• 제목/요약/키워드: Representative Strain

검색결과 208건 처리시간 0.025초

Determination of representative volume element in concrete under tensile deformation

  • Skarzyski, L.;Tejchman, J.
    • Computers and Concrete
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    • 제9권1호
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    • pp.35-50
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    • 2012
  • The 2D representative volume element (RVE) for softening quasi-brittle materials like concrete is determined. Two alternative methods are presented to determine a size of RVE in concrete subjected to uniaxial tension by taking into account strain localization. Concrete is described as a heterogeneous three-phase material composed of aggregate, cement matrix and bond. The plane strain FE calculations of strain localization at meso-scale are carried out with an isotropic damage model with non-local softening.

나노압입공정 해석에서 재료의 탄소성 특성 도출을 위한 대표변형률의 결정과 Dao의 Reverse 해석의 향상 (Improvement of Dao's Reverse Analysis and Determination of Representative Strain for Extracting Elastic-Plastic Properties of Materials in Analysis of Nanoindentation)

  • 이정민;이찬주;김병민
    • 대한기계학회논문집A
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    • 제32권2호
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    • pp.105-118
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    • 2008
  • The newly developed analysis method for nanoindentation load-displacement curves are focused on not only obtaining elastic modulus and hardness values but also other mechanical properties, such as yield strength and strain hardening properties. Dao et al. developed a forward and reverse algorithm to extract the elasto-plastic properties of materials from the load-displacement curves obtained in nanoindentation test. These algorithms were only applicable for engineering metals (Poisson#s ratio 0.3) using the equivalent conical indenter of the Berkovich. However, the applicable metals are substantially limited because range of used in the finite element analysis is narrow. This study is designed to expand range of the applicable metals in the reverse algorithms established by Dao et al. and to improve the accuracy of that for extracting the elasto-plastic properties of materials. In this study, a representative strain was assumed to vary according to specific range of $E^*/{\sigma}_r$ and was defined as function of $E^*/{\sigma}_r$. Also, an initial unloading slope in reverse algorithms improved in this study was not considered as independent parameters of the load-displacement curves. The mechanical properties of materials for finite element analysis were modeled with the elastic modulus, E, the yield strength, ${\sigma}_y$, and the strain hardening exponents, n. We showed that the representative strain (0.033) suggested by Dao et al. was no longer applicable above the $E^*/{\sigma}_r$ of 400 and depended on values of $E^*/{\sigma}_r$. From these results, we constructed the dimensionless functions, in where the initial unloading slope was not included, for engineering metals up to $E^*/{\sigma}_r$ of 1500. These functions allow us to determine the mechanical properties with greater accuracy than Dao#s study.

불규칙 섬유배열을 가진 일방향 복합재료의 경계면 변형률 분포 해석 (Interfacial Strain Distribution of a Unidirectional Composite with Randomly Distributed Fibers)

  • 하성규;진교국;오제훈
    • 대한기계학회논문집A
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    • 제30권3호
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    • pp.260-268
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    • 2006
  • The micromechanical approach was used to investigate the interfacial strain distributions of a unidirectional composite under transverse loading in which fibers were usually found to be randomly packed. Representative volume elements (RVE) for the analysis were composed of both regular fiber arrays such as a square array and a hexagonal array, and a random fiber array. The finite element analysis was performed to analyze the normal, tangential and shear strains at the interface. Due to the periodic characteristics of the strain distributions at the interface, the Fourier series approximation with proper coefficients was utilized to evaluate the strain distributions at the interface for the regular and random fiber arrays with respect to fiber volume fractions. From the analysis, it was found that the random arrangement of fibers had a significant influence on the strain distribution at the interface, and the strain distribution in the regular fiber arrays was one of special cases of that in the random fiber array.

겉보기 응력 개념에 기반한 공구각에 따른 비절삭저항 변화 분석 (Analysis on Specific Cutting Resistance Variation by Tool Angles Based on a Concept of Representative Stres)

  • 전은채;최환진;이규민;이윤희;제태진;김정환;최두선
    • 한국기계가공학회지
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    • 제13권2호
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    • pp.64-72
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    • 2014
  • In the past, prism patterns have been linear triangular shapeswith a $90^{\circ}$ angle; however, new micro prism patterns having acute angles or obtuse angles have recently been the subject of demandin the display, lighting and photovoltaic industries. Micro-cutting experiments for micro-prism patterns having $60^{\circ}$, $90^{\circ}$, and $120^{\circ}$ angles on an electroplated Ni mold were performed and it was found in this study that the specific cutting resistance increased with a decrease in the tool angles (prism pattern angles). The cause of this variation had been thought to be the increase of the ploughing force due to tip rounding and the friction force due to the edge effect. However, the depth of the cut was large enough that it was possible to neglect these effects. Therefore, this study introduced the concept of representative stress of indentation. The measured stress was varied according to the indentation depth eventhoughthetestedspecimenswereidentical ; the varied stress was termed the representative stress. According to indentation theory, the strain that the Ni mold experienced increased with a decrease in the tool angle. Based on the stress-strain relationship, higher strain means higher stress and higher specific cutting resistance. Therefore, the specific cutting resistance was higher at smaller tool angles that had higher strain and stress.

마이크로/나노 압입시험에 의한 재료특성평가 (Evaluation of Material Characteristics by Micro/Nano Indentation Tests)

  • 이형일;이진행
    • 대한기계학회논문집A
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    • 제32권10호
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    • pp.805-816
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    • 2008
  • The present work reviews the methods to evaluate elastic-plastic material characteristics by indentation tests. Especially the representative stress and strain values used in some papers are critically analyzed. The values should not only represent the load-depth curve, but also represent the whole of deformed material around the impression. We briefly introduce other indentation techniques to evaluate residual stresses, creep properties, and fracture toughness. We also review some technical problems that are related to the accuracy issues in indentation tests.

Homogenization based continuum damage mechanics model for monotonic and cyclic damage evolution in 3D composites

  • Jain, Jayesh R.;Ghosh, Somnath
    • Interaction and multiscale mechanics
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    • 제1권2호
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    • pp.279-301
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    • 2008
  • This paper develops a 3D homogenization based continuum damage mechanics (HCDM) model for fiber reinforced composites undergoing micromechanical damage under monotonic and cyclic loading. Micromechanical damage in a representative volume element (RVE) of the material occurs by fiber-matrix interfacial debonding, which is incorporated in the model through a hysteretic bilinear cohesive zone model. The proposed model expresses a damage evolution surface in the strain space in the principal damage coordinate system or PDCS. PDCS enables the model to account for the effect of non-proportional load history. The loading/unloading criterion during cyclic loading is based on the scalar product of the strain increment and the normal to the damage surface in strain space. The material constitutive law involves a fourth order orthotropic tensor with stiffness characterized as a macroscopic internal variable. Three dimensional damage in composites is accounted for through functional forms of the fourth order damage tensor in terms of components of macroscopic strain and elastic stiffness tensors. The HCDM model parameters are calibrated from homogenization of micromechanical solutions of the RVE for a few representative strain histories. The proposed model is validated by comparing results of the HCDM model with pure micromechanical analysis results followed by homogenization. Finally, the potential of HCDM model as a design tool is demonstrated through macro-micro analysis of monotonic and cyclic damage progression in composite structures.

미세조직이 고려된 이상 조직강의 유한 요소 해석 (Micro-mechanical FE Analysis of Dual-phase Steels)

  • 하진진;이진우;김지훈;;이명규
    • 소성∙가공
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    • 제24권3호
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    • pp.194-198
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    • 2015
  • Microstructure based FE simulations were conducted to investigate the micro-mechanical properties of ferrite-martensite dual-phase steels. The FE model was built based on real microstructure images which were characterized by optical microscopy through the thickness direction. Serial sectioned 2D images were converted into semi-2D representative volume elements (RVEs) model. Each RVE model was subjected to a non-proportional loading condition and the mechanical response was analyzed on both the macroscopic and microscopic levels. Macroscopically, stress-strain curves were described under tension-compression and tension-orthogonal tension conditions and the Bauschinger effect was well captured for both loading paths. In addition, micromechanical properties were investigated in the view of stress-strain partitioning and strain localization during monotonic tension.

압입시험 모델링을 통한 진응력-진변형율 관계 해석 (Analysis of True Stress - True Strain Relations through the Modeling of Ball Indentation Test)

  • 이호진;김기백;이봉상;이병섭
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2003년도 춘계학술대회
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    • pp.660-665
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    • 2003
  • The true stress - true strain relation of SA508 steel was evaluated with analytical and experimental equation on the base of the indentation load-depth curve obtained from the modeling of ball indentation test. The evaluated relation between true stress and true strain is agreed well with that of SA508 teel defined in the modeling. The distribution of effective stress along the center axis of indentation depth was calculated with Tresca criteria in the modeling. The representative strain, which are defined in this study as the corresponding strains obtained from the maximum effective stress, have a linear relation with the true strain. The true stress - true strain relation of austenitic stainless steel was evaluated by the modeling of ball indentation test to verify the case of A508 steel.

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A study of instrumented indentation by finite element analysis

  • Le Minh-quy;Kim Seock-sam
    • 한국윤활학회:학술대회논문집
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    • 한국윤활학회 2003년도 학술대회지
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    • pp.248-258
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    • 2003
  • Finite element computations were carried out to study the indentation by rigid cone with half-angle of $70.3^{\circ}$ for 72 different combinations of elasto-plastic properties that cover the wide range of mechanical parameters of common engineering solid materials. The dimensional analysis and representative strain concept were used in the analysis. It was shown that for the same representative strain value, the loading curvature C can be formulated under two different forms, which are based on two alternative dimensionless functions. The present study's one is simpler than the other previously found by other authors using the similar approach. For a wide range of material's parameters, the hardness-modulus ratio should be a parabolic function of ${\sigma}E$, rather than a power law function earlier proposed.

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국내 보조기층 재료의 변형특성을 고려한 전체 변형률 영역의 구성모델 개발 (Development of whole Strain Range Constitutive Model Considering Deformational Characteristics of Subbase Materials in Korea)

  • 권기철
    • 한국도로학회논문집
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    • 제6권3호
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    • pp.65-77
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    • 2004
  • 보조기층 재료의 변형특성은 역학적 포장설계에 있어서 대단히 중요한 입력변수이다 국내에서 사용되는 보조기층 재료는 대부분 입상의 자갈질 흙으로서, 실제 시공현장에서 7종의 시료를 채취하였다. 보조기층 재료의 변형특성 평가를 위하여 공진주/비틂전단시험 삼축압축시험,자유단공진주시험을수행하여 탄성계수에 대한 여러 영향요소를 검토하였다. 보조기층 재료의 탄성계수에 대한 하중주파수 및 하중반복횟수의 영향은 매우 작은 것으로 평가되었으며 공학적 관점에서 무시가능 할 것으로 생각된다 보조기층 재료의 탄성계수는 구속응력과 변형률 크기에 대단히 큰 영향을 받는 것으로 나타났고, 대표적인 정규화탄성계수 감소곡선과 구성모델을 제안하였다.

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