Belt friction

About: Belt friction is a(n) research topic. Over the lifetime, 942 publication(s) have been published within this topic receiving 9170 citation(s).

Time-dependent friction and the mechanics of stick-slip

Abstract: Time-dependent increase of static friction is characteristic of rock friction undera variety of experimental circumstances. Data presented here show an analogous velocity-dependent effect. A theor of friction is proposed that establishes a common basis for static and sliding friction. Creep at points of contact causes increases in friction that are proportional to the logarithm of the time that the population of points of contact exist. For static friction that time is the time of stationary contact. For sliding friction the time of contact is determined by the critical displacement required to change the population of contacts and the slip velocity. An analysis of a one-dimensional spring and slider system shows that experimental observations establishing the transition from stable sliding to stick-slip to be a function of normal stress, stiffness and surface finish are a consequence of time-dependent friction.

A numerical investigation of the influence of friction on energy absorption by a high-strength fabric subjected to ballistic impact

Abstract: A finite element analysis was conducted to study the influence of friction during ballistic impact of a rigid sphere onto a square fabric panel that was firmly clamped along its four edges. Projectile-fabric friction and yarn–yarn friction were investigated. Modeling indicates that friction dramatically affects the local fabric structure at the impact region by hindering the lateral mobility of principal yarns. Reduction of lateral yarn mobility allows the projectile to load and break more yarns so that fabric possessing a high level of friction absorbs more energy than fabric with no friction. The projectile-fabric friction delays yarn breakage by distributing the maximum stress along the periphery of the projectile-fabric contact zone. The delay of yarn breakage substantially increases the fabric energy absorption during the later stages of the impact. The yarn–yarn friction hinders the relative motion between yarns and thus resists de-crimping of fabric weave tightness. It induces the fabric to fail earlier during the impact process. The overall influence of projectile-fabric friction and yarn–yarn friction cannot be calculated by simply adding their individual effects.

Brittle frictional mountain building: 1. Deformation and mechanical energy budget

Abstract: An active fold-and-thrust belt is analogous to a wedge of soil or snow that forms in front of a moving bulldozer; such wedges exhibit a critical taper and a regional state of stress that is everywhere on the verge of Coulomb failure. The width of such a critically tapered fold-and-thrust belt does not depend on its brittle strength or frictional properties but rather on the accretionary influx rate of fresh material at its toe and on the rate of erosion; a steady state fold-and-thrust belt is one in which the accretionary influx is balanced by the erosive efflux. Rocks are accreted at the toe and then horizontally shortened as they are transported toward the rear; those that enter lower in the accreted section are more deeply buried before being uplifted by erosion. Mass balance and isotropy constrain the kinematics of this large-scale deformation, enabling us to infer the trajectories, residence times, and stress-strain histories of rocks incorporated into eroding fold-and-thrust belts. A typical rock resides in the steady state Taiwan wedge for 2–3 m.y. before it is uplifted and eroded; during its motion through the wedge, it experiences strain rates in the range 10−13 to 10−14 s−1. The mechanical energy budget of brittle frictional mountain building is described by the equation , where is the rate of work performed on the base and front of the fold-and-thrust belt by the subducting plate, is the rate at which energy is dissipated against friction on the decollement fault, is the rate at which energy is dissipated by internal frictional processes within the deforming brittle wedge, and is the rate of work performed against gravitational body forces in a reference frame attached to the overriding plate. The total mechanical power being supplied by the subducting Eurasian plate to the active fold-and-thrust belt in Taiwan is slightly over 3 GW. Approximately 60% of this work of steady state mountain building is being dissipated against friction on the decollement fault, and about another 25% is being dissipated against internal friction; this leaves only 15% or roughly half a gigawatt available to do useful work against gravity. In general, fold-and-thrust belts with moderate pore fluid pressures are dominated by work done against friction on the decollement fault; however, those with nearly lithostatic pore fluid pressures may be dominated by work done against gravity. Internal frictional dissipation is always less than basal frictional dissipation, as it is in Taiwan. An alternative and equivalent description of the mechanical energy balance of a steady state fold-and-thrust belt is provided by the equation . In this version the quantity on the left, , is the rate at which work is performed on the back of the wedge by the overriding plate and is the rate of work performed against gravity in a reference frame attached to the subducting plate. The latter quantity is always positive for any critically tapered fold-and-thrust belt whose decollement fault dips toward its rear, in contradiction to the central premise of the gravity spreading theory of fold-and-thrust tectonics.

Rubber friction, tread deformation and tire traction

Abstract: We study the role of rubber friction in tire traction with special emphasis on the load and velocity dependence of the friction coefficient. In the first part, we present some basic concepts of contact mechanics of slipping tires and analyze the influence of energy dissipation due to tread deformation on the friction force. Then, we apply a recently developed model of hysteresis and adhesion friction of rubber on self-affine road surfaces for estimating the load dependence of the kinetic friction coefficient in the contact area of slipping tires. In this context the impact of track morphology (sharp or blunt) on the kinetic friction characteristics is demonstrated. Finally, using the brush model for slipping tires we discuss consequences of the load dependence of the kinetic friction coefficient with respect to the overall tire friction and slip characteristics. We show that due to the presence of a load dependence of the local rubber-road friction coefficient the tread contact patch is globally never entirely in a fully sliding situation. The presented results yield a contribution to an improved physical understanding of the dynamic frictional contact of tires with road tracks during cornering and braking, especially in the case of cars equipped with Anti-Blocking Systems (ABSs).

The fall of a viscous thread onto a moving surface: a ‘fluid-mechanical sewing machine’

Abstract: A viscous thread falling onto a steadily moving horizontal belt shows a surprisingly complex range of behaviour in experiments. Low belt speeds produce coiling, as might be expected from the behaviour of a thread falling onto a stationary surface. High belt speeds produce a steady thread, whose shape is predicted well by theory developed to describe a stretching viscous catenary with surface tension and inertia. Intermediate belt speeds show several novel modes of oscillation, which lay down a wide variety of patterns on the belt. The patterns include meanders, side kicks, slanted loops, braiding, figures-of-eight, Ws, and also period-doubled versions of figures-of-eight, meanders and coiling. The experimental boundary between steady and unsteady behaviour occurs at a slightly lower belt speed than the loss of the steady solution for a stretching catenary.