• Journal of the Optical Society of Korea
• /
• v.17 no.4
• /
• pp.317-322
• /
• 2013

We have proposed and demonstrated a low numerical aperture technique to measure the depth of through silicon vias (TSVs) using white-light scanning interferometry. The high aspect ratio hole like TSV's was considered to be impossible to measure using conventional optical methods due to low visibility at the bottom of the hole. We assumed that the limitation of the measurement was caused by reflection attenuation in TSVs. A novel interference theory which takes the structural reflection attenuation into consideration was proposed and simulated. As a result, we figured out that the low visibility in the interference signal was caused by the unbalanced light intensity between the object and the reference mirror. Unbalanced light can be balanced using an aperture at the illumination optics. As a result of simulation and experiment, we figured out that the interference signal can be enhanced using the proposed technique. With the proposed optics, the depth of TSVs having an aspect ratio of 11.2 was measured in 5 seconds. The proposed method is expected to be an alternative method for 3-D inspection of TSVs.

• Journal of the Korean Society of Industry Convergence
• /
• v.23 no.6_2
• /
• pp.935-941
• /
• 2020

In this study, the effect of different shapes on the heat dissipation characteristics of other porous frames on LED lighting frames was studied using finite element analysis. In addition, the heat transfer characteristics of LED frames were tested using a thermal imaging camera and the results of finite element analysis were compared to derive the optimal hole shape. According to the study, the heat dissipation effect was better for frames with hole compared to existing ones without holes. In particular, the heat dissipation characteristics test showed that for frames with holes, the rise time to the maximum temperature is fast and the maximum temperature is significantly lower. Also, we could see that the square and diamond shapes were smaller than the circular pores, but had a greater heat dissipation effect. Through this study, we have concluded that there is a limit to increasing the heat dissipation effect of the frame with a perforated shape, and it is necessary to conduct further research on the change in the shape of the frame in order to achieve a better heat dissipation effect in the future.

• Steel and Composite Structures
• /
• v.11 no.2
• /
• pp.131-147
• /
• 2011

The aim of this work is to provide some insights into the elasto-plastic behaviour of plate girder web square and rectangular panels with centred and eccentric holes under both compression and in-plane bending moment. The numerical study was validated comparing the numerical results obtained for one simple steel plate configuration with the corresponding experimental results, obtained at the University of Padova, observing the influence of the initial out-of-plane imperfections on the force vs. displacement relationship and ultimate strength. Once validated the numerical approach, the effect of bending moment on the stability of the plate is studied and some differences with respect to the uniform compression load case are shown. The influence of dimension and position of the hole, the plate aspect ratio and the steel grade on elasto-plastic behaviour is observed. Some indications regarding the critical slenderness (at which transition from elastic to plastic collapse occurs) are given for square and rectangular plates with symmetric and eccentric holes having small, medium and large diameter.

• Journal of Advanced Marine Engineering and Technology
• /
• v.32 no.6
• /
• pp.841-846
• /
• 2008

Recently the LNG(liquified natural gas) public buses have been introduced to prevent the air pollution in metropolitan areas. As the LNG temperature in fuel tank is as low as $-162^{\circ}C$. the thermal and structural effects of tank components need to be studied for safe introduction in the market. Especially the support system of LNG fuel tank in vehicle, which has connected with inside and outside of tanks, should put attention to reduce the structural stress due to cryogenic temperature and to restrict the heat flux from ambient. There are two supporting systems in the tank, that one is connected between inside and outside tanks by welding, and the other is the inserted support system which is a cylindrical SUS bar inserted in a hole of the supporting plate. In this study the temperature distribution and thermal stress of the inserted support system were evaluated by using the utility program as ANSYS. The results showed that the rate of heat transfer to inner tank through this support system was quite small due to limited contact of support bar with plate. but the thermal stress of support plate was obtained beyond the limited tensile value of SUS304. The cautious design for the support plate part, therefore, should be given to make the safe support system of LNG vehicle fuel tank.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2006.04a
• /
• pp.240-247
• /
• 2006

Piezoelectric sensor-based health monitoring technique using a two-step support vector machine (SYM) classifier is discussed for damage identification of a railroad track. An active sensing system composed of two PZT patches was investigated in conjunction with both impedance and guided wave propagation methods to detect two kinds of damage of the railroad track (one is a hole damage of 0.5cm in diameter at web section and the other is a transverse cut damage of 7.5cm in length and 0.5cm in depth at head section). Two damage-sensitive features were extracted one by one from each method; a) feature I: root mean square deviations (RMSD) of impedance signatures and b) feature II: wavelet coefficients for $A_0$ mode of guided waves. By defining damage indices from those damage-sensitive features, a two-dimensional damage feature (2-D DF) space was made. In order to minimize a false-positive indication of the current active sensing system, a two-step SYM classifier was applied to the 2-D DF space. As a result, optimal separable hyper-planes were successfully established by the two-step SYM classifier: Damage detection was accomplished by the first step-SYM, and damage classification was also carried out by the second step-SYM. Finally, the applicability of the proposed two-step SYM classifier has been verified by thirty test patterns.

• Steel and Composite Structures
• /
• v.22 no.4
• /
• pp.837-853
• /
• 2016

This paper presents the experimental and numerical study on the distribution of transverse and longitudinal residual stresses in cold-formed thick-walled structural steel rectangular hollow sections manufactured by indirect technique. Hole-drilling method is employed to measure the magnitude of the transverse and longitudinal surface residual stress distribution, and the effects of the residual stresses are evaluated qualitatively by sectioning method. It is shown that compared to normal cold-formed thin-walled structural hollow sections (SHS), the cold-formed thick-walled SHS has similar level of residual stress in the flat area but higher residual stresses in the corner and welding areas. Both the transverse and longitudinal residual stresses tend to open the section. In order to predict the surface residual stresses in the corners of the cold-formed thick-walled SHS, an analytical model is developed. 2D finite element simulation of the cold bending process is conducted to validate the analytical approach. It is shown that in analyzing bending for thick-walled sections, shifting of neutral axis must be considered, since it would lead to nonlinear and non-symmetrical distribution of stresses through the thickness. This phenomenon leads to the fact that cold-formed thick-walled SHSs has different distribution and magnitude of the residual stresses from the cold-formed thin-walled SHSs.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.19 no.2
• /
• pp.211-215
• /
• 2010

Continuous contraction and expansion of disk brake can be due to friction and temperature difference at repeated sudden braking. As serious vibration at disk is produced, the braking force will be changed ununiformly and braking system can not be stabilized. Temperature and heat flux at disk brake are investigated by structural and thermal analysis in this study. The maximum equivalent stress and displacement are shown respectively at the ventilated hole and the lower part of disk plate. At thermal analysis of initial state, temperature on disk plate is distributed from $95.9^{\circ}C$ to $100^{\circ}C$. The maximum heat flux of $0.0168W/mm^2$ is shown at the inner friction part between disk plate and pad. At thermal analysis of transient state, temperature on disk plate is distributed from $95^{\circ}C$ to $96.5^{\circ}C$ after 100 second. The maximum heat flux of $0.0024W/mm^2$ is also shown at the inner friction part between disk plate and pad. By comparing with initial state, the temperature on disk plate is more uniformly distributed and heat flux is more decreased by 7 times at transient state.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2003.10a
• /
• pp.403-409
• /
• 2003

The finite element method is one of the most widely used method of structural analysis that has wide applications in diverse fields of engineering and science. The method has been proven effective and reliable in many practical problems. One of the reasons for the methods' popularity is its ease of use, but still the user has to input the finite element mesh which affects the accuracy of the results. The knowledge required to form an effective mesh for a given problem is somewhat complex and for sometime there has been research effort to automate the generation of the mesh and this is called the adaptive mesh generation scheme. A good adaptive mesh scheme seemed to require an accurate assessment of error and generally this requires some additional computation. This paper looks into the possibility of generating adaptive meshes based on representative strain values in each finite element method. The proposed adaptive scheme does not require additional computations other that looking up the data values already computed as finite element analysis results and simple manipulations of these data. Two plane stress problems, a plate with a hole and a deep beam with a concentrated load at the end are considered to show the progress of the improved generation of adaptive meshes using the scheme.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.28 no.6
• /
• pp.683-690
• /
• 2015

For demolition of offshore facilities, traditional methods such as jackhammer and explosive methods have been often used in construction industry. However, prohibitions for use of those methods are becoming more rigorous especially in environmentally and historically sensitive areas. It was also reported that the explosive demolition method on maritime bedrock can cause a disturbance of ecosystem. For those reasons, use of soundless chemical demolition agent(SCDA) is getting the spotlight. However, researches regarding the mechanical point of SCDA have seldom performed. There is no industrial standard for use of SCDA yet. In this study, a pilot experimental study in order to measure the required expansive pressure that could be generated from SCDA was conducted. Numerical models were developed in order to estimate the required expansive pressures of SCDA for initiating cracks depending on selected key parameters. Obtained results indicate that the required pressure does not decrease linearly as increasing the hole diameter, the number of holes, and the ratio of hole-distance to hole-diameter.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.22 no.5
• /
• pp.463-474
• /
• 2009

Double symmetric patch repair of existing structures always causes membrane action only, however, in many cases this technique is not practical. On the other hand, the bending stiffness of the patch and the skin increases as tensile loading is increased and affects the bending deformation significantly in the case of single-sided patch repair. In this study, the p-convergent full layerwise model has been proposed to determine the stress concentration factor in the vicinity of a circular hole as well as across the thickness of plates with single-sided patch repair. In assumed displacement field, the strain-displacement relations and 3-D constitutive equations of a layer are obtained by the combination of 2-D and 3-D hierarchical shape functions. The transfinite mapping technique has been used to represent a circular boundary and Gauss-Lobatto numerical integration is implemented in order to directly obtain stresses occurred at the nodal points of each layer without other extrapolation techniques. The accuracy and simplicity of the present model are verified with comparison of the previous results in literatures using experiment and conventional 3-D finite element. Also, the bending effect has been investigated with various patch types like square, circular and annular shape.