• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.671-682
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• 2012

The use of sinusoidal corrugated web girder for the box-type girders and gable steel main frames has recently been increasing very much. The reasons are that the thin web of the girder affords a significant weight reduction compared with rolled beam and welded built-up girder, and that corrugation prevents the buckling failure of the web. Improvements of the automatic fabrication process makes mass production of the corrugated web and unit possible, and applications of this girder have been extended considerably. Thus, the research for the optimum design processer considering the production data is needed practically. For doing this research, we develope the discrete optimum structural design program in consideration of production list data for the research, and the program apply to the single girder under the uniform load and the concentrated load as numerical example. We consider objective function as minimum weight of the girder, and use slenderness ratio, stress of flanges and corrugated web, and the girder deflection as the constraint functions. And also the Genetic Algorithms is adopted to search the global minimum point by using the production list as a discrete design variable. Finally, to verify the optimality of the design, we conduct a comparison of the results of the discrete optimum design with those of the continuous one, and also analyze the characteristics of the optimum cross-section.

• Journal of Korean Society of Steel Construction
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• v.24 no.2
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• pp.217-231
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• 2012

The flexural behavior of HSB I-girder with a non-slender web attributed to inelastic lateral-torsional buckling under uniform bending was investigated using nonlinear finite element analysis of ABAQUS. The girder was assumed to have a compact or noncompact web in order to prevent premature bend-buckling of the web. The unbraced length of the girder was selected so that inelastic lateral-torsional buckling governs the ultimate flexural strength. The compression flange was also assumed to be either compact or noncompact to prevent local buckling of the elastic flange. Both homogeneous sections fabricated from HSB600 or HSB800 steel and hybrid sections with HSB800 flanges and SM570-TMC web were considered. In the FE analysis, the flanges and web of I-girder were modeled as thin shell elements. Initial imperfections and residual stresses were imposed on the FE model. An elasto-plastic strain hardening material was assumed for steel. After establishing the validity of the present FE analysis by comparing FE results with test results in existing literature, the effects of initial imperfection and residual stress on the inelastic lateral-torsional buckling behavior were analyzed. Finite element analysis results for 96 sections demonstrated that the current inelastic strength equations for the compression flange in AASHTO LTFD can be applied to predict the inelastic lateral torsional buckling strength of homogeneous and hybrid HSB I-girders with a non-slender web.

• Journal of the Korean Geotechnical Society
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• v.16 no.1
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• pp.31-42
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• 2000

Consolidation and permeability are major engineering properties of soil. In clay, coefficient of permeability and consolidation can be calculated by incremental loading consolidation test. However, it is known that the incremental loading test has several deficiencies including long testing time, non-uniform stress state, very soft clay and problem of back pressure saturation. Specially, it is not performed with horizontal consolidation test. Several methods have been proposed for obtaining reliable values of $C_v$. Among these, the square root of time-fitting method proposed by Taylor(1948) and logarithm of time-fitting method, also called Casagrande's method, are used extensively in soil engineering practice. But these methods are not amenable for the absence of initial linear portion and have the difficulties involved in distinguishing secondary compression from primary compression. Rowecell consolidation tests were carried out in this study with different trimming axis and sample size. The results were compared with those of other methods; Casagrande,$Taylor,\; Casagrande,\; Hyperbolic,\; \delta/t-logt$. From the results, we explained a relationship between horizontal coefficient of permeability and void ratio was obtained. Finally, the directly measured horizontal coefficient of permeability obtained by using the Rowecell was compared with the permeability derived indirectly from the consolidation test result.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.3 s.36
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• pp.187-196
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• 2005

MEMS devices such as a vibratory gyroscope often suffer from a lower yield rate due to fabrication errors and the external stress. In the decoupled vibratory gyroscope, the main factor that determines the yield rate is the frequency difference between the sensing and driving modes. The gyroscope, fabricated with SOI (Silicon-On-Insulator) wafer and packaged using the anodic bonding, has a large wafer bowing caused by thermal expansion mismatch as well as non-uniform surfaces of the structures caused by the notching effect. These effects result in large distribution in the frequency difference, and thereby a lower yield rate. To improve the yield rate we propose a packaged SiOG (Silicon On Glass) technology. It uses a silicon wafer and two glass wafers to minimize the wafer bowing and a metallic membrane to avoid the notching. In the packaged SiOG gyroscope, the notching effect is eliminated and the warpage of the wafer is greatly reduced. Consequently the frequency difference is more uniformly distributed and its variation is greatly improved. Therefore we can achieve a more robust vibratory MEMS gyroscope with a higher yield rate.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.67-75
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• 2000

The numerical simulation of Brazilian fracture toughness test is carried out using PFC code and the influence parameters are analyzed such as shape of loading plane, size of Brazilian disc and unit panicle of model, loading angle and loading rate. The flattened Brazilian disc is adopted for applying uniform load. The range of loading angle(2$\alpha$) necessary to induce the tensile crack at disc center and to obtain the load-displacement curve giving the critical load for the stable crack propagation is shown as 20$^{\circ}$~40$^{\circ}$. In condition that the loading angle is 20$^{\circ}$, the mode-I fracture toughness is evaluated almost constant in the range of particle size less than I mm and loading rate less than 0.01 mm/s. This range of influence parameters seems appropriate condition for the tensile crack initiation at disc center and the control of stable crack propagation, which can give the reliance in evaluation of fracture toughness by Brazilian test.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.320-328
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• 2000

The numerical simulation of Brazilian fracture toughness test is carried out using PFC code and the influence parameters are analyzed such as shape of loading plane, size of Brazilian disc and unit particle of model, loading angle and loading rate. The flattened Brazilian disc is adopted for applying uniform load. The range of loading angle(2$\alpha$) necessary to induce the tensile crack at disc center and to obtain the load-displacement curve giving the critical load for the stable crack propagation is shown as 20°∼40°. In condition that the loading angle is 20°, the mode-I fracture toughness is evaluated almost constant in the range of particle size less than 1 mm and loading rate less than 0.01㎜/s. This range of influence parameters seems appropriate condition for the tensile crack initiation at disc center and the control of stable crack propagation, which can give the reliance in evaluation of fracture toughness by Brazilian test.

• Design & Manufacturing
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• v.13 no.4
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• pp.10-16
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• 2019

Semiconductor chip is bonded to the substrate by melting solder bumps. In general, the chip bonding is applied by a Reflow process or a Thermo-Compression(TC) bonding process. In this paper, we introduce a Laser Assisted Thermo-Compression bonding (LATCB) process to improve the anxiety of the existing process(Reflow, TC bonding). In the LATCB process, the chip is bonded to the substrate by irradiating a laser with a uniform energy density in the same area as the chip to melt only the solder bumps and press the chip with a Transparent Compression Module (TCM). The TCM consists of a fused silica header for penetrating the laser and pressurizing the chip, and a piezoelectric actuator (P.A.) coupled to both ends of the header for micro displacement control of the header. In addition, TCM is a structure that can pressurize the chip and deliver it to the chip and solder bumps without losing the energy of the laser. Fused silica, which is brittle, is vulnerable to deformation, so the header may be damaged when an external force is applied for pressurization or a displacement differenced is caused by piezoelectric actuators at both ends. On the other hand, in order to avoid interference between the header and the adjacent chip when pressing the chip using the TCM, the header has a notch at the bottom, and breakage due to stress concentration of the notch is expected. In this study, the thickness and notch length that the header does not break when the external force (500 N) is applied to both ends of the header are optimized using structural analysis and Coulomb-Mohr failure theory. In addition, the maximum displacement difference of the P.A.s at both ends where no break occurred in the header was derived. As a result, the thickness of the header is 11 mm, and the maximum displacement difference between both ends is 8 um.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.4
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• pp.329-336
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• 2000

Welding is a important technological method in mechanical engineering. $CO_2$MAG(metal active gas) welding means that metal part in double capstan drum for the inshore and costal vessels are joined by melting(with or without a filler material) or that new material is added to a metal part by melting. The thermal stresses appear due to a non-uniform temperature field, inhomogeneous material properties, external restraint and volume changes during phase transformations. In this study analysis the elasto-plastic thermal stresses distribution of welding part in double capstan drum for the inshore and costal vessels using finite element method (FBM). Therefore it calculates the numerical value that can be applied to the optimum design of welding parts and the shapes. The significant results obtained in this study are summarized as fellows. At early stage of the cooling after welding process, the abrupt thermal stresses gradient has been shown in the vicinity of welding part. In the thermal stresses analysis due to temperature gradient and heat shocking maximum stress was occurred of welding part and stresses were distributed from 54MPa~48MPa.

• Polymer(Korea)
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• v.36 no.5
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• pp.555-563
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• 2012

Warpage of injection molded product is caused by non-uniform shrinkage during shaping operation and relaxation of residual stress. Robust part design and glass fiber reinforced reins have been adopted to prevent warpage of part. Warpages for part designs have been investigated in this study according to the injection molding conditions. Part design contains flat specimen and two different rib designs in the flat part. Resins used in this study were glass fiber reinforced amorphous plastics, PC and ABS. Different rib designs showed significant differences of warpages in the parts. Various warpages have been observed in the three regions of the part, near gate region, opposite region to the gate, and flow direction region. Results of computer simulation revealed that the warpages were strongly related to glass fiber orientation. Flat specimen showed the smallest warpage and the specimen with ribs to the flow direction showed a high resistance to warpage. Warpage highly depended upon part design rather than molding condition. It was concluded that the rib design and selection of gate location in injection molding would be the most important factors for the control of warpage since those are directly related to the fiber orientation during molding.

• Journal of the East Asian Society of Dietary Life
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• v.22 no.6
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• pp.758-771
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• 2012

This research contains awareness of antioxidant and intakes of antioxidant foods for the present evaluate college students in Seoul, 375 patients were investigated. The subjects, the woman college student more than male's responded, showed a uniform distribution in the allowance, grade and the most type of residence is living apart from their family. All male and female college students recognize a lot about health, but male college students had higher than female students interested in the health, on the other hand, female college students had higher than male college students for the health efforts for the promotion of a healthy. Awareness about the oxide and active oxygen is moderate level, but knowledge about active oxygen is low level, they responded that active oxygen was caused when received stress or do strenuous exercise. General Health Functional Foods recognized that the usual intake, but intake of antioxidant was when the activity was caused by active oxygen. They recognized that the antioxidant effect is anti-aging and vitamin, wine and tea, were perceived as antioxidant foods, are popularly known. Usually, people was initially recognized through the internet in university or high school, they desire to obtain information was high but the effort to gain understanding and knowledge about antioxidant are relatively low. The result of comparing the difference of natural antioxidant foods and antioxidant healthy functional foods, recognizes of effects and absorption rate are similar, but recognizes that natural food intake is better recognition in the economics and health functional food is better recognition in the easy intake and nature foods was more preferred than functional foods because of nature friendly. Trying to intake of antioxidant foods is low, but people is expected anti-aging and fatigue recovery through the intake of antioxidant food. People think that intake is irrelevant to the season, but summer is higher than other seasons. Showed that efficacy perceptions about health supplements are higher, but efficacy perceptions about antioxidant health supplements when ingested are at a moderate level, which is lower, due to low antioxidant for understanding. Antioxidant functional health food intake will be affected the gifts or the people around them and purchase is also more influenced by surround people than themselves. So showed that most college students prefer natural antioxidant foods than antioxidant health supplements, in case of ingested antioxidant health supplements also showed that it was consumed by surround people than personal will.