• Title/Summary/Keyword: Micromechanics of failure

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Safety Evaluation of Carbon Fiber/Epoxy Composite Link Using Micromechanics of Failure Criterion (미시역학적 파손 기준을 이용한 탄소섬유/에폭시 복합재 링크의 안전성 평가)

  • Jae Ho Cha;Sung Ho Yoon
    • Composites Research
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    • v.36 no.3
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    • pp.154-161
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    • 2023
  • This study explored the feasibility of replacing a metal link with a carbon fiber/epoxy composite link and assessed its capacity to withstand a given load condition using failure criteria. The micromechanics of failure (MMF) criterion was employed to predict the failure mode of the composite material, and mechanical tests were conducted to obtain reference strength parameters for MMF. The findings revealed that the stress distribution was concentrated near the hole, and weaknesses were found around the hole and at the end of the link under bending conditions. Based on the failure index, matrix tensile failure was predicted at the end of the link, and fiber compression failure occurred near the hole. The methods and results obtained from this study can provide valuable guidelines for assessing the safety of composite materials under specific load conditions when replacing metal parts with carbon fiber/epoxy composites to achieve weight reduction.

Micromechanical failure analysis of composite materials subjected to biaxial and off-axis loading

  • Ahmadi, Isa
    • Structural Engineering and Mechanics
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    • v.62 no.1
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    • pp.43-54
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    • 2017
  • In this study, the failure behavior of composite material in the biaxial and off-axis loading is studied based on a computational micromechanical model. The model is developed so that the combination of mechanical and thermal loading conditions can be considered in the analysis. The modified generalized plane strain assumption of the theory of elasticity is used for formulation of the micromechanical modeling of the problem. A truly meshless method is employed to solve the governing equation and predict the distribution of micro-stresses in the selected RVE of composite. The fiber matrix interface is assumed to be perfect until the interface failure occurs. The biaxial and off-axis loading of the SiC/Ti and Kevlar/Epoxy composite is studied. The failure envelopes of SiC/Ti and Kevlar/Epoxy composite in off-axis loading, biaxial transverse-transverse and axial-transverse loading are predicted based on the micromechanical approach. Various failure criteria are considered for fiber, matrix and fiber-matrix interface. Comparison of results with the available results in the litreture shows excellent agreement with experimental studies.

Prediction of Fatigue life of Composite Laminates using Micromechanics of Failure (미시역학적 파손이론을 이용한 복합재 적층판의 피로수명 예측)

  • Jin, Kyo-Kook;Ha, Sung-Kyu;Kim, Jae-Hyuk;Han, Hoon-Hee
    • Composites Research
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    • v.24 no.1
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    • pp.10-16
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    • 2011
  • Many tests are required to predict the fatigue life of composite laminates made of various materials and having different layup sequences. Aiming at reducing the number of tests, a methodology was presented in this paper to predict fatigue life of composite laminates based on fatigue life prediction of constituents, i.e. the fiber, matrix and interface, using micromechanics of failure. For matrix, the equivalent stress model which is generally used for isotropic materials was employed to take care of multi-axial fatigue loading. For fiber, a maximum stress model considering only stress along fiber direction was used. The critical plane model was introduced for the interface of the fiber and matrix, but fatigue life prediction was ignored for the interface since the interface fatigue strength was presumed high enough. The modified Goodman equation was utilized to take into account the mean stress effect. To check the validity of the theory, the fatigue life of three different GFRP laminates, UDT[$90^{\circ}2$], BX[${\pm}45^{\circ}$]S and TX[$0^{\circ}/{\pm}45^{\circ}$]S was examined experimentally. The comparison between predictions and test measurements showed good agreement.

Micromechanical analysis on anisotropic deformation of granular soils (미시역학을 이용한 사질토의 이방적 변형 특성의 해석)

  • Jung, Young-Hoon;Chung, Choong-Ki
    • Proceedings of the Korean Geotechical Society Conference
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    • 2004.03b
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    • pp.129-136
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    • 2004
  • Anisotropic characteristics of deformation are important to understand the particular behavior in the pre-failure state of soils. Recent experiments shows that cross-anisotropic moduli of granular soils can be expressed by functions of normal stresses in the corresponding directions, which is closely linked to micromechanical characteristics of particles. Granular soils are composed of a number of particles so that the force-displacement relationship at each contact point governs the macroscopic stress-strain relationship. Therefore, the micromechanical approach in which the deformation of granular soils is regarded as a mutual interaction between particle contacts is one of the best ways to investigate the anisotropic deformation of soils. In this study, a numerical program based on the theory of micromechanics is developed. Modified Hertz-Mindlin model is adopted to represent the force-displacement relationship in each contact point for the realistic prediction of anisotropic moduli. To evaluate the model parameters, a set of analytical solutions of anisotropic moduli is derived in the isotropic stress condition. By comparing the analytical solutions with exact values, we confirm that the analytical solutions can be utilized to evaluate model parameters within the acceptable range of error of 10%.

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Effect of Intermediate Principal Stress on Rock Fractures

  • Chang, Chan-Dong
    • Journal of the Korean earth science society
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    • v.25 no.1
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    • pp.22-31
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    • 2004
  • Laboratory experiments were conducted in order to find effects of the intermediate principal stress of ${\sigma}_{2}$ on rock fractures and faults. Polyaxial tests were carried out under the most generalized compressive stress conditions, in which different magnitudes of the least and intermediate principal stresses ${\sigma}_{3}$ and ${\sigma}_{2}$ were maintained constant, and the maximum stress ${\sigma}_{1}$, was increased to failure. Two crystalline rocks (Westerly granite and KTB amphibolite) exhibited similar mechanical behavior, much of which is neglected in conventional triaxial compression tests in which ${\sigma}_{2}$ = ${\sigma}_{3}$. Compressive rock failure took the form of a main shear fracture, or fault, steeply dipping in ${\sigma}_{3}$ direction with its strike aligned with ${\sigma}_{2}$ direction. Rock strength rose significantly with the magnitude of ${\sigma}_{2}$, suggesting that the commonly used Mohr-type failure criteria, which ignore the ${\sigma}_{2}$ effect, predict only the lower limit of rock strength for a given ${\sigma}_{3}$ level. The true triaxial failure criterion for each of the crystalline rocks can be expressed as the octahedral shear stress at failure as a function of the mean normal stress acting on the fault plane. It is found that the onset of dilatancy increases considerably for higher ${\sigma}_{2}$. Thus, ${\sigma}_{2}$ extends the elastic range for a given ${\sigma}_{3}$ and, hence, retards the onset of the failure process. SEM inspection of the micromechanics leading to specimen failure showed a multitude of stress-induced microcracks localized on both sides of the through-going fault. Microcracks gradually align themselves with the ${\sigma}_{1}$-${\sigma}_{2}$ plane as the magnitude of ${\sigma}_{2}$ is raised.

Micromechanical Superplastic Model for the Analysis of Inhomogeneous Deformation in Heterogeneous Microstructure (비균일 조직에 따른 불균일 변형 해석을 위한 미시역학적 초소성 모텔)

  • Kim, Tae-Won
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.12
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    • pp.1933-1943
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    • 2001
  • A micromechanical model is presented for superplasticity in which heterogeneous microstructures are coupled with deformation behavior. The effects of initial distributions of grain size, and their evolutions on the mechanical properties can be predicted by the model. Alternative stress rate models such as Jaumann rate and rotation incremental rate have been employed to analyze uniaxial loading and simple shear problems and the appropriate modeling was studied on the basis of hypoelasticity and elasto-viscoplasticity. The model has been implemented into finite element software so that full process simulation can be carried out. Tests have been conducted on Ti-6Al-4V alloy and the microstructural features such as grain size, distributions of grain size, and volume fraction of each phase were examined for the materials that were tested at different strain rates. The experimentally observed stress-strain behavior on a range of initial grain size distributions has been shown to be correctly predicted. In addition, the effect of volume fraction of the phases and concurrent grain growth were analyzed. The dependence of failure strain on strain rate has been explained in terms of the change in mechanism of grain growth that occurs with changing strain rate.

Evaluation of Structural Performance of RC Beams retrofitted PVA Fiber to the Change of Replacement Ratio of Recycled Fine Aggregates and Blast Furnace Slag (고로슬래그 미분말 및 순환잔골재를 적용한 PVA섬유 보강 철근콘크리트 보의 구조성능 평가)

  • Ha, Gee-Joo;Yi, Dong-Ryul;Ha, Jae-Hoon
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.34 no.8
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    • pp.3-11
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    • 2018
  • In this study, total nine R/C beams, designed by the PVA Fiber with ground granulated blast furnace slag and recycled fine aggregate were constructed and tested under monotonic loading. In the material development, micromechanics was adopted to properly select the optimized range of the composite based on steady-state cracking theory and experimental studies on the matrix and interracial properties. Experimental programs were carried out to improve and evaluate the structural performance of the test specimens: the load-displacement, the failure mode, the maximum strength, and ductility capacity were assessed. Test results showed that test specimens (BSPR-20, 40) was increased the maximum load carrying capacity by 3~6% and the ductility capacity by 9~14% in comparison with the standard specimen (BSS). And the specimens (BSPR-60, 80, 100) was decreased the maximum load carrying capacity by 0~4% and the ductility capacity by 79% in comparison with the standard specimen (BSS) respectively.

Evaluation of cyclic fracture in perforated beams using micromechanical fatigue model

  • Erfani, Saeed;Akrami, Vahid
    • Steel and Composite Structures
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    • v.20 no.4
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    • pp.913-930
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    • 2016
  • It is common practice to use Reduced Web Beam Sections (RWBS) in steel moment resisting frames. Perforation of beam web in these members may cause stress and strain concentration around the opening area and facilitate ductile fracture under cyclic loading. This paper presents a numerical study on the cyclic fracture of these structural components. The considered connections are configured as T-shaped assemblies with beams of elongated circular perforations. The failure of specimens under Ultra Low Cycle Fatigue (ULCF) condition is simulated using Cyclic Void Growth Model (CVGM) which is a micromechanics based fracture model. In each model, CVGM fracture index is calculated based on the stress and strain time histories and then models with different opening configurations are compared based on the calculated fracture index. In addition to the global models, sub-models with refined mesh are used to evaluate fracture index around the beam to column weldment. Modeling techniques are validated using data from previous experiments. Results show that as the perforation size increases, opening corners experience greater fracture index. This is while as the opening size increases the maximum observed fracture index at the connection welds decreases. However, the initiation of fracture at connection welds occurs at lower drift angles compared to opening corners. Finally, a probabilistic framework is applied to CVGM in order to account for the uncertainties existing in the prediction of ductile fracture and results are discussed.

Evaluation of Structural Performance of Steel Fiber Reinforced Concrete Beams using Industrial By-products and Recycled Fine Aggregates (산업부산물과 순환잔골재를 적용한 강섬유 보강 철근콘크리트 보의 구조성능 평가)

  • Ha, Gee-Joo;Yi, Dong-Ryul;Ha, Jae-Hoon
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.34 no.11
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    • pp.11-18
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    • 2018
  • In this study, seven R/C beams, designed by the steel fiber with ground granulated blast furnace slag and recycled fine aggregate were constructed and tested under monotonic loading. In the material development, micromechanics was adopted to properly select the optimized range of the composite based on steady-state cracking theory and experimental studies on the matrix and interracial properties. Experimental programs were carried out to improve and evaluate the structural performance of the test specimens: the load-displacement, the failure mode, the maximum strength were assessed. Test results showed that test specimens (BSSR-20, 40, 60, 80) were increased the maximum load carrying capacity by 2~9% and the ductility capacity by 10~22% in comparison with the standard specimen (BSS) respectively. And the specimens (BSSR-100) was decreased the maximum load carrying capacity by 5% and the ductility capacity by 44% in comparison with the standard specimen (BSS) respectively.

Micromechanical Analysis on Anisotropic Elastic Deformation of Granular Soils (미시역학을 이용한 사질토의 이방적 탄성 변형 특성의 해석)

  • 정충기;정영훈
    • Journal of the Korean Geotechnical Society
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    • v.20 no.5
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    • pp.99-107
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    • 2004
  • Anisotropic characteristics of deformation are important to understand the particular behavior in the pre-failure state of soils. Recent experiments show that cross-anisotropic moduli of granular soils can be expressed by functions of normal stresses in the corresponding directions, which is closely linked to micromechanical characteristics of particles. Granular soils are composed of a number of particles so that the force-displacement relationship at each contact point governs the macroscopic stress-strain relationship. Therefore, the micromechanical approach in which the deformation of granular soils is regarded as a mutual interaction between particle contacts is one of the best ways to investigate the anisotropic elastic deformation of soils. In this study, a numerical program based on the theory of micromechanics is developed. Generalized contact model for the irregular contact surface of soil particles is adopted to represent the force-displacement relationship in each contact point far the realistic prediction of anisotropic moduli. To evaluate the model parameters, a set of analytical solutions of anisotropic elastic moduli is derived in the isotropic stress condition. A detailed procedure to determine the model parameters is proposed with emphasis on the practical applicability of micromechanical program to analyze the elastic behavior of the granular soils.