• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.181-188
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• 2004

Structural analysis for materials containing regularly spaced in-homogeneities is usually executed by using averaged material properties. For the homogenization process, a unit cell is defined and loaded somehow, and its response is investigated to evaluate the properties. The imposed loading conditions should accord to the behavior of unit cell immersed in the macroscopic structure in order to guarantee the accuracy of the effective properties. Each unit cell shows periodic variation of strain if the material is loaded uniformly, and in this study, direct implementation of this characteristic behavior is attempted on FE models of unit cell. Conventional finite element analysis tool can be used without any modification, and the boundary of unit cell is constrained in a way that the periodicity is satisfied. The proposed method is applicable to skew arrayed in-homogeneity problems. The flexibility matrix relating tonsorial stress and strain components in skewed rectilinear coordinate system is transformed so that the required engineering constants can be evaluated. Effective properties are computed for the materials with square and skew arrayed circular holes, and its accuracy is examined.

• Structural Engineering and Mechanics
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• v.53 no.5
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• pp.867-880
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• 2015

Mechanical fastening is still one of the main methods used for joining components. Different techniques have been applied to reduce the effect of stress concentration of notches like fastener holes. In this work we evaluate the feasibility of combining laser shock peening (LSP) and cold expansion to improve fatigue crack initiation and propagation of open hole specimens made of 6061-T6 aluminum alloy. LSP is a new and competitive technique for strengthening metals, and like cold expansion, induces a compressive residual stress field that improves fatigue, wear and corrosion resistance. For LSP treatment, a Q-switched Nd:YAG laser with infrared radiation was used. Residual stress distribution as a function of depth was determined by the contour method. Compact tension specimens with a hole at the notch tip were subjected to LSP process and cold expansion and then tested under cyclic loading with R=0.1 generating fatigue cracks on the hole surface. Fatigue crack initiation and growth is analyzed and associated with the residual stress distribution generated by both treatments. It is observed that both methods are complementary; cold expansion increases fatigue crack initiation life, while LSP reduces fatigue crack growth rate.

• Structural Engineering and Mechanics
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• v.76 no.2
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• pp.175-191
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• 2020

In this study, the effect of Nano silica (SiO2) on the buckling strength of the glass fiber reinforced laminates containing the machining process causes holes were investigated. The tests have been applied on two status milled and non-milled. To promote the mechanical behavior of the fiber-reinforced glass epoxy-based composites, Nano sio2 was added to the matrix to improve and gradation. Nano sio2 is chosen because of flexibility and high mechanical features; the effect of Nanoparticles on surface serenity has been studied. Thus the effect of Nanoparticles on crack growth and machining process and delamination caused by machining has been studied. We can also imply that many machining factors are essential: feed rate, thrust force, and spindle speed. Also, feed rate and spindle speed were studied in constant values, that the thrust forces were studied as the main factor caused residual stress. Moreover, entrance forces were measured by local calibrated load cells on machining devices. The results showed that the buckling load of milled laminates had been increased by about 50% with adding 2 wt% of silica in comparison with the neat damaged laminates while adding more contents caused adverse effects. Also, with a comparison of two milling tools, the cylindrical radius-end tool had less destructive effects on specimens.

• Journal of Computing Science and Engineering
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• v.6 no.3
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• pp.219-226
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• 2012

Recently, shape analysis of human organs has achieved much attention, owing to its potential to localize structural abnormalities. For a group-wise shape analysis, it is important to accurately restore the shape of a target structure in each subject and to build the inter-subject shape correspondences. To accomplish this, we propose a shape modeling method based on the Laplacian deformation framework. We deform a template model of a target structure in the segmented images while restoring subject-specific shape features by using Laplacian surface representation. In order to build the inter-subject shape correspondences, we implemented the progressive weighting scheme for adaptively controlling the rigidity parameter of the deformable model. This weighting scheme helps to preserve the relative distance between each point in the template model as much as possible during model deformation. This area-preserving deformation allows each point of the template model to be located at an anatomically consistent position in the target structure. Another advantage of our method is its application to human organs of non-spherical topology. We present the experiments for evaluating the robustness of shape modeling against large variations in shape and size with the synthetic sets of the second cervical vertebrae (C2), which has a complex shape with holes.

• Korean Journal of Materials Research
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• v.29 no.12
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• pp.764-773
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• 2019

The gas response characteristic toward C₂H₅OH has been demonstrated in terms of copper-vacancy concentration, hole density, and microstructural factors for undoped/Li(I)-doped CuO thin films prepared by sol-gel method. For the films, both concentrations of intrinsic copper vacancies and electronic holes decrease with increasing calcination temperature from 400 to 500 to 600 ℃. Li(I) doping into CuO leads to the reduction of copper-vacancy concentration and the enhancement of hole density. The increase of calcination temperature or Li(I) doping concentration in the film increases both optical band gap energy and Cu2p binding energy, which are characterized by UV-vis-NIR and X-ray photoelectron spectroscopy, respectively. The overall hole density of the film is determined by the offset effect of intrinsic and extrinsic hole densities, which depend on the calcination temperature and the Li(I) doping amount, respectively. The apparent resistance of the film is determined by the concentration of the structural defects such as copper vacancies, Li(I) dopants, and grain boundaries, as well as by the hole density. As a result, it is found that the gas response value of the film sensor is directly proportional to the apparent sensor resistance.

• Journal of the Korean Wood Science and Technology
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• v.34 no.5
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• pp.1-10
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• 2006

The objective of this study was to elucidate the microscopic patterns of decay caused by brown-rot fungi of Tyromyces palustri and Gloeophyllum trabeum in Korean red pine (Pinus densiflora) and radiata pine (Pinus radiata) woods through light and electron microscopies. The ultrastructural changes of cell walls attacked by the two brown-rot fungi were compared in this respect. Macroscopically, radiata pine showed more ring and radial checks than Korean red pine. Microscopically, with the progress of decay, spiral checks associated with cross-field pits and bore holes in the cell wall were more remarkably numerous in the radiata pine than in the Korean red pine. In the radiata pine, G. trabeum produced more spiral checks in the cell wall than T. palustris. In the advanced stages of decay by G. trabeum, the erosions of ray cell walls were identified both in the Korean red pine and radiata pine but $S_3$ layers of tracheid walls were eroded only in the Korean red pine.

• Steel and Composite Structures
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• v.21 no.3
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• pp.573-588
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• 2016

Carbon Fiber Reinforced Plastic (CFRP) and Titanium Alloy (Ti6Al4V) stack, extensively used in aerospace structural components are assembled by fasteners and the holes are made using drilling process. Drilling of stack in one shot is a complicated process due to dissimilarity in the material properties. It is vital to have optimal machining condition and tool geometry for better hole quality and tool life. In this study the tool wear and hole quality were analysed by experimental analysis using three modified twist drills and online tool condition monitoring using Acoustics Emission (AE) sensor. Helix angle and point angle influence tool performance and cutting force. It was found that a tool geometry (TG1) with high helix angle of $35^{\circ}$ with low point angle $130^{\circ}$ results in reduction in thrust force of 150-500 N range but the TG2 also perform almost similar to TG1, but when compared with the AErms voltage generated during drilling it was found that progressive rise in voltage in TG1 is less with respect to TG2 which can be attributed to tool life. In process wear monitoring was done using crest factor as monitoring index. AErms voltage were measured and correlated with the performance of the drills.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1882-1889
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• 2007

Surveying rocks for engineering aims for prediction of geological feature of the construction site. Conventionally, survey information at outcrops and bore holes are projected to the construction sites, such as tunnel and slopes, and rock properties of the sites are predicted by interpretations of specialists. This system, the "Fracjection", aims to assist the specialist for visualization of the projected fractures from borehole and outcrop survey. The Fracjection accepts the BIPS and outcrop survey data to its database and allows plotting them in AutoCad map. The software also reads elevation data from contours of the topographic map and constructs DEM of the construction sites. With user's guide, it generates 3D excavation sites such as slopes and tunnels at the topographic map. The s/w projects borehole and outcrop surveyed fractures onto the modeled excavation surface and allows analysis of failure criteria, such as plane, wedge, and toppling failures by built-in stereonet function. Projected fractures can further be analyzed for structural homogeneities and rock mass quality. Moving window style correlation comparison of stereonet plots are used for formal analyses, and RQD type counts of the projected fractures are adopted for the latter analyses.

• Journal of the Korean Wood Science and Technology
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• v.43 no.5
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• pp.652-660
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• 2015

To study the bearing characteristics of glass fiber reinforced glulam for structural design, bearing strength tests were performed. Bearing loads were applied in the direction parallel to the grains, and the holes were prepared in such a way that the bolts would bear and support all the layers. The yield bearing strengths of the glass fiber reinforced glulam were found to be similar to those of the non-reinforced glulam, and were almost constant regardless of increases in bolt diameter. The ratio of the experimental yield bearing strength to the estimated bearing strength according to the suggested equation of the Korea Building Code and National Design Specification was 0.91~1.03. For the non-reinforced glulam and the sheet glass fiber reinforced plastic glulam, the maximum bearing load was measured according to the splitting fracture of specimens under bolt. The textile glass fiber reinforced glulam underwent only an embedding failure caused by the bearing load. The failure mode of reinforced glulam according to bearing load will influence the failure behavior of bolted connection, and estimating the shear yield strength of the bolted connection of the reinforced glulam is necessary, not only by using the bearing strength characteristics but also using the fracture toughness of the reinforced glulam.

• Structural Engineering and Mechanics
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• v.47 no.6
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• pp.839-856
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• 2013

Metallic annular discs with their outer boundary fully constrained are studied with newly derived semi-analytical solutions for the effects of thickness variations under thermal loading and unloading. The plane stress and axisymmetric assumptions were adopted, and the thickness of the disk depends on the radius hyperbolically with an exponent n. Furthermore, it is assumed that the stress state is two dimensional and temperature is uniform in the domain. The solutions include the elastic, elastic-plastic and plastic-collapse behavior, depending on the values of temperature. The von Mises type yield criterion is adopted in this work. The material properties, Young's modulus, yield stress and thermal expansion coefficient, are assumed temperature dependent, while the Poisson's ratio is assumed to be temperature independent. It is found that for any n values, if the normalized hole radius a greater than 0.6, the normalized temperature difference between the elastically reversible temperature and plastic collapse temperature is a monotonically decreasing function of inner radius. For small holes, the n values have strong effects on the normalized temperature difference. Furthermore, it is shown that thickness variations may have stronger effects on the strain distributions when temperature-dependent material properties are considered.