• Proceedings of the KSR Conference
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• 2006.11b
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• pp.31-34
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• 2006

A new continuum damage theory (CDT) has been proposed by Lee et al. (1996) based on the SEEP. The CDT has the apparent advantage over the other related theories because the complete constitutive law can be readily derived by simply replacing the virgin elastic stiffness with the effective orthotropic elastic stiffness obtained by using the proposed continuum damage theory. In this paper, the CDT is evaluated by the numerical experiment comparing the mode shapes and natural frequencies of a square plate containing a small line-through crack with those of the same plate with a damaged site replaced with the effective orthotropic elastic stiffness computed by using the CDT.

• Speech Sciences
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• v.12 no.4
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• pp.247-254
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• 2005

This study aimed at clarifing clinical effects of eight-step continuum treatment in a patient who showed apraxia of speech after stroke. The eight-step continuum treatment consisted of 8 steps and its clinical efficacy has been proven with American apraxic patients. However, it has not been clinically proven to be effective in Korean patients with apraxia of speech as of yet. Therefore, this study was conducted in an effort to provide preliminary clinical evidence regarding its effectiveness regardless of the linguistic differences between Korean and English. The therapy took place twice a week for 6 months, a total of 48 times. The results showed that the patient's receptive language was improved from 83% to 89% and 37% in accuracy, and expressive language from 15% to 37%. It seemed that spontaneous recovery did not playa role in his improvement since the study was conducted 2 years after the stroke. In addition, the improvement of expressive language was much greater(22%) than that of receptive language(6%), which implied that the therapy was effective in apraxia of speech because apraxia of speech is relatively confined to expressive ability, more specifically motor programming and sequencing.

• The Journal of Engineering Geology
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• v.12 no.3
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• pp.319-332
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• 2002

This study is focused on the characterization of an effective hydraulic conductivity in each hydrogeologic unit assumed as an equivalent continuum medium in the granitic area. Four boreholes of 3" diameter were installed and a Multi-packer system was facilitated in the selected borehole. Various in-situ tests including the fracture logging, constant injection and fall-off tests, slug and pulse tests were carried out. A hydrogeologic unit was defined into the upper and lower zones based on the variation of fracture properties and hydraulic conductivities. The difference of the result obtained by the various hydraulic tests and the effective characterization techniques on rock mass permeability are also discussed. The effective hydraulic conductivity of the upper unit was measured by two times(5.27E-10 m/s~7.57E-10 m/s) that of the lower unit(2.45E-10 m/s~6.81E-10 m/s)through the constant injection and fall-off tests.

• Computers and Concrete
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• v.5 no.4
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• pp.375-388
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• 2008

Crack opening governs many transfer properties that play a pivotal role in durability analyses. Instead of trying to combine continuum and discrete models in computational analyses, it would be attractive to derive from the continuum approach an estimate of crack opening, without considering the explicit description of a discontinuous displacement field in the computational model. This is the prime objective of this contribution. The derivation is based on the comparison between two continuous variables: the distribution if the effective non local strain that controls damage and an analytical distribution of the effective non local variable that derives from a strong discontinuity analysis. Close to complete failure, these distributions should be very close to each other. Their comparison provides two quantities: the displacement jump across the crack [U] and the distance between the two profiles. This distance is an error indicator defining how close the damage distribution is from that corresponding to a crack surrounded by a fracture process zone. It may subsequently serve in continuous/discrete models in order to define the threshold below which the continuum approach is close enough to the discrete one in order to switch descriptions. The estimation of the crack opening is illustrated on a one-dimensional example and the error between the profiles issued from discontinuous and FE analyses is found to be of a few percents close to complete failure.

• Korean Journal of Materials Research
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• v.20 no.9
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• pp.478-482
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• 2010

A series of molecular dynamic (MD), finite element (FE) and ab initio simulations are carried out to establish suitable modeling schemes for the continuum-based analysis of aluminum matrix nanocomposites reinforced with carbon nanotubes (CNTs). From a comparison of the MD with FE models and inferences based on bond structures and electron distributions, we propose that the effective thickness of a CNT wall for its continuum representation should be related to the graphitic inter-planar spacing of 3.4${\AA}$. We also show that shell element representation of a CNT structure in the FE models properly simulated the carbon-carbon covalent bonding and long-range interactions in terms of the load-displacement behaviors. Estimation of the effective interfacial elastic properties by ab initio simulations showed that the in-plane interfacial bond strength is negligibly weaker than the normal counterpart due to the nature of the weak secondary bonding at the CNT-Al interface. Therefore, we suggest that a third-phase solid element representation of the CNT-Al interface in nanocomposites is not physically meaningful and that spring or bar element representation of the weak interfacial bonding would be more appropriate as in the cases of polymer matrix counterparts. The possibility of treating the interface as a simply contacted phase boundary is also discussed.

• Interaction and multiscale mechanics
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• v.4 no.2
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• pp.107-122
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• 2011

Mechanical behavior in nano-sized structures differs from those in macro sized structures due to surface effect. As the ratio of surface to volume increases, surface effect is not negligible and causes size-dependent mechanical behavior. In order to identify this size effect, atomistic simulations are required; however, it has many limitations because too much computational resource and time are needed. To overcome the restrictions of the atomistic simulations and graft the well-established continuum theories, the continuum model considering surface effect, which is based on the bridging technique between atomistic and continuum simulations, is introduced. Because it reflects the size effect, it is possible to carry out a variety of analysis which is intractable in the atomistic simulations. As a part of the application examples, the homogenization method is applied to micro/nano thin films with porosity and the homogenized elastic coefficients of the nano scale thickness porous films are computed in this paper.

• Journal of Theoretical and Applied Mechanics
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• v.2 no.1
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• pp.31-50
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• 1996

In this paper, a finite element analysis based on the local approach concept to fracture in the continuum damage mechanics is performed to analyze ductile fracture in two dimensional quasi-static state. First an isotropic damage model based on the generalized concept of effective stress is proposed for structural materials in the context of large deformation. In this model, the stiffness degradation is taken as a measure of damage and so, the fracture phenomenon can be explained as the critical deterioration of stiffness at a material point. The modified Riks' continuation technique is used to solve incremental iterative equations. Crack propagation is achieved by removing critically damaged elements. The mesh size sensitivity analysis and the simulation of the well known shearing mode failure in plane strain state are carried out to verify the present formulation. As numerical examples, an edge cracked plate and the specimen with a circular hole under plane stress are taken. Load-displacement curves and successively fractured shapes are shown. From the results, it can be concluded that the proposed model based on the local approach concept in the continuum damage mechanics may be stated as a reasonable tool to explain ductile fracture initiation and crack propagation.

• Journal of Mechanical Science and Technology
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• v.16 no.9
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• pp.1156-1165
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• 2002

The characteristics of combustion and radiation heat transfer of an oxygen-enhanced diffusion flame was experimentally analyzed. An infrared radiation heat flux gauge was used to measure the thermal radiation of various types of flames with fuel, air and pure oxygen. And the Laser Induced Incandescence (LII) technique was applied to characterize the soot concentrations which mainly contribute to the continuum radiation from flame. The results show that an oxygen-enhanced inverse diffusion flame is very effective in increasing the thermal radiation compared to normal oxygen diffusion flame. This seems to be caused by overlapped heat release rate of double flame sheets formed in inverse flame and generation of higher intermediate soot in fuel rich zone of oxygen-fuel interface, which is desirable to increase continuum radiation. And the oxygen/methane reaction at slight fuel rich condition (ø=2) in oxygen-enhanced inverse flame was found to be more effective to generate the soot with moderate oxygen availability.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.4
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• pp.361-367
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• 2015

This paper presents the design concept of an intrinsic continuum robot for safe man-machine interface and characteristic behaviors of its end-effector based on real experiments. Since pneumatic artificial muscles having similar antagonistic actuation to human muscles are used for main backbones of the proposed robot as well as in the role of the actuating devices, variable stiffness of robotic joints can be available in the actual environment. In order to solve the inherent shortcoming of an intrinsic continuum robot due to bending motion of the backbone materials, a Kalman filter scheme based on a triaxial accelerometer and a triaxial gyroscope was proposed to conduct an attitude estimation of the end-effector of the robot. The experimental results verified that the proposed method was effective in estimating the attitude of the end-effector of the intrinsic continuum robot.

• Structural Engineering and Mechanics
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• v.44 no.4
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• pp.431-448
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• 2012

In this paper, the first-order shear deformation theory (FSDT) (Mindlin) for continuum incorporating surface energy is exploited to study the static behavior of ultra-thin functionally graded (FG) plates. The size-dependent mechanical response is very important while the plate thickness reduces to micro/nano scales. Bulk stresses on the surfaces are required to satisfy the surface balance conditions involving surface stresses. Unlike the classical continuum plate models, the bulk transverse normal stress is preserved here. By incorporating the surface energies into the principle of minimum potential energy, a series of continuum governing differential equations which include intrinsic length scales are derived. The modifications over the classical continuum stiffness are also obtained. To illustrate the application of the theory, simply supported micro/nano scaled rectangular films subjected to a transverse mechanical load are investigated. Numerical examples are presented to present the effects of surface energies on the behavior of functionally graded (FG) film, whose effective elastic moduli of its bulk material are represented by the simple power law. The proposed model is then used for a comparison between the continuum analysis of FG ultra-thin plates with and without incorporating surface effects. Also, the transverse shear strain effect is studied by a comparison between the FG plate behavior based on Kirchhoff and Mindlin assumptions. In our analysis the residual surface tension under unstrained conditions and the surface Lame constants are expected to be the same for the upper and lower surfaces of the FG plate. The proposed model is verified by previous work.