Molecular Dynamics Finite Element Method Research Articles

Tensile Stress Reduction and Strain Concentration of Epoxy Resin Caused by Heterogeneity: A Multiscale Approach Combining Molecular Dynamics Simulation and Finite Element Method.

In this study, we investigated the effect of heterogeneity on the mechanical properties of epoxy resin by combining coarse-grained molecular dynamics (CG-MD) and finite element method (FEM) simulations. To evaluate the heterogeneity effect in the uniaxial elongation, heterogeneous and homogeneous FEM models of micrometer-scale cubic epoxy resin were constructed. For the heterogeneous FEM model, parameters of nanometer-scale elements were determined by CG-MD simulations, where nanometer-scale blocks have different cross-linked structures. For the homogeneous FEM model, the averaged parameters were used for all elements. The calculated stress-strain (S-S) curves of the heterogeneous model exhibit similar tensile stress values when compared to the experimental data, whereas the homogeneous model yields notably higher values. Moreover, a clear strain concentration associated with the formation of the shear band-like structure was observed in the heterogeneous model and not in the homogeneous model.

Molecular dynamics simulation and finite element method investigation of PTFE/carbon fiber composite tribological properties

The mechanical parameters of polytetrafluoroethylene (PTFE), microstructures of carbon fiber (CF) and PTFE-CF interface were calculated based on the density function theory, molecular dynamics and finite element simulations. Then the friction models of GCr15-PTFE/CF composite were constructed, and the friction mechanisms of PTFE/CF composite were analyzed. The results show that the friction coefficients of composite materials containing different CF defect ratios are almost the same, indicating that the defect ratio has little influence on the friction coefficient. The position of CF in the PTFE matrix has a great impact on CF damage; the closer it is to the upper specimen during friction, the more serious the damage. In addition, the disordered structure was observed to have the most serious damage.

Transference Number Reinforced-Based Gel Copolymer Electrolyte for Dendrite-Free Lithium Metal Batteries.

The progress of electric vehicles is highly inhibited by the limited energy density and growth of dendrite Li in current power batteries. Breakthroughs and improvements in electrolyte chemistry are highlighted to directly address the above issues, namely, the development of electrolytes with a high lithium-ion transference number (tLi+), enabling one to effectively restrict the concentration polarization during repetitious cycling. Herein, we propose a novel ether-based copolymer-based gel polymer electrolyte (ECP-based GPE) by in situ copolymerization as an intriguing strategy to achieve a high tLi+ of ∼0.64. Molecular dynamics simulations and finite element method analyses illustrate the enhanced Li+ diffusion process (DLi+, ∼1.76 × 10-10 m2 s-1) in ECP-based GPE with a homogeneous electric potential accommodated around the lithium metal anode. Therefore, such a high-tLi+-based electrolyte renders a high reversibility of dendrite-free lithium plating/stripping at a high areal capacity (5 mA cm-2/5 mA h cm-2) in an Li||Li symmetric cell and facilitates superior cycling performances (over 1000 cycles) at a high rate (5 C) with a capacity retention of ∼91.1% in Li||LiFePO4 batteries, promoting the practical application of solid-state lithium metal batteries.

A comparative study of crack detection in nanobeams using molecular dynamics simulation, analytical formulations, and finite element method

The study of material behavior in the presence of defects is one of the studies that can help us recognize and predict material behavior. Studying the behavior of materials in nanoscale illuminates a broad view of the behavior of materials. A variety of studies are available for such a study: numerical, experimental, and quasi-experimental methods. Molecular dynamics is one of the methods that can be used to study the behavior of materials. The vibrational behavior of structures has been the focus of many researchers to analyze and investigate mortar materials' properties. The study of vibrational behavior at the nanoscale can give us a broad view of materials' properties. Therefore, in this study, we study nanowires' vibrational behavior in the presence of edge cracks using molecular dynamics. The influence of crack position and depth on the natural frequencies and shape of iron nanobeam modes with BCC crystal structure have been investigated. Clamped-Clamped boundary conditions with different cracks position and depth have been applied by simulating molecular dynamics. Also, the data obtained from molecular dynamics simulations have been compared with the finite element method and different crack models in one dimensional beams . In order to extract the shape of natural modes and frequencies by molecular dynamics method, FFT applied on the displacement history of nanobeam atoms after excitation of an amplitude in the center of nanobeam in x and y directions have been used. The crack models studied in this study were linear and rotational crack models on beams with Timoshenko theory. Molecular dynamics simulation data compared to other methods have shown a decrease in the value of natural frequencies in the presence of cracks. Also, finite element data and molecular dynamics are well matched. However, the molecular dynamics method has shown a more significant reduction in natural frequency values than finite element methods and various crack models with Timoshenko theory. We have also found that in molecular dynamics bribery, the initial excitation type of nanobeams is very useful in extracting nanobeam modes' shape.

A molecular dynamics simulation on the static calibration test of a revised thin-film thermopile heat-flux sensor

A revised thin-film thermopile heat-flux sensor with cooper-based heat sink is calibrated at a static calibration system that provides a stable heat flux source in the range of 0.1–10.0 MW/m2. The calibration results show that sensitivity coefficients (SCs) of the revised heat-flux sensor are quadratically dependent on surface temperatures, which is different from the linear SCs of original heat-flux sensors. A molecular dynamics simulation is applied to predict the thermal conductivity (TC) of thin-film thermal resistance layer and the interfacial thermal resistivity at the interface with film thickness and substrate material being considered. With the aid of the molecular dynamics simulation and finite element method, the reason for such a difference is analyzed to be the coupled effect of temperature-dependent thermal conductivity (TC) of thin-film thermal resistance layer and the interfacial thermal impedance at the interface.

Atomistic simulation of the uniaxial compression of black phosphorene nanotubes

We study through molecular dynamics finite element method with Stillinger-Weber potential the uniaxial compression of (0, 24) armchair and (31, 0) zigzag black phosphorene nanotubes with approximately equal diameters. Young's modulus, critical stress and critical strain are estimated with various tube lengths. It is found that under uniaxial compression the (0, 24) armchair black phosphorene nanotube buckles, whereas the failure of the (31, 0) zigzag one is caused by local bond breaking near the boundary.

Fracture properties of nanoscale single-crystal silicon plates: Molecular dynamics simulations and finite element method

The thickness- and chirality-dependent mixed-mode I-II critical stress strength factors (SIFs) and crack growth angles of single-crystal silicon (SCS) [1 0 0] and [1 1 0] plates are investigated using molecular dynamics (MD) simulations and finite element (FE) method based on the boundary layer model, respectively. The silicon-silicon (SiSi) bond in the FE method is modeled as a nonlinear Timoshenko beam based on the Tersoff potential (T3) for the first time, where all the parameters of the nonlinear beam are completely determined based on the continuum modeling. The present MD and FE results show that both critical SIFs and crack growth angles obviously depend on chiral angles, thicknesses and loading angles of SCS plates. Our FE results agree well with those from present MD simulations using the modified Tersoff potential. Checking against the SIFs of available results shows that present MD and FE results are reasonable. This study should be of great help for understanding thickness- and chirality-dependent fracture properties of SCS and designing silicon-based nanodevices.

Mode-I stress intensity factors of silicene, AlN, and SiC hexagonal sheets

The crack-tip displacement field and molecular dynamics finite element method with Tersoff potentials were used to find the mode-I stress intensity factors (SIF) of silicene, aluminum nitride (AlN), and silicon carbide (SiC) hexagonal sheets. Fracture properties of graphene and boronitrene are also included for comparison. It is found that KIct (KIc is mode-I critical SIF and t is the sheet’s thickness) of silicene, AlN, and SiC sheets are approximately 80, 66, and 47%; and 73, 64, and 45% smaller values of those of graphene for crack along the armchair and zigzag directions, respectively. The estimated fracture toughness of silicene is close to the experimental data of single-crystal silicon.

Compressive buckling of black phosphorene nanotubes: an atomistic study

We investigate through molecular dynamics finite element method with Stillinger-Weber potential the uniaxial compression of armchair and zigzag black phosphorene nanotubes. We focus especially on the effects of the tube’s diameter with fixed length-diameter ratio, effects of the tube’s length for a pair of armchair and zigzag tubes of equal diameters, and effects of the tube’s diameter with fixed lengths. Their Young’s modulus, critical compressive stress and critical compressive strain are studied and discussed for these 3 case studies. Compressive buckling was clearly observed in the armchair nanotubes. Local bond breaking near the boundary occurred in the zigzag ones under compression.

Bending of boron nitride nanotubes: An atomistic study

ABSTRACTThe present work investigates through molecular dynamics finite element method with Tersoff potential the buckling behavior of boron nitride (BN) armchair and zigzag nanotubes under bending. The critical bending buckling angle, moment, and curvature are studied and discussed with respect to the tube length-diameter ratios from 10 to 50. Effects of a Stone-Wales defect in the middle tube on the bending behavior are also examined. The bending buckling mechanism is governed by the local instabilities and bond breaking in the compressive zone of the tubes. Results are useful for the design of nanocomposites and nano-devices with BN nanotubes.

Atomistic simulation of the uniaxial tension of black phosphorene nanotubes

In the present work, the uniaxial tensile tests of 3 pairs black phosphorene nanotubes are simulated by molecular dynamics finite element method with Stillinger-Weber potential. Each pair contains an armchair black phosphorene nanotube and a zigzag one, which have approximately equal diameters. Three armchair black phosphorene nanotubes, namely (0, 15), (0, 19) and (0, 21); and three zigzag black phosphorene nanotubes, namely (20, 0), (26, 0) and (28, 0), are considered. We found that the Young's modulus of these tubes increases when their diameter increases. Their fracture stress and fracture strain are also investigated.

Effects of various defects on the mechanical properties of black phosphorene

The present work investigates the effects of seven types of defects on the mechanical properties of black phosphorene. Molecular dynamics finite element method with Stillinger-Weber potential is used to simulate the uniaxial tensile tests of the pristine and defective black phosphorene sheets. Young's modulus, fracture stress, and fracture strain of the pristine and defective black phosphorene sheets are estimated. Comparison of the influence of different types of defects on the mechanical response of black phosphorene is considered. Fracture mechanism of various defective black phosphorene sheets is also analyzed. It is found that effect of the defects on Young's modulus of black phosphorene is insignificant. In contrast, due to defects fracture stress and fracture strain can reduce up to 53% and 69%, respectively. Results provide a landscape on the mechanical properties of defective black phosphorene and are useful for the design of nanodevices with black phosphorene in future applications.

The chirality-dependent fracture properties of single-layer graphene sheets: Molecular dynamics simulations and finite element method

The chirality-dependent mixed-mode I-II fracture toughness and crack growth angles of single-layer graphene sheets are determined using molecular dynamics (MD) simulations and the finite element (FE) method based on the boundary layer model, respectively. The carbon–carbon bond in the FE method is equivalent to a nonlinear Timoshenko beam based on the Tersoff–Brenner potential. All the results of the present FE method agree well with those of our MD simulations performed using the REBO potential. The chiral crack angles of α = 0° (zigzag), 15°, 30° (or 90°, armchair), and 45° at different loading angles from 0° ≤ φ ≤ 90° (φ = 90° for mode I and φ = 0° for mode II) are studied. The present results show that both critical stress intensity factors (SIFs) and crack growth angles strongly depend on the chiral angle α, the dimensions [in two-dimensional (2D) or three-dimensional (3D) states], as well as the temperature, for a given loading angle φ. The critical equivalent SIFs change from 2.52 to 4.07 nN Å−3/2 in the 2D state and from 2.46 to 5.06 nN Å−3/2 in the 3D state at different loading angles. The SIFs are around one order of magnitude smaller than those of ordinary steel, which indicates that chiral graphene is remarkably brittle in contrast to its ultrahigh strength. These findings should be of great help in understanding the chirality-dependent fracture properties of graphene sheets and designing graphene-based nanodevices.

Characterization of interfacial delamination in multi-layered integrated circuit packaging

It is challenging to understand and predict interfacial delamination in multi-layered integrated circuit (IC) packaging due to the difficulties in experimentally quantifying the critical fracture energy of interfacial adhesion. This study takes a combined approach based on molecular dynamics (MD) simulation and finite element method (FEM) to characterize the interfacial fracture energy and predict delamination in the Cu/Ti/SiO2/Si multilayer systems. MD simulation is first conducted on each interface of the multiple layers at the atomistic level to obtain the material parameters such as the critical interfacial fracture energy that are required for the interfacial cohesive constitutive relation. Then, FEM is used to model and predict the interfacial delamination of the multi-layered system under indentation loading at the macroscale with the cohesive zone being considered around the delamination or crack tips. Finally, the indentation damage test is performed to validate the modeling results. The proposed combined modeling approach will have the potential to provide guidance in design and applications of IC packaging for improved stability and reliability.

Atomistic simulation of free transverse vibration of graphene, hexagonal SiC, and BN nanosheets

Free transverse vibration of monolayer graphene, boron nitride (BN), and silicon carbide (SiC) sheets is investigated by using molecular dynamics finite element method. Eigenfrequencies and eigenmodes of these three sheets in rectangular shape are studied with different aspect ratios with respect to various boundary conditions. It is found that aspect ratios and boundary conditions affect in a similar way on natural frequencies of graphene, BN, and SiC sheets. Natural frequencies in all modes decrease with an increase of the sheet’s size. Graphene exhibits the highest natural frequencies, and SiC sheet possesses the lowest ones. Missing atoms have minor effects on natural frequencies in this study.

Vibrational band structure of nanoscale phononic crystals

AbstractThe vibrational properties of two‐dimensional phononic crystals are studied with large‐scale molecular dynamics simulations and finite element method calculation. The vibrational band structure derived from the molecular dynamics simulations shows the existence of partial acoustic band gaps along the –M direction. The band structure is in excellent agreement with the results from the finite element model, proving that molecular dynamics simulations can be used to study the vibrational properties of such complex systems. An analysis of the structure of the vibrational modes reveals how the acoustic modes deviate from the homogeneous bulk behavior for shorter wavelengths and hints toward a decoupling of vibrations in the phononic crystal.

Mechanical properties of various two-dimensional silicon carbide sheets: An atomistic study

We investigate through molecular dynamics finite element method with Tersoff potential the mechanical properties of 13 SimCn sheets under uniaxial tension in the armchair and zigzag directions. It is found that the presence and dispersion of silicon atoms in SimCn sheets affect strongly the mechanical properties and the anisotropy of these sheets. The Young's modulus and fracture stress of the SimCn sheet decrease in general when the silicon concentration increases from 0 to 0.2. In contrast, the mechanical properties (Young's modulus, fracture stress, and fracture strain) increase slightly when the silicon concentration increases from 0.3 to 0.5 due to an increase of the degree of dispersion of silicon atoms in the SimCn sheet. The mechanical properties of the sheet are relatively high when the silicon concentration is low or silicon atoms are well dispersed.

Two dimensional nanoscale reciprocating sliding contacts of textured surfaces

Detailed behaviors of nanoscale textured surfaces during the reciprocating sliding contacts are still unknown although they are widely used in mechanical components to improve tribological characteristics. The current research of sliding contacts of textured surfaces mainly focuses on the experimental studies, while the cost is too high. Molecular dynamics(MD) simulation is widely used in the studies of nanoscale single-pass sliding contacts, but the CPU cost of MD simulation is also too high to simulate the reciprocating sliding contacts. In this paper, employing multiscale method which couples molecular dynamics simulation and finite element method, two dimensional nanoscale reciprocating sliding contacts of textured surfaces are investigated. Four textured surfaces with different texture shapes are designed, and a rigid cylindrical tip is used to slide on these textured surfaces. For different textured surfaces, average potential energies and average friction forces of the corresponding sliding processes are analyzed. The analyzing results show that “running-in” stages are different for each texture, and steady friction processes are discovered for textured surfaces II, III and IV. Texture shape and sliding direction play important roles in reciprocating sliding contacts, which influence average friction forces greatly. This research can help to design textured surfaces to improve tribological behaviors in nanoscale reciprocating sliding contacts.

Using molecular dynamics simulations and finite element method to study the mechanical properties of nanotube reinforced polyethylene and polyketone

Molecular dynamics simulations are used to study the mechanical behavior of single-walled carbon nanotube reinforced composites. Polyethylene and polyketone are selected as the polymer matrices. The effects of nanotube atomic structure and diameter on the mechanical properties of polymer matrix nanocomposites are investigated. It is shown that although adding nanotube to the polymer matrix raises the longitudinal elastic modulus significantly, the transverse tensile and shear moduli do not experience important change. As the previous finite element models could not be used for polymer matrices with the atom types other than carbon, molecular dynamics simulations are used to propose a finite element model which can be used for any polymer matrices. It is shown that this model can predict Young’s modulus with an acceptable accuracy.

OS0302-212 大規模数値解析を用いた充填ゴムの粘弾性特性に関する研究

Visco-elastic property of filled rubber is analyzed by large scale numerical simulations. Combining Coarse Grained Molecular Dynamics and large scale Finite Element Method, molecular scale interphase properties and nano-scale filler structure are considered in the analyses. Effect of filler-matrix interaction and filler dispersion are observed in the stress relaxation behavior of filled rubber composite.