Micromechanical Study Research Articles

Coupled Molecular Dynamics and Micromechanical Study of Interphase Effects in CNT-Reinforced Nanocomposites Considering RVE Aspect Ratio

Coupled Molecular Dynamics and Micromechanical Study of Interphase Effects in CNT-Reinforced Nanocomposites Considering RVE Aspect Ratio

Micro-mechanism study of charge transfer at heterojunction interface based on first-principles theory: MoS2/SnO2 as the prototype

Gas sensors made of semiconductor heterojunctions have excellent gas-sensitive properties. However, sufficient theoretical evidence is still needed to prove that heterojunction improve gas sensitivity of a single-material. A typical case is studied here: MoS2/SnO2 heterojunction absorption of NO2 is investigated by first-principles calculations, to explore the enhancing-mechanism. Interestingly, it is found that electron transfer not only occurs between the material surface of the heterojunction and gas, but also involves the substrate atoms transferring electrons to the gas molecules through the surface atoms. This finding fills the response mechanism of heterojunction gas sensors and provides a theoretical basis for experiments.

Micro-buckling resistant unidirectional glass fiber composites with excellent transverse and longitudinal flexural properties from cross-linking by nano-/micro-aramid fibers

This study aims at obtaining an effective structural design strategy for stronger and more reliable Unidirectional glass fiber (UD-GF) composites by in-situ formed cross-linking from randomly distributed nano-/micro- Aramid pulp (AP) fibers. The flexural strength and stiffness have shown substantial improvements in both the transverse and longitudinal directions due to the AP cross-linking and the “brick-slurry” structure. With AP of 8 g/m2, up to 60–70 % improvement in flexural strengths (both transverse and longitudinal directions) and up to 20–37 % improvement in “effective modulus” have been observed. The noticeable longitudinal improvements have been attributed to the resin reinforcement and interlayer cross-linking provided by ultra-thin AP interlayers, and the resultant improvement in micro-buckling resistance under compression. Since sparsely distributed nano-/micro-AP can be readily incorporated in pultrusion and pre-preg manufacturing processes, this study is not only important for micro-mechanism study, but also provides a plausible improvement in manufacturing.

A micromechanical study on sand − FRP interface subjected to cyclic loading

Fibre-reinforced polymer (FRP) is a promising composite to be used in construction in coastal and marine environments to resist seawater corrosion that deteriorates the properties of conventional civil engineering materials. A classical ground or seabed − structure interaction problem that is involved in the design of FRP structures, is however less understood when the soft nature of FRP is in subjection to the cyclic loadings from traffic, wind, wave and currents, causing penetration and abrasion at the soft FRP − soil interface. This study has downscaled the preceding problem into a micromechanical study at a benchmark sand grain − FRP interface. A large number of cyclic loading is applied, for the first time, at the sand − FRP composite interface, focusing on the development of the elastoplastic behaviour in the normal direction and the evolution of friction and energy dissipation in the tangential direction. The study combines the understanding from the tribology with the knowledge of civil engineering involved in the sand − FRP interaction, suggesting that a larger stick zone at the contact subjected to cyclic shearing is a key triggering of the simultaneous occurrence of the increased coefficient of friction and reduced damping ratio.

A micromechanical study on shear performance of unidirectional composites with randomly distributed fibers in the transverse cross‐section

AbstractThe properties of unidirectional (UD) composites has been investigated by analyzing their elastic and strength characteristics under shear loading. The UD fiber‐reinforced polymer (FRP) composites usually consist of fibers randomly dispersed throughout the cross‐section in the transverse direction which is generally not accounted for. A micromechanical model based on finite element analysis (FEA) approach is utilized here to examine these properties. The study begins by identifying micro scale unit cells or repetitive unit cells (RUCs) at the micro scale, as well as representative volume elements (RVEs). The distribution of fiber volume fraction (Vf) varies among various micro scale unit cells positioned in the transverse cross‐section. The elastic properties and strength are estimated by considering the properties of the matrix and fibers, and the configuration of micro scale unit cells, which feature a fiber arrangement which is categorized as hexagonal and varying Vf at different locations (from 0.35 to 0.75). However, the overall Vf for the UD composite remains constant at 0.65. Studies are also carried out with the random distribution of fibers at micro scale unit cells. The findings reveal that the random distribution of fibers significantly impacts the shear behavior of the composite. This investigation provides valuable insights into how the mechanical properties of the UD composite are subjective by the distribution of fiber, thereby contributing to the design and development of this light weight high‐performance material.Highlights Elastic and strength analysis of UD composites is presented. Emphasis is on fiber dispersion in transverse plane. Microscale unit cells, RUCs and RVE are identified. Studies are carried out based on micromechanical model. Influence of fiber distribution on shear behavior is investigated.

Micromechanical study of nano-cutting metal-ceramic WC/Cu by diamond tools

In this paper, the effect of the distribution of ceramic particles WC in Cu matrix on the nano-cutting behavior was investigated using molecular dynamics, and the cutting force, friction coefficient, machined surface quality, sub-surface damage depth, atomic displacement and internal defects were systematically studied, and the performance comparison at different cutting speeds was also investigated. It was found that due to the location of the WC phase, the overall removal of the material by the tool can be divided into the following three ways: When WC particles are above the cutting plane, there is less fluctuation in cutting forces and friction coefficients, and less impact on machined surface and subsurface damage; When the WC particles are below the cutting plane, the fluctuation of cutting force and friction coefficient is slow. Meanwhile, shallow craters are produced at the WC location; When the center of mass of WC particles is on the same level as the cutting plane, the cutting force and friction coefficient fluctuate drastically, the quality of the machined surface deteriorates sharply, and at the same time the hard particles pulled out by the tool remain on the machined surface. It was also found that the WC particles underwent different degrees of counterclockwise deflection in the three stages and caused a diversion of the atomic displacement in front of the tool. In addition, different degrees of dislocation plugging are formed between the WC and the tool at different positions, and the density of dislocation lines increases, which makes the substrate near the WC particles strengthened.

Micromechanism study on the influence of particle deposition angle on mechanical properties of sand

Micromechanism study on the influence of particle deposition angle on mechanical properties of sand

Micromechanical modeling and experimental study of the flexural properties of impregnated woven textile-reinforced concrete

As a high-performance composite material in construction, textile-reinforced concrete has been of interest in recent years. This study significantly contributes to the characterization of textile-reinforced concrete through an extensive experimental and analytical investigation, focusing on impregnated textile-reinforced concrete under flexural loading. For this purpose, two sets of experiments were conducted. The first set involved model input parameters tests, including the tensile test of epoxy resin and E-glass yarn, as well as the compression and flexural tests of concrete. The second set is related to validation tests, specifically focused on the flexural behavior of textile-reinforced concrete. Micromechanical frameworks were employed to model the flexural behavior of textile-reinforced concrete and a multiscale micromechanical model based on the classical lamination theory was developed to predict the load-deflection diagram of textile-reinforced concrete in the three-point bending test setup. The modeling results demonstrated a remarkable agreement between predictions and experimental data. Key performance indicators, including the first crack force, ultimate force, flexural modulus, and maximum deflection, were accurately predicted with errors of 2.4%, 6.1%, 11.1%, and 6.3%, respectively. Furthermore, from a parametric study, it is perceived that the flexural modulus of elasticity in textile-reinforced concrete is predominantly influenced by concrete properties, while the ultimate strength of textile-reinforced concrete is significantly affected by the properties of the impregnated fabric.

Micromechanical Analysis of GFRP Composite with Micro-Level Defects

Fiber-reinforced plastic (FRP) composites are subjected to micro-level defects such as fiber-matrix debond and/or matrix cracks after a period of their service due to the increasing brittleness of matrix material. Prediction of the degraded elastic properties of a lamina through micromechanical studies by incorporating micro-level defects gives an idea of the health condition of such structures. Due to the limitations of classical mathematical approaches in solving complex structures, numerical mathematical methods like the finite element method (FEM) can be employed. The present investigation deals with the micromechanical analysis of Glass fiber-reinforced plastic (GFRP) composite with micro-level defects to predict some of the elastic properties. The composite is idealized as an array of square unit cells, and the micromechanical behavior of one such unit cell is simulated in ANSYS software using the three-dimensional finite element method to predict Young’s moduli and Poisson’s ratios in principal material directions. The converged finite element solution for longitudinal modulus is validated by the rule of mixtures and the other properties using the Maxwell–Betti reciprocal theorem. Variations of Young’s moduli and Poisson’s ratios due to an incremental internal failure of composite such as low-level, medium-level, and high-level defects at an expected range of fiber volume fractions (50% - 60%) are evaluated and estimated the percentage degradation with respect to a corresponding defect-free composite.

A Micromechanical Study of Interactions of Cyanate Ester Monomer with Graphene or Boron Nitride Monolayer.

Polymer composites, hailed for their ultra-strength and lightweight attributes, stand out as promising materials for the upcoming era of space vehicles. The selection of the polymer matrix plays a pivotal role in material design, given its significant impact on bulk-level properties through the reinforcement/polymer interface. To aid in the systematic design of such composite systems, molecular-level calculations are employed to establish the relationship between interfacial characteristics and mechanical response, specifically stiffness. This study focuses on the interaction of fluorinated and non-fluorinated cyanate ester monomers with graphene or a BN monolayer, representing non-polymerized ester composites. Utilizing micromechanics and the density functional theory method to analyze interaction energy, charge density, and stiffness, our findings reveal that the fluorinated cyanate-ester monomer demonstrates lower interaction energy, reduced pull-apart force, and a higher separation point compared to the non-fluorinated counterpart. This behavior is attributed to the steric hindrance caused by fluorine atoms. Furthermore, the BN monolayer exhibits enhanced transverse stiffness due to increased interfacial strength, stemming from the polar nature of B-N bonds on the surface, as opposed to the C-C bonds of graphene. These molecular-level results are intended to inform the design of next-generation composites incorporating cyanate esters, specifically for structural applications.

Surface decoration of graphene oxide with tragacanth gum as a promising way to improve the mechanical properties of chitosan nanocomposite; experimental, micromechanical, and simulation study

The interfacial interaction of graphene oxide (GO) with the host polymer is of particular importance in the development of new nanocomposites with ultimate performance. In this perspective, the influence of functionalized GO with the tragacanth gum (TG) polysaccharide on the mechanical characteristic of chitosan (CS) biopolymer was investigated. Spectroscopic and microscopic analysis thoroughly confirmed the TG functionalization process of GO (TG-GO). The understanding of the reinforcement behavior of TG-GO in the host polymer (CS) was constructed by combination of tensile, micro-mechanical/structural testing, as well as molecular dynamic simulation of interfacial interaction. Our finding represented that this functionalization put a remarkable impact on the mechanical properties of CS, which is evident on the microstructure of the fracture surface. The Halpin-Tsai model verified the observed increasing trend in mechanical performance. Simulation results revealed that TG-GO has better interfacial interaction with CS, which is highly in good agreement with the boosted mechanical performance.

Micromechanical study of loess permeability and seepage erosion based on microstructure functional basic unit and seepage simulation in pore domain

Micromechanical study of loess permeability and seepage erosion based on microstructure functional basic unit and seepage simulation in pore domain

Micromechanical study of intragranular stress and strain partitioning in an additively manufactured AlSi10Mg alloy

This study addresses the effect of a cellular-dendritic microstructure on the intragranular deformation behavior of an additively manufactured AlSi10Mg alloy. Experimental investigations have revealed the Al dendritic cells with a characteristic size of several hundred nanometers. The cells are decorated by a thin eutectic layer which consists of an aluminum matrix reinforced by silicon nanoparticles. Based on the experimental data, a set of micromechanical models are constructed and implemented in finite-element calculations. The constitutive behavior of an aluminum phase is described in terms of anisotropic elasticity to take into account the crystal lattice effects. Calculation results are analyzed and discussed with the main focus being placed on the effect of microstructure-resolved stress and strain partitioning between Al and Si phases. The silicon content is shown to impact the range of stress variation at the intragranular scale and the places of stress concentration in the Al phase. The eutectic layer behaves as a metal matrix composite where reinforcing silicon particles restrict deformation of the aluminum matrix.

Micromechanics study of short carbon fiber-reinforced thermoplastics fabricated via 3D printing using design of experiments

In this study, short carbon fiber-reinforced thermoplastic (sCFRTP) was 3D-printed under different printing parameters, and the influence of the combination of printing parameters on the tensile properties and internal structure (void volume fraction, fiber orientation, and fiber length) of the 3D-printed sCFRTP was investigated through tensile testing, X-ray computed tomography, microscopic observations and theoretical analysis based on a micromechanics model (MM). A total of ten printings and characterizations were performed via the design of experiments, and the outcomes displayed specimens that were fabricated under optimal printing parameters (specimen DoE) exhibited a Young's modulus of 5.1 ± 0.3 GPa and a tensile strength of 73.3 ± 0.9 MPa, resulting in the highest Young's modulus and tensile strength. The MM analysis successfully reproduced the experimental stress-strain response as well as the equivalent stiffness of the sCFRTPs with a much shorter time than finite element analysis by inputting the measured fiber length, void volume fraction, and fiber orientation distribution into the in-house MM code. From this MM analysis, it was suggested the higher Young's modulus and tensile strength observed in the specimen DoE is due to more of the relatively long fibers are oriented in the print direction with fewer voids. Furthermore, the influence of internal structure parameters on the mechanical properties of the 3D-printed sCFRTPs was analyzed, revealing that fiber length has a greater impact on the mechanical properties than void volume fraction and fiber orientation distribution.

Evolution law study of pore and fracture of coal gangue cemented filling body under axial compression using PFC2D

Filling body is an important structure to support the safety of coal mine goaf. The cemented gangue backfill (CGB) is a multiphase heterogeneous brittle material composed of coal gangue, hydration reactants, pores and microcracks. According to Micromechanics studies, the accumulation and development of meso-structural damage in heterogeneous brittle materials is the direct cause of macroscopic failure. In this paper, particle flow numerical software PFC2D is used to simulate the meso-structure evolution of CGB. Considering the particle size of filling material, the coal gangue particles are drawn according to the real shape by vector software, then import it into PFC2D by FISH language and constructed as Clump unit. The relationship between micro-characteristics such as particle force chain distribution, cracks and pores and mechanical properties of CGB is analyzed. The results show that the stress-strain and crushing mode of the numerical simulation model have a good correspondence with the laboratory test results. The internal force chain distribution and fracture-pore evolution law of the model particles are analyzed. It is found that most of the force chains are concentrated near the larger particle units, forming the 'skeleton force chain' phenomenon. The initial cracks are mainly produced around the coal gangue particle unit. With the increase of axial pressure, the cracks grow obliquely from 30° to 45°, and finally macroscopic cracks are generated. Due to the hydration product generated, the internal porosity is gradual decrease. Other than that, during the uniaxial compression process，the porosity of the same curing age decreases first and then increases, and the pores are sudden increase after the complete crushing stage.

An in vitro study of micromechanics, cellular proliferation and viability on both decellularized porcine dura grafts and native porcine dura grafts

Damage to the dura mater may occur during intracranial or spinal surgeries, which can result in cerebrospinal fluid leakage and other potentially fatal physiological changes. As a result, biological and synthetic derived scaffolds are typically used to repair dura mater post intracranial or spinal surgeries. The extracellular matrix of xenogeneic dura scaffolds has been shown to exhibit increased cell infiltration and regeneration than synthetic dura materials. In this study, we investigated the biocompatibility of native and decellularized porcine dura by seeding rat fibroblast cells onto the constructs. Cell proliferation, cell viability, and the mechanical properties of these dural grafts were evaluated post-re-seeding on days 3,7 and 14. Live-dead staining and resazurin salts were used to quantify cell viability and cell proliferation, respectively. Micro indentation was conducted to quantify the mechanical integrity of the native and acellular dura graft. The findings indicate that the acellular porcine dura graft creates a beneficial setting for infiltrating rat fibroblast cells. Cell viability, proliferation, and micro indentation results on the acellular grafts are comparable with the native control porcine dura tissue. In conclusion, the porcine scaffold material showed increased cell viability at each time point evaluated. The sustained mechanical response and favorable viability of the cells on the decellularized grafts provide promising insight into the potential use of porcine dura in clinical cranial dura mater graft applications.

Study of viscoelastic damage and micromechanism of polyurethane in freeze-thaw cycle environment

To investigate the viscoelastic properties of polyurethane under the action of freeze-thaw cycles. Polyurethane specimens excessed examined using atomic force microscopy, nanoindentation tests, and differential scanning calorimetry (DSC) after 0, 3, 5, and 7 freeze-thaw cycles. The molecular structure and property damage process was also investigated using molecular dynamics. The findings of molecular simulations revealed that the freeze-thaw cycle causes the aggregated system to disperse within the polyurethane molecule, resulting in an increase in its modulus. The testing findings revealed that the roughness of the polyurethane surface steadily decreased as the number of freeze-thaw cycles increased, as did the adhesion to various substrates. In the test results of nanoindentation, the elastic modulus showed an increasing trend, and the contact indentation depth gradually decreased. This suggests that freeze-thaw cycles impair polyurethane's elastic and flexible characteristics. The freeze-thaw cycle raised the melting temperature of polyurethane in the differential scanning calorimetry experiment findings. This confirms the experimental findings of increased elastic modulus and hardness in nanoindentation. In conclusion, further study may be undertaken to change polyurethanes by adding water-repellent compounds to them, which can be accomplished by modifying the molecular structure inside the polyurethanes to withstand environmental harm. The findings of this research lay a theoretical foundation for the resilience of polyurethane materials to environmental deterioration in a variety of industries, such as construction, where freeze-thaw cycles exist.

Shear resistance reduction of granular materials subjected to high-frequency and low-intensity vibration: A micro-mechanical study

高速铁路速度的进一步提升，需要解决轨下土工基础在高频振动作用下的稳定性问题。前期通过试验研究发现，即使在动应力水平相对较低的条件下，高频振动作用仍会导致颗粒材料出现流态化、强度衰减等一系列区别于低频振动的现象。这些现象的力学机理目前尚未完全明确，不利于未来更高速铁路的轨下土工基础设计。结合离散元数值模拟开展了双轴试验，分析了高频低幅振动下力链数量、各向异性及遗传颗粒等细观指标的演化规律，量化了颗粒材料中承载主体骨架结构的发展变化。结果表明，颗粒材料宏观偏应力的发展、波动等与细观力链的演化规律表现出较强的一致性；高频低幅振动作用下骨架结构的变异程度与抗剪强度衰减存在线性关系，骨架结构变异越大，归一化的抗剪强度衰减越大。

Influence of Si addition on the phase structure and oxidation behavior of PVD AlTiN and AlTiCrN coatings using high-resolution characterization techniques

The influence of Si concentrations on AlTiN and AlTiCrN coatings deposited by PVD has been investigated by using high-resolution characterization techniques: TEM, Dynamic SIMS, Atom Probe Tomography (APT) analyses and nano hardness measurements. First, investigations focus on crystallographic phase stability, microstructural observations and micromechanical studies to understand the effect of the Si addition on these two nitride coatings. Second, the oxidation mechanisms and the kinetics of oxide growth at 950 °C for various durations are examined. Results indicate that the addition of Si introduces high compressive stresses in both coating groups, reaching values in the range of − 6 GPa. However, the behavior of Si content differs for AlTiN coatings with and without chromium. In AlTiSiN coatings, increasing Si addition leads to reduce residual stresses, while no significant change is observed for AlTiCrSiN coatings. This stress evolution is associated with a decrease in crystallinity density of the TiAlN coatings due to Si addition, but this structural phenomenon is not observed when Si is added to the quaternary metallic coatings TiAlCrN. Si content also influences the nanohardness, but the variation among coating is not substantial, with values around 34 + /− 2 GPa, and an elastic-modulus around 443 + /− 40 GPa. Regarding oxidation resistance at 950 °C, the addition of Si in AlTiN coating results in the formation of an external alumina oxide layer and beneath it, a nanometer sized TiO2 anatase crystallites layer. After the growth of this bi-layer oxide scale, the inward cationic diffusion of the oxygen is very significantly reduced, and it can explain its high oxidation resistance. In contrast, for AlTiCrSiN coatings, the oxide scale morphology is different, consisting of a pure TiO2rutile outer layer, followed by an Al-rich oxide and a mixed oxide region of (AlCr)2O3 with small islands of TiO2. The growth of this last oxide scale shows a regular increase over time, primarily driven by inward oxygen diffusion at the nitride coating interface.

Micromechanism Study on Deterioration Effect of Vegetable Oil and Mineral Oil on Insulating Paper by Molecular Dynamics

In the era of low carbon and environmental protection, sustainable development ideas win support among the people. Vegetable oils have excellent environmental performance compared with traditional mineral insulating oils. The aging characteristics of insulating paper in vegetable oil have been discussed in experiments, but the deterioration mechanism at the microscopic level is still lacking. In this paper, the microscopic deterioration mechanism of insulating paper in vegetable oil and mineral oil is investigated by molecular dynamics. In addition, the intermolecular properties of insulating paper under different insulating oils are compared. It is found that the cellulose cleavage in insulating paper is divided into three ways: glycosidic bond breaking, pyran ring opening and dehydroxylation. The number of hydrogen bonds, binding energy and electrostatic energy between insulating paper and vegetable oil are higher than those of mineral oil. It proves that there is a stronger interaction between insulating paper and vegetable oil. Finally, the change rules of characteristic products CO, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and formic acid are counted. It is found that vegetable oil can delay the deterioration and prolong the life of insulating paper compared to mineral oil. The above study reveals the microscopic influence law of vegetable oil and mineral oil on the degradation of insulating paper. It provides theoretical support for the large-scale application of vegetable oil in oil-immersed transformers.