• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2A
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• pp.185-191
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• 2010

Because the concrete crack that is the reason of the serviceability and durability degradation of concrete structure can be arisen from either the stress magnitude and gradient or other structural and material defects, the crack strength of concrete is hard to accurately evaluate. Especially, stress-state in concrete plate components such as rigid pavement and long span slab is biaxial flexure stress, and the flexural strength of those component may be different than the traditional rupture modulus of concrete subjected to uniaxial stress. In this study, an experimental investigation to assess of mechanical behavior under uniaxial and biaxial flexure stress is conducted and the proposed optimum specimen configuration is adopted. From the test, the modulus of rupture under uniaxial and biaxial stress are decreased as the size of aggregate or specimen is larger. And biaxial flexure strength of concrete specimens is varied from 39.5 to 99.2% as compared with that of uniaxial strength, and the biaxial strength of specimen with 20mm aggregate size is only 76% of uniaxial strength.

• The Journal of Engineering Geology
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• v.11 no.2
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• pp.191-203
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• 2001

We investigate mechanical anisotropy dependent of rock fabric and its relationship with microcracks in the Pocheon Granite. Uniaxial compressive strengths range from 177MPa to 212MPa and the elastic constants are 48GPa-62GPa. The tensile strengths are 6.9MPa~8.5MPa and ultrasonic wave velocities range between 3,200m/sec and 3,700m/sec, indicating that mechanical anisotropy is strongly dependent of rock fabric. The minimum anisotropy ratio is 14% and the maximum is 24%, depend on the mechanical properties. The preferred orientations of microcracks are closely related with the directions of rock fabric. The preferred orientations of microcracks in feldspar are governed by the direction of mineralogical axis and are different from the directions of rock fabric. However, microcracks in quartz grains are very long and parallel to the directions of rock fabric, indicating that directions of rock fabric may be governed by the preferred orientations of microcracks in quartz grains. The preferred orientations of microcracks measured by differential strain analysis and microscopic observation are slightly different. That may be caused by different methodology. Lengths and numbers of microcrack are measured by microscopic observation. However, differential strain analysis measures the widths of microcracks.

• Tunnel and Underground Space
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• v.25 no.5
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• pp.423-434
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• 2015

Scaled model tests were performed to investigate the influence of pillar width, rock strength and isotropy/anisotropy on the stability of twin tunnels. Test models had respectively different pillar widths, uniaxial compressive strengths of modelling materials and model types, where both the deformation behaviors around tunnels and the biaxial pressure data at a time of pillar cracking were analysed. The cracking pressures of the higher strength models were higher than the lower strength models, whereas the percentage of cracking pressure to uniaxial compressive strength of modelling materials showed an opposite tendency. The cracking pressures of the shallower pillar width models were lower than the thicker models, moreover the percentage of that showed a same tendency. It has been found that the pillar width was one of the main factors influencing on the stability of twin tunnels. Model types such as isotropy/anisotropy also influenced on the stability of twin tunnels. The anisotropic models showed lower values of both cracking pressures and the percentage of that than the isotropic models, where the pillar cracks of anisotropic models were generated with regard to the pre-existing joint planes.

• Tunnel and Underground Space
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• v.18 no.4
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• pp.252-262
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• 2008

In the uniaxial compressive test of a single specimen of transversely isotropic rock, its 5 independent elastic constants can not be defined since maximum 4 independent strain measurements are available theoretically. In order to solve this problem, one equation proposed by Saint Venant in 19C and confirmed by Lekhnitskii through the test experiences has been used for long time. Accordign to authors' experiences, however, this equation turned out to give erroneous elastic constants in some cases. Three new equations are suggested and their compatibilities are discussed in this paper. As the results of the analyses of the models, Lekhnitskii's suggested equation is effective for the specimen with the high dip angle whereas it results in the large erred output for that with dip angle less than $25{\sim}30$. It was found that the effectivenesses of three suggested equations and their compatibilities are subject to the dip angle and not to the amounts of elastic constants. Guide map to the selection of the compatible one of those suggested equations is presented as a result of the study.

• Journal of the Korean Magnetics Society
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• v.18 no.5
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• pp.180-184
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• 2008

The relation of ferromagnet anisotropic magnetization and the antiferromagnet atomic spin configuration has been investigated for variously angles of unidirectional deposition magnetic field of FeMn layer in Corning glas/Ta(5 nm)/NiFe(7 nm)/FeMn(25 nm)/ Ta(5 nm) multilayer prepared by ion beam deposition. Three unidirectional deposition angles of FeMn layer are $0^{\circ},\;45^{\circ}$, and $90^{\circ}$, respectively. The exchange bias field ($H_{ex}$) obtained from the measuring easy axis MR loop was decreased to 40 Oe in deposition angle of $45^{\circ}$, and to 0 Oe in the angle of $90^{\circ}$. One other side hand, $H_{ex}$ obtained from the measuring hard axis MR loop was increased to 35 Oe in deposition angle of $45^{\circ}$, and to 79 Oe in the angle of $90^{\circ}$. Although the difference of uniderectional axis between ferromagnet NiFe and antiferromagnet FeMn was 90o, the strong antiferromagnetic dipole moment of FeMn caused to rotate the weak ferromagnetic dipole moment of NiFe in the interface. This result implies that one of origins for exchange coupling mechanism depends on the effect of magnetic field angle during deposition of antiferromgnet FeMn layer.

• Composites Research
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• v.13 no.5
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• pp.18-30
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• 2000

In order to optimize the design of unidirectional fiber reinforced composite C-rings, a viscoelastic load relaxation behavior was analyzed under a point load. Initially, the deflection and bending stiffness were calculated based on the elastic beam theory and the viscoelastic relaxation and creep behaviors were derived from the elastic solution using the correspondence theorem. Besides the orthotropic mechanical properties of the composite, asymmetric mechanical property due to the different tensile and compressive properties were also considered. Except the deviation affected by the relatively large thickness of the specimen compared to the radius, the calculated relaxation showed good agreement with the experimental result.

• Journal of the Korean Magnetics Society
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• v.9 no.6
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• pp.301-305
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• 1999

NiFe(60$\AA$)/Co(5$\AA$)/Cu(60$\AA$)/Co(30$\AA$) spin valve thin films were patterned into magnetoresistive random access memory (MRAM) cells by a conventional optical lithography process and their output and switching properties were characterized with respect to the cell size and geometry. When 1 mA of constant sense current was applied to the cells, a few or a few tens of mV of output voltage was measured within about 30 Oe of external magnetic field, which is an adequate output property for the commercializing of competitive MRAM devices. In order to resolve the problem of increase in the switching thresholds of magnetic layers with the downsizing of MRAM cells, a new approach using the controlled shape anisotropy was suggested and interpreted by a simple calculation of anisotropy energies of magnetic layers consisting of the cells. This concept gave a reduced switching threshold in NiFe(60$\AA$)/Co(5$\AA$) layer consisting of the patterned cells from about 15 Oe to 5 Oe and it was thought that this concept would be much helpful for the realization of competitive MRAM devices.

• The Journal of Engineering Geology
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• v.1 no.1
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• pp.54-67
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• 1991

In geological media with anisotropic properties, the strength anisotropy in intact rock is the most important issue in engineering aspects. Point-ioad(P/L) strength test designed to estimate the uniaxial compressive strength(${\sigma}_c$) can be used to evaluate the anisotropic strength characteristics of rocks. The relationship between ${\sigma}_c$ and P/L strength indices(I$_s$), obtained from the banded gneisses distributed in the Cheongyang area, varies depend mainly on the dip angle($\beta$) of foliation. The axial P/L strength indicies(I$_{sa}$) decreases with the increment of $\beta$, whereas diametral P/L strength indices(I$_{sa}$) increase with it. However, the ${\sigma}_c$ decreases with the increments of $\beta$ below about 40$^{\circ}$, but it increases with the increments of $\beta$ over about 40$^{\circ}$ in general. The correlation between ${\sigma}_c$ and I$_s$ suggests that ${\sigma}_c$ is related to the Isa withing low angle($\beta$<40$^{\circ}$) and the I$_{sd}$ within high angle ($\beta$>40$^{\circ}$), respectively. The ratios of I$_s$ to ${\sigma}_c$ are obtained as 11 to 14 in the the gneisses in the study area. The ratio of 24, which is generally adopted value, cannot always be truthworth to the gneisses in the study area. The ratio for the dykes, however, show a good correlation as 21 to 24.5 and, the value of 24 can be used for a homogeneous and isotropic materials such as dykes.

• Journal of the Korean Magnetics Society
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• v.6 no.5
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• pp.323-328
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• 1996

NiFe($60\;{\AA}$)/Cu($60\;{\AA}$)/Co($30\;{\AA}$) trilayers were formed on the $4^{\circ}$ tilt-cut Si(111) substrate by rf magnetron sputtering method. With a Cu($50\;{\AA}$) underlayer, NiFe($60\;{\AA}$)/Cu($60\;{\AA}$)/Co($30\;{\AA}$) trilayers developed in-plane magnebc anisotropy and in-plane perpendicular alignment of easy axes in two magnetic components of NiFe($60\;{\AA}$)/Cu($60\;{\AA}$)/Co($30\;{\AA}$) trilayers has been found. The easy axis of Co layer consisbng of NiFe($60\;{\AA}$)/Cu($60\;{\AA}$)/Co($30\;{\AA}$) trilayers turned out to be along $4^{\circ}$ tilt Si <112> direcbon and that of NiFe layer along Si <110> direction. [NiFe($60\;{\AA}$)/Cu($60\;{\AA}$)/Co($30\;{\AA}$)]/Cu($50\;{\AA}$)/Si(111, $4^{\circ}$ tiIt-cut) trilayers showed about 2.2 % MR ratio at room temperature and large plateau in MR curves, which are more improved MR characteristics than those in [NiFe($60\;{\AA}$)/Cu($60\;{\AA}$)/Co($30\;{\AA}$)]/Cu($50\;{\AA}$)/glass trilayers with no appreciable magnetic anisotropy.

• Tunnel and Underground Space
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• v.20 no.6
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• pp.455-464
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• 2010

The variations of the uniaxial compressive strength, the strains and the elastic constants with respect to the angle of anisotropy are analyzed in order to investigate the characteristics of a transversely isotropic rock experimentally. Total 35 specimens of 7 different angles from a large block of rhyolite presenting the flow structure obviously are used in tests. This study is composed of two reports; the elastic constants are mainly analyzed for the every individual angle in the report No. 1 and they will be discussed synthetically in the report No. 2. From the specimens of 0 and 90 degree, 4 independent elastic constants which can directly be obtained without the help of any other suggested equations, may be referred to the true values. Data variation in the strain measurements differs on the angle is analyzed. That of small angle specimens tends higher than that of large angle specimens. The relation of apparent Young’s modulus and angle is found to be M- or U-shaped. For small angle specimens, Saint-Venant approximation cannot be applied successfully on account of showing the non-monotonous increase, and E1 is analyzed out of the true value range. In the specimen of $\phi$ = 75, the deviation of strain measurement and strength are smallest and 4 all constants are analyzed in the true value range. Therefore, specimen of the angle of around 75 may become preferable if only one specimen should be used in test of a transversely isotropic rock.