• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.630-633
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• 2004

Generally, component and FR-4 board are connected by solder joint. Because material properties of components and FR-4 board are different, component and FR-4 board show different coefficients of thermal expansion (CTE) and thus strains in component and board are different when they are heated. That is, the differences in CTE of component and FR-4 board cause the dissimilarity in shear strain and BGA solder joint s failure. The first order Taylor series expansion of the limit state function incorporating with thermal fatigue models is used in order to estimate the failure probability of solder joints under heated condition. A model based on plastic-strain rate such as the Coffin-Manson Fatigue Model is utilized in this study. The effects of random variables such as frequency, maximum temperature, and temperature variations on the failure probability of the BGA solder joint are systematically investigated by using a failure probability model with the first order reliability method(FORM).

• Journal of the Korea Institute of Military Science and Technology
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• v.5 no.3
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• pp.89-97
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• 2002

In this study, the effect of $\alpha$-phase morphology on the dynamic deformation behavior at ultra high strain rate was investigated by EBW(Explosive Bridge Wire) test. All of tests and analyses were conducted on three typical microstructures of Ti-6Al-4V alloy, i.e. equiaxed, widmanstatten and bimodal microstructures. The spall strength and HEL(Hugoniot Elastic Limit) of the specimens that have the thickness of 2mm and 4mm were highest with the bimodal microstructure. These results were similar with previous study which was performed by dynamic torsion test(Kolsky torsion test).

• Journal of Food Hygiene and Safety
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• v.11 no.2
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• pp.129-132
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• 1996

Recently, as concern about the residual antibiotics in milk increase, the detection methods of residual antibiotics used extensevely at the present time were investigated and compared to their properties and the detection limits of variable antibiotics. At first, comparactive tests of the detectable sensitivity of 4 test organisms, B. cereus, B. subtilis, M.luteus, B.stearothermophilus C-953, were performed by disc assay. As a result, B.stearothermophilus was the most sensitive strain of all other strains and showe the detect limit of 5-50 ppb for penlicillins (PCs). And also, B.subitilis was showed the more effective detection limit, 200-400 ppb, for aminoglycosides (AGs) and M.luteus was showed predominant sensitivity , 50-500 ppb for macrolides(MLs) and B.cereus was the most sensitive strain for tetracyclines (TCs) and showed the detection limit of 100-400 ppb. Therefore, each test strains were showed a different sensitivity in the detection of the different antibiotic families. When the detection limit of disc assay and other methods were compared, TTCmethod was less sensitive than other methods showing 5-50 ppb detectable lebel for PCs. Also, for the detection of other antibiotic families TTC method was showed the worst sensitivity and Delvo and Charm Farm tests were similar to the detectable properties of AGs and MLs. Although disc assay was showed the similar detection limit for PCs with Delvo and Charm Farm, it was more widely effective for the detection of kanamycin, erythromycin, chlortetracycline, doxycycline, verginiamycin and so on than Delvo or Charm Farm. CharmII test was showed the best sensitivity for the most of antibiotics except neomycin and gentamycin. But it was necessary that different tests must be performed to each antibiotic family and so it was regarded that the effectiveness of that method was low.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.1
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• pp.158-166
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• 2008

Member force, strain and stress distribution of a section are obtained for prestressed steel and concrete(PSSC) composite bridge subjected to dead and live load in order to interpret the effect of prestressing and deformation of tendon. The stress and strain distribution and moment capacity are obtained for both noncomposite and composite section and for allowable stress limit state, yield limit state and strength limit state. Reliability analysis is conducted after assuming limit states for deflection, stress and flexural strength. Comparing that the reliability index for stress is near 0 for example section which is designed to satisfy the allowable stress exactly, the reliability indexes for deflection and flexural strength are high. Reliability of PSSC girder which is designed based on allowable stress of bridge design code is high for deflection and flexural strength.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.214-224
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• 2008

Member force, strain and stress distribution of a section are obtained for optimized standard 25m~45m PSSC composite bridge subjected to dead and live load in order to interpret the effect of prestressing and deformation of tendon. The stress and strain distribution and moment capacity are obtained for both noncomposite and composite section and for allowable stress limit state, yield limit state and strength limit state. Reliability analysis is conducted after assuming limit states for stress and flexural strength. The reliability index for standard PSSC composite bridge which is designed to satisfy the allowable stress for flexural strength are higher than 3.5 which is required reliability indexes on American code for LRFD. Reliability of PSSC girder which is designed based on allowable stress of bridge design code is high for flexural strength.

• Transactions of Materials Processing
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• v.25 no.2
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• pp.91-95
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• 2016

This paper is concerned with modeling of a ductile fracture criterion for sheet metal considering anisotropy to predict the sudden fracture of advanced high strength steel (AHSS) sheets during complicated forming processes. The Lou−Huh ductile fracture criterion is modified using the Hill’s 48 anisotropic plastic potential instead of the von Mises isotropic plastic potential to take account of the influence of anisotropy on the equivalent plastic strain at the onset of fracture. To determine the coefficients of the model proposed, a two dimensional digital image correlation (2D-DIC) method is utilized to measure the strain histories on the surface of three different types of specimens during deformation. For the derivation of an anisotropic ductile fracture model, principal stresses (𝜎₁,𝜎₂, 𝜎₃) are expressed in terms of the stress triaxiality, the Lode parameter, and the equivalent stress (𝜂_𝐻, 𝐿,) based on the Hill’s 48 anisotropic plastic potential. The proposed anisotropic ductile fracture criterion was quantitatively evaluated according to various directions of the maximum principal stress. Fracture forming limit diagrams were also constructed to evaluate the forming limit in sheet metal forming of AHSS sheets over a wide range of loading conditions.

• Steel and Composite Structures
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• v.49 no.1
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• pp.19-30
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• 2023

Steel-concrete composite slabs represent a very efficient floor solution combining the key performance of two different materials: the steel and the concrete. Composite slab response is governed by the degree of the interaction between these two materials, mainly depending by chemical and mechanical bond. The latter is characterized by a limited degree of confinement if compared with the one of the rebars in reinforced concrete members while the former is remarkably influenced by the type of concrete and the roughness of the profiled surface, frequently lubricated during the cold-forming manufacturing processes. Indeed, owing to the impossibility to guarantee a full interaction between the two materials, a key parameter governing slab design is represented by the horizontal shear-bond strength, which should be always experimentally estimated. According to EC4, the design of the slab bending resistance, is based on the simplified assumption that the decking sheet is totally yielded, i.e., always in plastic range, despite experimental and numerical researches demonstrate that a large part of the steel deck resists in elastic range when longitudinal shear collapse is achieved. In the paper, the limit strain for composite slab, which corresponds to the slip, i.e., the debonding between the two materials, has been appraised by means of a refined numerical method used for the simulation of experimental results obtained on 8 different composite slab types. In total, 71 specimens have been considered, differing for the properties of the materials, cross-section of the trapezoidal profiled metal sheets and specimen lengths.

• Geomechanics and Engineering
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• v.4 no.1
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• pp.19-37
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• 2012

This paper presents the results of analytical and numerical analyses of the effects of performing a pressuremeter test or driving a pile in clay. The geometry of the problem has been simplified by the assumptions of plane strain and axial symmetry. Pressuremeter testing or installation of driven piles has been modelled as an undrained expansion of a cylindrical cavity. Stresses, pore water pressures, and deformations are found by assuming that the clay behaves like normally consolidated modified Cam clay. Closed-form solutions are obtained which allow the determination of the principal effective stresses and the strains around the cavity. The analysis which indicates that the intermediate principal stress at critical state is not equal to the mean of the other two principal stresses, except when the clay is initially isotropically consolidated, also permits finding the limit expansion and excess pore water pressures by means of the Almansi finite strain approach. Results are compared with published data which were determined using finite element and finite difference methods.

• Microbiology and Biotechnology Letters
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• v.29 no.4
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• pp.212-220
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• 2001

Rare mating was used to select a respiratory deficient mutant of Saccharomyces cerevisiae HDC52 strain. Glucoamylase gene of S. diastaticus K114 was developed into the RD mutant which could uptake maximum amount of non-fermentable sugars through the expression of glu- coamplyase gene and the fermentation characteristics of the developed strain HCS were investigated. The size of HCS yeast and HBD52 yeast strain were 13 $\mu\textrm{m}$ and 10$\mu\textrm{m}$ respectively. HCS strain which can uptake maximum amount of non-fermentable sugar through the expression of glucoamylase gene was developed. By karyotype anal- ysis. HCS stain but not RD mutant HBC52 showed a band of 1150 kb chromosome DNA This band should include glcoamylase gene from Saccharomyces diataticus K114 THis strain has glucoamylase which can degrade starch By transduction and contrnuance of glucoamylase gene HCS strain gegraded strach and formed halo. Also, HCS strain maintained the character after 50 generations. Glucoamylase activities of Saccharomyces diastaticus K114 and HCS yeast strains are 9.5 and 2.7~3.4(unit/ml) HCS and HBC52 strain showed similar sugar fermentation patterns and low flocculation In spore and film forming test, HCS and HBC52 strain formed neither spores nor films. In the limit fermentation test, HBC52 strain showed fermentation level of 68% and HCS strain showed 76~78% As the limit attenuation of HBC52 and HCS were ($2.00^{\circ}$P) and ($0.7~0.93^{\circ}$P) This study demon- strates and HCS strain may be used for low carbohydrate beer fermentation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.5
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• pp.562-569
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• 2007

This paper presents plastic limit loads and approximate J estimates for axial through-wall cracked pipe bends under internal pressure and in-plane bending. Geometric variables associated with a crack and pipe bend are systematically varied, and three possible crack locations (intrados, extrados and crown) in pipe bends are considered. Based on small strain finite element limit analyses using elastic-perfectly plastic materials, effect of bend and crack geometries on plastic limit loads for axial through-wall cracked pipe bends under internal pressure and in-plane bending are quantified, and closed-form limit solutions are given. Based on proposed limit load solutions, a J estimation scheme for axial through-wall cracked pipe bends under internal pressure and in-plane bending is proposed based on reference stress approach.