• Smart Structures and Systems
• /
• 제18권1호
• /
• pp.139-154
• /
• 2016

This paper is concerned with the dynamics of hyperelastic solids and structures. We seek for a smart control actuation that produces a desired (prescribed) displacement field in the presence of transient imposed forces. In the literature, this problem is denoted as displacement tracking, or also as shape morphing problem. One talks about shape control, when the displacements to be tracked do vanish. In the present paper, it is assumed that the control actuation is provided by imposed eigenstrains, e.g., by the electric field in piezoelectric actuators, or by thermal actuators, or via analogous physical effects, such as magneto-striction or pre-stress. Structures with a controlled eigenstrain-type actuation belong to the class of smart structures. The action of the eigenstrains can be conveniently characterized by actuation stresses. Our theoretical derivations are performed in the framework of the theory of small incremental dynamic deformations superimposed upon a statically pre-deformed configuration of a hyperelastic solid or structure. We particularly ask for a distribution of incremental actuation stresses, such that the incremental displacements follow exactly a prescribed trajectory field, despite the imposed incremental forces are present. An exact solution of this problem is presented under the assumption that the actuation stresses can be tailored freely and applied everywhere within the body. Extending a Neumann-type solution strategy, it is shown that the actuation stresses due to the distributed control eigenstrains must satisfy certain quasi-static equilibrium conditions, where auxiliary body-forces and auxiliary surface tractions are to be taken into account. The latter auxiliary loading can be directly computed from the imposed forces and from the desired displacement field to be tracked. Hence, despite the problem is a dynamic one, a straightforward computation of proper actuator distributions can be obtained in the framework of quasi-static equilibrium conditions. Necessary conditions for the functioning of this concept are presented. Particularly, it must be required that the intermediate configuration is infinitesimally superstable. Previous results of our group for the case of shape control and displacement tracking in linear elastic structures are included as special cases. The high potential of the solution is demonstrated via Finite Element computations for an irregularly shaped four-corner plate in a state of plain strain.

• 한국산학기술학회논문지
• /
• 제10권6호
• /
• pp.1275-1280
• /
• 2009

최근 교량설계에서 외부 프리스트레스를 도입한 장지간 및 효율적인 단면활용 등과 같은 연구가 활발하게 진행되고 있다. 강구조물에 프리스트레스를 도입하면 큰 하중에서 탄성변형의 극한값이 증가하게 되어, 강재량을 줄일 수 있고, 비용의 측면에서 경제성이 있는 것으로 평가 되었다. 이러한 이유 때문에 우리나라에서도 최근 가설교량 시공시 프리스트레스를 도입하여 응력보정 및 처짐보정이 가능하고, 비교적 작은 단면으로 장지간 교량을 시공할 수 있어 통수단면을 충분히 할 수 있는 여러 가지 공법이 개발되고 있다. 따라서 본 논문에서는 가설 강교량에 프리스트레스 도입방법 및 고강도 텐던의 배치에 따른 영향, 강판과 고강도 텐던의 복합구조에 대한 효과를 기존 가설공법과 비교하여 검증 하고자 한다.

• 한국농공학회지
• /
• 제38권3호
• /
• pp.82-91
• /
• 1996

This is a basic study for the static and dynamic analysis on the elasto-plastic and elasto-viscoplastic of an axi-symmetric shell. The objective of this study was to investigate the mechanical characteristics of a nuclear reinforced concrete containment structure, which was selected as a model, by a numerical analysis using a finite element method. The structure was modeled with discrete ring elements of 8-noded isoparametric element rotating against the symmetrical axis, and the interaction between the foundation and the structure was modeled by Winkler's model. Also, the meridional tendon was modeled with 2-node truss elements, and the hoop tendon was done with point elements in two degrees of freedom. The effect of the tendon was considered without the increasement in total degree of freedom as the stiffness matrix of modeled tendon elements was assembled on the stiffness matrix of ring elements linked with the tendon. The results obtained from the analysis of an example were summarized as follows : 1. The stresses in the hoop direction on the interior and exterior surfaces of the structure were shown in changes of similar trend, and high stresses appeared on the structure wall 2. The stresses in the meridional direction on the interior and exterior surfaces were shown in change of different trend. Especially, the stresses at the junctions between the dome and the wall and between the wall and the bottom plate of the structure were very high, compared with those at other parts of the structure. 3. The stress changes in the direction of thickness on the crown of the dome were much linearly distributed. However, as the amount of tendon increased, the stresses in the upper and lower parts of the wall established with the tendon were shown stress concentration. 4. The stress changes in the direction of thickness on the center of the structure wall was linearly distributed in the all cases, and special stress due to the use of the tendon was not shown.

• 융합신호처리학회논문지
• /
• 제9권1호
• /
• pp.10-17
• /
• 2008

본 논문은 설비진단에 있어 크랙 성장부터 누설에 이르기까지 결함으로 발생하는 AE 신호를 통하여 위치를 표정하여 진단 시스템의 오차를 줄이는 것이다. wavelet을 이용한 잡음 제거로서 위치표정의 개선을 제안하였고, 실험을 위한 신호원으로 알루미늄 평판에 샤프심 파단음을, 공기압축기의 누설음을 사용하였다. 신호원에 대하여 웨이블릿 Shrinkage방법과 Soft Threshold을 이용한 신호의 잡음제거 및 시간 도달차 법과 물성치를 적용한 속도 값으로 시뮬레이션을 통하여 위치표정 결과를 확인하였다. 그 결과 웨이블릿 변환을 이용한 잡음제거는 크랙실험의 경우 평균거리 10.46mm이하로 30% 이상과 누설 실험의 경우 평균필터에 비해 2%의 개선된 위치표정을 확인하였다.

• 대한조선학회지
• /
• 제14권1호
• /
• pp.1-10
• /
• 1977

The major objects of this report are to supplement data of natural frequencies of thin elastic rectangular plates to the available data, and to give an experimental verification for natural frequencies obtained by Rayleigh-Ritz method, the generation set of which are eigenfunctions of Euler beams. For the first object the following five models, for which data only for the fundamental mode or data only for square plates are available, are adopted; (1) two opposed edges are clamped and the other two opposed edges simply supported (C-C, S-S), (2) one edge is simply supported and the other three edges clamped (C-C, C-S), (3) one edge is free and the other three edges clamped (C-C, C-F), (4) two adjacent edges are clamped and the other two adjacent edges free (C-F, C-F). For the (C-C, S-S) model the frequency equation obtained with the mode shapes assumed as of a single trigonometric series is solved. And for the other four models Rayleigh-Ritz method taking eigenfunctions of Euler beams as the generating set is applied. The numerical examples are obtained up to the fourth, the fifth or the sixth order depending on the range of the aspect ratio (0.1-10.0). The number of terms in the generating set for Rayleigh-Ritz method is fifteen for all models. For the experiment three models made of 3.2mm thickness mild steel plate for general structure use were prepared in following size; $300mm{\times}600mm,\;600mm{\times}600mm\;and\;900mm{\times}600mm$. Their boundary conditions are made to fit (C-C, C-F) condition. From the experiment mechanical impedance curves based on the frequency response method were obtained together with phase relation diagrams. The experimental data are resulted in good conformity to calculated values.

• 접착 및 계면
• /
• 제5권2호
• /
• pp.22-36
• /
• 2004

Several in-situ testing methods of adhesively bonded joints under static short-time tensile loading are critically analyzed in terms of experimental procedure and data evaluation. Due to its rather homogeneous stress state across the glue line, the tensile-shear test with thick single-lap specimens, according to ISO 11003-2, has become the most important test process for the determination of realistic materials parameters. This basic method, which was improved in both, the experimental part by stepped adherends and easily attachable extensometers and the evaluation procedure by numeric substrate deformation correction and test simulation based on the finite element method (FEM), is therefore demonstrated by application to several kinds of adhesives and metallic adherends. Multi-axial load decreases the strength of a joint. This effect, which is illustrated by an experimental comparison, impedes the derivation of realistic mechanical characteristics from measured force-displacement curves. It is shown by numeric modeling that tensile-shear tests with thin plate substrates according to ISO 4587, which are widely used for quick industrial quality assurance, reveal an inhomogeneous stress state, especially because of relatively large adherend deformation. Complete experimental determination of the elastic properties of bonded joints requires independent measurement of at least two characteristics. As the thick-adherend tensile-shear test directly yields the shear modulus, the tensile butt-joint test according to ISO 6922 represents the most obvious complement of the test programme. Thus, validity of analytical correction formulae proposed in literature for the derivation of realistic materials characteristics is verified by numeric simulation. Moreover, the influence of the substrate deformation is examined and a FEM correction method introduced.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2008년도 추계 학술발표회
• /
• pp.1427-1439
• /
• 2008

The quality of track-bed fills of railways has been controlled by field measurements of density (${\gamma}_d$) and the results of plate-load tests. The control measures are compatible with the design procedures whose design parameter is $k_{30}$ for both ordinary-speed railways and high-speed railways. However, one of fatal flaws of the design procedures is that there are no simple laboratory measurement procedures for the design parameters ($k_{30}$ or, $E_{v2}$ and $E_{v2}/E_{v1}$) in design stage. A new quality control procedure, in parallel with the advent of the new design procedure, is being proposed. This procedure is based upon P-wave velocity involving consistently the evaluation of design parameters in design stage and the field measurements during construction. The key concept of the procedure is that the target value for field compaction control is the P-wave velocity determined at OMC using modified compaction test, and direct-arrival method is used for the field measurements during construction. The procedure was verified at a test site and the p-wave velocity turned out to be an excellent control measure. The specifications for the control also include field compaction water content of $OMC{\pm}2%$ as well as the p-wave velocity.

• 전산구조공학
• /
• 제10권4호
• /
• pp.217-228
• /
• 1997

p-version 유한요소법에 의한 고정밀해석은 응력특이가 발생하는 선형탄성 문제에 매우 적합한 방법으로 인식되고 있다. 해석 결과의 정확도, 모델링의 단순성, 입력자료에 대한 통용성 및 사용자와 CPU 시간의 절감 등 여러장점이 선형탄성 문제에 적용되어 우수성이 입증되었지만, 탄소성 해석분야는 아직 적용이 이루어지지 않고 있다. 그러므로 본 논문에서는 일-경화재료에 대한 구성방정식을 이용하여 정식화된 증분소성이론과 소성유동법칙에 근거한 재료비선형 p-version 유한요소모델이 제안되었다. 비선형방정식을 풀기 위해 Newton-Raphson법과 초기강성도법 등의 반복법이 모색되었다. 제안된 모델을 이용하여 개구부를 가진 사각형 평판과 내압을 받는 두꺼운 실린더, 그리고 등분포하중을 받는 원판해석 등의 수치실험이 수행되었다. 한편, p-version 모델에 의한 해석결과는 문헌의 이론값과 상용유한요소프로그램인 ADINA의 해석결과와 비교 검증되었다.

• Advanced Composite Materials
• /
• 제17권1호
• /
• pp.57-73
• /
• 2008

The present paper focuses on experimental verification of the ply-by-ply basis inelastic analysis of multidirectional laminates. First of all, rate dependence of the tensile behavior of balanced symmetric cross-ply T800H/epoxy laminates with a $[0/90]_{3S}$ lay-up under off-axis loading conditions at $100^{\circ}C$ is examined. Uniaxial tension tests are performed on plain coupon specimens with various fiber orientations $[{\theta}/(90-{\theta})]_{3S}$ ($\theta$ = 0, 5, 15, 45 and $90^{\circ}C$) at two different strain rates (1.0 and 0.01%/min). The off-axis stress.strain curves exhibit marked nonlinearity for all the off-axis fiber orientations except for the on-axis fiber orientations $\theta$ = 0 and $90^{\circ}$, regardless of the strain rates. Strain rate has significant influences not only on the off-axis flow stress in the regime of nonlinear response but also on the apparent off-axis elastic modulus in the regime of initial linear response. A macromechanical constitutive model based on a ply viscoplasticity model and the classical laminated plate theory is applied to predictions of the rate-dependent off-axis nonlinear behavior of the cross-ply CFRP laminate. The material constants involved by the ply viscoplasticity model are identified on the basis of the experimental results on the unidirectional laminate of the same carbon/epoxy system. It is demonstrated that good agreements between the predicted and observed results are obtained by taking account of the fiber rotation induced by deformation as well as the rate dependence of the initial Young's moduli.

• Composites Research
• /
• 제33권4호
• /
• pp.220-227
• /
• 2020

탄소 섬유 강화 복합재료 성형 시 섬유는 열변형이 거의 없는 반면에 수지는 시간 및 온도변화에 따라 물성이 변화하며 제품에 잔류응력이 발생한다. 잔류응력의 원인은 경화 과정에서의 섬유와 수지의 열팽창 계수 차이, 수지의 화학 수축이며 이로 인해 스프링 인, 뒤틀림 등의 열 변형이 발생한다. 열 변형은 제품의 품질을 결정하는 주요한 요인으로 복합재료 공정에 있어 반드시 고려되어야 한다. 본 연구는 잔류응력에 의한 열 변형을 예측하기 위해 3-D 점탄성 모델을 적용하여 서브루틴을 제작하고 기존의 2-D 점탄성 모델의 평판 유한 요소 해석결과와 비교해 유한 요소 해석 기법을 검증하였다. 검증된 기법으로 L-형상 구조를 해석하여 스프링 인 현상을 예측, 분석하였다.