• 한국전산구조공학회논문집
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• 제21권1호
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• pp.51-58
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• 2008

본 연구에서는 입자강화 복합재료(particle-reinforced composites)의 거동을 예측하기 위하여 Lee and Pyo(2007)에 의해 제안된 계면손상을 고려한 복합재료의 미세역학 탄성모델과 Karihaloo and Fu(1989)의 미세균열 생성모델을 결합하여, 보강입자의 계면손상(imperfect interface)과 기지 내 미세균열을 고려하여 탄성구성모델(constitutive model)의 거동해석을 수행하였다. 제안된 탄성구성모델의 적용성 검증과 주요손상변수가 거동예측에 미치는 영향을 알아보기 위해 일축 하중 하에서의 응력-변형률 관계를 수치적으로 나타내었다. 또한, 기존의 관련 실험결과와 본 해석결과와의 비교를 통하여 제안된 모델의 정확도를 검증하였다.

• Advances in aircraft and spacecraft science
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• 제9권3호
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• pp.217-242
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• 2022

This paper proposes a novel time-domain homogenization model combining the viscoelastic constitutive law with Eshelby's inclusion theory-based micromechanics model to predict the mechanical behavior of the particle reinforced composite material. The proposed model is intuitive and straightforward capable of predicting composites' viscoelastic behavior in the time domain. The isotropization technique for non-uniform stress-strain fields and incremental Mori-Tanaka schemes for high volume fraction are adopted in this study. Effects of the imperfectly bonded interphase layer on the viscoelastic behavior on the dynamic mechanical behavior are also investigated. The proposed model is verified by the direct numerical simulation and DMA (dynamic mechanical analysis) experimental results. The proposed model is useful for multiscale analysis of viscoelastic composite materials, and it can also be extended to predict the nonlinear viscoelastic response of composite materials.

• Interaction and multiscale mechanics
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• 제4권3호
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• pp.173-185
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• 2011

A multiscale modeling scheme that addresses the influence of the nanoparticle size in nanocomposites consisting of nano-sized spherical particles embedded in a polymer matrix is presented. A micromechanics-based constitutive model for nanoparticle-reinforced polymer composites is derived by incorporating the Eshelby tensor considering the interface effects (Duan et al. 2005a) into the ensemble-volume average method (Ju and Chen 1994). A numerical investigation is carried out to validate the proposed micromechanics-based constitutive model, and a parametric study on the interface moduli is conducted to investigate the effect of interface moduli on the overall behavior of the composites. In addition, molecular dynamics (MD) simulations are performed to determine the mechanical properties of the nanoparticles and polymer. Finally, the overall elastic moduli of the nanoparticle-reinforced polymer composites are estimated using the proposed multiscale approach combining the ensemble-volume average method and the MD simulation. The predictive capability of the proposed multiscale approach has been demonstrated through the multiscale numerical simulations.

• 소성∙가공
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• 제19권8호
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• pp.468-473
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• 2010

Shape memory alloys (SMAs) have the ability to recover their original shape upon thermo-mechanical loading even after large inelastic deformation. The unique feature is known as pseudoelasticity and shape memory effect caused by the crystalline structural transformation between two solid-state phases called austenite and martensite. To support the engineering application, a number of constitutive models, which can be formally classified into either micromechanics-based or phenomenological model, have been developed. Most of the constitutive models include a kinetic law governing the crystallographic transformation. The present work presents a one-dimensional, phenomenological constitutive model for SMAs in the context of the unified viscoplasticity theory. The proposed model does not incorporate the complex mechanisms of phase transformation. Instead, the effects induced by the transformation are depicted through the growth law for the back stress that is an internal state variable of the model.

• Earthquakes and Structures
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• 제4권6호
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• pp.607-627
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• 2013

The application of shape memory alloys (SMAs) to the seismic response reduction of civil engineering structures has attracted growing interest due to their self-centering feature and excellent fatigue performance. The loading rate dependence of SMAs raises a concern in the seismic analysis of SMA-based devices. However, the implementation of micromechanics-based strain-rate-dependent constitutive models in structural analysis software is rather complicated and computationally demanding. This paper investigates the feasibility of replacing complex rate-dependent models with rate-independent constitutive models for superelastic SMA elements in seismic time-history analysis. Three uniaxial constitutive models for superelastic SMAs, including one rate-dependent thermomechanical model and two rate-independent phenomenological models, are considered in this comparative study. The pros and cons of the three nonlinear constitutive models are also discussed. A parametric study of single-degree-of-freedom systems with different initial periods and strength reduction factors is conducted to examine the effect of the three constitutive models on seismic simulations. Additionally, nonlinear time-history analyses of a three-story prototype steel frame building with special SMA-based damping braces are performed. Two suites of seismic records that correspond to frequent and design basis earthquakes are used as base excitations in the seismic analyses of steel-braced frames. The results of this study show that the rate-independent constitutive models, with their parameters properly tuned to dynamic test data, are able to predict the seismic responses of structures with SMA-based seismic response modification devices.

• Structural Engineering and Mechanics
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• 제30권2호
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• pp.247-261
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• 2008

Performance of shear-deficient reinforced concrete (RC) beams strengthened with carbon fiber-reinforced polymer (CFRP) strips/sheets is analyzed through numerical simulations on four-point bending tests. The numerical simulations are carried out using the finite element (FE) program ABAQUS. A micromechanics-based constitutive model (Liang et al. 2006) is implemented into the FE program ABAQUS to model CFRP strips/sheets. The predicted results are compared with experiment data (Khalifa and Nanni 2002) to assess the accuracy of the proposed FE analysis approach. A series of numerical tests are conducted to investigate the influence of stirrup lay-ups on the shear strengthening performance of the CFRP strips/sheets, to illustrate the influence of the damage parameters on the microcrack density evolution in concrete, and to investigate the shear and flexural strengthening performance of CFRP strips/ sheets. It has been shown that the proposed FE analysis approach is suitable for the performance prediction of RC beams strengthened with CFRP strips/sheets.

• 한국지반공학회논문집
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• 제23권3호
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• pp.77-88
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• 2007

본 연구에서는 사질토의 탄성 및 탄소성 거동을 모사하기 위한 미시역학 기반의 구성 모델을 개발하였다. 개발 모델은 접촉 방향의 공간 분포를 통계적으로 처리한 조직 이방성, 응력비에 따른 조직 이방성의 변화, 간극비 변화에 따른 접촉점 수의 변화, 그리고 미시적 탄성-탄소성 접촉 강성을 고려하였다. 금속 재료에 대한 시험결과를 이용하여 미시적 탄소성 접촉 강성 모델을 수직 접촉력과 입자의 항복 접촉력에 대한 거듭제곱 함수의 형태로 유도하였다. 모델 변수를 정량적으로 평가하기 위해 직교 이방 탄성 계수의 근사식을 유도하였다.

• 한국지반공학회논문집
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• 제23권3호
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• pp.89-100
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• 2007

본 논문과 함께 제출한 논문에서는 미시역학 기반의 새로운 탄소성 모델의 정식화에 대해 설명하였다. 본 논문에서는 사질토 변형의 탄성 및 탄소성 거동을 미시역학에 근거하여 자세히 분석하였다. 모델에 필요한 변수 평가를 위한 과정을 제시하였다. 등방 및 삼축 압축 시험에서 나타난 사질토의 탄성 거동을 분석한 결과, 직교 이방 탄성계수의 응력 종속성은 미시적 수직 강성에서 나타난 수직 접촉력의 거듭제곱 함수 형태가 반영되어 나타나며, 삼축 압축 응력 상태에서는 조직 이방성의 변화가 응력 종속성에 영향을 미침을 알 수 있었다. 미시역학적 해석을 통해 소성 변형이 매우 낮은 변형률 수준에서도 발현되며, 변형 중 사질토 강성의 비선형적 감소는 접촉점에서의 접선 방향 소성 변형에 의해 나타남을 밝혔다.

• 한국전산구조공학회논문집
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• 제22권6호
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• pp.579-585
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• 2009

본 연구에서는 분사식 섬유보강 코팅층(sprayed fiber reinforced polymer, SFRP)으로 보강된 RC보의 성능평가를 위하여 유한요소해석을 수행하였다. 이를 위하여 미세역학을 기반으로 한 구성모델(micromechanical constitutive model)(Lee, 2001)과 손상모델(Damage models)(Lee 등, 2000; 2005)을 결합시킨 손상구성모델(damage constitutive model)을 유한요소 프로그램인 ABAQUS에 적용하였다. 유한요소해석 결과를 실험값(Ha, 2007; Ha 등, 2009)과 비교하여 손상구성모델의 정확성을 증명하고자 하였다. 비교분석 결과, 손상구성모델을 유한요소 프로그램에 적용한 해석은 실험결과(Ha, 2007; Ha 등, 2009)를 비교적 잘 예측하고 있음을 보여주었다.

• Journal of Theoretical and Applied Mechanics
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• 제3권1호
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• pp.45-65
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• 2002

A constitutive model on oorthotropic thermo-elasto-viscoplasticity for fiber-reinforced composite materials Is illustrated, and their thermomechanical responses are predicted with the fully-coupled finite element formulation. The unmixing-mixing scheme can be adopted with the multipartite matrix method as the constitutive model. Basic assumptions based upon the composite micromechanics are postulated, and the strain components of thermal expansion due to temperature change are included In the formulation. Also. more than two sets of mechanical variables, which represent the deformation states of multipartite matrix can be introduced arbitrarily. In particular, the unmixing-mixing scheme can be used with any well-known isotropic viscoplastic theory of the matrix material. The scheme unnecessitates the complex processes for developing an orthotropic viscoplastic theory. The governing equations based on fully-coupled thermomechanics are derived with constitutive arrangement by the unmixing-mixing concept. By considering some auxiliary conditions, the Initial-boundary value problem Is completely set up. As a tool of numerical analyses, the finite element method Is used with isoparametric Interpolation fer the displacement and the temperature fields. The equation of mutton and the energy conservation equation are spatially discretized, and then the time marching techniques such as the Newmark method and the Crank-Nicolson technique are applied. To solve the ultimate nonlinear simultaneous equations, a successive iteration algorithm is constructed with subincrementing technique. As a numerical study, a series of analyses are performed with the main focus on the thermomechanical coupling effect in composite materials. The progress of viscoplastic deformation, the stress-strain relation, and the temperature History are careful1y examined when composite laminates are subjected to repeated cyclic loading.