Effective Friction Coefficient Research Articles

Effects of crustal rheology and fault strength on the formation of the Qaidam Basin: Results from 2-D mechanical modeling

The Cenozoic Qaidam Basin on the northern Tibetan Plateau is bounded by the foreland thrust belts of the East Kunlun Mountains to the south and Qilian Mountains to the north. In this basin, the maximum thickness of the accumulated sedimentary strata is ∼17 km near the geographic center of the basin. Such a basin architecture challenges the classic foreland-basin deformation model, wherein substantial sediments should be localized near the basin margins owing to thrust loads on a bending plate. Based on the available geological and geophysical constraints, we built a two-dimensional viscoelastoplastic finite element model to investigate whether the unique pattern of the Qaidam Basin was mechanically related to the rheological structure of the crust and frictional strength of the basin-bounding thrust fault. By testing reasonable bounds on the viscosity of the ductile crust and effective frictional coefficient of the thrust faults, we modeled a basin framework that fits well with that of Qaidam Basin. The model parameters include a layered rheological structure, with the viscosity of the ductile crust of the basin being two orders of magnitude greater than that of the adjacent mountain belts and an effective frictional coefficient of >0.2. Furthermore, the initial width of the basin significantly affected its deformation style. Therefore, the layered rheological structure of the crust and frictional strength of the basin-bounding thrust faults played important roles in the formation of the Qaidam Basin. Our findings suggest that the inelastic behavior of the crust affects foreland deformation, highlighting that the classic foreland basin model must be revised for some tectonic settings.

Diffusion of nanochannel-confined knot along a tensioned polymer* *The National Natural Science Foundation of China under Grant Nos. 11864006, 11874309, 12164007, and 12204118.

The knots frequently occur in biopolymer and their diffusion plays an active role in the gene regulation. In this work, Langevin dynamics simulations were carried out to detect the diffusion behaviours of a knot along a tensioned polymer in different spatial constraints. The polymer accommodating a knot was tethered to two macrospheres to block the unravelling of the knot. As a result, the curves for the diffusion coefficients of the knot with different bending stiffness as a function of the tension in different spatial constraints were obtained. In the space without constraints or with weak constraints, the corresponding curves for the knot with relatively large bending stiffness exhibited two turnover behaviours. On the contrary, for the knot with relatively small bending stiffness, the diffusion coefficients were monotonically reduced with increasing tension. However, in a space with strong constraints, all the curves showed one turnover behaviour regardless of the bending stiffness. The turnover behaviours divided the curves into different regimes, and the dominant diffusion mechanisms in the regimes, namely, knot-region breathing, self-reptation, and internal friction, were clearly identified. The effective friction coefficients ξ of the knots with 31, 41, 51 and 52 types as a function of the knot size N at a fixed tension were well fitted by the relation ξ ∝ N. The effective friction coefficients of the knots at relatively large tension f > 3 sharply increased with the knot complexity, which is not dependent on the spatial constraints. By contrast, the values of these coefficients at relatively small tension f ≤ 3 were remarkably dependent on the spatial constraints. Our work not only provides valuable simulation results to assist the understanding of the diffusion of DNA knot, but also highlights the single-molecule design for the manipulation of DNA knots in future.

Experimental investigation on rheological behavior of dry granular mixtures based on direct measurement of basal friction

Geophysical flows, characterized by diverse particle-size mixtures, pose challenges for hazard risk assessment due to their anomalous fluidity and rheological behavior. This study investigates the rheological behavior of dry granular mixture flow in a flume setup using particle image velocimetry and triaxial force measurement. Key findings include a power-law relationship between the inertia value and the internal friction coefficient, affirming the applicability of the monodisperse friction model in mixed particle-size scenarios. A strong positive correlation is identified between the effective basal friction coefficient and internal friction coefficient, suggesting an influence of internal frictional properties on basal friction for granular flows on a flat surface. Additionally, positive correlations are observed between normalized stress fluctuation and both internal friction coefficient and inertia number, linking basal stress fluctuations to variations in internal frictional characteristics. These insights enhance our understanding of granular material dynamics, holding potential implications for geological disaster risk assessment.

Dynamical yield criterion for granular matter from first principles.

We investigate, using a recently developed model of liquid state theory describing the rheology of dense granular flows, how a yield stress appears in granular matter at the yielding transition. Our model allows us to predict an analytical equationof the corresponding dynamical yield surface, which is compared to the usual models of solid fracture. In particular, this yield surface interpolates between the typical failure behaviors of soft and hard materials. This work also underlines the central role played by the effective friction coefficient at the yielding transition.

Not a Rolling Stone: On Dragging a Stone Weight-Anchor on the Seabed

The force required to drag a stone anchor over several types of surfaces was measured, recorded, and analyzed. It was found that the force involved in the movement of the anchor over the various surfaces cannot be described just by the sliding solids theory, but it involves several additional physical processes, such as increasing the sand shear strength by the pressure the anchor applies on the sand under it; the sinking of the anchor into the saturated sand; shearing the sand in front of the moving anchor and accelerating it to the velocity of the anchor; accumulating sand in front of the anchor, thus adding to the pulled mass; and moving some of the accumulated sand sideways. In many instances, the beginning of the anchor movement involves the liquefaction of the sand under it, thus enabling the relatively easier sliding of the anchor. In addition, movement over rocky surfaces, encountering the irregularities that abound on such surfaces, also differs from classic sliding friction theory. In several situations, the use of an effective coefficient of friction, combining all the processes, can serve to obtain approximate values of the required forces.

Insights on the 2023 Kahramanmaraş Earthquake, Turkey, from InSAR: fault locations, rupture styles and induced deformation

SUMMARY We successfully detected widely distributed ground displacements for the 2023 Kahramanmaraş, Turkey, earthquakes by conducting interferometric synthetic aperture radar (InSAR) analyses using a ScanSAR observation mode. Major deformation extended approximately 350 and 150 km along the southern and northern strands bifurcating in the west of the East Anatolian Fault, produced by the main shock and the largest aftershock. The deformation map reveals that the ruptures propagated on the Erkenek, Pazarcık and Amanos segments on the southern strand and the Çardak segment on the northern strand. The fault plane of the northern strand bends approximately 45° at both edges with Z-shaped crank geometry. The bending fault at the western edge runs just along the Çardak segment but does not reach the Savrun segment, while at the eastern edge it deviates from known active faults such as Sürgü, Malatya faults and Doğansehır fault zone. A 3-D displacement map demonstrates that almost pure left-lateral fault motions were distributed along the two strands, with little vertical deformation. The moment magnitudes estimated from the slip distribution model were 7.82 and 7.66 for the southern and northern strands, respectively, with the Erkenek and Çardak segments having the largest released seismic moments on each strand, corresponding to approximately 31 and 57 per cent of the total, respectively. The Coulomb Failure Function change values indicate that the main shock can promote the largest aftershock with a standard value of the effective friction coefficient. Additionally, the unclamping effect controlled by the frictional property of the rock was a key factor in pulling the trigger of the seismic event on the northern strand. The historically accumulated and released seismic energies were imbalanced for the Pazarcık and Erkenek segments, suggesting that the 2023 event does not support a simple characteristic earthquake model; rather, it may be consistent with a supercycle model, in which the slip remnants from the characteristic earthquakes have been historically accumulated as coupling on a fault and released as huge earthquakes at longer intervals.

Numerical heat transfer of non-similar ternary hybrid nanofluid flow over linearly stretching surface

The primary objective of this research is to construct a 2D mathematical model to understand the heat transfer phenomena in a ternary hybrid nanofluid across a stretched surface. We endorsed viscous dissipation formulations in energy equations and the radiation impacts may also be precisely handled by using Rosseland approximation. Nanoparticles and their effects are also considered including and The equations used in the model are made nondimensional through non-similarity transformation. In addition, the local non-similarity approach is employed to convert non-similar partial differential equations into ordinary differential equations. These equations can subsequently be solved using the bvp4c MATLAB tool. Key factors have been thoroughly mapped out in graphical form for easy comprehension. In a flow regime, increasing nanoparticle concentration, magnetic number, and Eckert number lowers heat transmission and raises the ternary hybrid nanofluid's temperature profile. The effective skin friction coefficient and Nusselt number are tabulated concerning the aforementioned important factors.

Development of an automated reliable method to compute transport properties from DPD equilibrium simulations: Application to simple fluids

Dissipative particle dynamics (DPD) is a promising candidate technique for modeling rheological properties of soft matter systems. However, several methodological issues inhibit its exploitation as a computational rheology tool. In this work, we focus on the development of an automated method to compute transport properties from equilibrium simulation with particular attention to the assessment of the Green-Kubo approach reliability and computational feasibility for a large set of simple DPD systems with increasing Schmidt number. Furthermore, we investigate the time step size dependency of dynamic properties and the role of different time integration schemes. In particular, we assess the performance of the Shardlow-splitting algorithm against the most popular modified velocity-Verlet algorithm. We consider, for the first time, application of the Shardlow-splitting algorithm to the transverse DPD thermostat in different friction regimes relying on systematic numerical experiments. In addition, we make use of these findings to perform a multi-parametric study aiming to investigate the Schmidt number relationship with the effective friction coefficient.

Numerical and experimental analysis of the isothermal high temperature pneumoforming process

The isothermal high temperature pneumoforming process to form tubes at constant elevated temperatures by means of internal pressure is investigated. Two materials, a ferritic (X2CrTiNb18) and a martensitic stainless steel (X12Cr13) are used for the investigations. The required material characterization is performed at the temperature and strain rate of the actual process. A new method for quantifying thermal softening via the time-dependent decrease in static yield stress is presented. At a temperature of 1000 °C, the static yield stress decreases by 50% within 100 s for both materials. The numerical models are validated on the basis of the formed geometry and used to study the influence of maximum internal pressure, axial feed, holding time under load and die edge length on the final part geometry. It was observed, that with higher internal pressures and longer holding times smaller corner radii are formed for both materials. In contrast, a superimposed axial feed as well as the effective friction coefficient have a negligible influence on the formed geometry. With an increasing die edge length, smaller radii are formed with the ferritic stainless steel numerically and experimentally. By contrast, for the martensitic stainless steel, larger radii are observed numerically. Experimentally, the limited formability of these tubes weld seam becomes apparent. Based on the findings, process windows depending on the process parameters internal pressure and die edge length were derived. Numerically, forming limit curves of tubular semi-finished products under comparable conditions serve as a failure criterion. Good agreement with experiments was observed.

Insight into the Viscoelasticity of Self-Assembling Smectic Liquid Crystals of Colloidal Rods from Active Microrheology Simulations.

The rheology of colloidal suspensions is of utmost importance in a wide variety of interdisciplinary applications in formulation technology, determining equally interesting questions in fundamental science. This is especially intriguing when colloids exhibit a degree of long-range positional or orientational ordering, as in liquid crystals (LCs) of elongated particles. Along with standard methods, microrheology (MR) has emerged in recent years as a tool to assess the mechanical properties of materials at the microscopic level. In particular, by active MR one can infer the viscoelastic response of a soft material from the dynamics of a tracer particle being dragged through it by external forces. Although considerable efforts have been made to study the diffusion of guest particles in LCs, little is known about the combined effect of tracer size and directionality of the dragging force on the system's viscoelastic response. By dynamic Monte Carlo simulations, we apply active MR to investigate the viscoelasticity of self-assembling smectic (Sm) LCs consisting of rodlike particles. In particular, we track the motion of a spherical tracer whose size is varied within a range of values matching the system's characteristic length scales and being dragged by constant forces that are parallel, perpendicular, or at 45° to the nematic director. Our results reveal a uniform value of the effective friction coefficient as probed by the tracer at small and large forces, whereas a nonlinear, force-thinning regime is observed at intermediate forces. However, at relatively weak forces the effective friction is strongly determined by correlations between the tracer size and the structure of the host fluid. Moreover, we also show that external forces forming an angle with the nematic director provide additional details that cannot be simply inferred from the mere analysis of parallel and perpendicular forces. Our results highlight the fundamental interplay between tracer size and force direction in assessing the MR of Sm LC fluids.

Particle fluctuations and their effects on the rheological behavior of sheared granular flows

We present numerical simulations of plane-sheared granular flows in two pressure-controlled configurations and investigate the particle fluctuations over a wide range of the inertial number I. Quantities affecting the velocity fluctuations, including the granular temperature and the stress ratio, are shown to be intrinsically related and to exhibit similar I-dependent characteristics. We first propose a scaling law describing the one-to-one relationship between the granular temperature and I in both the inertial and collisional regimes, where the volume fraction plays an important role. This relation differs from the power-law dependence between the stress ratio and I. However, for low values of I, these two velocity fluctuation quantities deviate from the one-to-one relation, similar to the effective friction coefficient μ. Based on the obtained inverse power law, we propose a new unified model incorporating the stress ratio to describe the rheological behaviors in the quasistatic, inertial, and collisional regimes. The proposed model is more applicable than the one that integrates the granular temperature, allowing nonlocal effects to be roughly eliminated at low values of I and the rheological dependence on the volume fraction to be effectively removed at high values of I. This provides an alternative approach for developing rheological models for granular materials under complex flow conditions.

Quantifying the probability and uncertainty of multiple-structure rupture for Taiwan

This study identifies structure pairs with the potential for simultaneous rupture in a coseismic period and quantifies their rupture recurrence intervals. To assess the potential for a multiple-structure rupture, we calculated the probability of Coulomb stress triggering between seismogenic structures in Taiwan. We assumed that a multiple-structure rupture would occur if two structures could trigger each other by enhancing the plane with thresholds of a Coulomb stress increase and the distance between the structures and identified various sets of seismogenic structure pairs accordingly. We discussed the uncertainty of multiple-structure pair identification from various thresholds of stress change and structure distances, effective friction coefficient, and rotation of rake angles. To estimate the recurrence intervals for multiple-structure ruptures, we implemented a scaling law and the Gutenberg-Richter law in which the slip rate could be partitioned based on the magnitudes of the individual structure and multiple-structure ruptures. Considering that one structure may be involved in multiple cases of multiple-structure ruptures, we developed new formulas for slip partitioning in a complex fault system. By implementing the range of rupture area and slip rate of each structure, the magnitudes and recurrence intervals of multiple-structure ruptures could be estimated. We discussed the epistemic uncertainties of recurrence interval from deviations of slip rate and rupture area, various empirical formula of rupture parameters. The multiple-structure rupture with a larger characteristic magnitude would be crucial for the safety evaluation of infrastructures.

Beam-Like Topologically Interlocked Structures With Hierarchical Interlocking

Abstract Topologically interlocked materials and structures, which are assemblies of unbonded interlocking building blocks, are promising concepts for versatile structural applications. They have been shown to exhibit exceptional mechanical properties, including outstanding combinations of stiffness, strength, and toughness, beyond those achievable with common engineering materials. Recent work has established a theoretical upper limit for the strength and toughness of beam-like topologically interlocked structures. However, this theoretical limit is only attainable for structures with unrealistically high friction coefficients; therefore, it remains unknown whether it is achievable in actual structures. Here, we demonstrate that a hierarchical approach for topological interlocking, inspired by biological systems, overcomes these limitations and provides a path toward optimized mechanical performance. We consider beam-like topologically interlocked structures that present a sinusoidal surface morphology with controllable amplitude and wavelength and examine the properties of the structures using numerical simulations. The results show that the presence of surface morphologies increases the effective frictional strength of the interfaces and, if well-designed, enables us to reach the theoretical limit of the structural carrying capacity with realistic friction coefficients. Furthermore, we observe that the contribution of the surface morphology to the effective friction coefficient of the interface is well described by a criterion combining the surface curvature and surface gradient. Our study demonstrates the ability to architecture the surface morphology in beam-like topological interlocked structures to significantly enhance its structural performance.

The fragmentation-induced fluidisation of pyroclastic density currents

Pyroclastic density currents (PDCs) are the most lethal volcanic process on Earth. Forecasting their inundation area is essential to mitigate their risk, but existing models are limited by our poor understanding of their dynamics. Here, we explore the role of evolving grain-size distribution in controlling the runout of the most common PDCs, known as block-and-ash flows (BAFs). Through a combination of theory, analysis of deposits and experiments of natural mixtures, we show that rapid changes of the grain-size distribution transported in BAFs result in the reduction of pore volume (compaction) within the first kilometres of their runout. We then use a multiphase flow model to show how the compressibility of granular mixtures leads to fragmentation-induced fluidisation (FIF) and excess pore-fluid pressure in BAFs. This process dominates the first ~2 km of their runout, where the effective friction coefficient is progressively reduced. Beyond that distance, transport is modulated by diffusion of the excess pore pressure. Fragmentation-induced fluidisation provides a physical basis to explain the decades-long use of low effective friction coefficients used in depth-averaged simulations required to match observed flow inundation.

Nonreciprocal forces enable cold-to-hot heat transfer between nanoparticles

We study the heat transfer between two nanoparticles held at different temperatures that interact through nonreciprocal forces, by combining molecular dynamics simulations with stochastic thermodynamics. Our simulations reveal that it is possible to construct nano refrigerators that generate a net heat transfer from a cold to a hot reservoir at the expense of power exerted by the nonreciprocal forces. Applying concepts from stochastic thermodynamics to a minimal underdamped Langevin model, we derive exact analytical expressions predictions for the fluctuations of work, heat, and efficiency, which reproduce thermodynamic quantities extracted from the molecular dynamics simulations. The theory only involves a single unknown parameter, namely an effective friction coefficient, which we estimate fitting the results of the molecular dynamics simulation to our theoretical predictions. Using this framework, we also establish design principles which identify the minimal amount of entropy production that is needed to achieve a certain amount of uncertainty in the power fluctuations of our nano refrigerator. Taken together, our results shed light on how the direction and fluctuations of heat flows in natural and artificial nano machines can be accurately quantified and controlled by using nonreciprocal forces.

Unravelling the dynamics and hazards of the June 3rd, 2018, pyroclastic density currents at Fuego volcano (Guatemala)

The June 3rd, 2018, eruption of Fuego volcano (Guatemala) produced a complex sequence of small-volume pyroclastic density currents (PDCs) that inundated all sectors around the volcano and propagated >12 km on the southeastern flank, deposited ~50 million m3 of pyroclastic material, and killed at least 430 people in the village of San Miguel de Los Lotes and along the RN-14 road. This eruption has illustrated once again that the behavior of small-volume PDCs remains difficult to predict, demonstrating the need for an improved physical understanding of their generation, transport and depositional processes to ultimately improve assessment of their local hazard potential. In this work, we present preliminary results of an interdisciplinary study of the 2018 PDC deposits of Fuego, integrating: (1) field data of the pristine deposit characteristics recorded immediately after the eruption and after one rainy season, (2) sedimentological data (including grain size distributions and componentry) from samples collected at each lobe front and several exposed stratigraphic sections inside three principal ravines draining the volcano and affected by the eruption (Seca, Ceniza and Las Lajas), (3) preliminary quantification of the observed range of different clast surface textures, shape and vesicularities, as determined by SEM analyses, (4) surface morphological data from high-resolution satellite and aerial photography, and (5) advanced digital terrain model analysis correlated with sedimentological data to reconstruct the sequence of events on June 3rd and propose a conceptual model of PDC generation and emplacement on the SE flank of Fuego. In this model, a sequence of packages of material involved in discrete failure events of a perched mass of pyroclastic material accumulated within an old collapse structure on the upper SE flank, corresponds to the emplacement of a series of pulses of valley-confined PDCs down the Las Lajas channel. Headwall failures and gravitational collapses correlate with specific stratigraphic, sedimentological and textural characteristics of the valley-confined PDC units. The duration of individual granular collapse events serves as a proxy for the mobility of the triggered series of PDCs. Also, our detailed stratigraphic work shows evidence of stacked, massive flow units deposited by rapid stepwise aggradation of successive block-and-ash flow (BAF) pulses and their distribution along the southeastern flank supports the interpretation that the June 3rd PDCs, including the dilute parts of the currents, were largely controlled by the topography. The lack of strong changes in the grain size distributions of the fine sub-populations inside the seven valley-confined BAF lobate front units, together with their high content of fines, imply the presence of a self-limiting attrition process, decreasing the bulk porosity of such long-runout BAFs and lowering their effective friction coefficient during transport to reach longer runout distances. This multi-faceted approach completes previous studies already performed on small-volume PDCs at other volcanoes (Merapi, Colima, Unzen) and opens a unique perspective that will provide a significant step forward in our understanding of how such currents are emplaced.

Stochastic microcontact model for the prediction of gear mechanical power loss

Gears serve as the primary power transmission element in many industrial and automotive applications. Power loss in the form of heat generation contributes both to reduced fuel economy and elevated transmission operating temperatures which can lead to premature failure of components. The power loss is made up of both load independent losses and load dependent losses. Gear designers need engineering tools to estimate both components to determine overall system efficiency. This research seeks to utilize stochastic descriptions of surface asperity profiles with simplified Elastohydrodynamic lubrication (EHL) metrics to estimate the effective friction coefficient in mixed lubrication gear contacts. Power loss experiments are performed to measure load dependent gear losses and compare them to the model results.

Experimental determination of basal gas pressure and effective coefficient of friction for dry granular flow

Experimental determination of basal gas pressure and effective coefficient of friction for dry granular flow

Effective friction in adhesive mixtures intended for inhalation: Simulation of oblique impact of adhesive units

Oblique impact between adhesive units was studied using the Discrete Element Method (DEM) as a means to assess the effective friction coefficient and its dependence on particle shape, surface coverage ratio (SCR; 0.5, 0.75 and 1) and impact angle ( 1 5 ∘ − 7 5 ∘ ) in a low handling velocity regime (0.6 – 1.6 m/s). Adhesive units were created in silico from a spherical carrier particle (100 μm diameter) and monodisperse fine (drug) particles (3 μm large) of a spherical, triangular bipyramidal or tetrahedral shape. The particle interaction was modeled using the Hertz-Mindlin contact model with JKR adhesion (surface energy 0.03 J/m 2 ). A total of over 300 simulations were performed and the effective friction coefficient was extracted from the normal and tangential forces experienced by the carrier particles. The adhered fines resulted in a significantly reduced friction coefficient in comparison to the bare carriers but no additional reduction was observed with increasing SCR, suggesting a saturation already at an SCR of 0.5. The effective friction coefficient was independent of the impact velocity for relative velocities over 1 m/s. The impact angle had a significant effect on the friction coefficient, with head-on type collisions (15°) resulting in the lowest and grazing-type collisions (75°) the highest values. This was especially pronounced for the spherical fines whereas the triangular bipyramidal and especially the tetrahedral fines resulted in a more modest dependence on impact angle but overall considerably higher friction coefficients. These results could be used to better understand and formulate adhesive mixtures. • Adhesive units with different fine shapes were formed in-silico. • Binary collisions with different impact angle to study effective friction. • Effective friction is signifcantly lower compared to bare carrier particles. • Tetrahedral shape with angles towards grazing impact showed highest friction.

A constitutive model for sheared dense fiber suspensions

We propose a constitutive model to predict the viscosity of fiber suspensions, which undergoes shear thinning, at various volume fractions, aspect ratios, and shear stresses/rates. We calibrate the model using the data from direct numerical simulation and prove the accuracy by predicting experimental measurements from the literature. We use a friction coefficient decreasing with the normal load between the fibers to quantitatively reproduce the experimentally observed shear thinning in fiber suspensions. In this model, the effective normal contact force, which is directly proportional to the bulk shear stress, determines the effective friction coefficient. A rise in the shear stress reduces the effective friction coefficient in the suspension. As a result, the jamming volume fraction increases with the shear stress, resulting in a shear thinning in the suspension viscosity. Moreover, we extend the model to quantify the effects of fiber volume fraction and aspect ratio in the suspension. We calibrate this model using the data from numerical simulations for the rate-controlled shear flow. Once calibrated, we show that the model can be used to predict the relative viscosity for different volume fractions, shear stresses, and aspect ratios. The model predictions are in excellent agreement with the available experimental measurements from the literature. The findings of this study can potentially be used to tune the fiber size and volume fraction for designing the suspension rheology in various applications.