• Coupled systems mechanics
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• 제7권4호
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• pp.373-393
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• 2018

This paper is concerned with the wave propagation behavior of rotating functionally graded temperature-dependent nanoscale beams subjected to thermal loading based on nonlocal strain gradient stress field. Uniform, linear and nonlinear temperature distributions across the thickness are investigated. Thermo-elastic properties of FG beam change gradually according to the Mori-Tanaka distribution model in the spatial coordinate. The nanobeam is modeled via a higher-order shear deformable refined beam theory which has a trigonometric shear stress function. The governing equations are derived by Hamilton's principle as a function of axial force due to centrifugal stiffening and displacement. By applying an analytical solution and solving an eigenvalue problem, the dispersion relations of rotating FG nanobeam are obtained. Numerical results illustrate that various parameters including temperature change, angular velocity, nonlocality parameter, wave number and gradient index have significant effect on the wave dispersion characteristics of the understudy nanobeam. The outcome of this study can provide beneficial information for the next generation researches and exact design of nano-machines including nanoscale molecular bearings and nanogears, etc.

• Nuclear Engineering and Technology
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• 제45권2호
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• pp.223-236
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• 2013

In the present study the behavior of fire and the residual strength of fire-ignited RC slabs are investigated by experimental tests and numerical simulations. The fire tests of RC slabs were carried out in a furnace using the ISO 834 standard fire. The load capacity of the cooled RC slabs that were not loaded during the fire tests was evaluated by additional 3 point bending tests. The influence of the proportion of PP (polypropylene) fibers in the RC slabs on the structural behavior of the RC slabs after the fire loading was investigated. The results of the fire tests showed that the maximum temperature of concrete with PP fiber was lower than that of concrete without PP fiber. As the concrete was heated, the ultimate compressive strength decreased and the ultimate strain increased. The load-deflection relations of RC slabs after fire loading were compared by using existing stress-strain-temperature models. The comparison between the numerical analysis and the experimental tests showed that some numerical analyses were reliable and therefore, can be applied to evaluate the ultimate load of RC slabs after fire loading. The ultimate load capacity after cooling down the RC slabs without PP fiber showed a considerable reduction from that of the RC slabs with PP fiber.

• Steel and Composite Structures
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• 제33권3호
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• pp.463-472
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• 2019

Initial thermo-elastic and steady state creep deformation of a rotating functionally graded simple blade is studied using first-order shear deformation theory. A variable thickness model for cantilever beam has been considered. The blade geometry and loading are defined as functions of length so that one can define his own blade profile and loading using any arbitrary function. The blade is subjected to a transverse distributed load, an inertia body force due to rotation and a distributed temperature field due to a thermal gradient between the tip and the root. All mechanical and thermal properties except Poisson's ratio are assumed to be longitudinally variable based on the volume fraction of reinforcement. The creep behaviour is modelled by Norton's law. Considering creep strains in stress strain relation, Prandtl-Reuss relations, Norton' law and effective stress relation differential equation in term of effective creep strain is established. This differential equation is solved numerically. By effective creep strain, steady state stresses and deflections are obtained. It is concluded that reinforcement particle size and form of distribution of reinforcement has significant effect on the steady state creep behavior of the blade.

• Structural Engineering and Mechanics
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• 제81권3호
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• pp.335-348
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• 2022

It is well known that after finding the displacement in the structural mechanics, strain and stress can be obtained in the straight-forward process. The main purpose of this paper is to unify the displacement functions for solving the solid body. By performing mathematical operations, three sets of these key relationships are found in this paper. All of them are written in the Cartesian Coordinates and in terms of a simple function. Both analytical and numerical approaches are utilized to validate the correctness of the presented formulations. Since all required conditions for the bodies with self-equilibrated loadings are satisfied accurately, the authors' relations can solve these kinds of problems. This fact is studied in-depth by solving some numerical examples. It is found that a very simple function can be used for each formulation instead of ten different and complex displacement potentials defined by previous studies.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.272-275
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• 2007

This paper is concerned with modified integration algorithm on the strain-space for rate and temperature dependent elasto-plastic constitutive relations in order to obtain more accurate results in numerical implementation. The proposed algorithm is integrated analytically using integration by part and chain rule and then is applied to the 2-stage Lobatto IIIA with second-order accuracy. It has advantage that is able to consider the convective stress rates on the yield surface of the strain-space. Also this paper is carried out the iteration procedure using the Newton-Raphson method to enforce consistency at the end of the step. And the performance of the proposed algorithm for rate and temperature dependent constitutive relation is illustrated by means of analysis of adiabatic shear bands.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2000년도 가을 학술발표회논문집
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• pp.182-189
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• 2000

This paper presents a simple and reliable constitutive model for predicting the nonlinear response of reinforced concrete subjected to general membrane loadings. Based on the concept of equivalent uniaxial strain, constitutive relations of concrete are presented in the axes of orthotropy. The behavior of cracked concrete is described by a system of orthogonal cracks, which follows the principal strain directions and rotates according to the loading history. Simple hysteretic rules defining the cyclic stress-strain curves of concrete and steel are used. In addition, the stiffness and strength degradation of cracked concrete is included in the formulation. Correlation studies between analytical results and experimental values from idealized shear panel tests are conducted with the objective to establish the validity of the proposed model.

• 한국구조물진단유지관리공학회 논문집
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• 제18권2호
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• pp.108-116
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• 2014

강교의 정확한 피로균열의 발생원인 또는 교량의 피로안전성을 검토하기 위해서는 적합한 응력이력 측정이 요구된다. 그러나 실제 현장에서의 응력이력 측정은 현장 여건과 경제성, 작업성 등의 이유로 1개소의 스트레인게이지를 설치하여 계측을 실시한다. 이는 특정 구조물의 실제 치수와 게이지 길이 용접부 응력집중 등의 영향을 고려하지 못하고, 구조 모델링을 통한 응력해석에도 많은 어려움이 있다. 그러므로 본 연구에서는 용접단부에 다수의 게이지 설치, 최소 길이 게이지 사용, 설치 위치 등의 개선된 방법을 적용하여 용접단부와 스트레인게이지 설치 거리에 따른 변형률 진폭에 대한 상관식을 도출하고 국제용접협회 (IIW)의 제안식과 비교하였다. 또한 적합한 피로등급 상세범주 선정을 통해 공용중인 교량의 피로손상도 평가 및 잔존수명을 예측하고 분석하였다. 그 결과 피로균열 발생빈도가 높은 부재파악, 용접 단부와 게이지 설치 거리에 따른 변형률의 정량적 파악으로 정확한 피로손상도 평가 및 잔존수명 예측이 가능하므로 향후 교량의 응력이력 계측 시 개선된 방법을 적용해야 할 것이다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1997년도 제8회 학술강연회논문집
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• pp.133-143
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• 1997

In this paper, some of the critical factors in Necking-In process are investigated using a numerical analysis. The optimal processing parameters are established and applied to the actual processes. FEM analysis is carried out based on elastic-plastic work hardening model using ABAQUS/Standard. The results obtained from the commercially available code ABAQUS/Standard are compared with the experimental data and shows a good agreement with experimental data. The purpose of this paper is to search for the relations among the roller angle, feed length, and working force. Stress, strain distribution, displacement and increase in the length of the workpiece are also investigated.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.910-920
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• 1997

In this paper, some of the critical factors in Necking-In process are investigated using a numerical analysis. The optimal processing parameters are established and applied to the actual processes. FEM analysis is carried out based on elastic-plastic work hardening model using ABAQUS / Standard. The results obtained form the commercially available code ABAQUS / standard are compared with the experimental data and shows a good agreement with experimental data. The purpose of this paper is to search for the relations among the roller angel, feed length, and working force. Stress, strain distribution, displacement and increase in the length of the workpiece are also investigated.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.357-362
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• 2000

In the present paper the plastic buckling of thin-walled rectangular tube is analyzed. The stress-strain relations of the plates of the tube are idealized into nonlinear material of Ramberg and Osgood. Computing elastic moduli of the nonlinear material a precise plastic buckling stress has determined. The plastic buckling stress of the wider plate of the tube is considered as the crippling strength of the tube. The present theory is in good agreement with the experiments in various thickness-width ratios and materials.