Nonequilibrium molecular dynamics (NEMD) modeling of nanoscale hydrodynamics of clay‐water system at elevated temperature

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The atomic‐scale cracking mechanism in clay is vital in discovering the cracking mechanism of clay at the continuum scale in that clay is a nanomaterial. In this article, we investigate mechanisms of modes I and II crack propagations in pyrophyllite and Ca‐montmorillonite with water adsorption through reactive molecular dynamics (MD) with a bond‐order force field. Clay water adsorption is considered by adding water molecules to the clay surface. During the equilibration stage, water adsorption could cause bending deformation of the predefined edge crack region. The relatively small orientating angle of water molecules indicates the formation of hydrogen bonds in the crack propagation process. The peak number density of adsorbed water decreases with the increasing strains. The atomistic structure evolution of the crack tip under loading is analyzed to interpret the nanoscale crack propagation mechanism. The numerical results show that the crack tip first gets blunted with a significant increase in the radius of the curvature of the crack tip and a slight change in crack length. The crack tip blunting is studied by tracking the crack tip opening distance and O–Si–O angle in the tetrahedral Si–O cell in modes I and II cracks. We compare bond‐breaking behaviors between Al–O and Si–O. It is found that Si–O bond breaking is primarily responsible for crack propagation. The critical stress intensity factor and critical energy release rate are determined from MD simulation results.

Section: Introductionmentioning

confidence: 99%

“…For example, the formation of strong hydrogen bonds could alter the layout of water molecules 16,17 . Studies have also clarified the structure of electrical double layers formed on hydrated clay mineral surfaces 18 . Sposito et al 19 .…”

Section: Introductionmentioning

confidence: 99%

Nanoscale crack propagation in clay with water adsorption through reactive MD modeling

Zhang

Song

2023

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“…20 Lastly, it allows for examining materials at an atomic scale, surpassing the resolution of numerous experimental techniques. 21,22 This level of detail is crucial for understanding complex systems such as interfaces or composite materials. On the other hand, experimental methods may present certain limitations, including constraints in the conditions and difficulties in directly observing the underlying mechanisms.…”

Section: Introductionmentioning

confidence: 99%

“…Besides, it helps reveal the underlying physical mechanisms that govern material behavior by simulating interactions among individual atoms and molecules 20 . Lastly, it allows for examining materials at an atomic scale, surpassing the resolution of numerous experimental techniques 21,22 . This level of detail is crucial for understanding complex systems such as interfaces or composite materials.…”

Section: Introductionmentioning

confidence: 99%

FRP–soil interfacial mechanical properties with molecular dynamics simulations: Insights into friction and creep behavior

Yin

Yuan-Yuan

2023

The fiber‐reinforced polymer (FRP) has attracted much attention in civil engineering due to its durability and cost‐effectiveness. The soil–FRP structure interface plays an essential role when the FRP is adopted in geotechnical engineering, but its fundamental interfacial behavior remains unclear. In the present study, the atomistic models of silica representing sand, water film representing the lubricated condition, and cross‐linked epoxy representing FRP are constructed to investigate the FRP–sand interfacial properties at the nano‐scale through molecular dynamics (MD) simulations. The epoxy model geometry and forcefield are first validated by comparing the thermodynamic and mechanical parameters with experimental and simulation measurements. The silica–epoxy interfacial tribological and rheological behavior is then explored by conducting friction and creep simulations under dry and lubricated conditions. The friction force has been found linearly dependent on the normal load and increases with the sliding velocity while decreasing against water content. The modified Amontons law for the adhering surface could describe the silica–epoxy interfacial friction well. The shear stress level influences the creep characteristics with primary, secondary, and tertiary (or rupture) creep modes. The results of this study at the nano‐scale can be further developed to enhance the current contact laws of sand–FRP structure in micromechanics‐based modeling approaches.

“…We note that the molecular clay models in most MD studies are limited to perfect infinite clay platelets rather than a disordered system representing the actual clay assemblages (e.g., ref. [30][31][32][33][34]). The macroscopic behavior of clay is controlled by complex interparticle physical and chemical interactions at the nanoscale.…”

Section: Introductionmentioning

confidence: 99%

Nanoscale creep mechanism of clay through MD modeling with hexagonal particles

Zhang,

Song

2023

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In this article, we investigate the creep mechanism of clay at the nanoscale. We conduct the molecular dynamics (MD) modeling of clay samples consisting of hexagonal particles under compression and shear. The MD simulations include oedometer creep, shear creep, direct shear tests, and stress relaxation. The numerical results show that the nanoscale creep mechanism of clay is related to particle rotation, translation, and stacking under different loading conditions. The clay sample under creep shows two types of particle arrangements, that is, the shifted face‐to‐face configuration and the face‐to‐edge configuration. The orientation angle of clay particles is computed to track the rotation of individual particles due to creep. The fabric variation of the clay under creep is characterized by the dihedral angle between the basal particle plane and the x‐y plane and the order parameter. It is found that the factors affecting the microstructure variation of the clay aggregate include stress levels, loading rates, and particle sizes. In the nanoscale shear creep test, the creep process comprises three stages, that is, primary, secondary, and tertiary. The microstructure change during creep depends on the initial alignment of clay particles. The clay creep under a more significant stress level results in a more considerable order parameter and a more orientated clay structure.