• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.3
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• pp.249-257
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• 2011

In this paper, an systematic approach is presented, in which the mixed variational theorem is employed to incorporate independent transverse shear stresses into a classical higher-order shear deformation theory(HSDT). The HSDT displacement field is taken to amplify the benefits of using a classical shear deformation theory such as simple and straightforward calculation and numerical efficiency. Those independent transverse shear stresses are taken from the fifth-order polynomial-based zig-zag theory where the fourth-order transverse shear strains can be obtained. The classical displacement field and independent transverse shear stresses are systematically blended via the mixed variational theorem. Resulting strain energy expressions are named as an enhanced higher-order shear deformation theory via mixed variational theorem(EHSDTM). The EHSDTM possess the same computational advantage as the classical HSDT while allowing for improved through-the-thickness stress and displacement variations via the post-processing procedure. Displacement and stress distributions obtained herein are compared to those of the classical HSDT, three-dimensional elasticity, and available data in literature.

• Smart Structures and Systems
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• v.19 no.2
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• pp.115-126
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• 2017

In this paper, size dependent bending and free flexural vibration behaviors of functionally graded (FG) nanobeams are investigated using a nonlocal quasi-3D theory in which both shear deformation and thickness stretching effects are introduced. The nonlocal elastic behavior is described by the differential constitutive model of Eringen, which enables the present model to become effective in the analysis and design of nanostructures. The present theory incorporates the length scale parameter (nonlocal parameter) which can capture the small scale effect, and furthermore accounts for both shear deformation and thickness stretching effects by virtue of a hyperbolic variation of all displacements through the thickness without using shear correction factor. The material properties of FG nanobeams are assumed to vary through the thickness according to a power law. The neutral surface position for such FG nanobeams is determined and the present theory based on exact neutral surface position is employed here. The governing equations are derived using the principal of minimum total potential energy. The effects of nonlocal parameter, aspect ratio and various material compositions on the static and dynamic responses of the FG nanobeam are discussed in detail. A detailed numerical study is carried out to examine the effect of material gradient index, the nonlocal parameter, the beam aspect ratio on the global response of the FG nanobeam. These findings are important in mechanical design considerations of devices that use carbon nanotubes.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.39.1-39.1
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• 2009

NiTi alloy is widely used innumerous biomedical applications (orthodontics, cardiovascular, orthopaedics, etc.) for its distinctive thermomechanical and mechanical properties such as shape memory effect, super elasticity, low elastic modulus and high damping capacity. However, NiTi alloy is still a controversial biomaterial because of its high Ni content which can trigger the risk of allergy and adverse reactions when Ni ion releases into the human body. In order to improve the corrosion resistance of the TiNi alloy and suppress the release of Ni ions, many surface modification techniques have been employed in previous literature such as thermal oxidation, laser surface treatment, sol-gel method, anodic oxidation and electrochemical methods. In this paper, the NiTi was electrochemically etched in various electrolytes to modify surface. The microstructure, element distribution, phase composition and roughness of the surface were investigatedby scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry(EDS), X-ray diffractometry (XRD) and atomic force microscopy (AFM). Systematic controlling of nano and submicron surface features was achieved by altered density of hydro fluidic acid in etchant solution. Nanoscale surface topography, such as, pore density, pore width, pore height, surface roughness and surface tension were extensively analyzed as systematical variables.Importantly, bone forming cell, osteoblast adhesion was increased in high density of hydro fluidic treated surface structures, i.e., in greater nanoscale surface roughness and in high surface areas through increasing pore densities.All results delineate the importance of surface topography parameter (pores) inNiTi to increase the biocompatibility of NiTi in identical chemistry which is crucial factor for determining biomaterials.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.4
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• pp.769-777
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• 2015

In this study, the rheological models were introduced and developed to reflect rate dependent tensile behaviour of concrete. In general, mechanical properties(e.g. strength, elasticity, and fracture energy) of concrete are increased under high loading rates. The strength of concrete shows high rate dependency among its mechanical properties, and the tensile strength has higher rate dependency than the compressional strength. To simulate the rate dependency of concrete, original spring set of RBSN(Rigid-Body- Spring-Network) model was adjusted with viscous and friction units(e.g. dashpot and Coulomb friction component). Three types of models( 1) visco-elastic, 2) visco-plastic, and 3) visco-elasto- plastic damage models) are considered, and the constitutive relationships for the models are derived. For validation purpose, direct tensile test were simulated, and characteristics of the three different rheological models were compared with experimental stress-strain responses. Simulation result of the developed visco-elasto-plastic damage(VEPD) model demonstrated well describing and fitting with experimental results.

• Steel and Composite Structures
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• v.36 no.2
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• pp.213-228
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• 2020

Shape Memory Alloys (SMAs) are new materials used in various fields of science and engineering, one of which is civil engineering. Owing to their distinguished capabilities such as super elasticity, energy dissipation, and tolerating cyclic deformations, these materials have been of interest to engineers. On the other hand, the connections of a steel structure are of paramount importance because of their vulnerabilities during an earthquake. Therefore, it is indispensable to find approaches to augment the efficiency and safety of the connection. This research investigates the behavior of steel connections with extended end plates equipped hybridly with 8 rows of high strength bolts as well as Nitinol superelastic SMA bolts. The connections are studied using component method in dual form. In this method, the components affecting the connections behavior, such as beam flange, beam web, column web, extended end plate, and bolts are considered as parallel and series springs according to the Euro-Code3. Then, the nonlinear force- displacement response of the connection is presented in the form of moment-rotation curve. The results obtained from this survey demonstrate that the connection has ductility, in addition to its high strength, due to high ductility of SMA bolts.

• Journal of Astronomy and Space Sciences
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• v.15 no.1
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• pp.209-220
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• 1998

The stability problem of steady motion of a rigid body with multi-elastic appendages and multi-liquid-filled cavities, in the presence of no external forces or torque, is considered in this paper. The flexible appendages are modeled as the clamped -free-free-free rectangular plates, or/and as the discrete mass- spring sub-system. The motion of liquid in every single ellipsoidal cavity is modeled as the uniform vortex motion with a finite number of degrees of freedom. Assuming that stationary holonomic constraints imposed on the body allow its rotation about a spatially fixed axis, the equation of motion for such a systematic configuration can be very complex. It consists of a set of ordinary differential equations for the motion of the rigid body, the uniform rotation of the contained liquids, the motion of discrete elastic parts, and a set of partial differential equations for the elastic appendages supplemented by appropriate initial and boundary conditions. In addition, for such a hybrid system, under suitable assumptions, their equations of motion have four types of first integrals, i.e., energy and area, Helmholtz' constancy of liquid - vortexes, and the constant of the Poisson equation of motion. Chetaev's effective method for constructing Liapunov functions in the form of a set of first integrals of the equations of the perturbed motion is employed to investigate the sufficient stability conditions of steady motions of the complete system in the sense of Liapunov, i.e., with respect to the variables determining the motion of the solid body and to some quantities which define integrally the motion of flexible appendages. These sufficient conditions take into account the vortexes of the contained liquids, the vibration of the flexible components, and coupling among the liquid-elasticity solid.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.2
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• pp.87-100
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• 2006

A kinematically constrained microplane constitutive model is developed for intact granite. The model is verified by fitting the experimented data of Westerly granite and Bonnet granite. Using the model with the standard finite element method, the behavior of the intact granite subjected blasting impact is studied. What is studied includes the attenuation of the blasting waves, the size of the fractured zone and the effect of the charge condition to avoid overbreak of the rock mass. The model developed captures the energy loss due to the inelastic behavior and the microcracking of granite during blasting very well. The attenuation of the blasting waves calculated based on the model is much more than that based on the linear-elastic constitutive law. The size of damaged (or fractured) zone is calculated directly from the principal strain as blasting impact is spreading, not like in the case with the linear elasticity model.

• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.311-317
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• 2015

Cement zero concrete produced by alkali-activators and industrial by-products such as slag instead of cement, enables to solve the environmental pollution problems provoked by the exhaustion of natural resources and energy as well as the discharge of carbon dioxide. However, researches on the cement zero concrete are still limited to material studies and thus, study on the structural behavior of relevant members is essential to use the cement zero concrete as structural materials. This paper aims to evaluate experimentally and analytically the flexural behavior of RC beams using 50 MPa alkali activated slag concrete. To achieve such a goal, flexural tests on three types of RC beam specimens were conducted. A nonlinear analysis model is proposed using the modulus of elasticity and stress-strain relationship of alkali activated slag concrete. The analysis results obtained by the proposed model agree well with the experimental results, which could verify the validity of the proposed model.

• Journal of the Korean Society of Radiology
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• v.8 no.7
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• pp.397-400
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• 2014

This study purpose is to know about the effect of Cobb's angle of scoliosis patient by Pilates ecercise. It was executed for prove this exercise with Pilates Postural Correct Exercise(PCE), Spine Stretching Exercis(SSE), Muscle Strengthing Exercise(MSE). PCE is useful for unbalanced muscle energy and SSE gives relax for hypertensioned muscles and MSE is correcting balance for prime mover and secondary mover and so it will be recovery for elasticity and flexibility of paraspine muscles. The method study was proved with a Cobb's angle measurement of Lumbar spine by X-ray test before and after. As a result for the test, Cobb's angle by X-ray it shows reduced about 5 degree in statistics(p=0.005). And so It shows the Pilates exercise gives reduce for Scoliosis.

• Asian-Australasian Journal of Animal Sciences
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• v.19 no.7
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• pp.1033-1039
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• 2006

The metabolic response of Labeo rohita to thermal acclimation was assessed. Advanced fingerlings of L. rohita (average weight $31{\pm}1.4g$) were acclimated to 31, 33 and $36^{\circ}C$ compared with ambient temperatures ($26^{\circ}C$) for 30 days and different enzymes associated with stress response were estimated. Glycolytic enzyme-Lactate dehydrogenase, (LDH, E.C.1.1.1.27), TCA cycle enzyme-Malate dehydrogenase (MDH, E.C.1.1.1.37), Protein metabolizing enzymes-Aspartate amino transferase (AST, E.C.2.6.1.1) and Alanine amino transferase (ALT, E.C.2.6.1.2) of liver, gill and muscle, Gluconeogenic enzymes-Fructose 1,6 Bi phosphatase (FBPase, E.C. 3.1.3.11) and Glucose 6 phosphatase (G6Pase, E.C. 3.1.3.9) of liver and kidney were significantly (p<0.05) different with increasing acclimation temperatures. Heat Shock Protein-70 (HSP-70) was expressed in increasing intensity at 31, 33 and $36^{\circ}C$ but was not expressed at $26^{\circ}C$. Results suggest that higher acclimation temperatures enhance metabolism and L. rohita maintains homeostasis between $26-36^{\circ}C$ via an acclimation episode. Such adaptation appears to be facilitated by resorting to gluconeogenic and glycogenolytic pathways for energy mobilization and induction of HSPs.