Showing papers on "Representative elementary volume published in 2016"

Anm: a geometrical model for the composite structure of mortar and concrete using real-shape particles

Abstract: The composite geometrical structure of mortar composites can be represented by a model consisting of sand embedded in a cement paste matrix and the structure of concrete by gravel embedded in a mortar matrix. Traditionally, spheres have often been used to represent aggregates (sand and gravel), although the accuracy of properties computed for structures using spherical aggregates as inclusions can be limited when the property contrast between aggregate and matrix is large. In this paper, a new geometrical model is described, which can simulate the composite structures of mortar and concrete with real-shape aggregates. The aggregate shapes are either directly or statistically taken from real particles, using a spherical harmonic expansion, where a set of spherical harmonic coefficients, a nm , is used to describe the irregular shape. The model name of Anm is taken from this choice of notation. The take-and-place parking method is employed to put multiple irregular particles together within a pre-determined empty container, which becomes a representative volume element. This representative volume element can then be used as input into some kind of computational material model, which uses other numerical techniques such as finite elements to compute properties of the Anm composite structure.

Micromechanical Modeling of Fiber-Reinforced Composites with Statistically Equivalent Random Fiber Distribution

Abstract: Modeling the random fiber distribution of a fiber-reinforced composite is of great importance for studying the progressive failure behavior of the material on the micro scale. In this paper, we develop a new algorithm for generating random representative volume elements (RVEs) with statistical equivalent fiber distribution against the actual material microstructure. The realistic statistical data is utilized as inputs of the new method, which is archived through implementation of the probability equations. Extensive statistical analysis is conducted to examine the capability of the proposed method and to compare it with existing methods. It is found that the proposed method presents a good match with experimental results in all aspects including the nearest neighbor distance, nearest neighbor orientation, Ripley’s K function, and the radial distribution function. Finite element analysis is presented to predict the effective elastic properties of a carbon/epoxy composite, to validate the generated random representative volume elements, and to provide insights of the effect of fiber distribution on the elastic properties. The present algorithm is shown to be highly accurate and can be used to generate statistically equivalent RVEs for not only fiber-reinforced composites but also other materials such as foam materials and particle-reinforced composites.

Discrete element method for generating random fibre distributions in micromechanical models of fibre reinforced composite laminates

Abstract: A new approach is presented for generating random distribution of fibres in the representative volume element (RVE) of fibre reinforced composite laminates. The approach is based on discrete element method (DEM) and experimental data of fibre diameter distribution. It overcomes the jamming limit appeared in previous methods and is capable of generating high volume fractions of fibres with random distributions and any specified inter-fibre distances. Statistical analysis is then carried out on the fibre distributions generated within the RVEs, which show good agreement with experiments in all statistics analysed. The effective elastic properties of the generated RVEs are finally analysed by finite element method, which results show more reasonable agreement with the experimental results than previous methods.

Micromechanics-based viscoelastic analysis of carbon nanotube-reinforced composites subjected to uniaxial and biaxial loading

Abstract: Viscoelastic response of carbon nanotubes (CNTs) reinforced polyimide nanocomposites subjected to the action of uniaxial and biaxial loads is studied using a micromechanical model based on the unit-cell method. The developed micromechanical model is simple and efficient, and provides closed-form expressions for the effective viscoelastic response of nanocomposites. The representative volume element (RVE) of nanocomposites consists of three phases including continuous CNTs, polyimide matrix and interphase. The state of dispersion of CNTs into the polymer matrix is considered to be random. The obtained elastic and viscoelastic responses are found to be in good agreement with those predicted through other methods and experimental data. The model is then used to study the effects of interphase materials (elastic and viscoelastic) on the creep behavior of nanocomposites. Also, the effects of stress level, CNT radius and interphase on the viscoelastic response of nanocomposites under uniaxial and equi-biaxial including transverse/transverse and longitudinal/transverse loading conditions are examined.

Computational modeling of dual-phase steels based on representative three-dimensional microstructures obtained from EBSD data

Abstract: The microstructure of dual-phase steels consisting of a ferrite matrix with embedded martensite inclusions is the main contributor to the mechanical properties such as high ultimate tensile strength, high work hardening rate, and good ductility Due to the composite structure and the wide field of applications of this steel type, a wide interest exists in corresponding virtual computational experiments For a reliable modeling, the microstructure should be included For that reason, in this paper we follow a computational strategy based on the definition of a representative volume element (RVE) These RVEs will be constructed by a set of tomographic measurements and mechanical tests In order to arrive at more efficient numerical schemes, we also construct statistically similar RVEs, which are characterized by a lower complexity compared with the real microstructure but which represent the overall material behavior accurately In addition to the morphology of the microstructure, the austenite–martensite transformation during the steel production has a relevant influence on the mechanical properties and is considered in this contribution This transformation induces a volume expansion of the martensite phase A further effect is determined in nanoindentation test, where it turns out that the hardness in the ferrite phase increases exponentially when approaching the martensitic inclusion To capture these gradient properties in the computational model, the volumetric expansion is applied to the martensite phase, and the arising equivalent plastic strain distribution in the ferrite phase serves as basis for a locally graded modification of the ferritic yield curve Good accordance of the model considering the gradient yield behavior in the ferrite phase is observed in the numerical simulations with experimental data

Analysis of mechanical properties of carbon nanotube reinforced polymer composites using multi-scale finite element modeling approach

Abstract: In this paper, a multiscale finite element (FE) modeling approach is proposed for studying the pinhole defects in CNT reinforced polymer composites. Two configurations of CNT i.e. armchair (5, 5) and zigzag (9, 0) are selected for analyses wherein C–C bonds at atomic scale are modeled as Euler beam. The three dimensional solid elements are used for matrix material and square representative volume element (RVE) is constructed for the nanocomposite. These composite materials consist of aligned carbon nanotubes that are uniformly distributed within the matrix. The presence of chemical covalent bonding between functionalized CNT and matrix are modeled as elastic cross links. The influence of the pinhole defects on the nanocomposite are studied under axial load condition. It has been observed that with the increase in the number of atomic vacancies, the elastic modulus of the composite are reduced significantly. The effects of nanotubes chirality and composite stiffness ratio on the elastic properties are also analyzed in presence of atomic vacancies. It has been found from simulation results that zigzag nanotubes provides better reinforcement to composite compared to armchair nanotubes.

Modeling of the effect of particles size, particles distribution and particles number on mechanical properties of polymer-clay nano-composites: Numerical homogenization versus experimental results

Abstract: The main goal of this paper is to predict the elastic modulus of partially intercalated and exfoliated polymer-clay nano-composites using numerical homogenization techniques based on the finite element method. The representative volume element was employed here to capture nano-composites microstructure, where both intercalated exfoliated and clay platelets coexisted together. The effective macroscopic properties of the studied microstructure are obtained with two boundary conditions: periodic boundary conditions and kinematic uniform boundary conditions. The effect of particle volume fractions, aspect ratio, number and distribution of particles and the type of boundary conditions are numerically studied for different configurations. This paper investigate also the performance of several classical analytical models as Mori and Tanaka model, Halpin and Tsai model, generalized self consistent model through their ability to estimate the mechanical properties of nano-composites. A comparison between simulation results of polypropylene clay nano-composites, analytical methods and experimental data has confirmed the validity of the set results.