Micromechanics Of Composite Materials Research Articles

Carbon fibre lattice strain mapping via microfocus synchrotron X-ray diffraction of a reinforced composite

Synchrotron X-ray diffraction (SXRD) strain analysis is well established for high crystalline materials such as metals and ceramics, however, previously it has not been used in Carbon Fibre Reinforced Polymer (CFRP) composites due to their complex turbostratic atomic structure. This paper will present the feasibility of using SXRD for fibre orientation and lattice strain mapping inside CFRPs. In particular, it is the first time that the radial {002} and axial {100} strains of carbon fibre crystal planes have been analysed and cross-validated via numerical multi-scale simulation in a two-scale manner. In order to simplify the analysis and provide comparable estimates, an UniDirectional (UD) CFRP formed into a well-established humpback bridge shape was used. The lattice strain estimates obtained from SXRD showed localised stress concentrations and effectively matched the numerical results obtained by modelling. The mean absolute percentage differences between the two were 25.8% and 28.5% in the radial and axial directions, respectively. Differences between the two measurements are believed to originate from the non-uniform thermal history, forming geometry and tool-part interaction which leads to localised residual strains in the laminate which are unable to be fully captured by the numerical simulation performed. The carbon fibre microstructures of the inner plies adjacent to the tool were found to be significantly influenced by these factors and therefore the largest errors were observed at these locations. The approach presented has significant promise and implications for research into the micromechanics of composite materials and areas for future improvement have been outlined. • First quantification of micro-scale lattice strain in Carbon Fibre Reinforced Polymers (CFRPs). • Microfocus Synchrotron X-ray diffraction used to quantify microstructural changes. • Effective match between experimental lattice strain and simulations. • Errors/uncertainties and improvements identified to overcome challenges associated with the turbostratic structure of CFRPs.

In-depth study of the microstructure of bamboo fibres and their relation to the mechanical properties

The mechanical properties of bamboo technical fibre, from the species Guadua angustifolia, have been studied showing values of strength up to 800 MPa and E-modulus up to 43 GPa, proving their adequate tensile properties that make this natural fibre suitable as reinforcement in composite materials. To fully explore the good mechanical properties and to make an adequate use of this new reinforcement, it is indispensable to comprehensively understand the fibre behaviour as a function of the microstructure. Microscopic observations have provided us with an extensive knowledge of the complex microstructure of this natural fibre from the macroscale down to the microscale level where different features like the distribution of the elementary fibres within the fibre bundle, dimensions and layering pattern of the elementary fibres and the main microfibrillar angles could be measured. The Young’s modulus of the elementary fibre is analysed based on the micromechanics of composite materials, commonly used for unidirectional short fibre composites, and the fibre microstructure. The predicted results are in reasonable agreement with experimental data, showing the appropriateness of the model for describing the elementary fibre stiffness. Also, the failure modes of single fibres after tensile testing are analysed by microscopic observations, to have an indication of the stress development in the elementary fibres and the different failure mechanisms.

Research of the micromechanics of composite materials with polymer matrix failure under static loading using the acoustic emission method

Micromechanics of composite materials’ failure has been investigated under static loading by means of acoustic emission (AE) method. The results showed that for samples made of fiberglass with transverse fibers with respect to the applied load, the process of destruction both in the deformation parameters and in the parameters of total AE has two stages of damage accumulation. At the same time the parameter of total AE shows that the process of destruction begins 5–6% earlier than it is shown by the deformation parameter. Also the nature of the total AE change was analysed.

Ground Supported Short Fiber Reinforced Concrete Industry Plate

Abstract The present paper describes the elastic theory and Losberg Yield Line theory with plastic approach of solution. The finite element method for modeling of fiber reinforced concrete plates placed on Winkler foundation was used. There is presented Tsai and Pagano model within micromechanics of composite materials with short fibers. As the application problem it was used example of fiber-reinforced concrete industry plate. The strength obtained from elastic and plastic approach was compared and discussed in the conclusion of the paper.

Book Review On: Micromechanics of Composite Materials,

Book Reviews Book Review On: Micromechanics of Composite Materials, J. Appl. Mech. Nov 2013, 80(6): 066501 (1 pages) Paper No: JAM-13-1295 https://doi.org/10.1115/1.4025042 Published Online: September 6, 2013 Article history Received: July 18, 2013 Revision Received: July 18, 2013 Accepted: July 18, 2013

Prediction of Saturate Concrete Elastic Modulus by Considering Pores and Microcracks

The elastic modulus of saturate concrete is investigated in this paper. Based on micromechanics of composite materials, the elastic modulus of saturate concrete is obtained by considering the deformation of both pore and microcracks in concrete. It is assumed that concrete deformation includes the contribution of concrete matrix, pore water and microcracks. The water viscosity between microcracks and the further hydration of cement are both taken into account too in this paper. The comparison between the results by the model proposed in this paper and by existed experiments indicates a favorable agreement.

Meshless Local Petrov-Galerkin Formulation for Problems in Composite Micromechanics

In this paper we present the meshless local Petrov-Galerkin formulation for the generalized plane strain problem with specific emphasis on micromechanics of composite materials containing material discontinuities. The problem requires the introduction of an extra discrete degree of freedom, the out-of-plane uniform normal strain. The treatment of material discontinuity at the interface between the two phases of the composite is presented by means of direct imposition of interface boundary conditions. The meshless local Petrov-Galerkin method is used in the micromechanical model for predicting the elastic constants of the composite. To our knowledge, this is the first study in which the meshless local Petrov-Galerkin method is formulated for the so-called meshless local Petrov-Galerkin method based micromechanical analysis. Examples are presented to illustrate the effectiveness of the current method, and it is validated by comparing the results with available analytical and numerical solutions. The current method has the potential for use in micromechanics, especially for textile composites, where the meshing of the unit cell has been quite difficult.

Sensitivity of structural models of composite material to structural length scales

It is shown that there are models in the micromechanics of composite materials (so-called structural models of the second order) that are sensitive to structural change from micro-to nanoscale, whereas the model of effective constants (structural model of the first order) in the mechanics of composites does not have such a property. The structural model of elastic mixture is used as an example to reveal a distinction between the descriptions of the dispersion of plane waves propagating in fibrous micro-and nanocomposites of similar structure

Developing the mechanical models for nanomaterials

Abstract This paper revisits some of the well-known models in the mechanics of structurally heterogeneous media for the purpose of analysing their suitability to describe properties of nanomaterials (nanoparticles and nanocomposites) and their mechanical behaviour including statics, dynamics, stability and fracture. The paper gives an overview of existing knowledge on the nanomaterials and nanotechnologies, with the emphasis on their mechanical properties. A number of the macro-, meso- and micromechanical models are then reviewed and new nanomechanical models are suggested based on the knowledge accumulated within the micromechanics of composite materials. New directions of research in nanomechanics of materials are also pointed out. As an example of application of the developed models, the paper contains results of determination of the effective properties for particular nanocomposites.

Effective elastic moduli of nanocomposites with prescribed random orientation of nanofibers

Nanocomposite is modeled as a linearly elastic composite medium, which consists of a homogeneous matrix containing a statistically homogeneous random field of homogeneous prolate spheroidal nanofibers with prescribed random orientation. Estimation of effective elastic moduli of nanocomposites was performed by the version of effective field method (see for references Buryachenko VA. Multiparticle effective field and related methods in micromechanics of composite materials. Appl Mech Rev 2001;54:1–47) developed in the framework of quasi-crystalline approximation when the spatial correlations of inclusion location take particular ellipsoidal forms. The independent justified choice of shapes of inclusions and correlation holes provide the formulae of effective moduli which are symmetric, completely explicit and easily to use. The parametric numerical analyses revealed the most sensitive parameters influencing the effective moduli which are defined by the axial elastic moduli of nanofibers rather than their transversal moduli as well as by the justified choice of correlation holes, concentration and prescribed random orientation of nanofibers.

Effective elastic moduli of triply periodic particulate matrix composites with imperfect unit cells

In many problems the material may possess a periodic microstructure formed by the spatial repetition of small microstructures, or unit cells. Such a perfectly regular distribution, of course, does not exist in actual cases, although the periodic modeling can be quite useful, since it provides rigorous estimations with a priori prescribed accuracy for various material properties. Triply periodic particulate matrix composites with imperfect unit cells are analyzed in this paper. The multiparticle effective field method (MEFM) is used for the analysis of the perfect and imperfect periodic structure composites. The MEFM is originally based on the homogeneity hypothesis (H1) (see for details [Buryachenko, V.A., 2001. Multiparticle effective field and related methods in micromechanics of composite materials. Appl. Mech. Rev. 54, 1–47]) of effective field acting on the inclusions. In this way the pair interaction of different inclusions is taken directly into account by the use of analytical approximate solution. For perfect periodic structures the hypothesis (H1) is enough for estimation of effective properties. Imperfection of packing necessitates exploring some additional assumption called a closing hypothesis. The next imperfections are analyzed. (A) The probability of location of an inclusion in the center of a unit cell below one (missing inclusion). (B) Some hard inclusions are randomly replaced by the porous (modeling the complete debonding) with some probability. At first, one obtains general explicit integral representations of the effective elastic moduli and strain concentrator factors depending on three numerical solutions: for the perfect periodic structure, for the infinite periodic structure with one imperfection, and for the infinite periodic structure with two arbitrary located imperfections. The method proposed is general; it is not limited by concrete numerical scheme. No restrictions were assumed on both the concrete microstructure and inhomogeneity of stress fields in the inclusions. The inclusions of one kind are assumed to be aligned. The problem (A) is solved at the level of numerical results obtained in the framework of the hypothesis (H1). For the problem (B) the numerical results are obtained if the elastic inclusions (for example hard inclusions) are randomly replaced by another inclusion (for example by the voids modeling the complete debonding). The mentioned problems are solved by three methods. The first one is a Monte Carlo simulation exploring an analytical approximate solution for the binary interacting inclusions obtained in the framework of the hypothesis (H1). The second one is a generalization of the version of the MEFM proposed for the analysis of the perfect periodic particulate composites and based on the choice of a comparison medium coinciding with the matrix. The third method uses a decomposition of the desired solution on the solution for the perfect periodic structure and on the perturbation produced by the imperfections in the perfect periodic structure. All three methods lead to close results in the considered examples; however, the CPU times expended for the solution estimation by Monte Carlo simulation differ by a factor of 1000.

MECHANICAL PROPERTIES AND MORPHOLOGY OF POLYPROPYLENE/POLYSTYRENE BLENDS1*

In this article the relation between the morphology and macroscopic mechanical properties, i.e., stiffness and strength, of blends of polypropylene (PP) and polystyrene (PS) within the framework of micromechanics of composite materials was studied. Test results on tensile properties of immiscible PP/PS blends showed that the micromechanical models were valid for the prediction of elastic moduli. The Mori–Tanaka model would be a more effective method for designing materials in comparison with the Halpin–Tsai model and the modified mixture model because there is no restriction on the experimental parameters. The ultimate strengths were predicted in terms of pure component strength and composition. On the basis of the assumption that the ultimate strength will be controlled by the dispersed phase when the blend has more than the minimum fraction, the minimum fraction of dispersed phase calculated was found close to the phase inversion region determined by observing the blend morphologies. It is confirmed that the blends have a stationary mechanical property at the phase inversion region. Because the poor interface was not taken into account and an assumption was made for the failure of the entire dispersed phase, the model gave an overestimate for strength. *Contract grant sponsor: National Natural Science Foundation, China (Grant No. 59733070).

Multiparticle Effective Field and Related Methods in Micromechanics of Composite Materials

The numerous approaches used in micromechanics can be classified into four broad categories: perturbation methods, self-consistent methods of truncation of a hierarchy, variational methods, and the model methods. In detail we will consider the self-consistent methods applied to linear elastic problems, based on some approximate and closing assumptions for truncating of an infinite system of integral equations involved and their approximate solution. We consider multiparticle effective field methods, effective medium methods, the Mori-Tanaka method, differential methods and some others. This review article tends to concentrate on methods and concepts, their possible generalizations, and connections of different methods, rather than explicit results. In the framework of a unique scheme, we undertake an attempt to analyze the wide class of statical and dynamical, local and nonlocal, linear and nonlinear micromechanical problems of composite materials with deterministic (periodic and non-periodic) and random (statistically homogeneous and inhomogeneous, so-called graded) structures, containing coated or uncoated inclusions of any shape and orientation and subjected to coupled or uncoupled, homogeneous or inhomogeneous, external fields of different physical natures. The last section contains a discussion of prospects for future work. The article includes 540 references.

General structural equilibrium solutions of boundary-value problems in the mechanics of composites

Based on the theory of R-functions, we have constructed general structural equilibrium solutions for stresses identically satisfying both the differential equilibrium equations and the contact conditions at the three-identically boundaries of inhomogeneities of arbitrary shape. These solutions can be used in developing the next generation of numerical and analytical methods in the mechanics of inhomogeneous bodies and the micromechanics of composite materials.

Micromechanics of composite materials under compressive loading

A common thread joining many engineered materials used dominantly under compressive loading is the presence of a high modulus secondary phase, either fiber or particulate, embedded within a lower modulus matrix phase. To improve their toughness, a frictional or a less-than-coherent interface is strived for in the manufacture of these composite materials. To form a better understanding of the complex behavior of these materials, numerical and experimental models were developed by the U.S. Bureau of Mines that allowed a wide range of micromechanical and fracture behavior to be investigated under compressive loading. Finite element modeling illustrates the effects of interfacial friction and elastic moduli mismatch between the reinforcement and the matrix. Additional results show that packing density or non-dilute concentration of reinforcements have little effect upon the micromechanical behavior under uniaxial compressive loading. These numerical results were then substantiated by crack initiation experiments on model composite materials.

Reliability and micromechanics of Composite Materials

A methodology is proposed to evaluate the reliability of composites. Micromechanical analysis is utilized as a basis for the representation of the effects of constituent properties on global response. The analysis is then combined with the models of structural reliability to study the influence of micro-level material parameters on reliability of composites under static loadings.

Special Issue on Micromechanics of Composite Materials: Focus on Ukrainian Research—Introduction

Special Issue on Micromechanics of Composite Materials: Focus on Ukrainian Research—Introduction

A contribution to the application of photoelasticity to the micromechanics of composite materials

Photoelastic-model methods can prove advantageous for the investigation of microstresses in composite materials. Some two-dimensional investigations of this type are discussed and the extension of this work into three dimensions is considered. It is suggested that more than one approach to the three-dimensional problem may be practicable, and special attention is paid to obtaining the maximum amount of information from a sandwiched polariscope by means of light-intensity measurements. A cold-casting technique for the fabrication of composite models is also described.