Friction-induced vibration and noise (FIVN), exemplified by automotive brake squeal, lacks a single accepted generative mechanism. Chen, Ouyang and Wang (Friction 11(2):302–315, 2023) demonstrated on a simplified plate–slider rig — a steel plate carrying a small slider with a foam friction film — that squeal can arise without mode coupling and far from resonant frequencies, and proposed repeated cycles of partial detachment and reattachment of the contact surfaces, which provide a periodic impulsive excitation, as a candidate fundamental mechanism of FIVN. The mechanism has been demonstrated only on this simplified structure. The open problem is to establish it quantitatively in real, geometrically complex friction systems such as production automotive disc brakes, which involve multiple structural modes, thermal effects, wear, and realistic friction materials: to determine the onset thresholds in sliding speed and normal pressure that govern detachment–reattachment cycles and their impulsive excitation. The source further suggests, as a forward-looking engineering application, that controlling the contact dynamics could impede and suppress unwanted FIVN. A 2026 field review still classifies the proposal as one unproven candidate theory among several, and no follow-up work has validated it in production brakes.

Background

Friction-induced vibration and noise (FIVN) denotes self-excited vibration and the accompanying audible noise generated at sliding contact interfaces — the archetypal example being automotive disc brake squeal, a persistent source of warranty cost, and related phenomena such as clutch squeal and rail corrugation. Several mechanisms have been proposed over the past century to explain FIVN (reviewed in Kinkaid, O'Reilly and Papadopoulos, Journal of Sound and Vibration 267:105–166, 2003): mode coupling, in which friction-induced asymmetry of the stiffness matrix causes two structural modes to coalesce so that one becomes unstable (the basis of the complex eigenvalue analysis, CEA, used in industrial brake-squeal simulation software such as ABAQUS); stick–slip oscillation driven by the difference between static and kinetic friction; sprag–slip, in which the geometry of the contact makes the normal force self-amplifying; instability from a negative slope of the friction–velocity characteristic; and moving-load (follower-force) effects of the sliding contact. Further proposals include a hammering theory and friction time-delay effects. None of these mechanisms explains all observed FIVN phenomena — notably, squeal is observed without detectable mode coupling and at frequencies far from any structural resonance, so no fundamental mechanism is currently accepted. Chen, Ouyang and Wang (Friction 11(2):302–315, 2023) designed a deliberately simple test structure to probe this gap: a rectangular steel plate (with well-separated resonant frequencies) sliding against a small, effectively rigid slider whose contact face carries a smooth foam film that simulates a brake friction material. Measuring friction-induced vibration under various normal forces and sliding velocities, they found that squeal frequencies are highly sensitive to contact pressure even though the structural resonances do not change. A three-dimensional finite-element model of the rig was analyzed by both CEA and transient dynamic analysis (TDA, a time-stepping simulation of the dynamic contact). CEA found no mode coupling at any coefficient of friction examined (up to 1.0), whereas TDA reproduced the measured squeal and revealed a (nearly) periodic, time-varying contact-pressure distribution together with repeated cycles of partial detachment and subsequent reattachment of the friction pair at the interface. The authors proposed this detachment–reattachment process — a periodic impulsive excitation of the structure — as a foremost and fundamental mechanism of FIVN, noting that interfacial separation and reattachment in frictional sliding of an elastic disc under a moving slider had earlier been shown to be theoretically possible (Li, Ouyang and Guan, Nonlinear Dynamics 87:1045–1067, 2017). The proposal's significance is conditional on transfer to engineering systems: the authors suggest that controlling the detachment–reattachment of the brake pad and disc of an automobile brake system could impede and suppress unwanted FIVN. What the 2023 study did not do — and what remains open — is establish the mechanism quantitatively in real, geometrically complex brake systems with multiple vibration modes, thermal effects, wear, and realistic friction material properties, and determine the onset thresholds (in sliding speed and normal pressure) for detachment–reattachment cycles and the resulting impulsive excitation; turning the paper's illustrative control suggestion into concrete, validated engineering suppression strategies remains a forward-looking application.

Problem Statement

Establish the detachment–reattachment mechanism of friction-induced vibration and noise (FIVN), demonstrated by Chen, Ouyang and Wang on a simplified plate–slider test structure, as a quantitative, engineering-actionable account of FIVN in real, geometrically complex friction systems — with production automotive disc brakes (multiple structural vibration modes, thermal effects, wear, realistic friction material properties) as the reference case. This objective comprises two jointly supporting parts: (1) determine whether, and how quantitatively, repeated cycles of partial detachment and reattachment of the contact interfaces occur in real brake systems during sliding and whether they provide the impulsive excitation that generates the observed squeal, including the relative contribution of this mechanism versus co-existing candidate mechanisms (mode coupling, i.e. friction-induced coalescence of two structural modes; stick–slip oscillation, driven by the difference between static and kinetic friction; sprag–slip, where contact geometry self-amplifies the normal force; and instability from a negative friction–velocity slope); and (2) characterize systematically the onset thresholds — in sliding speed and normal pressure — that govern when detachment–reattachment cycles and the resulting impulsive excitation arise, as onset boundaries over the operating parameter range in the manner standard in FIVN research. An answer that conclusively shows the mechanism does not quantitatively transfer to real systems (for example, squeal persisting under measured continuous contact where the mechanism predicts detachment) resolves the problem in the negative direction.

References

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