Function Of Slip Rate Research Articles

Generation of airborne wear particles from wheel–rail contact during rolling/sliding and pure sliding contact

Electric railway transportation is considered an environmentally friendly transport system. However, it releases airborne wear particles (AWPs), which have an adverse effect on human health. AWP generation from wheel–rail contact during rolling/sliding and pure sliding contact has not been studied extensively. This study aims to investigate the generation of AWPs and their particle size distribution under both rolling/sliding and pure sliding contact by analyzing AWP generation under three different normal loads at a circumferential velocity of 90 km/h. AWP number concentrations (NCs) were measured using two particle sizing instruments, which are a fast mobility particle sizer (FMPS) that measures particles in the range 5.6–560 nm and an optical particle sizer (OPS) that measures particles in the range 0.3–10 µm. Total and maximum AWPNCs were analyzed as a function of slip rate, and particle size distribution analysis was conducted. Results indicated that AWPNCs measured by both instruments under all load conditions increased with an increase in the slip rate until it reached the maximum AWPNC value and decreased thereafter. The total and maximum AWPNCs measured by both instruments increased with an increase in the normal load. Particle size distribution results indicated that most generated particles were fine particles under all load conditions. Size distribution peaks occurred at 0.01 and 0.16 µm for ultrafine and fine particles, respectively. All results indicate that the normal load has a significant effect on AWP generation and that ultrafine and fine particles are generated even during rolling/sliding contact.

Effect of train velocity on the amount of airborne wear particles generated from wheel–rail contacts

Railways are considered as an environment friendly transport system. However, railway transportation produces airborne wear particles (AWPs) from the brake systems, wheel–rail contact, contact-strip–overhead-contact-wire contact, and third-rail contact, which have adverse effects on human health. The generation of AWPs from wheel–rail contact has hardly been studied. In this study, we used a twin-disc rig to investigate the generation of AWPs from both rolling/sliding and pure sliding contacts at different train velocities. AWP number concentrations (AWPNCs) were measured at three different train velocities, i.e., 28, 45, and 90 km/h. The measurement was done using two particle counting instruments, a fast mobility particle sizer (FMPS) that measures particles in the range of 5.6–560 nm and an optical particle sizer (OPS) that measures particles in the range of 0.3–10 µm. AWPNCs were analyzed as a function of slip rate. AWPNCs measured by both the instruments and by FMPS continued to increase with slip rate at 28 and 45 km/h, respectively. AWPNCs measured by OPS and by both instruments increased during a rolling/sliding contact and then decreased during a pure sliding contact at 45 and 90 km/h, respectively. The total and maximum AWPNCs measured by both instruments increased with an increase in the train velocity. Furthermore, size distribution analysis showed that the AWPNCs for the peak particle diameter increased with an increasing train velocity. These results indicate that train velocity has a significant effect on the generation of AWPNCs.

A Physics‐Based Rock Friction Constitutive Law: Steady State Friction

AbstractExperiments measuring friction over a wide range of sliding velocities find that the value of the friction coefficient varies widely: friction is high and behaves according to the rate and state constitutive law during slow sliding, yet markedly weakens as the sliding velocity approaches seismic slip speeds. We introduce a physics‐based theory to explain this behavior. Using conventional microphysics of creep, we calculate the velocity and temperature dependence of contact stresses during sliding, including the thermal effects of shear heating. Contacts are assumed to reach a coupled thermal and mechanical steady state, and friction is calculated for steady sliding. Results from theory provide good quantitative agreement with reported experimental results for quartz and granite friction over 11 orders of magnitude in velocity. The new model elucidates the physics of friction and predicts the connection between friction laws to independently determined material parameters. It predicts four frictional regimes as function of slip rate: at slow velocity friction is either velocity strengthening or weakening, depending on material parameters, and follows the rate and state friction law. Differences between surface and volume activation energies are the main control on velocity dependence. At intermediate velocity, for some material parameters, a distinct velocity strengthening regime emerges. At fast sliding, shear heating produces thermal softening of friction. At the fastest sliding, melting causes further weakening. This theory, with its four frictional regimes, fits well previously published experimental results under low temperature and normal stress.

Friction properties and deformation mechanisms of halite(-mica) gouges from low to high sliding velocities

The evolution of friction as a function of slip rate is important in understanding earthquake nucleation and propagation. Many laboratory experiments investigating friction of fault rocks are either conducted in the low velocity regime (10−8–10−4 ms−1) or in the high velocity regime (0.01–1 m s−1). Here, we report on the evolution of friction and corresponding operating deformation mechanisms in analog gouges deformed from low to high slip rates, bridging the gap between these low and high velocity regimes. We used halite and halite–muscovite gouges to simulate processes, governing friction, active in upper crustal quartzitic fault rocks, at conditions accessible in the laboratory. The gouges were deformed over a 7 orders of magnitude range of slip rate (10−7–1 m s−1) using a low-to-high velocity rotary shear apparatus, using a normal stress of 5 MPa and room-dry humidity. Microstructural analysis was conducted to study the deformation mechanisms. Four frictional regimes as a function of slip rate could be recognized from the mechanical data, showing a transitional regime and stable sliding (10−7–10−6 m s−1), unstable sliding and weakening (10−6–10−3 m s−1), hardening (10−2–10−1 m s−1) and strong weakening (10−1–1 m s−1). Each of the four regimes can be associated with a distinct microstructure, reflecting a transition from mainly brittle deformation accompanied by pressure solution healing to temperature activated deformation mechanisms. Additionally, the frictional response of a sliding gouge to a sudden acceleration of slip rate to seismic velocities was investigated. These showed an initial strengthening, the amount of which depended on the friction level at which the step was made, followed by strong slip weakening.

Development and response of a coupled catchment fan system under changing tectonic and climatic forcing

Sediment fans are a potentially useful and underexploited recorder of Earth's climatic and tectonic history, but historical observations have led to conflicting views on the importance of tectonic, climatic, and lithologic variables in controlling fan morphology and deposition. A one‐dimensional model of a sediment fan and its associated catchment is used to explore the sensitivity of such simple sediment routing systems to perturbations in fault slip and precipitation rates. A transport‐limited catchment is coupled to a fan whose surface slope is set by the balance between catchment sediment efflux and the available tectonically generated basin accommodation. Rock uplift rate is spatially variable across the model space. Increasing the fault slip rate, or decreasing the precipitation rate, leads to an increase in fan slope, temporary back‐stepping of the fan toe, and a pronounced angular unconformity. Conversely, a decrease in slip rate, or an increase in precipitation rate, results in a decrease in fan slope, and progradation and eventual stabilization of the fan toe. Once perturbed, the system evolves toward a new equilibrium state with time constants of ∼0.5 to 2 Myr; these response times are insensitive to slip rate but are strongly dependent on precipitation rate. Variations in fan slope are well described by a dimensionless parameter that expresses equilibrium slope as a function of slip rate, precipitation rate, system size, and catchment lithology. This parameter holds promise as a predictive tool in inverting the morphology of natural fans for environmental variables.

Spatial and temporal evolution of stress and slip rate during the 2000 Tokai slow earthquake

We investigate an ongoing silent thrust event in the Tokai seismic gap along the Suruga‐Nankai Trough, central Japan. Prior to the event, continuous GPS data from April 1996 to the end of 1999 show that this region displaced ∼2 cm/yr to the northwest relative to the landward plate. The GPS time series show an abrupt change in rate in mid‐June 2000 that continues as of mid‐2005. We model this transient deformation, which we refer to as the Tokai slow thrust slip event, as caused by slip on the interface between the Philippine Sea and Amurian plates. The spatial and temporal distribution of slip rate is estimated with Kalman filter based inversion methods. Our inversions reveal two slow subevents. The first initiated in late June 2000 slightly before the Miyake‐jima eruption. The locus of slip then propagated southeast in the second half of 2000, with maximum slip rates of about 15 cm/yr through 2001. A second locus of slip initiated to the northeast in early 2001. The depth of the slip zone is about 25 km, which may correspond to the transition zone from a seismogenic to a freely sliding zone. The cumulative moment magnitude of the slow slip event up to November 2002 is Mw ∼ 6.8. We calculate shear stress changes on the plate interface from the slip histories. Stress change as a function of slip rate shows trajectories similar to that inferred for high‐speed ruptures; however, the maximum velocity is 8 orders of magnitude less than in normal earthquakes.