Showing papers on "Micromechanics published in 2019"

Multiscale approach for three‐phase CNT/polymer/fiber laminated nanocomposite structures

Abstract: The free vibration analysis of laminated nanocomposite plates and shells using first-order shear deformation theory and the generalized differential quadrature method is presented. Each layer of the laminate is modeled as a three-phase composite. An example of such composite material is given by a polymeric matrix reinforced with carbon nanotubes (CNTs). CNTs enhance the mechanical properties of the polymer matrix and the nanocomposite is treated as an isotropic material; a micromechanics model is used to compute the engineering constants of the isotropic hybrid material. This approach based on the Eshelby–Mori–Tanaka scheme takes into account the agglomeration of the nanoparticles in the matrix. The second step consists in combining this enriched matrix with unidirectional and oriented reinforcing fibers to obtain a fibrous composite with improved mechanical features. The overall mechanical properties of each orthotropic ply are evaluated through different micromechanics approaches. Each technique is illustrated in detail and the transversely isotropic properties of the three-phase layers are completely defined. The effects of both CNTs agglomeration and the mass fraction of these particles are investigated comparing with the results obtained by various homogenization techniques. POLYM. COMPOS., 2017. © 2017 Society of Plastics Engineers

Consistent application of periodic boundary conditions in implicit and explicit finite element simulations of damage in composites

Abstract: This paper presents an implementation-dedicated analysis of Periodic Boundary Conditions (PBCs) for Finite Element (FE) models incorporating highly non-linear effects due to plasticity and damage. This research addresses fiber-reinforced composite materials modeled at micros-scale level using a Representative Volume Element (RVE), where its overall mechanical response is obtained via homogenization techniques. For the sake of clearness, a unidirectional ply with randomly distributed fibers RVE model is assumed. PBCs are implemented for implicit and explicit FE solvers, where conformal and non-conformal meshes can be used. The influence of applying PBCs in the reliability of the mechanical response under tension and shear loading is assessed. Furthermore, the Poisson effect and the consistency of damage and fiber debonding propagation through the periodic boundaries are reported as well as their impact on the homogenized results. Likewise, numerical aspects like computational performance and accuracy are evaluated comparing implicit- versus explicit-based solutions.

Multiscale modeling of the elastic moduli of CNT-reinforced polymers and fitting of efficiency parameters for the use of the extended rule-of-mixtures

Abstract: In this work, a bottom-up multiscale modeling approach is developed to estimate the effective elastic moduli of Carbon NanoTube (CNT)-reinforced polymer composites. The homogenization process comprises two successive steps, including an atomistic-based computational model and a micromechanics approach at the nano- and micro-scales, respectively. Firstly, the atomistic-based finite element model defines a cylindrical Representative Volume Element (RVE) that accounts for a carbon nanotube, the immediately surrounding matrix, and the CNT/polymer interface. The carbon-carbon bonds of the CNT are modeled using Timoshenko beams, whilst three-dimensional solid elements are used for the surrounding matrix. Through the application of four loading conditions, the RVEs are homogenized into transversely isotropic equivalent fibers by equating the associated strain energies. Secondly, the equivalent fibers are employed in a micromechanics approach to estimate the macroscopic response of non-dilute composites. This is performed using both the analytical Mori-Tanaka model and a computational RVE model with a hexagonal packing geometry. A wide spectrum of single- and multi-walled carbon nanotubes are studied, as well as two different polymeric matrices. Furthermore, the so-called efficiency parameters, imperative for the application of the simplified extended rule of mixtures, are characterized by polynomial expressions for practical filler contents. Finally, detailed parametric analyses are also provided to give insight into the sensitivity of the macroscopic response of CNT-reinforced polymer composites to microstructural features such as filler volume fraction, chirality or aspect ratio.

Simulation of the Mechanical Response of Thin-Ply Composites: From Computational Micro-Mechanics to Structural Analysis

Abstract: This paper provides an overview of the current approaches to predict damage and failure of composite laminates at the micro-(constituent), meso-(ply), and macro-(structural) levels, and their application to understand the underlying physical phenomena that govern the mechanical response of thin-ply composites In this context, computational micro-mechanics is used in the analysis of ply thickness effects, with focus on the prediction of in-situ strengths At the mesoscale, to account for ply thickness effects, theoretical results are presented related with the implementation of failure criteria that account for the in-situ strengths Finally, at the structural level, analytical and computational fracture approaches are proposed to predict the strength of composite structures made of thin plies While computational mechanics models at the lower (micro- and meso-) length-scales already show a sufficient level of maturity, the strength prediction of thin-ply composite structures subjected to complex loading scenarios is still a challenge The former (micro- and meso-models) provide already interesting bases for in-silico material design and virtual testing procedures, with most of current and future research focused on reducing the computational cost of such strategies In the latter (structural level), analytical Finite Fracture Mechanics models—when closed-form solutions can be used, or the phase field approach to brittle fracture seem to be the most promising techniques to predict structural failure of thin-ply composite structures

Multiscale modeling of carbon fiber- graphene nanoplatelet-epoxy hybrid composites using a reactive force field

Abstract: Numerous research efforts have been focused on developing lightweight epoxy-based composite materials that rival expensive metal alloys in aerospace structural components. Due to their high specific stiffness and strength, carbon fiber (CF)/graphene nanoplatelet (GNP)/epoxy hybrid composites are excellent candidates for this purpose. The objective of this study is to develop a multiscale modeling approach to predict the effective mechanical properties of a CF/GNP/epoxy composite material. The work-flow of this study involves molecular dynamics (MD) simulation with a reactive force field to predict the structure and behavior of the GNP/epoxy material at the molecular level and micromechanics to predict the mechanical properties of the CF/GNP/epoxy hybrid composite at the bulk level. The study provides evidence of an alignment behavior of phenyl rings in epoxy with the planar GNP surface at the interphase region. The results also indicate the validity of using a reactive force field as they compare well with experiment.

A new numerical approach and visco-refined zigzag theory for blast analysis of auxetic honeycomb plates integrated by multiphase nanocomposite facesheets in hygrothermal environment

Abstract: The current work suggests a mathematical model for the dynamic response of sandwich plates subjected to a blast load using a numerical method. The sandwich structure is made from an auxetic honeycomb core layer integrated by multiphase nanocomposite facesheets. The facesheets are composed of polymer–carbon nanotube (CNT)–fiber where the equivalent material properties of the multiphase nanocomposite layers are obtained using fiber micromechanics and Halpin–Tsai equations in hierarchy. The top and bottom layers are subjected to magnetic field and the material properties of them are assumed temperature and moisture dependent. The Kelvin–Voigt model is employed to consider the viscoelastic properties of the structure. The sandwich structure is rested on a viscoelastic foundation which is modeled by orthotropic visco-Pasternak medium. Based on refined zigzag theory (RZT), energy method and Hamilton’s principle, the motion equations are derived. A new numerical method, namely differential cubature method (DCM) in conjunction with Newmark method is utilized for obtaining the dynamic deflection of the structure for different boundary conditions. The effects of various parameters such as blast load, viscoelastic foundation, structural damping, magnetic field, volume fraction of CNTs, temperature and moisture changes, geometrical parameters of honeycomb layer and sandwich plate are considered on the dynamic deflection of the structure. The results show that the magnetic field to the facesheets can be considered as effective parameters to control the dynamic deflection. In addition, hygrothermal condition leads to increase of 24% in the dynamic displacement of system.

On micromechanics approach to stiffness and strength of unidirectional composites

Abstract: The purposes of this paper are sixfold. First, any micromechanics model for predicting elastic property (stiffness) of a composite is applicable to a reasonable prediction of a composite strength, ...

An equivalent elastoplastic damage model based on micromechanics for hybrid fiber-reinforced composites under uniaxial tension:

Abstract: A micromechanics-based equivalent elastoplastic damage model for both notch-sensitive and multiple cracking hybrid fiber reinforced composite is proposed in this study. In this model, the elastic m...

Thermo-mechanical behavior prediction of particulate reinforced shape memory polymer composite

Abstract: A micromechanics model based on thermal viscoelasticity constitutive relation is presented to investigate the thermal-mechanical behavior of particulate reinforced shape memory polymer composite (SMPC). Based on the thermomechanical constitutive relation assumption and linear elastic constitutive relation assumption, the effective properties of SMPC are studied by using a micromechanics method. Through analyzing the constitutive theories of polymer and multi-walled carbon nanotubes (MWCNTs), as well as the filling quality of particles, the generalized Maxwell model (GMM) combined with Mori-Tanaka theory is developed, and the thermo-mechanical cycle behavior of SMPC is studied emphatically. Moreover, a set of uniaxial tensile experiments, stress relaxation tests and thermal-mechanical cycle tests are performed to verify the developed model. Eventually, the developed model is validated using a simulated example and experiment to ensure its creditability.

Vibration and Buckling Characteristics of Functionally Graded Graphene Nanoplatelets Reinforced Composite Beams with Open Edge Cracks.

Abstract: This paper investigates the free vibration and compressive buckling characteristics of functionally graded graphene nanoplatelets reinforced composite (FG-GPLRC) beams containing open edge cracks by using the finite element method. The beam is a multilayer structure where the weight fraction of graphene nanoplatelets (GPLs) remains constant in each layer but varies along the thickness direction. The effective Young's modulus of each GPLRC layer is determined by the modified Halpin-Tsai micromechanics model while its Poisson's ratio and mass density are predicted according to the rule of mixture. The effects of GPLs distribution pattern, weight fraction, geometry, crack depth ratio (CDR), slenderness ratio as well as boundary conditions on the fundamental frequency and critical buckling load of the FG-GPLRC beam are studied in detail. It was found that distributing more GPLs on the top and bottom surfaces of the cracked FG-GPLRC beam provides the best reinforcing effect for improved vibrational and buckling performance. The fundamental frequency and critical buckling load are also considerably affected by the geometry and dimension of GPL nanofillers.

Effect of piezoelectric interphase on the effective magneto-electro-elastic properties of three-phase smart composites: A micromechanical study

Abstract: A unit cell-based micromechanical model is presented to investigate the effect of PZT-7A piezoelectric interphase on the effective magneto-electro-elastic properties of CoFe2O4 piezomagneti...

Micromechanical modeling of particle breakage of granular materials in the framework of thermomechanics

Abstract: The particle breakage of granular materials under compression is a phenomenon of great importance. In this paper, a micromechanically based model for the compression of crushable granular materials is developed in the framework of thermomechanics. Both the internal and dissipative energies in the model are derived using the micro–macro volume averaging approach to ensure that all parameters involved have concrete physical meanings. The particle breakage is quantified by the change of the maximum particle size, the size polydispersity and the fractal dimension of the gradation. Compared to other breakage models, there is a major difference that highlights the novelty of the proposed model: neither the ultimate particle size distribution, nor the evolution path of the gradation is predefined in the model. The initiation, evolution and the attenuation of the breakage can be determined by the maximum dissipation principle using thermomechanics and micromechanics. Finally, it is demonstrated that the proposed model can predict the stress dependence of the elastic bulk modulus, the size dependence of the yielding stress and the elastic–plastic-pseudoelastic phase transition of granular materials.

Multi-stage micromechanical modeling of effective elastic properties of carbon fiber/carbon nanotube-reinforced polymer hybrid composites

Abstract: A multi-stage hierarchical micromechanical approach is presented to predict the elastic properties of unidirectional carbon fiber (CF)-reinforced polymer hybrid composites containing carbon...

Compressive response of hybrid 3D woven textile composites (H3DWTCs): An experimentally validated computational model

Abstract: The compressive response of hybrid 3D woven textile composites (H3DWTCs) is studied experimentally and the results obtained are used to motivate the development of a mechanics model, implemented computationally. The H3DWTCs considered consist of carbon, glass and kevlar fiber tows and a polymer matrix material. The novelty of the modeling approach is to include the in-situ geometric imperfections of the microstructural level composite architecture, measured using high resolution Micro-CT methods, in the micromechanics model and to carefully relate the details of the macroscopic response to the microstructure. A detailed Micro-CT study of the failed specimens reveals details of the dominant failure mechanisms which include multiple and progressive kink banding and matrix damage, responsible for limiting compressive strength. In the numerical predictive model development, the Mohr–Coulomb (MC) criterion is used to model matrix compressive failure in combination with the smeared crack approach (SCA) in the surrounding matrix outside of fiber tows. The fiber tow is modeled as macroscopically homogeneous, but a two-scale method is developed that uses an analytical closed-form micromechanics model at each integration point of the homogenized fiber tow which allows to calculate the fiber and matrix stress states within a tow. The experimental results suggest that carbon fiber compressive strength dictates the initiation of kink banding failure in carbon tows, while glass fiber tow compressive strength dictates the maximum load attainable. This suggests that different aspects of the compressive response are related to constituent structural properties. The experimental results and observations are predicted by the computational model which is useful for structural applications where damage tolerance and strength allowables dictate the boundaries of the design envelope.

Molecular dynamics and micromechanics study of hygroelastic behavior in graphene oxide-epoxy nanocomposites

Abstract: The hygroelasticity of oxygen-functionalized graphene (GO)-epoxy nanocomposites is studied. Two different transversely isotropic nanocomposite molecular models are constructed: with uniformly distributed and interface-concentrated water molecules, respectively. The stress-strain curves and coefficients of moisture expansion (CMEs) are determined according to moisture content. The degradation of the GO/epoxy interface due to the infiltrated moisture is characterized by interfacial decohesion tests. The micromechanics model is used to derive new closed-form solutions for the effective elastic stiffness and CME of multi-phase composites with interfacial imperfections. Regardless of the moisture distribution, the overall hygroelastic behavior of nanocomposites clearly degrades upon moisture absorption.