorbing materials into wall. These shapes are taken limitations because sound-absorbing materials should be fixed. Therefore, the sound absorption is changed by environment that used the sound-absorbing materials. On the other hand, we will take same effect without sound-absorbing material, if we change the shape of wall to sound absorbing structure. If we use this sound absorbing structure, we can get benefits by removing limitation of materials. Therefore we suggest perforated plate for effective sound-absorbing structure. We confirmed the function of sound-absorption of this structure using equivalent property. Then, we found the similarity between perforated plate and resonator. Also, we verify these theories through computer simulation by FEM(Finite Element Method). Finally, we validated that perforated plate has function of sound absorption without sound-absorbing material. This perforated plate is used for sound-absorbing material of buildings and transportations such as vehicle, train etc. Also, these results could be further used basic tool for design of sound-absorption structure.