• Title/Summary/Keyword: Effective Stiffness Matrix

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A study on Improving the Reliability of a Finite Elements Model and Stiffness Damage Detection by Dynamic Characteristics Measurements (동특성 측정에 의한 유한요소 모델의 신뢰도 제고 및 파손부위 색출에 관한 연구)

  • 박윤식;박형순
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.10 no.1
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    • pp.157-163
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    • 1986
  • A method to improve the Finite Elements Model and to identify structure stiffness damages utilizing measured dynamic characteristics is suggested. In order to show the effectiveness of the proposed method, a sample structure is adopted and tested. It is found that; (1) the Finite Elements Model can be improved with experimentally obtained dynamic characteristics satisfactorily and (2) the test results are also very helpful to search the stiffness damaged part of the sample structure via plotting the error matrix[E], especially it is aboved that the weighted error matrix is very effective to detect even the stiffness changes are relatively small.

Effect of Interfacial Debonding on the Material Properties of Brittle Matrix Composites (취성기지 복합재료의 물성치에 미치는 계면분리의 영향)

  • 염영진;진민철
    • Composites Research
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    • v.16 no.1
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    • pp.42-49
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    • 2003
  • Brittle matrix composites often have interfacial debonding between the fiber and matrix which may lead to strength and stiffness degradation. The effect of interfacial debonding and fiber volume fraction on the mechanical properties of composite material were studied by using finite element method. Firstly, the modelling of fiber and matrix constituting the composite material was simplified under some assumptions. Traction and displacement continuity conditions were imposed along the boundary of adjacent representative volume elements. In order to obtain the effective material properties of composite material, stiffness constants were inverted. Numerical values of longitudinal moduli in case of perfect bonding were compared with theoretical values obtained by rule of mixtures and yielded consistency. Material properties of composite with large debonding an81e were found to decrease even though the fiber volume fraction increased.

Flexural behavior of reinforced concrete beams strengthened with a hybrid inorganic matrix - steel fiber retrofit system

  • Papakonstantinou, Christos G.;Katakalos, Konstantinos
    • Structural Engineering and Mechanics
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    • v.31 no.5
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    • pp.567-585
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    • 2009
  • The aim of this study was to investigate the flexural behavior of reinforced concrete beams strengthened with a novel strengthening system. Concrete beams were strengthened with a hybrid retrofit system consisting of high strength steel cords impregnated in an inorganic fireproof matrix (Geopolymer). The strengthened reinforced concrete beams along with non-strengthened control beams were tested monotonically under four point bending loading conditions. Moreover, an analytical model is introduced, that can be used to analyze the flexural performance of the strengthened beams. The experimental results indicate that the failure of the strengthened beams was based on the yielding of the reinforcement in the tension face of the beams, followed by a local slippage of the steel cords. The flexural stiffness of the strengthened beams was significantly improved compared to the stiffness of the non-strengthened beams. In conclusion, the strengthening system can provide an effective alternative to commercially available systems.

NLP Formulation for the Topological Structural Optimization (구조체의 위상학적 최적화를 위한 비선형 프로그래밍)

  • Bark, Jaihyeong;Omar N. Ghattas;Lee, Li-Hyung
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 1996.04a
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    • pp.182-189
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    • 1996
  • The focus of this study is on the problem of the design of structure of undetermined topology. This problem has been regarded as being the most challenging of structural optimization problems, because of the difficulty of allowing topology to change. Conventional approaches break down when element sizes approach to zero, due to stiffness matrix singularity. In this study, a novel nonlinear Programming formulation of the topology Problem is developed and examined. Its main feature is the ability to account for topology variation through zero element sizes. Stiffness matrix singularity is avoided by embedding the equilibrium equations as equality constraints in the optimization problem. Although the formulation is general, two dimensional plane elasticity examples are presented. The design problem is to find minimum weight of a plane structure of fixed geometry but variable topology, subject to constraints on stress and displacement. Variables are thicknesses of finite elements, and are permitted to assume zero sizes. The examples demonstrate that the formulation is effective for finding at least a locally minimal weight.

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Elastic properties of CNT- and graphene-reinforced nanocomposites using RVE

  • Kumar, Dinesh;Srivastava, Ashish
    • Steel and Composite Structures
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    • v.21 no.5
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    • pp.1085-1103
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    • 2016
  • The present paper is aimed to evaluate and compare the effective elastic properties of CNT- and graphene-based nanocomposites using 3-D nanoscale representative volume element (RVE) based on continuum mechanics using finite element method (FEM). Different periodic displacement boundary conditions are applied to the FEM model of the RVE to evaluate various elastic constants. The effects of the matrix material, the volume fraction and the length of reinforcements on the elastic properties are also studied. Results predicted are validated with the analytical and/or semiempirical results and the available results in the literature. Although all elastic stiffness properties of CNT- and graphene-based nanocomposites are found to be improved compared to the matrix material, but out-of-plane and in-plane stiffness properties are better improved in CNT- and graphene-based nanocomposites, respectively. It is also concluded that long nanofillers (graphene as well as CNT) are more effective in increasing the normal elastic moduli of the resulting nanocomposites as compared to the short length, but the values of shear moduli, except $G_{23}$ of CNT nanocomposite, of nanocomposites are slightly improved in the case of short length nanofillers (i.e., CNT and graphene).

Character Writing Using Multi-Fingered Hands : Grasp Modeling and Compliance Analysis (다지 손을 이용한 문자 쓰기 : 파지 모델링 및 컴플라이언스 특성 해석)

  • Kim, Byoung-Ho;Yeo, Hee-Joo
    • Journal of Institute of Control, Robotics and Systems
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    • v.7 no.11
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    • pp.927-932
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    • 2001
  • When people write a character with a pen stably, proper compliance planning is necessary. In this paper, after investigating the property of character writing task, we propose a fundamental grasp model for character writing and also analyze compliance characteristics for effective character writing using multi-fingered hands. For this, the general stiffness relation of multi-fingered hand is firstly described. Next, we investigate the grasp configurations for grasping a pen and then, we analyze the conditions of the specified stiffness matrix in the operational space to successfully and more effectively achieve the given character writing task. Through the analysis, an effective grasp modeling for successful character writing is shown. And also, we conclude that the operational compliance characteristics should be properly planned for character writing, stably and precisely.

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Continuous element method for aeroacoustics' waves in confined ducts

  • Khadimallah, Mohamed A.;Harbaoui, Imene;Casimir, Jean B.;Taieb, Lamjed H.;Hussain, Muzamal;Tounsi, Abdelouahed
    • Advances in nano research
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    • v.13 no.4
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    • pp.341-350
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    • 2022
  • The continuous elements method, also known as the dynamic stiffness method, is effective for solving structural dynamics problems, especially over a large frequency range. Before applying this method to fluid-structure interactions, it is advisable to check its validity for pure acoustics, without considering the different coupling parameters. This paper describes a procedure for taking wave propagation into account in the formulation of a Dynamic Stiffness Matrix. The procedure is presented in the context of the harmonic response of acoustic pressure. This development was validated by comparing the harmonic response calculations performed using the continuous element model with the analytical solution. In addition, this paper illustrates the application of this method to a simple compressible flow problem, since it has been applied solely to structural problems to date.

Finite Element Analysis Through Mechanical Property Test and Elasto-plastic Modeling of 2.5D Cf/SiCm Composite Analysis (2.5D Cf/SiCm 복합재의 기계적 물성 시험과 탄소성 모델링을 통한 유한요소해석)

  • Lee, MinJung;Kim, Yeontae;Lee, YeonGwan
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.48 no.9
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    • pp.663-670
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    • 2020
  • A study on mechanical property characterization and modeling technique was carried out to approximate the behaviour of structures with 2.5D C/SiC material. Several tensile tests were performed to analyze the behaviour characteristics of the 2.5D C/SiC material and elastic property was characterized by applying a mathematical homogenization and a modified rule of mixture. SiC matrix representing the elasto-plastic behavior approximates as a bilinear function. Then the equivalent yield strength and equivalent plastic stiffness were calculated by minimizing errors in experiment and approximation. RVE(Representative Volume Element)was defined from the fiber and matrix configuration of 2.5D C/SiC and a process of calculating the effective stiffness matrix by applying the modified rule of mixture to RVE was implemented in the ABAQUS User-defined subroutine. Finite element analysis was performed by applying the mechanical properties of fiber and matrix calculated based on the proposed process, and the results were in good agreement with the experimental results.

Compliance Analysis for Effective Peg-In-Hole Task (팩인홀 작업을 효율적으로 수행하기 위한 컴플라이언스 해석)

  • Kim, Byeong-Ho;Lee, Byeong-Ju;Seo, Il-Hong;O, Sang-Rok
    • Journal of the Korean Society for Precision Engineering
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    • v.17 no.9
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    • pp.181-188
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    • 2000
  • This paper deals with an analysis of the compliance characteristic for effective peg-in-hole task using robot hand without inter-finger coupling. We first observe the fact that some of coupling stiffness elements cannot be planned arbitrary. next we classify the task of inserting a peg-in-a-hole into two contact styles between the peg and the hole. Then we analyze the conditions of the specified stiffness matrix in the operational space to successfully and more effectively achieve the give peg-in-hole task for each case. It is concluded that the location of compliance center on the peg and the coupling stiffness element existing between the translational and the rotational direction play important roles for successful peg-in-hole task. Simulation results are included to verify the feasibility of the analytic results.

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A Nonlinear Programming Formulation for the Topological Structural Optimization (구조체의 위상학적 최적화를 위한 비선형 프로그래밍)

  • 박재형;이리형
    • Computational Structural Engineering
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    • v.9 no.3
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    • pp.169-177
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    • 1996
  • The focus of this study is on the problem of the design of structure of undetermined topology. This problem has been regarded as being the most challenging of structural optimization problems, because of the difficulty of allowing topology to change. Conventional approaches break down when element sizes approach to zero, due to stiffness matrix singularity. In this study, a novel nonlinear programming formulation of the topology problem is presented. Its main feature is the ability to account for topology variation through zero element sizes. Stiffness matrix singularity is avoided by embedding the equilibrium equations as equality constraints in the optimization problem. Although the formulation is general, two dimensional plane elasticity examples are presented. The design problem is to find minimum weight of a plane structure of fixed geometry but variable topology, subject to constraints on stress and displacement. Variables are thicknesses of finite elements, and are permitted to assume zero sizes. The examples demonstrate that the formulation is effective for finding at least a locally minimal weight.

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