Mechanical characterization of hexagonal boron nitride nanocomposites: A multiscale finite element prediction (original) (raw)
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Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2020
The mechanical response of two-dimensional nanostructures may be significantly affected by their size. In this work, a molecular structural mechanics model is developed and is implemented in order to predict the nanomechanical behavior and calculate the corresponding elastic properties of hexagonal boron nitride sheets and describe their size-dependence. The finite element approach utilizes appropriate spring-like elements for the modeling of interactions between atoms within the hexagonal boron nitride structure, the stiffness constants of which are obtained by the molecular mechanics theory. Adopting conventional finite element techniques, the global stiffness matrix of the structure of a desired sheet size can be assembled. Applying appropriate boundary conditions, the governing equilibrium static equation can be solved and the elastic mechanical properties as Young's modulus, shear modulus, and Poisson's ratio of the structure can be calculated. Fitting the results of the mechanical properties calculated by the finite element analysis, analytical-empirical equations are proposed for their direct prediction for an hexagonal boron nitride sheet having the size parameters of the structure as independent variables.
Evaluations of Young's Modulus of Boron Nitride Nanotube Reinforced Nano-composites
Procedia Materials Science, 2014
Boron Nitride Nanotubes (BNNTs) possess extremely high stiffness and strength and may provide the ultimate reinforcing materials for the development of nano-composites. In this paper, the Young's modulus of BNNT based composites are evaluated using a 3-D nanoscale representative volume element (RVE) based on continuum mechanics and using the finite element method (FEM). Formulas to extract the Young's modulus from solutions for the RVE are derived, based on the elasticity theory. An extended rule of mixtures, based on the strength of materials theory for estimating the effective Young's modulus in the axial direction of the RVE, is applied for comparisons with the numerical solutions based on the elasticity theory. It is observed that with additions of 5% of volume fraction of the BNNTs in a matrix of various materials, the strength of the composite can increases by an amount 20-55% depending on material of matrix, suggesting possible use of BNNT as reinforcing material to strengthen the matrix material in composite.
Elastic moduli of boron nitride nanotubes based on finite element method
Journal of Mechanics of Materials and Structures, 2018
Boron nitride nanotubes (BNNTs) possess superior thermal conductivity and mechanical/electrical properties, and are a suitable and favourable reinforcement for binanocomposites. Experimental studies on nanoscale materials are time-consuming, costly, and require accurate implementation. Therefore, a threedimensional finite element (FE) model of a space-frame structure is proposed for BNNTs, which is based on molecular structural mechanics. The effects of length, chirality, diameter, and defect on the elastic moduli of BNNTs are investigated. The results show that defects in the nanotubes decrease the mechanical properties. The values of the Young's modulus and shear modulus of BNNTs without defects change from 1.022 TPa to 1.042 TPa and from 0.33 TPa to 0.536 TPa, respectively. It is found that, with increasing chirality and radius of BNNTs, the Young's modulus and shear modulus increase. As the length of zigzag and armchair BNNTs increases, the Young's modulus increases and the shear modulus decreases. Also, it was observed that by using the finite element method (FEM) based on molecular dynamics, one can accurately determine the mechanical properties of BNNTs. The results demonstrate that the proposed FE model is a valuable tool for studying the mechanical behaviour of BNNTs.
Development and Characterization of Boron-Nitride Reinforced Nickel Matrix Composites
MATEC Web of Conferences
In this work, pure nickel was reinforced with various contents of h-BN (4 & 8wt.%) and SiC (2, 4, 6 & 8wt.%) prepared via PM route. The synergistic effect of h-BN and SiC on mechanical and microstructural behaviour was investigated. The microstructure and crystal structure were characterized by scanning electron microscope and X-ray diffractometer. The density and microhardness were eveluated via He pycnometer and microhardness tester. SEM results revealed that the exfoliation reduced the particle size of h-BN from approximately 105 nm to 30-40 nm. Furthermore, the addition of h-BN and SiC improved the mechanical properties of the composite. The maximum hardness value of 420 HV was obtained for Ni-8BN-6SiC. This improvement in hardness was attributed to uniform dispersion and high hardness of h-BN and SiC. However, more addition of SiC (>6 wt.%) deteriorated the hardness of the composite due to generated porosity.
Mechanical properties of the hexagonal boron nitride monolayer: Ab initio study
Computational Materials Science, 2012
Using density functional theory (DFT) calculations we found that hexagonal boron nitride monolayer (h-BN) shows a non-linear elastic deformation up to an ultimate strength followed by a strain softening to the failure. To develop a continuum based model for such non-linear behavior, we proposed a method to study high order elastic constants of the 2D hexagonal structures. The continuum description of the elastic properties of monolayer h-BN is obtained using this method through ab initio density functional theory. This rigorous continuum description of the elastic response is formulated by expanding the elastic strain energy density in a Taylor series in strain truncated after the fifth-order term. we obtained a total of fourteen non-zero independent elastic constants for up to tenth-order tensor.
Mechanical properties of the hexagonal boron nitride monolayer:< i> Ab initio study
2012
Using density functional theory (DFT) calculations we found that hexagonal boron nitride monolayer (h-BN) shows a non-linear elastic deformation up to an ultimate strength followed by a strain softening to the failure. To develop a continuum based model for such non-linear behavior, we proposed a method to study high order elastic constants of the 2D hexagonal structures. The continuum description of the elastic properties of monolayer h-BN is obtained using this method through ab initio density functional theory.
Journal of materials science, 2002
The second and third order elastic constants and pressure derivatives of second order elastic constants of hexagonal boron nitride have been obtained using the deformation theory. The strain energy derived using the deformation theory is compared with the strain dependent lattice energy obtained from elastic continuum model approximation to get the expressions for second and third order elastic constants. Higher order elastic constants are a measure of anharmonicity of crystal lattice. The six second-order elastic constants and the ten non-vanishing third order elastic constants and six pressure derivatives of hexagonal boron nitride are obtained in the present work and are compared with available experimental values. The second order elastic constant C 11 which corresponds to the elastic stiffness along the basal plane of the crystal is greater than C 33 . Since C 33 being the stiffness tensor component along the c-axis of the crystal, this result is expected from a layer-like material like boron nitride (BN). The third order elastic constants of hexagonal BN are generally one order of magnitude greater than the second-order of elastic constants as expected of a crystalline solid. The pressure derivative dC 33 /dp obtained in the present study is greater than dC 11 /dp which indicates that the compressibility along c-axis is higher than that along ab-plane of hexagonal BN. C 2002 Kluwer Academic Publishers
Ceramics International, 2020
This present work investigated the mechanical properties and microstructure of h-BN based ceramic composites reinforced with CNTs and GNPs. Accordingly, two different batches of pure h-BN, h-BN/0.1 wt%CNTs and h-BN/ 0.1 wt% GNPs were prepared through a high energy mixer mill to gain a uniform dispersion of reinforcement with the initial stable CNTs or GNPs solution in ethanol. After drying the mixtures, the pure h-BN and also, two different composite components were directly inserted into the graphite mold and the sintering process was performed with the initial and final pressure of 10 and 50 MPa, respectively, at 1900°C, under the vacuum condition of 15-35 Pa. The relative density of the samples was calculated based on the Archimedes principle. The densification behavior of the samples showed the maximum amount of 98.31% for the theoretical density of the h-BN/GNPs composite. On the other hand, the minimum relative density of 96.41% was obtained for the h-BN/CNTs composite. The microstructure studies of the prepared sample showed the uniform distribution of GNPs in the h-BN layers; however, when the CNTs were added, some agglomerated area was found. Moreover, the fracture surface of all samples showed a laminar fracture as a result of the layer-by-layer structure of h-BN. The investigation of the mechanical properties of the prepared specimens also revealed the highest bending strength, fracture toughness and Vickers hardness of 199 MPa, 1.26 GPa and 3.62 MPa m −1/2 , respectively, which belonged to the h-BN/GNPs composite. In the case of CNTs, this trend exhibited lower amounts, probably due to the agglomeration of CNTs.