Intermediate Friction Research Articles

Study on the application amount optimization of water-based friction modifier based on field experiments

The utilization of friction modifiers (FMs) can reduce the adhesion coefficient of the top-of-rail to a moderate level, yielding a series of benefits. In this study, the influence of the FM application amount on the adhesion coefficient, noise, and braking distance was explored under field conditions. Results showed that when the FM application amount exceeded threshold values, the braking distance of the locomotive was greatly extended and the friction control performance of FM reached saturation. The FM application amount and application frequency were put forward through a simplified calculation process, which gave values of 0.33 mL/axle and 10axles/application, respectively. These application parameters achieve the desired intermediate friction level along with appropriate reductions in the noise and the lateral force.

A benchmarking methodology for top-of-rail products: Carry distance and retentivity

Top-of-rail (TOR) products are used in railways to reduce wear and noise by providing an intermediate friction level and a positive creep curve. In addition to these general requirements, retentivity and carry distance are important for their effectiveness on the track. This study aims to determine these track performance parameters for three commercial TOR products. A contact simulator and portable tribometer were used to simulate track conditions. The results show that carry distance is the most limiting performance parameter of TOR products, especially for water-based products. TOR lubricants, on the other hand, caused a more significant drop in friction after application. A predictive model simulating product redistribution along the track was introduced for the best-performing product.

Microstructure evolution and mechanical properties of friction welded IN713LC and AISI 4140

The microstructure and mechanical behavior of rotary friction-welded IN713LC nickel-base superalloy with AISI 4140 steel have been investigated. The microstructure of IN713LC changed from a columnar dendritic structure to equiaxed grains due to dynamic recrystallization with considerable change in in-grain misorientation, morphology, and volume fraction of gamma prime (γ′) precipitates. The observations indicate a counteracting effect of heat input and degree of deformation which resulted in achieving minimum grain size at an intermediate friction pressure. Phase transformation was observed in the weld interface/thermomechanically affected zone region of AISI 4140 steel. These changes in microstructure contribute to the variation in the microhardness across the weld joint. Furthermore, a maximum weld joint tensile strength of 922 MPa was observed at an intermediate friction pressure of 110 MPa.

Understanding slow compression of frictional granular particles by network analysis.

We consider frictional granular packings exposed to quasi-static compression rates, with a focus on systems above the jamming transition. For frictionless packings, earlier work (S. Luding et al., Soft Matter, 2022, 18(9), 1868-1884) has uncovered that the system evolution/response involves smooth evolution phases, interrupted by fast transitions (events). The general finding is that the force networks' static quantities correlate closely with the pressure, while their evolution resembles the kinetic energy for both frictionless and frictional packings. The former represents reversible (elastic) particle deformations with affine and non-affine components, whereas the latter also involves much stronger, irreversible (plastic) rearrangements of the packings. Events are associated with jumps in the overall kinetic energy as well as dramatic changes in the force networks describing the particle micro-structure. The frictional nature of particle interactions affects both their frequency and the relevant time scale magnitude. For intermediate friction, events are often followed by an unexpected slow-down during which the kinetic energy drops below its average value. We find that these slow-downs are associated with a significant decrease in the non-affine dynamics of the particles, and are strongly influenced by friction. Friction modifies the structure of the networks, both through the typical number of contacts of a particle, and by influencing topological features of the resulting networks. Furthermore, friction modifies the dynamics of the networks, with larger values of friction leading to smaller changes of the more stable networks.

Flight to safety, intermediation frictions, and US Treasury floating rate note prices

While US Treasury floating rate notes (FRNs) are typically traded at a premium, they often experience significant price discounts. We find that this significant discount in US Treasury FRNs can be partly attributed to intermediation friction. The results reveal that new intermediation friction and canonical fight-to-safety channels can better explain the price changes in US Treasury FRNs.

What drives the TIPS–Treasury bond mispricing?

Inflation-swapped Treasury Inflation-Protected Securities (TIPS) are usually undervalued compared to cash flow-matched Treasury bonds. From 2005 to 2022, TIPS discounts are persistent, averaging approximately 3.18 % of the face value, with a peak of 16.10 %. We elucidate the factors associated with this persistent mispricing and the extent of this association. The results from feature selection techniques and the variable importance-in-projection method reveal that marking-to-market concerns and intermediation frictions are key to understanding the underpricing of TIPS relative to comparable nominal Treasury securities. We conclude that when strategic concerns overwhelm fundamental analysis, asset prices could deviate from fundamental values over a prolonged period.

Top-of-rail friction modifier performance assessment: High pressure torsion testing; creep force modelling and field validation

Top-of-Rail products that give intermediate friction offer many benefits when applied to the wheel/rail interface. Water-based top-of-rail friction modifiers (TOR FMs), have been shown to reduce energy consumption, wear, noise, corrugation and rolling contact fatigue. This work was aimed at developing a test approach, based on the High Pressure Torsion (HPT) method, that allowed an improved assessment of their performance over those that recycle constantly over the same test surface. The outputs would then be used to parameterise the Extended Creep Force (ECF) model to enable full-scale predictions to be made that could be compared with field measurements of wheel/rail interface friction.The HPT method developed used representative amounts of product based on assessment of wayside and on-board application rates. Friction levels achieved matched those expected for intermediate levels. The friction level was sensitive to the amount applied though. The parameterised ECF model was able to predict friction levels that matched those from the field very closely. A framework for using friction measured in small-scale tests has been developed that could now be applied to other third body materials for making valid predictions of full-scale performance.

Do Community Banks Stabilize Housing Prices?

This paper examines the influence that community bank residential mortgage lending has on regional housing prices and ultimately the housing price bubble that culminated with the Great Recession of 2007–09. Previous research suggests that community bank lending is influenced by financial intermediation frictions, such as difficulty attracting uninsured deposits and limited access to the bond market. Such frictions cause bank liquidity to play an important role in the ability of community banks to navigate swings in the local economy as well as real estate prices. We take these frictions as the starting point in our analysis and contribute to literature by focusing on the impact that community banks exert on housing prices. Specifically, we find that while community bank residential mortgage holdings are marginally related to housing price cycles, their mortgage lending does not contribute in an economically meaningful way to housing price bubbles. Even though bank liquidity, defined as the ratio of securities-to-assets, plays a role in the degree of community bank residential mortgage lending, it is not sufficiently strong enough to influence housing prices.

Development and Evaluation of a New Orthodontic Ligature: Frictional Force Analysis.

To evaluate and compare the friction of different ligature modes used in orthodontics, and to propose a new ligature model for conventional brackets ("H low-friction orthodontic ligature). Samples were randomly divided into seven experimental groups: (1) resin H ligature (H3D), designed by the authors of this study and produced in a 3D printer, with conventional bracket; (2) metal H ligature (HFM), with conventional bracket; (3) passive self-ligating bracket (SLP); (4) "8" low-friction unconventional elastic (LT8), with conventional bracket; (5) loose conventional metal ligature (MLS), with conventional bracket; (6) conventional metal ligature fully tightened (MLT), with conventional bracket; (7) conventional elastic ligature (CEL), with conventional bracket-control. All samples were subjected to mechanical static friction testing using the EMIC DL 2000 universal testing machine. To assess the normality requirement, the Shapiro-Wilk test was used, which showed a non-normal distribution for the means of the groups (p < 0.05). Therefore, statistical tests were performed to assess the existence of statistically significant differences between the groups through the Kruskal-Wallis, followed by Dunn's test, pairwise comparison, p < 0.05. The results obtained showed lower friction values for HFM (0.002 kgf), SLP (0.003 kgf), and LT8 (0.004 kgf)-these did not differ statistically from each other. These were followed by H3D (0.020 kgf), MLS (0.049 kgf), CEL (0.12 kgf), and, finally, MLT (0.21 kgf). The lowest friction value was found for the metal H ligature, similar to the self-ligating bracket and the "8" low-friction unconventional elastic. The resin H ligature presented intermediate friction values and the highest friction force was found for the MLT group.

Non-Markovian dynamics of black hole phase transition

We provide a comprehensive study on the non-Markovian dynamics of the black hole phase transitions based on the underlying free energy landscape. By assuming that the transition processes between different black hole states are stochastic, the non-Markovian dynamics of the black hole phase transition is governed by the generalized Langevin equation with the time-dependent friction that represents the memory effect from the effective thermal bath when the timescale of the system is comparable or shorter than the timescale of the effective thermal bath. We consider the first passage problem associated with the black hole phase transitions and derive the analytical expressions of the mean first passage time in the weak, intermediate, and large friction regimes. As the concrete examples, we study the effects of three types of time dependent friction kernel (delta function friction, exponentially decayed friction, and oscillatory friction) on the dynamics of Hawking-Page phase transition and the small/large RNAdS black hole phase transition. we found that there is a kinetic turnover point for each type of friction kernel when the friction strength varies. For the exponentially decayed friction kernel, it is shown that the non-Markovian effect slows down the phase transition dynamics in the weak friction regime and speeds up the transition process in the strong friction regime. For the oscillating decayed friction kernel, we found kinetic resonances when the oscillating frequency of the effective thermal bath is equal to the oscillating frequency of the black hole state in the initial potential well on the free energy landscape.

An experimental study on the effects of friction modifiers on wheel–rail dynamic interactions with various angles of attack

By modifying friction to the desired level, the application of friction modifiers (FMs) has been considered as a promising emerging tool in the railway engineering for increasing braking/traction force in poor adhesion conditions and mitigating wheel/rail interface deterioration, energy consumption, vibration and noise. Understanding the effectiveness of FMs in wheel–rail dynamic interactions is crucial to their proper applications in practice, which has, however, not been well explained. This study experimentally investigates the effects of two types of top-of-rail FM, i.e. FM-A and FM-B, and their application dosages on wheel–rail dynamic interactions with a range of angles of attack (AoAs) using an innovative well-controlled V-track test rig. The tested FMs have been used to provide intermediate friction for wear and noise reduction. The effectiveness of the FMs is assessed in terms of the wheel–rail adhesion characteristics and friction rolling induced axle box acceleration (ABA). This study provides the following new insights into the study of FM: the applications of the tested FMs can both reduce the wheel–rail adhesion level and change the negative friction characteristic to positive; stick–slip can be generated in the V-Track and eliminated by FM-A but intensified by FM-B, depending on the dosage of the FMs applied; the negative friction characteristic is not a must for stick–slip; the increase in ABA with AoA is insignificant until stick–slip occurs and the ABA can thus be influenced by the applications of FM.

Intermediation Frictions in Debt Relief: Evidence from CARES Act Forbearance

&lt;ns2:p&gt;We study the role of mortgage servicers in implementing the CARES Act mortgage forbearance program during the COVID-19 pandemic. Despite universal eligibility, around one-third of the nonperforming federally-backed loans in our sample fail to enter into forbearance. The relative frequency of these "missing" forbearances varies significantly across servicers for observably similar loans, with small servicers and nonbanks, and especially nonbanks with small liquidity buffers, having a lower propensity to provide forbearance. The incidence of forbearance-related complaints by borrowers is also higher for these servicers. We also use servicer-level variation to estimate the causal effect of forbearance on borrower outcomes. Assignment to a "high-forbearance" servicer translates to a significant increase in the probability of nonpayment, which moves essentially 1:1 with the forbearance probability. Part of this additional household liquidity is used to pay down high-cost credit card debt.&lt;/ns2:p&gt;

Comparing Search and Intermediation Frictions Across Markets

Comparing Search and Intermediation Frictions Across Markets

Intermediation Frictions in Debt Relief: Evidence from CARES Act Forbearance

Intermediation Frictions in Debt Relief: Evidence from CARES Act Forbearance

Comparing Search and Intermediation Frictions across Markets

Comparing Search and Intermediation Frictions across Markets

A generalized Langevin equation approach for barrier crossing dynamics in conformational transitions of proteins

Barrier crossing dynamics in conformational transitions of proteins are investigated in the framework of the inertial generalized Langevin equation with an exponential memory kernel in a parabolic potential. This approach yields an exact analytical expression for the time dependent Grote–Hynes rate and the transmission coefficient, which typically determines the kinetics of such transitions. The complete transition path time distribution (TPTD) and the mean transition path time (MTPT) are evaluated as a function of the frictional coefficient and barrier curvature. The results of TPTD show an excellent agreement with the experimental results of TPTD for the PrP prion protein and theoretical results in the high friction limit, while they exhibit a considerable deviation from the results of theory at the intermediate and low friction limits. The inertial terms significantly affect the short time dynamics of such transitions. The results of the TPTD and MTPT are discussed at low and high frictional limits with varying curvatures of the potential barrier. The TPTD decreases with an increase in the barrier curvature at the high friction limit and exhibits an exponential decay at long times. The MTPT decreases with an increase in the curvature of the barrier.

Tribofilm formation during dry sliding of graphite- and MoS2- based composites obtained by spark plasma sintering

Composites of Astaloy 85Mo with the addition of MoS2, graphite or a mixture of graphite/MoS2 were consolidated using Spark Plasma Sintering. Dry sliding wear tests were conducted at different normal loads (5, 10, and 20 N) using the sintered samples against an AISI 52100 ball. The effect of contact pressure on the extrusion of solid lubricant was investigated using scratch tests. Graphite addition to the matrix provided the formation of a tribofilm, which lead to the lowest values of friction and wear. For the MoS2-composites, the formation of iron sulfides and oxidative products resulted in an increase in the friction coefficient at the highest normal loads. For the MoS2/graphite-composite, the samples exhibited an intermediate friction coefficient and the highest hardness.

On the fatigue and fracture behavior of keyhole-free friction stir spot welded joints in an aluminum alloy

The target of this research study was to evaluate the shear-tensile and fatigue behavior of aluminum 6061 alloy welds, in two different heat treatment conditions, joined by the recently developed intermediate layer friction stir spot welding (FSSW) technique. The keyhole, which is the disadvantage of the conventional FSSW process, was avoided using an additional intermediate layer (IL) accompanied by a simple tooling. Shear-tensile experiments demonstrated acceptable mechanical performance of IL-FSSW joints in comparison with that obtained using alternative methods. Fatigue behavior of the joints revealed a dependency to pre-processing temper especially at high cyclic load levels with improved life for the aged condition. Observations on the failure regions under shear-tensile experiments exhibited plug type and shear-plug type fracture modes for the aged and annealed conditions, respectively. In contrast, the fracture mode showed variation with respect to the load level but not to the type of temper during cyclic loading.

Intermediation Frictions in Debt Relief: Evidence from CARES Act Forbearance

We study the role of mortgage servicers in implementing the CARES Act mortgage forbearance program during the COVID-19 pandemic. Despite universal eligibility, we document that a significant number of federally backed mortgage borrowers become delinquent during the pandemic without successfully entering into a forbearance program, and that the relative frequency of these "missing'' forbearances varies significantly across mortgage servicers for otherwise identical loans. Forbearance outcomes are systematically related to servicer characteristics including size, liquidity and organizational form, consistent with the role of economic incentives in shaping servicer behavior. We also use servicer-level variation in forbearance outcomes to estimate the causal effect of forbearance on borrower outcomes. We find that assignment to a "high-forbearance" servicer translates to a significantly higher non-payment rate, and we find evidence that part of this additional household liquidity is used to pay down high-cost credit card debt.

The effect of a gouge layer on rupture propagation along brittle shear fractures in deep and high-stress mines

The presence of fault gouge and the generation of wear material between two sliding rock surfaces plays a critical role in slip weakening and propagation of ruptures along underground brittle shear fractures forming ahead of tabular excavations in deep and high stress gold mining. We performed two types of friction experiments: one with a fault gouge layer between two sliding surfaces, and the other without a fault gouge layer ‘rock-on-rock’, both under room dry conditions at slip velocities ranging from ~1.0 mm/s to 1200 mm/s. These friction experiments revealed a remarkable difference in the frictional weakening behaviour, e.g., rock-on-rock friction experiments show weakening behaviour at lower slip velocity (~5 mm/s) and generally has lower frictional strength than those with the intervening fault gouge between sliding surfaces. This study shows that the existence of the fault gouge layer between sliding rock surfaces delays the onset of fault weakening (i.e., slip weakening displacement of gouge layer experiments is larger compared to rock-on-rock experiments). It is proposed that flash heating may be the main active weakening mechanism within both our gouge and rock-on-rock experiments, and provides a feasible account for the observed weakening. The observed slip weakening displacement (Dc) differences may be attributed to the presence of a gouge layer between sliding surfaces, which has many more contacts during sliding compared to rock-on-rock experiments, thus reducing the average slip velocity per contact, consequently, the potential for activation of flash heating which delays the onset of weakening. Here we suggest that we may be able to describe brittle shear fracture rupture propagation process along underground brittle shear zones by conducting low, intermediate and high slip velocity friction experiments with and without an intervening fault gouge between sliding rock surfaces. These findings should have important implications for the modelling of rupture propagation processes in underground shear zones, a phenomenon that influences the severity of rockbursts, and hence the safety of mine workers and mining operations.