Showing papers on "Micromechanics published in 2020"

Granular micromechanics model for damage and plasticity of cementitious materials based upon thermomechanics

Abstract: The mechanical behavior of monolithic cementitious materials is known to be significantly affected by their granular nature. This paper describes an approach to incorporate the effects of granulari...

Micromechanics of Composites: Multipole Expansion Approach

Abstract: Micromechanics of Composites: Multipole Expansion Approach is the first book to introduce micromechanics researchers to a more efficient and accurate alternative to computational micromechanics, which requires heavy computational effort and the need to extract meaningful data from a multitude of numbers produced by finite element software code. In this book Dr. Kushch demonstrates the development of the multipole expansion method, including recent new results in the theory of special functions and rigorous convergence proof of the obtained series solutions. The complete analytical solutions and accurate numerical data contained in the book have been obtained in a unified manner for a number of the multiple inclusion models of finite, semi- and infinite heterogeneous solids. Contemporary topics of micromechanics covered in the book include composites with imperfect and partially debonded interface, nanocomposites, cracked solids, statistics of the local fields, and brittle strength of disordered composites. Contains detailed analytical and numerical analyses of a variety of micromechanical multiple inclusion models, providing clear insight into the physical nature of the problems under study Provides researchers with a reliable theoretical framework for developing the micromechanical theories of a composite’s strength, brittle/fatigue damage development and other properties Includes a large amount of highly accurate numerical data and plots for a variety of model problems, serving as a benchmark for testing the applicability of existing approximate models and accuracy of numerical solutions

Buckling analyses of functionally graded graphene-reinforced porous cylindrical shell using the Rayleigh–Ritz method

Abstract: In this article, buckling analysis of a porous nanocomposite cylindrical shell reinforced with graphene platelets (GPLs) using first-order shear deformation theory is carried out. Internal pores and GPLs are scattered uniformly and/or nonuniformly in the thickness direction. The mechanical properties such as the effective modulus of elasticity through the thickness direction are computed by the modified Halpin–Tsai micromechanics approach, whereas density and Poisson ratio are in accordance with the rule of mixtures. The Rayleigh–Ritz method is employed to obtain a critical buckling load of the graphene-reinforced porous cylindrical shell. The accuracy of the obtained formulation is validated by comparing the numerical results with those reported in the available literature as well as with the software ABAQUS. Moreover, the effects of patterns of internal pores and GPLs distribution, GPLs weight fraction, density and size of internal pores, different boundary conditions, geometric factors such as mid-radius to thickness ratio and shape of graphene platelets on the buckling performance of the functionally graded graphene platelet-reinforced composite porous cylindrical shell are explored.

A coupled thermomechanics approach for frequency information of electrically composite microshell using heat-transfer continuum problem

Abstract: This article analyzes critical voltage and frequency information of functionally graded graphene nanoplatelets-reinforced composite (FG-GPLRC) porous cylindrical microshell embedded in piezoelectric layer, subjected to temperature gradient. The current non-classical model is capable of capturing the size dependency in the microshells by using only one material length scale parameter; moreover, the mathematical formulation of microshells based on the classical model can be recovered from the present model by neglecting the material length scale parameter. To satisfy temperature boundary conditions, the Fourier series solution is extracted. In addition, for the first time, thermal conductivity coefficients regarding each GPL’s distribution pattern are presented. The thermally equations are solved via Heun’s differential equation. The mechanical properties of FG-GPLRC layer are estimated based on modified Halpin–Tsai micromechanics and rule of mixtures. Hamilton’s principle is utilized to develop governing equations of motion and boundary conditions. Finally, an analytical solution is carried out based on Navier method to obtain critical voltage and frequency in the case of simply supported shell, whereas a semi-analytical solution is proposed based on differential quadrature method (DQM) for other boundary conditions. The results show that piezoelectric layer, graphene nanoplatelets’ (GPLs) distribution pattern, porosity distribution, difference gradient thermal, length scale parameter and GPL weight function play important roles on the natural frequency and critical voltage of the GPL porous cylindrical microshell coupled with piezoelectric actuator. The results of the current study are useful suggestions for the design of materials science, micro-electromechanical systems and nano-electromechanical systems such as nano-actuators and nano-sensors.

Processing, mechanical characterization, and micrography of 3D-printed short carbon fiber reinforced polycarbonate polymer matrix composite material

Abstract: The objective of this research is to perform the processing and mechanical characterization on 3D-printed high-temperature polymer (polycarbonate) reinforced with short carbon fiber (SCF) composite material fabricated with the help of fused filament fabrication process. For this study, different SCF volume fractions (3%, 5%, 7.5%, 10%) with varying printing speed (25, 50, 75 mm/s) are taken as the input variables. It was observed that tensile, flexural, compressive properties and micro-hardness were greatly affected by varying the input processing parameters. To find the orthotropic properties of 3D-printed specimens, tensile properties are analyzed on 0° in the X-Y plane, 90° in the X-Y plane, and 90° in Z-axis. Scanning electron microscopy (SEM) is performed to study the effect of fiber breakage, fiber distribution, fiber accumulation, and fiber length on the mechanical performance of the final part. After performing mechanical testing, investigation of microstructural behavior of tensile, flexural, and compressive samples is accomplished using SEM. From the micrograph analysis and mechanical testing, it was noticed that fiber behavior inside the composite has created a great influence in deciding the mechanical performance of the final part. Micromechanics and classical lamination theory phenomena are followed to determine the effective young’s modulus of 3D-printed samples mathematically. Printing direction and reinforcement percentage are found out to be the most influential parameters in deciding the final properties of 3D-printed specimens by using the statistical tool ANOVA. Response surface methodology is used to determine the optimum parameters to get good-quality print with SCF-reinforced PC.

Micromechanics Study on Actuation Efficiency of Hard-Magnetic Soft Active Materials

Abstract: Hard-magnetic soft active materials have drawn significant research interest in recent years due to their advantages of untethered, rapid and reversible actuation, and large shape change. These materials are typically fabricated by embedding hard-magnetic particles in a soft matrix. Since the actuation is achieved by transferring the microtorques generated on the magnetic particles by the applied magnetic field to the soft matrix, the actuation depends on the interactions between the magnetic particles and the soft matrix. In this paper, we investigate how such interactions can affect the actuation efficiency by using a micromechanics approach through the representative volume element simulations. The micromechanics reveals that particle rotations play an essential role in determining the actuation efficiency, i.e., the torque transmission efficiency. In particular, a larger local particle rotation in the matrix would reduce the effective actuation efficiency. Micromechanics simulations further show that the efficiency of the torque transmission from the particles to the matrix depends on the particle volume fraction, the matrix modulus, the applied magnetic field strength, as well as the particle shape. Based on the micromechanics simulations, a simple theoretical model is developed to correlate the torque transmission efficiency with the particle volume fraction, the matrix modulus, as well as the applied magnetic field strength. We anticipate this study on the actuation efficiency of hardmagnetic soft active materials would provide optimization and design guidance to the parameter determination for the material fabrication for different applications. [DOI: 10.1115/1.4047291]

A review on micromechanical methods for evaluation of mechanical behavior of particulate reinforced metal matrix composites

Abstract: Particulate reinforced metal matrix composites (PRMMC) are the most promising alternative for applications where the combination of high strength, elastic modulus, specific stiffness, strength-to-weight ratio and ductility is essential. Experimental investigation does not provide insightful information about microstructural aspects affecting the mechanical behavior of PRMMC, while the micromechanical methods can describe effectively. This paper presents the review on various analytical and computational micromechanical methods to evaluate the mechanical properties of particulate reinforced metal matrix composites. The effects of particle size, shape and orientation and interface strength on the mechanical behavior are presented. Stress–strain relationships, damage evolution, elastic and plastic deformations are also described. Computational micromechanical methods were found to provide better estimate of properties than analytical micromechanical methods. The order of preference among computational micromechanical methods is serial sectioning method, statistical synthetic method, multi-cell method, 2D real microstructure method and unit-cell method. However, serial sectioning method is highly expensive and demands lot of experimental and computational resources while the statistical synthetic method is economical and doesn’t require many resources. Therefore, statistical synthetic method can be a better choice for computational micromechanics of particulate reinforced metal matrix composites to evaluate the mechanical behavior without experimentation.

Effects of microvoids on strength of unidirectional fiber-reinforced composite materials

Abstract: Microvoids are common defects generated during manufacturing or prolonged services of composites. Depending on the local physical environment, microvoids may form as two types, namely, matrix voids and interfiber voids. These voids are known to have detrimental effects on the load bearing capacity of composites. However, it is relatively unknown the quantitative influence of these voids on the mechanical strength of composites. Without a direct mapping between defects and ply-level constitutive behavior, high-fidelity progressive failure predictions of composite structures is challenging. To bridge the gap, a micromechanics-based finite element framework is developed to investigate composites failure in the presence of three interfiber voids and the matrix void under transverse compression, tension, shearing, and longitudinal shearing. Mechanical strengths under these four loading modes are correlated with microstructural parameters including the void volume fraction, fiber-to-void number ratio, and void orientation. In general, at the same void volume fraction, the pentagonal interfiber void lowers strength the most, followed by the square interfiber void, the triangular interfiber void, and the circular matrix void. The weakening effect is strongly associated with stress concentration in the vicinity of voids, making the fiber-to-void number ratio an important parameter as it determines the local geometry. While void orientation shows limited influence, void size is found to play an important role. Results are expected to guide design and manufacturing of composite materials to achieve less critical flaws and higher strengths. Quantitative understanding of the criticality of voids of various configurations will also assist in-situ evaluation of composite materials.

Chiral metamaterial predicted by granular micromechanics: verified with 1D example synthesized using additive manufacturing

Abstract: Granular micromechanics approach (GMA) provides a predictive theory for granular material behavior by connecting the grain-scale interactions to continuum models. Here, we have used GMA to predict the closed-form expressions for elastic constants of macroscale chiral granular metamaterial. It is shown that for macroscale chirality, the grain-pair interactions must include coupling between normal and tangential deformations. We have designed such a grain-pair connection for physical realization and quantified with FE model. The verification of the prediction is then performed using a physical model of 1D bead string obtained by 3D printing. The behavior is also verified using a discrete model of 1D bead string.

Nonlocal bending and buckling of agglomerated CNT-Reinforced composite nanoplates

Abstract: The study presents a nonlocal bending and buckling analysis of agglomerated carbon nanotube-reinforced composite nanoplates resting on a Pasternak foundation. A two-parameter micromechanics model incorporating agglomeration is used to obtain the effective mechanical properties of the nanoplates. Using Hamilton's principle, the governing differential equations are derived based on the Eringen's nonlocal elasticity theory and the sinusoidal shear deformation theory. The deflection and critical buckling load of the nanoplates are obtained by Navier's analytical solution. To verify the approach, the results are compared with experimental, analytical, and numerical findings in the literature. Detailed parametric studies are then performed to discuss the influences of the following parameters on the static bending and buckling response of the nanoplates with agglomerated CNTs: degree of agglomeration, nonlocal material scale parameter, temperature, foundation properties, volume fraction of CNTs, and length-to-thickness aspect ratio for the plate.

Free vibration analysis of smart laminated carbon nanotube-reinforced composite cylindrical shells with various boundary conditions in hygrothermal environments

Abstract: Free vibration analysis is carried out for piezoelectric coupled carbon nanotube (CNT)-reinforced composite cylindrical shells with the influences of various boundary conditions and hygrothermal environmental conditions for the first time. A simple and effective non-iterative mathematical method is used to calculate the natural frequencies. The equilibrium equations of motion are obtained based on the first-order shear deformation shell theory with the coupling effects of piezoelectricity, temperature, and moisture, respectively based on the Maxwell equation, the Fourier heat conduction equation, and the Fickian moisture diffusion equation. The Mori-Tanaka micromechanics model is used to estimate the resulting material properties for a composite shell reinforced with CNTs. Presented methodology and attained results are validated with the existing results in the literature. The effects of the boundary conditions, lamination stacking sequence, volume fraction and orientation of CNTs, piezoelectricity, and geometry of the shell on the natural frequencies of the shell are investigated. A moderate effect of temperature/moisture variation on the natural frequencies is also observed. It is found that the influence of structural boundary conditions is more significant at higher CNT volume fractions and for thicker and shorter shells, and the piezoelectricity effect is more obvious at higher circumferential mode. The model and results presented in this study can be utilized to determine vibration characteristics of smart CNT-reinforced composites subjected to hygrothermal loading as well as mechanical loading.

Vibration of smart laminated carbon nanotube-reinforced composite cylindrical panels on elastic foundations in hygrothermal environments

Abstract: This paper studies vibration characteristics of smart laminated carbon nanotube-reinforced composite cylindrical panels resting on elastic foundations affected by hygrothermal environmental conditions. Effective material properties are estimated by the Mori-Tanaka micromechanics model. The motion equations for the vibration problem of the laminated composite panel are derived from the lamination theory and the first order shear deformation theory and take into consideration of the effects of elastic foundations, piezoelectricity, and temperature and moisture variations. Natural frequencies of panel vibration under various mechanical boundary conditions are computed using wave propagation approach. Parametric studies with the effects of boundary conditions, elastic foundations, panel geometry, carbon nanotube reinforcement, piezoelectricity, and hygrothermal conditions on frequencies are presented. Adding more ending supports, elastic foundations, and increase of nanotube volume fraction have increasing influence on the frequencies, while increase of panel length and decrease of its thickness, bonding piezoelectric materials, and increase of temperature and moisture lead to the decrease of frequencies.

Mechanical and fracture behavior of MWCNT/ZrO2/epoxy nanocomposite systems: Experimental and numerical study

Abstract: Funding information Indian Space Research Organisation, Grant/Award Number: ISRO/ RES/3/813/19-20 Abstract Although carbon nanotubes (CNTs) have displayed great potential for enhancement of multifunctional properties of a polymer matrix, still incorporation of CNTs with the polymeric matrices requires further improvement in terms synthesis, processing, functionalization etc. In this study, we decorated the surfaces of multi-walled CNTs (MWCNTs) by zirconium dioxide (ZrO2) nanoparticles to fully utilize former's remarkable mechanical properties, and then MWCNT/ZrO2-based hybrid epoxy nanocomposites (MNCs) were synthesized via a novel ultrasonic dual mixing (UDM) technique. The fracture strength and toughness of prepared MNCs were studied using a 3-point (3-P) single edge notch bending test. The surface morphology and fracture mechanisms were examined through field emission scanning electron microscope images of the fracture surfaces of samples of MNCs. Apart from experimental investigations, the mechanics of materials (MOM) and finite element (FE) models were also developed to predict the effective elastic properties of twoand three-phase MNCs. The mechanical response of MNC-based beams was studied using 3-P bending test via FE simulations and the numerical predictions are found to be in good agreement with the experimental results with maximum discrepancy of ~6% at 1 wt% loading of hybrid nanofillers. Our results also reveal that the fracture toughness of MNCs is improved by ~31% compared to the neat epoxy when 1.0 wt% loading of MWCNT/ZrO2 hybrid nanofillers is used to fabricate MNC.

High fidelity simulation of the mechanical behavior of closed-cell polyurethane foams

Abstract: The mechanical behavior of closed-cell foams in compression is analyzed by means of the finite element simulation of a representative volume element of the microstructure. The digital model of the foam includes the most relevant details of the microstructure (relative density, cell size distribution and shape, fraction of mass in the struts and cell walls and strut shape), while the numerical simulation takes into account the influence of the gas pressure in the cells and of the contact between cell walls and struts during crushing. The model was validated by comparison with experimental results on isotropic and anisotropic polyurethane foams and it was able to reproduce accurately the initial stiffness, the plateau stress and the hardening region until full densification in isotropic and anisotropic foams. Moreover, it also provided good estimations of the energy dissipated and of the elastic energy stored in the foam as a function of the applied strain. Based on the simulation results, a simple analytical model was proposed to predict the mechanical behavior of closed-cell foams taking into the effect of the microstructure and of the gas pressure. An example of application of the simulation tool is presented to design foams with an optimum microstructure from the viewpoint of energy absorption for packaging.

Computational micromechanics-based prediction of the failure of unidirectional composite lamina subjected to transverse and in-plane shear stress states:

Abstract: This paper presents a micromechanics-based 3D finite element model for predicting the damage initiation, propagation, and failure strength of TC33/Epoxy carbon fiber reinforced polymer (CFRP) unidi...

Nonlinear bending of elastically restrained functionally graded graphene nanoplatelet reinforced beams with an open edge crack

Abstract: This paper investigates the nonlinear bending behaviours of multilayer functionally graded graphene nanoplatelet-reinforced composite (FG-GPLRC) beams elastically restrained at both ends and with an open edge crack. The GPLs are uniformly distributed in each individual layer but follow a layer-wise variation along the thickness direction. The effective Young's modulus is predicted by the modified Halpin-Tsai micromechanics model while both the thermal expansion coefficient and Poisson's ratio are determined by the rule of mixture. The finite element method is employed to discretize the edge cracked beam, with a particular focus on the influences of the location and depth of the open edge crack on the nonlinear bending deflections of FG-GPLRC beams. It is found that adding a higher content of GPLs into the matrix, dispersing more GPLs near the top and bottom surfaces of the beam and increasing the elastic stiffness of the end constraints can effectively strengthen the beam stiffness hence considerably reduce the deflection. An increase in the crack depth ratio (CDR) and temperature rise weaken the structure and consequently lead to bigger deflections. The nonlinear bending performance of the beam is also found to be highly sensitive to the location of the crack.

Micro-CT-based micromechanics and numerical homogenization for effective elastic property of ultra-high performance concrete:

Abstract: A computational homogenization model using microstructures obtained from X-ray micro-CT is developed to estimate the porosity-based elastic properties of ultra-high performance concrete under freez...

Mechanical and fracture behavior of high strength steels under high strain rate deformation: Experiments and modelling

Abstract: By the automotive structure design, crashworthiness has become also an important issue so that a better understanding of plastic deformation of material at high velocity is necessary. The effects of strain rate on mechanical properties and fracture mechanism of ferritic-martensitic dual phase (DP) steel grades 780 and 1000 were investigated by both experiments and micromechanics based modeling. For the examined steels, quasi-static (0.001 s−1) and medium strain rate (0.5–1 s−1) tensile tests were carried out on a universal testing machine, while high strain rate (1500-2500 s−1) tests were performed by a Split-Hopkinson tensile bar. Afterwards, FE simulations using 2D representative volume elements (RVEs) were conducted for investigating microstructure effects on local deformation and damage of DP steels under varying strain rates. Flow curves of observed phase constituents at different strain rates were described by using a dislocation based theory and local chemical composition in combination with the Johnson-Cook (JC) hardening model. Furthermore, individual damage criteria based on the rate-dependent JC failure model were applied to describe the local crack mechanisms in DP microstructures. Calculated local stresses, strains and damage developments of deformed phases were studied. It was found that microstructure characteristics especially phase fraction differently affected the strain hardening and ductility of DP steels under low and high strain rate deformation. The damage initiation and propagation in microstructures of both steels at various strain rates predicted by RVE simulations were well correlated with the experimental results.

Homogenized modeling and micromechanics analysis of thin-walled lattice plate structures for brake discs:

Abstract: Periodic cellular structures, especially lattice designs, have potential to improve the cooling performance of brake disk system. In this paper, the method of two scales asymptotic homogenization w...

Multiscale numerical and experimental investigation into the evolution of process-induced residual strain/stress in 3D woven composite

Abstract: The process-induced residual strain and stress have a significant impact on the forming quality and service performance of 3D woven composites (3DWC). A multiscale model of 3DWC is developed to predict the residual strain and stress after the manufacturing process. Representative volume element at fiber scale and yarn scale are developed according to the geometric characteristics of 3DWC, and the modulus-development model is developed with respect to finite element based micromechanics method. An equivalent temperature load method is proposed to develop the cure shrinkage strain model. A thermal-chemical-mechanical coupling analysis of 3DWC curing process is carried out by integrating the abovementioned models, and the evolutions of temperature, degree of cure and residual strain/stress are obtained. Fiber Bragg Grating sensors are hybridized into the fabrics before Resin Transfer Molding (RTM) processing. The signal from sensors during RTM shows that the residual strain evolution is in good agreement with our modeling prediction.