Interfacial Friction Coefficient Research Articles

Theoretical Evaluation of Lubrication Performance of Thrust-Type Foil Bearings in Liquid Nitrogen

The development of reusable liquid rocket turbopumps has gradually highlighted the disadvantages of rolling bearings, particularly the contradiction between long service life and high rotational speed. It is critical to explore a feasible bearing scheme offering a long wear life and high stability to replace the existing rolling bearings. In this study, liquid nitrogen is adopted to simulate the ultra-low temperature environment of liquid rocket turbopumps, and theoretical evaluations of the lubrication performance of thrust-type foil bearings in liquid nitrogen are conducted. A link-spring model for the bump foil structure and a thin-plate finite element model for the top foil structure are established. The static and dynamic characteristics of the bearings are analyzed using methods including the finite difference method, the Newton–Raphson iteration method, and the finite element method. Detailed analysis includes the effects of factors such as rotational speed, fluid film thickness, thrust disk tilt angle, and the friction coefficient of the bump foil interface on the static and dynamic characteristics of thrust-type foil bearings. The research results indicate that thrust-type foil bearings have a good load-carrying capacity and low frictional power consumption. The adaptive deformation of the foil structure increases the fluid film thickness, preventing dry friction due to direct contact between the rotor journal and the bearing surface. When faced with thrust disk tilt, the direct translational stiffness and damping coefficient of the bearing do not undergo significant changes, ensuring system stability. Based on the results of this study, the exceptional performance characteristics of thrust-type foil bearings make them a promising alternative to rolling bearings for the development of reusable liquid rocket turbopumps.

Synergistic Effect of Microconvex Texture and Particle Medium on the Tribological Property of the Rubber Sliding Interface.

In this study, we examined how surface topography and particle medium interact to affect the tribological performance of rubber sliding interfaces, uncovering the mechanisms of particle lubrication under various conditions. We found that microtextured surfaces, created using a mold transfer method, modestly reduced the friction coefficient of rubber under both dry and lubricated states, primarily by altering the real contact area. Additionally, the presence of different microconvex textures on the surface topography significantly influenced rubber's tribological properties. Our three-dimensional morphological analysis revealed that microtextured rubber surfaces with higher Sa, Sku, and Sal and lower Str values consistently showed lower friction coefficients during sliding. The friction mechanism was attributed to the combined effects of the material properties, surface topography, and contact area. With the addition of a particle medium, the dry friction coefficient of the rubber interface decreased but exhibited an initial increase, followed by a decrease with increasing particle diameter. When particles were mixed with a water-based cutting fluid, the concentration, diameter, and wettability of the particles significantly impacted the tribological properties due to the synergistic effects of surface topography and particle lubrication. This work enhances our understanding of tribological control for viscoelastic materials through surface design, providing a theoretical basis for the tribological optimization of rubber surfaces.

Direct shear behaviors of excavated clay reinforced with geocomposite drainage layer encapsulated in thin sand layers.

The objective of this study is to assess the effectiveness of a novel structure comprising a geocomposite drainage layer and a thin sand layer (GDL + sand) in mitigating the rapid dumping of excavated clay and its associated issues, such as landslides. Two sets of direct shear tests were conducted to investigate the influence of sand layer thickness and compaction degree on the interface shear behavior of the GDL + sand structure. As the sand layer thickness increased, both the interface shear strength and friction angle gradually increased, first more sharply and then at a slower rate toward stability, while the interface cohesion decreased gradually. The optimal sand layer thickness for achieving the most effective reinforcement in stabilizing the clay was identified as 10 mm. A higher sand layer compaction degree was found to result in increased interface shear strength, interface friction angle, and interface cohesion. Building on these findings, the reinforcing efficiency of the GDL + sand structure was investigated through mechanism analysis in comparison to that of a geogrid + sand structure and GDL structure as per the interface friction coefficient. The ranking of interface friction coefficients among the three structures emerged as: geogrid + sand > GDL + sand > GDL. These results suggests that the GDL + sand structure exhibits superior reinforcement efficiency compared to the GDL structure and offers better drainage efficiency than the geogrid + sand structure.

Experimental and numerical studies of mechanical performance of an assembled friction type structural underpinning joint

This paper proposed an assembled underpinning joint (UPJ) based on the interfacial friction action between the underpinned concrete member and the underpinning steel beams (UPSBs). To investigate the mechanical performance and failure modes of the proposed UPJ, 20 specimens with different concrete strengths were fabricated and tested with varied preloading levels. Experimental results showed that the proposed UPJs could effectively transfer the vertical loads in the concrete columns through the friction action and all specimens failed due to the slip between the underpinned concrete column and the UPSBs. The failure loads of the specimens were in a positively linear relationship with the preloading levels and an interfacial friction coefficient of 0.46 was found. Numerical models were also created to further examine the detailed structural behaviours of each components in the UPJs, which confirmed that, the UPSBs were subjected to a composite action mainly combining both bending and torsion. The frictional stresses between the UPSBs and the concrete column were concentrated in the regions of the web of UPSBs near flanges and stiffeners. The load transfer mechanisms of the proposed UPJs under complex loading conditions were clarified. The damages, occurred at the corners of concrete columns due to high stress and strain concentrations, should be alleviated or prevented by protective measures in practice.

Hydrodynamic slip characteristics of shear-driven water flow in nanoscale carbon slits.

This paper reports on the effects of shear rate and interface modeling parameters on the hydrodynamic slip length (LS) for water-graphite interfaces calculated using non-equilibrium molecular dynamics. Five distinct non-bonded solid-liquid interaction parameters were considered to assess their impact on LS. The interfacial force field derivations included sophisticated electronic structure calculation-informed and empirically determined parameters. All interface models exhibited a similar and bimodal LS response when varying the applied shear rate. LS in the low shear rate regime (LSR) is in good agreement with previous calculations obtained through equilibrium molecular dynamics. As the shear rate increases, LS sharply increases and asymptotes to a constant value in the high shear regime (HSR). It is noteworthy that LS in both the LSR and HSR can be characterized by the density depletion length, whereas solid-liquid adhesion metrics failed to do so. For all interface models, LHSR calculations were, on average, ∼28% greater than LLSR, and this slip jump was confirmed using the SPC/E and TIP4P/2005 water models. To address the LS transition from the LSR to the HSR, the viscosity of water and the interfacial friction coefficient were investigated. It was observed that in the LSR, the viscosity and friction coefficient decreased at a similar rate, while in the LSR-to-HSR transition, the friction coefficient decreased at a faster rate than the shear viscosity until they reached a new equilibrium, hence explaining the LS-bimodal behavior. This study provides valuable insights into the interplay between interface modeling parameters, shear rate, and rheological properties in understanding hydrodynamic slip behavior.

Discrete element modelling of rotary CPT and its applications

The cone penetration test (CPT) is a major in-situ testing with advantages in efficiency, reliability, and continuous measurement. However, it is often limited in penetration depth in soils such as dense sand and gravel due to high resistance and insufficient pushing force. Studies have shown that rotation can reduce penetration resistance, leading to the development of the rotary CPT. In addition, the torque measurement in rotary CPT could potentially provide extra information for soil behavior. This study simulates regular and rotary CPT tests with varied confining pressure and initial relative density using the discrete element method (DEM). Macroscale results verify that rotation can improve the penetrability of CPT by reducing vertical soil resistance. The reduction mechanism was explained by the microscopic observations and theoretical calculations that rotation can reduce the magnitude of the contact force and tilt its main direction horizontally. To advance the application of rotary CPT, a strong linear correlation between the measurements in rotary and regular CPTs was established, enabling interpretation of the rotary CPT measurements via the vast knowledge accumulated for regular CPT soundings. Furthermore, a theoretical derivation was developed to calculate the soil-probe interface friction coefficient directly by using the measurements of rotary CPT. The influence of the confining pressure, probe friction coefficient, and rotational speed ratio on the calculation accuracy are discussed and explained via particle-scale observations.

Pore-scale modeling of preformed particle gel (PPG) extrusion in porous media

Preformed particle gel (PPG) is a promising profile control agent for enhanced oil recovery in heterogeneous reservoirs. For an improved sweep, the remigration behavior of PPG once blocked by pore throats is of crucial importance. In this paper, the process of a hyper-elastic particle passing through a pore throat is simulated, allowing investigation of the extrusion mechanism of PPG with deformation under a certain hydraulic pressure. The results reveal that PPG is subjected to a varying resistance during the process of entering, penetrating and leaving the throat. The maximal radial resistance occurs when the particle center arrives at the narrowest throat, whereas the maximal axial resistance occurs before that. In the meantime, it is shown that the particle gel bears over 80% body strain during the extrusion process through frictional pore throat. The hydraulic pressure needed for the PPG extrusion through the pore throat depends on the mechanical behaviors (hyper-elasticity of PPG, and friction coefficient of the PPG-throat interface) and geometrical properties (the particle size, and the shape of throat wall) of the PPG-throat system. Based on the simulation results, an empirical model is finally established to predict the required driving pressure. Eventually, the pore-scale model is upscaled and employed to attain effective pressure windows for profile-control in a reservoir scale formation with 10 times permeability heterogeneity.

Role of Carbon Nanotube Wetting Transparency in Rapid Water Transport for a Nanopore Membrane.

A carbon nanotube (CNT) may facilitate near-frictionless water transport within it. In this work, we elucidate the slip flow characteristics for a CNT embedded in a silicon nitride matrix using the molecular dynamics (MD) method. We reveal that the wetting transparency of a CNT, the transmission of the membrane matrix wetting property over a CNT, cannot be ignored. Due to the effect of CNT wetting transparency, the orientation flip behavior of water molecules should be the primary cause of the entrance and exit losses, which is a dominant factor influencing the interfacial friction coefficient for the thin CNT membrane. The relationship between the friction coefficient and pore size follows a logarithmic function, which agrees well with the reported experimental data. Our findings bridge the gap between the MD prediction and experimental observation for water transport in a CNT membrane and provide a clear understanding of the mechanism behind its ultrafast flow performance.

Large-scale field test on the shear behavior of concrete pipe-silty soil interfaces in pipe jacking: A case study

With the rapid advancement of urbanization, research on the shear behavior of concrete pipe-silty soil interfaces in pipe jacking has a high engineering application value. In this study, a large-scale field direct shear test apparatus and the corresponding test method were designed and proposed to investigate the shear properties of the concrete-silty soil interfaces in pipe jacking. A series of in-situ direct shear tests were conducted at five normal stress levels under four interface contact conditions. The results show that the shear stress-displacement relationships of the interfaces conform to the typical elastic-plastic constitutive relations, the shear strength-normal stress relationships of the interfaces can be well fitted by the Mohr-Coulomb failure criterion, and the interface shear properties are influenced by soil properties, normal stress, lubrication conditions and stagnation time. Without lubrication, the concrete-silty soil interfaces have a shear stress-displacement curve shape similar to that of the test results obtained from indoor direct shear tests, but their ductility and shear strengths are lower. Under lubrication conditions, the paraffin wax and thixotropic slurry can both effectively diminish the interface friction angle, thereby reducing the concrete-silty clay interface friction coefficient by 62.8% and 72.2% and reducing the concrete-silty sand interface friction coefficient by 60.8% and 59.2%, respectively. Based on the macroscopic and microscopic images observed in the tests, the lubrication mechanisms of the lubricants were analysed. The research results can provide a reference for the prediction of jacking force and construction disturbance in adjacent pipe jacking projects.

A novel 3D train–bridge interaction model for monorail system considering nonlinear wheel-track slipping behavior

Variable speed operation of the train cause easily the wheel-track slipping phenomenon, inducing strong nonlinear dynamic behavior of the suspended monorail train and bridge system (SMTBS), especially under an insufficient wheel-track friction coefficient. To investigate the coupled vibration features of the SMTBS under variable speed conditions, a novel 3D train–bridge interaction model for the monorail system considering nonlinear wheel-track slipping behavior is developed. Firstly, based on the D’Alembert principle, the vibration equations of the vehicle subsystem are derived by adequately considering the nonlinear interactive behavior among the vehicle components. Then, a high-efficiency modeling method for the large-scale bridge subsystem is proposed based on the component mode synthesis (CMS) method. The vehicle and bridge subsystems are coupled with a spatial wheel-track interaction model considering the nonlinear wheel-track sliding behavior. Furtherly, by a comprehensive comparison with the field test data, the effectiveness of the proposed method is verified, as well as the reasonable modal truncation frequencies of the bridge subsystem are determined. On this basis, the dynamics performances of the SMTBS are evaluated under different initial braking speeds and wheel-track interfacial adhesion conditions; besides, the nonlinear wheel-track slipping characteristics and their influences on the vehicle–bridge interaction are also revealed. The analysis results indicate that the proposed model is reliable for investigating the time-varying dynamic features of SMTBS under variable train speeds. Both the axle load transfer phenomenon and longitudinal slip of the driving tire would be easy to appear under the braking condition, which would significantly increase the longitudinal vehicle–bridge dynamic responses. To ensure a good vehicle–bridge dynamics performance, it is suggested that the wheel-track interfacial friction coefficient is larger than 0.35.

Shearing behavior of suction caisson wall-sand interface throughout the suction caisson life-cycle

Suction caissons are widely used as foundations for offshore platforms and offshore wind turbines. The life-cycle of a suction caisson includes penetration, service and retrieval. The mechanical characteristics of the interface between sand and suction caisson wall are crucial for assessing the penetration behavior and bearing capacity of suction caissons. Interfacial shear tests under constant normal loading (CNL) and variable normal loading (VNL) conditions were conducted to investigate the shearing behavior of suction caisson wall-sand interface throughout the suction caisson life-cycle. Results show that the interfacial shear stress increases with an increase in normal stress and decreases with an increase in penetration rate throughout the life-cycle of the suction caisson. The value of vertical displacement of the interface decreases with an increase of cycle times during service and the sand particles’ movement, rotation and rolling were observed by visualization tests. Under the test conditions, the interface frictional coefficient ranges from 0.46 to 0.80 and the interface friction angle varies between 25.64° and 27.43° during retrieval. Both the interface friction angle and interface friction coefficient during the penetration stage are greater than those during the retrieval stage, indicating that retrieval stage is not an inverse process of penetration stage. In addition, the control groups were carried out to investigate the effect of penetration on service stage and the effect of service on retrieval stage. It was also found that the influence of the penetration stage on shear stress during service stage is mainly observed in the first two cycles. The influence of service stages on shear stress during retrieval stage is more obvious. After prolonged cycling during service stage, the strength of the interface would be reduced.

Study on frictional behavior of SiCf/SiC composite clad tube clamping condition under nuclear irradiation

Silicon carbide fiber reinforced silicon carbide matrix (SiCf/SiC) composite is the key cladding material of nuclear fuel, which determines the safety and reliability of nuclear fuel storage and transportation. The replacement of its storage and transportation scenario needs to be completed by the manipulator, but the application of SiCf/SiC wear, fracture, and nuclear leakage in the snatching process of brittle-flexible-rigid contact in the irradiation environment has been seriously restricted due to unclear understanding of the damage mechanism. Therefore, the effects of irradiation dose and clamping load on the friction characteristics of the contact interface between SiCf/SiC clad tube are studied in this paper, and the effects of irradiation parameters and clamping force on the static friction coefficient of the contact interface between the clad tube and flexible nitrile are obtained. Based on the Greenwood-Williamson tribological model, a numerical model of the shape and structure of the contact micro-convex at the micro-scale of the clamping interface is constructed by introducing the multi-surface integral, and finally verified by experiments. The research results show that there is a unique “Irradiation suppression zone” under the clamping condition of SiCf/SiC cladding tube under the nuclear irradiation environment, and the growth of static friction coefficient slows down until stagnates after irradiation reaches a certain extent (600 kGy), and there will be a decline when the irradiation dose continues to increase, among which the clamping force of 15.2 N within the irradiation interval of 1,000 kGy can meet the safety of nuclear environment operation. The results of this paper can provide an important theoretical basis and application guidance for the safe operation of SiCf/SiC cladding tubes in the storage and transportation clamping process.

Sensitivity factor analysis of seismic performance of seismically isolated girder bridges during the operation period

The seismic performance of isolated girder bridges is accurately investigated and addressed by considering the theoretical foundation of seismic isolation, taking into account the operational period’s service state and changes in relevant performance indicators of vulnerable components. The analysis encompasses a comprehensive parameter analysis of seismic performance during the operational period, utilizing finite element analysis software, which involves comparing and analyzing structural deflections, deformation performance, and damage performance of seismically isolated girder bridges under varying parameters. The research findings indicate that, in terms of evaluating the damage state of the member, the displacement of the girder end of the main girder is primarily influenced by the interface friction coefficient of the isolation device, followed by the post-yield stiffness of the bearing. Conversely, abutment lateral stiffness has a relatively minor influence. Moreover, it is observed that the mechanical properties of the bearing (friction coefficient and post-yield stiffness) exert a significant impact on the structural seismic response. Therefore, more attention should be paid to the functional condition and the variation of mechanical performance parameters of the seismic isolation bearing during the operational phase.

Pullout behavior of geogrid reinforcement in calcareous sand

This study conducts a series of large-scale pullout tests to explore the pullout behavior of the biaxial geogrid-calcareous sand interface. It investigates the effects of normal stress, relative density, and embedded length on the interface pullout behavior of geogrid reinforcement in calcareous sand. In addition, this research examines changes in interface shear strength and the interface friction coefficient. The interface interaction mechanism of geogrid reinforcement in calcareous sand and the evolution of pullout force-clamp displacement curves are determined. The results indicated that the pullout force-clamp displacement curve primarily exhibits softening and hardening behaviors. The passive resistance of the geogrid mesh significantly influences the softening behavior, while shear friction predominantly affects the hardening behavior. The interface friction coefficient ranged from 0.28 to 0.88 for embedded lengths of 300 − 460 mm. The effects of relative density and embedded length on interface cohesion are more pronounced than those on the interface friction angle. When the embedded length increased from 300 to 460 mm, the rise in interface cohesion ranged from 42.0% to 47.7%, whereas the increase in internal friction angle ranged from 9.5% to 14.5%.

Interfacial friction effects on sealing performances of elastomer packer

Elastomer sealing performance is of critical importance for downhole tools application including the use of fracturing (Frac) plugs during multi-stage hydraulic fracking. In practice sealing performances of such plugs are normally evaluated through pressure tests, and in numerical simulation studies, maximum contact stress, average contact stress and contact length data are used to determine sealing quality between a packer and casing. In previous studies, the impact of friction forces on sealing performance is often overlooked. This work aims to fill this knowledge gap in determining the influence of friction forces on elastomer packer sealing performances. We first determined the most appropriate constitutive hyperelastic model for the elastomers used in frac plug. Then we compared analytical calculation results with Finite Element Analysis simulation using a simplified tubular geometry and showed the significant influences on interfacial friction on elastomer packer stress distribution, deformation, and contact stress after setting. With the demonstration of validity of FEA method, we conducted systematic numerical simulation studies to show how the interfacial friction coefficients can affect the maximum contact stress, average contact stress, contact stress distribution, and maximum mises stress for an actual packer used in plug products. In addition, we also demonstrated how the groove in a packer can affect packer deformation and evolvement during setting with the consideration of interfacial stress. This study underscores the critical role that friction forces play in Frac plug performance and provides a new dimension for optimizing packer design by controlling interfacial interactions at the packer contact surfaces.

Effect of different friction coefficient models on numerical simulation of inertia friction welding of 2219 Al alloy to 304 stainless steel

In inertia friction welding (IFW) of Al alloy to steel, the friction coefficient of interface influences the friction heat production and determines the accuracy of the numerical simulation of welding process. A fully coupled three-dimensional model was established to simulate the IFW process of 2219 Al alloy to 304 stainless steel. By taking different simplifications in the influencing factors (i.e., temperature, sliding velocity, and pressure) of friction coefficient, three types of friction coefficient models were established and utilized in the simulation of IFW process. The strain compensated Arrhenius and Johnson-Cook models were employed to describe the deformation behavior of Al alloy and steel, respectively. Both Al alloy and steel were assumed to be the elastic-plastic body, and the friction stress was calculated by the Coulomb friction model. The friction interface temperature, angular velocity attenuation, axial shortening distance, and joint appearance were measured to verify and compare the accuracy of the established models. The temperature and stress evolutions during the IFW process were also analyzed. With the smallest error in validation, the friction coefficient model, which was a function of temperature, sliding rate, and pressure, showed the best accuracy in describing the friction behavior. By considering the effect of pressure, a more accurate shear stress at the center region of the interface was calculated with a lower value. It means that the friction resistance at the region was lower, promoting the flow of internal Al alloy and the formation of curly-shape flash.

Study on the mechanism of coal pillar instability in coal seam sections containing gangue

The tail entry of the Shanxi Mine No. 10103 working face is a gob-side roadway featuring a 25 m protective coal pillar that contains double-strata gangue. This composition poses a risk of instability and failure, which can endanger personnel safety and mining efficiency. To address this issue, a mechanical model of coal pillars containing gangue was constructed, and a combination of discrete element modeling and engineering monitoring was utilized to reveal the failure mechanism and influencing factors of such coal pillars. The study offers a sound theoretical foundation for the support of coal pillars in gob-side roadways. Through an examination of the friction coefficient (f) of the coal gangue interface in relation to the Barton peak shear strength (τmax), it was determined that coal pillars containing gangue are susceptible to slip instability failure at the coal gangue interface when the normal stress (σR) reaches 20 MPa. The stability of coal pillars containing gangue was further analyzed using discrete element numerical simulation software, which identified key factors such as gangue hardness, thickness, location, and number of strata. Utilizing the outcomes of discrete element simulation, the FLAC-PFC coupling model was formulated to meticulously scrutinize the temporal and spatial progression of the deformation of the surrounding rock, as well as the features of its deformation and failure. As a result of this research, the implementation of the grouting cable + through layer bolt anchoring technique is proposed, wherein the bolt is inclined on both sides to traverse through the coal seam and gangue, thereby stabilizing the interface between the two.

Repairing Behaviors of Cracked Steel Plates Based on Bolted Fiber-Reinforced Polymer Plates.

The use of FRP materials to repair cracked/damaged steel structures has gradually been adopted by researchers. This paper investigates the repairing effect of bolted FRP plates for cracked steel plates based on experimental and numerical simulation methods. In the experimental investigation, the tensile strengths of six specimens, including three repaired specimens and three pure cracked steel specimens, were evaluated. The test outcomes indicated that the bolt repairing method significantly enhanced the tensile strengths of the cracked steel plates. As an example, the failure of a pure steel plate with a 1 mm width crack occurred at 813 N, whereas after being repaired, a tensile strength of 1298 N was observed. Based on finite element (FE) analysis, the influence of bolt preloads and interfacial friction coefficients were verified. The stress-relative ratio for specimens was contingent on the bolt preload magnitude and gradually decreased as the preload was augmented. By exploring the repairing effect for varied friction coefficients, it was concluded that using a higher bolt preload can aid in eliminating the performance discrepancy of the overall component caused by interface treatment errors.

Proposal of a coupled DDA-SPH method incorporating a new contact algorithm for soil-structure interaction simulations in geotechnical hazards

Accurate description of soil-structure interaction problems in geotechnical hazards is challengeable. A coupled method is a potential approach to solve such problems. Discontinuous deformation method (DDA) can be used to describe structure behavior and smoothed particle hydrodynamics (SPH) suits well for capturing soil behavior; meanwhile, the coupled DDA-SPH method can simulate complex soil-structure interaction through a contact algorithm. In the original contact algorithm, a penalty method using the Mohr-Coulomb failure criterion is utilized to embody the interaction forces. However, five calculation parameters are involved and should be chosen carefully. Moreover, the energy dissipation cannot be considered quantitatively and suitably. To overcome these drawbacks, a new contact algorithm is proposed in this study. This new contact algorithm can consider the friction and energy dissipation at contacts between DDA blocks and SPH particles using two physical parameters (including the interface friction angle and coefficient of restitution). Several validation examples were carried out to investigate the performance of the newly coupled DDA-SPH method. The simulated results were compared with theoretical solutions or those obtained by other different numerical methods, which shows good agreements. This suggests that the newly coupled DDA-SPH method can be applied to conduct the soil-structure interaction simulations with ease.

Water flow in a polymeric nanoslit channel with graphene and hexagonal boron nitride wall coatings: An atomistic study

Low flow resistance is essential for the design of nanofluidic platforms. Here, we present a comparative atomic-level study analyzing the fundamentals of water flow enhancement in a polymeric nanochannel due to the implementation of monatomic thick coatings—specifically, graphene and hexagonal boron nitride (hBN). Our results obtained employing large scale non-equilibrium molecular dynamics simulations and continuum models, revealing significant values of slip lengths of ∼29 and ∼6 nm for graphene- and hBN-coated nanochannels, respectively. Equilibrium molecular dynamics simulations, using the Green–Kubo relation, show the significant effect that the partial charges of hBN coating layer have on the water–wall friction. In addition, consistent values of the slip length are obtained from independent sets of equilibrium and non-equilibrium molecular dynamics simulations, confirming that the computed interfacial friction coefficients hold across flow regimes where water molecules no longer occupy the most energetically stable zones at the interface. Hence, the lower interfacial friction observed in the graphene-coated channel leads to a higher water flow enhancement than the one computed in the hBN-coated channel. We also show that the natural undulations of two-dimensional honeycomb-like materials, implemented as wall coatings, remain largely unhindered due to strong interfacial coupling facilitated by π−π stacking between the underlying aromatic polymer substrate and coating monolayers. This is particularly relevant for graphene coatings, which display significant out-of-plane thermal rippling that further enhances water flow. This observation is supported by a stronger atomic-scale vibrational coupling at the water–graphene interface compared to that computed at the water–hBN interface.