Random Sequential Adsorption Method Research Articles

Finite element analysis of effect of grain orientation on the thermal conduction of h-BN ceramics

Study of thermal conduction process of ceramics by experimental and theoretical model analysis methods is complicated and non-intuitive. In this work, to analyze the influence mechanism of h-BN grain orientation on the thermal conduction of h-BN ceramics, new mesoscale finite element models considering the anisotropy in the thermal conductivity of h-BN grain were established based on random sequential adsorption method and periodic boundary condition. And the accuracy of the finite element models was verified by theoretical model and experimental results. The heat flux vector and temperature distributions intuitively show that the orientation of h-BN grains will significantly affect the thermal conduction process of the ceramics by affecting the heat flow path. The heat flow will propagate mainly along the “thermal conducting pathways” formed by the h-BN grains when the h-BN layer direction shows small angle with the external temperature difference direction, otherwise, h-BN grains will act as barriers to the heat conduction.

Study of the Effectiveness of the RVEs for Random Short Fiber Reinforced Elastomer Composites

The effectiveness of the representative volume elements (RVEs) established by a modified random sequential adsorption method for random short fiber reinforced elastomer composites (SFECs) was studied. The RVE is considered to be effective when the RVE’s fiber orientation is isotropic. And the effectiveness of the RVEs was verified by evaluating the mechanical properties in different loading directions based on the finite element method. The results show that the fiber number N=4000 can be regarded as a steady threshold for the isotropy of the fiber orientation in RVEs with various fiber aspect ratios and dilute volume fraction.

Development of the RSA method for random short fiber reinforced elastomer composites with large fiber aspect ratios

Two random sequential adsorption (RSA) methods for the generation of the representative volume element (RVE) were developed for the short fiber reinforced elastomer composites (SFECs) with large fiber aspect ratio. These two RSA methods use two different fiber intersection test methods respectively (the ‘straightforward method’ developed by Rahman and the method of Tian et al). Also, a new iteration method was developed to realize geometric periodicity. The maximum fiber fraction that can be reached by two RSA methods were obtained respectively and compared with the theoretical and experimental formulas by Evans and Gibson. The results show that the ‘straightforward method’ may result in misjudgments in some special cases, especially when the fiber aspect ratio is large. Therefore, the RSA method using the ‘straightforward method’ is not exactly a perfect RSA method. In contrast, there is no fiber overlap found in the RVEs established by the RSA method using the fiber intersection test method of Tian et al. Moreover, the maximum fiber volume fraction that can be generated by this RSA method is close to the theoretical limits when the fiber aspect ratio is larger than 50 and meets the requirement of common SFECs with large fiber aspect ratio. Therefore, the RSA method using the fiber intersection test method of Tian et al is considered to be suitable for the satisfactory generation of the RVE for SFECs with large fiber aspect ratios.

Numerically-aided 3D printed random isotropic porous materials approaching the Hashin-Shtrikman bounds

The present study introduces a methodology that allows to combine 3D printing, experimental testing, numerical and analytical modeling to create random closed-cell porous materials with statistically controlled and isotropic overall elastic properties that are extremely close to the relevant Hashin-Shtrikman bounds. In this first study, we focus our experimental and 3D printing efforts to isotropic random microstructures consisting of single-sized (i.e. monodisperse) spherical voids embedded in a homogeneous solid matrix. The 3D printed specimens are realized by use of the random sequential adsorption method. A detailed FE numerical study allows to define a cubic representative volume element (RVE) by combined periodic and kinematically uniform (i.e. average strain or affine) boundary conditions. The resulting cubic RVE is subsequently assembled to form a standard dog-bone uniaxial tension specimen, which is 3D printed by use of a photopolymeric resin material. The specimens are then tested at relatively small strains by a proper multi-step relaxation procedure to obtain the effective elastic properties of the porous specimens.

Elastic and plastic properties of epoxy resin syntactic foams filled with hollow glass microspheres and glass fibers

ABSTRACTRepresentative volume elements of syntactic foams with a random filling of short glass fibers and hollow glass microspheres in epoxy resin were established by a random sequential adsorption method. The fiber volume fraction was set at 4%, and the microsphere volume fraction range was from 5 to 30%. This numerical simulation was studied with ANSYS software. The influence on the elastic and plastic mechanical properties of syntactic foams of the microsphere volume fraction and relative wall thickness were investigated, and the plastic strain evolution process in the composites was analyzed. The results show that the compressive yield limit and Young's modulus values of the syntactic foams decreased with increasing microsphere volume fraction when the microsphere relative wall thickness was 0.02, but these properties were enhanced with increasing microsphere volume fraction when the relative wall thickness exceeded 0.04. The specific strength and tangent modulus values of the composites increased with increasing microsphere volume fraction. In addition, we observed that the yield stress, Young's modulus, and tangent modulus values of the syntactic foams were obviously enhanced by the addition of glass fibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44188.

Monte carlo study of the percolation in two-dimensional polymer systems

The structure of a two-dimensional film formed by adsorbed polymer chains was studied by means of Monte Carlo simulations. The polymer chains were represented by linear sequences of lattice beads and positions of these beads were restricted to vertices of a two-dimensional square lattice. Two different Monte Carlo methods were employed to determine the properties of the model system. The first was the random sequential adsorption (RSA) and the second one was based on Monte Carlo simulations with a Verdier-Stockmayer sampling algorithm. The methodology concerning the determination of the percolation thresholds for an infinite chain system was discussed. The influence of the chain length on both thresholds was presented and discussed. It was shown that the RSA method gave considerably lower thresholds for longer chains. This behavior can be explained by a different pool of chain conformations used in the calculations in both methods under consideration. FigureThe percolation cluster (in red) in the system consisting of long flexible chains

Prediction on macroscopic elastic properties of interphase-contained long-fiber-reinforced composites and multiple nonlinear regression analysis

A convenient method to predict the macroscopic elastic performance of composite containing interphase was developed in this paper based on a new modified random sequential adsorption method and multiple nonlinear regression analysis. First, a three-phase micromechanical model with randomly distributed fibers was established with a new modified random sequential adsorption method named the Moving Window Method. Second, the macroscopic elastic behaviors of T300/914C were predicted based on micromechanical parameters of constituent materials using energy method, and the influence of the randomness of fiber distribution on the prediction was analyzed. Third, the effects of interphase thickness, interphase modulus and Poisson’s ratio on the macroscopic elastic properties of the composite were studied by changing these interphase micromechanical parameters gradually within certain ranges. Finally, the multiple nonlinear regression models that describe the relationship between the macroscopic elastic properties of T300/914C and micromechanical characteristic parameters of the interphase were established using a limited number of data from numerical simulation. Results indicate that the relative errors for the longitudinal modulus and the major Poisson's ratio are within ±1% while for the transverse modulus, shear modulus and Poisson’s ratio at cross section, the relative errors are within 5%.

Note: Percolation in two-dimensional flexible chains systems

The structure of a two-dimensional film formed by adsorbed polymer chains was studied by means of Monte Carlo simulations. The polymer chains were represented by linear sequences of lattice beads and positions of these beads were restricted to vertices of a two-dimensional square lattice. Two different Monte Carlo methods were employed to determine the properties of the model system. The first was the random sequential adsorption (RSA) and the second one was based on Monte Carlo simulations with a Verdier-Stockmayer sampling algorithm. The methodology concerning the determination of the percolation thresholds for an infinite chain system was discussed. The influence of the chain length on both thresholds was presented and discussed. It was shown that the RSA method gave considerably lower thresholds for longer chains. This behavior can be explained by a different pool of chain conformations used in the calculations in both methods under consideration.