• Journal of Korean Society of Steel Construction
• /
• v.26 no.5
• /
• pp.397-405
• /
• 2014

A shear-flexible beam element is presented for the flexural analysis of laminated composite T-beams with arbitrary lay-ups. Based on the first-order shear deformable beam theory, the derived element takes into account warping shear deformation and all coupling coming from material anisotropy. Three different types of beam elements, namely, the two-noded, three-noded, and four-noded beam elements with seven degree-of-freedom per node are developed to solve governing equations. To demonstrate the versatility and accuracy of the beam element formulated, numerical results are performed for symmetric and anti-symmetric angle-ply composite T-beams under the uniformly distributed and concentrated load. The effects of fiber angle and shear deformation are investigated for different laminated stacking sequence. The quadratic and cubic elements are shown to be applicable to the flexural analysis of composite T-beams.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.23 no.3
• /
• pp.237-245
• /
• 2003

Since the velocity is dependent on the fiber orientation in anisotropic composites, the application of traditional acoustic emission (AE) source location techniques based on the constant velocity to composite structures has been practically impossible. The anisotropy makes the source location procedure complicated and deteriorates the accuracy of the location. In this study, we have divided the region of interest(ROI) into a set of finite elements, taken each element as a virtual source, and calculated the arrival time differences between sensors by using the velocities at every degree from 0 to 90. The calculated and the experimentally measured values of the arrival time difference aye then compared to minimize the location error. The results from two different materials, namely AA6061-T6 and CFRP(uni-directional; UD, $[0]_{32}4$) laminate confirmed the practical usefulness of the proposed method.

• Explosives and Blasting
• /
• v.23 no.1
• /
• pp.9-17
• /
• 2005

This study is to clarify the comparative relationship and mechanical anisotropy of granite distributed in the Nam-weon on the subject of weathered rock mass sea water surroundings. Artificial weathering test is defined as a test, which controls the weathering rate and agents by controlling the weathering rate and agents by artificial environmental of salt water. Increased weathering degree is large indicated by weathering salt water, such as apparent specific gravity, absorption, porosity, uniaxial compression strength, P-wave velocity, slake durability, shore hardness, indirect tensile strength(brazilian test) and cohesion were measured. As the Weathering salt water proceeds, cracks develope increasingly. A number the cracks affect the rock deformation. Therefore, stress-strain curve of weathered salt water rock in one confined state are quite differ from weathered fresh water rock those. A reason of their deformation type is the formation of micro-cracks and potential porosity caused by artificial weathering test.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
• /
• 2001.06a
• /
• pp.1182-1182
• /
• 2001

In this study, the newly constructed optical measurement system, which was mainly composed of a parametric tunable laser and a near infrared photoelectric multiplier, was introduced to clarify the optical characteristics of wood as discontinuous body with anisotropic cellular structure from the viewpoint of the time-of-flight near infrared spectroscopy (TOF-NIRS). The combined effects of the cellular structure of wood sample, the wavelength of the laser beam λ, and the detection position of transmitted light on the time resolved profiles were investigated in detail. The variation of the attenuance of peak maxima At, the time delay of peak maxima Δt and the variation of full width at half maximum Δw were strongly dependent on the feature of cellular structure of a sample and the wavelength of the laser beam. The substantial optical path length became about 30 to 35 times as long as sample thickness except the absorption band of water. Δt ${\times}$ Δw representing the light scattering condition increased exponentially with the sample thickness or the distance between the irradiation point and the end of sample. Around the λ=900-950 nm, there may be considerable light scattering in the lumen of tracheid, which is multiple specular reflection and easy to propagate along the length of wood fiber. Such tendency was remarkable for soft wood with the aggregate of thin layers of cell walls. When we apply TOF-NIRS to the cellular structural materials like wood, it is very important to give attention to the difference in the light scattering within cell wall and the multiple specular-like reflections between cell walls. We tried to express the characteristics of the time resolved profile on the basis of the optical parameters for light propagation determined by the previous studies, which were absorption coefficient K and scattering coefficient S from Kubelka-Munk theory and n from nth power cosine model of radiant intensity. The wavelength dependency of the product of K/S and n, which expressed the light-absorbing and -scattering condition and the degree of anisotropy, respectively, was similar to that of the time delay of peak maxima Δt. The variation of the time resolved profile is governed by the combination of these parameters. So, we can easily find the set of parameters for light propagation synthetically from Δt.

• Applied Chemistry for Engineering
• /
• v.18 no.1
• /
• pp.24-28
• /
• 2007

The etching of zinc oxide (ZnO) thin films has been studied using a high density plasma in a $Cl_2/Ar$ gas. The etch characteristics of ZnO thin films were systematically investigated on varying $Cl_2$ concentration, coil rf power, dc-bias voltage, and gas pressure. With increasing $Cl_2$ concentration, the etch rate of ZnO thin film increased, the redeposition around the etched patterns decreased but the sidewall slope of the etched patterns slanted. As the coil rf power and dc-bias voltage increased, the etch rates of ZnO thin films increased and etch profiles of ZnO thin films were improved. With increasing gas pressure, the etch rate of ZnO thin films slightly increased but little change in etch profile was observed. Based on these results, the optimal etching conditions of ZnO thin film were selected. Finally, the etching of ZnO thin films with a high degree of anisotropy of approximately $75^{\circ}{\sim}80^{\circ}$ without the redepositions and residues was successfully achieved at the etching conditions of 20% $Cl_2$ concentration, coil rf power of 1000 W, dc-bias voltage of 400 V, and gas pressure of 5 mTorr.

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

• Applied Chemistry for Engineering
• /
• v.19 no.5
• /
• pp.504-511
• /
• 2008

Two kinds of nitroazobenzene derivatives: 4-{4'-(nitrophenylazo)phenoxy}alkanoic acids (NAAn, n = 2~8, 10, number of methylene units in the alkyl chain) and 4-{4'-(nitrophenylazo)phenoxy}alkanoyl chlorides (NACn, n = 2~8, 10) were synthesized, and their thermotropic liquid crystalline behaviors were investigated. NAA6 formed an enantiotropic nematic phase, while the remainders, except NAA2, showed monotropic nematic phases. Isotropic-nematic transition temperature ($T_{iN}$) and change of entropy (${\Delta}S$) at $T_{iN}$ for both of NAAn and NACn varied by the change of n, and pronounced odd-even effects of n were also observed. However, the $T_{iN}$ and ${\Delta}S$ values of NAAn were much higher than those of NACn. This fact may be attributed to the hydrogen bonding between carboxyl groups. Thermal properties and degree of order in the mesophase and the magnitude of the odd-even effects of both NAAn and NACn were significantly different from those reported for 4-(alkoxy)-4'-nitroazobenzenes. It was discussed in terms of the differences in the molecular anisotropy and the temperature-dependent flexibility of the substituted groups.

• Journal of Biomedical Engineering Research
• /
• v.25 no.6
• /
• pp.519-523
• /
• 2004

This study investigates micro-structural and mechanical properties of trabecular bone in human femoral head with and without osteoporosis using Micro-CT and finite element-model. 15 cored trabecular bone specimens with 20min of diameter were obtained from femoral heads with osteoporosis (T-score > -2.5 ) resected for total hip arthroplasty, and 5 specimens were removed from femoral head of cadavers, which has no history of musculoskeletal diseases. A high-resolution micro-CT system was used to scan each specimen to obtain histomorphometry indices. Based on obtained micro-images(pixel size=21.31㎛), a FE-model was created to determine mechanical property indices. While non-osteoporosis group had increases trabecular thickness, bone volume, bone volume fraction, degree of anisotropy and trabecular number compared with those of non-osteoporotic group, the non-osteoporotic group showed decreases in trabecular separation and structure model index. Regarding the mechanical property indices, reaction force, apparent stress and young's modulus were 1ower in osteoporotic group than in non-osteoporotic group. Our data shows salient deteriorations in trabecular micro-structural and mechanical properties in human femoral head with osteoporosis.

• Journal of the Korean earth science society
• /
• v.21 no.3
• /
• pp.349-358
• /
• 2000

Compressional and shear wave velocities (Vp and Vs) and densities have been measured for serpentinite, amphibolite, amphibole and biotite schist, and gneiss from western part of Chungnam Province at room temperature. Ranges of the density are 2.6${\sim}$2.86g/cm$^3$ for serpentinite, 2.25${\sim}$2.81g/cm$^3$ for talc, and 2.74${\sim}$3.07g/cm$^3$ for metamorphic rocks. Of these rocks, talc shows wider ranges than serpentinite and amphibolites due to its metamorphic process from serpentinite. Values of Vp and Vs are 5719${\sim}$6062m/s and 2898${\sim}$3351m/s for serpentinites, 4019${\sim}$5478m/s and 2241/${\sim}$2976m/s for talc, 5375${\sim}$6372m/s and 3042${\sim}$3625m/s for amphibolite, 5290${\sim}$5499m/s and 2968${\sim}$3137m/s for schist, and 4788m/s and 2804m/s for gneiss, respectively. Velocity of P wave increases 1.47 times faster than S wave with increase of density. The results of seismic velocity measurement show anisotropy, higher velocity across than along the schistocity of rocks, especially in metamorphic rocks. This fact indicates that there were regional metamorphism related with tectonic forces. Values of seismic velocity increase with increasing pressure from 20 MPa to 70 MPa, especially in metamorphic rocks. Overall recalculated Vp and Vs values suggest that the serpentinite indicates for upper mantle in the respects of seismic characteristics, in spite of high degree of serpentinization. In addition, those of the amphibolite do for low crust, and gneiss and schist for upper crust.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.33 no.4
• /
• pp.643-652
• /
• 2006

The purpose of this study was to elucidate the size and morphologic characteristics of maxillary primary first molars in Korean children using three-dimensional laser scanner and compare three-dimensional image with preformed stainless steel crown. Scanned three-dimensional images of dental cast taken from 132 children(male 62, female 70) by three-dimensional laser scanner(Breuckmann opto-Top HE100, INUS, Korea) were used. Mesiodistal diameter, buccolingual diameter, occlusogingival height and crown shape of each image were calculated by Rapidform 2004 program(INUS, Korea). The values were statistically compared by independent samples t-test with 95% of significant level. The results were as follows : 1. No significant difference in crown size was found between left and right maxillay primary first molar(p>0.05). 2, Significant difference in mesiodistal diameter, buccolingual diameter, buccal occlusogingival height was found between male and female (p<0.05), and crown size of male was bigger than that of female. 3. Average image of maxillay primary first molar was shaped three-dimensionally and measured. In comparison with 3M stainless steel crown, this image was similar with No.4 or No.5 SS crown in male, No.4 in female. In comparison with ILSUNG SS crown, this image was similar with No.5 in male, No.4 in female. 4 Mesiolingual line angle area, distolingual line angle area and buccogingival ridge were more obvious in average image than 3M stainless steel crown. ILSUNG SS crown was more square and had longer mesiodistal diameter than average 3D image.