Electrostatic sensing of wear and friction dynamics in dry and starved-lubricated tribocontacts

Abstract

Wear mechanisms in dry and starved-lubricated contacts are critical factors contributing to the degradation of component surfaces. Real-time monitoring of wear progression presents significant challenges due to the complex nature of these mechanisms and the varying conditions under which they occur. Electrostatic sensing offers a way of monitoring wear progression as it is correlated with surface charging from wear debris, contact potential differences associated with surface films, material phase transformations and wear transitions as well as from additive adsorption. This research employs two types of electrostatic wear sensor: a bar sensor for in-situ monitoring of wear progression and an array sensor for charge mapping of the resultant wear mechanisms in the scar.

Two sliding wear tests with tool steel against bearing steel are presented. Tests were conducted under dry sliding conditions or partially lubricated. Positive charge signals were detected for oxidational wear under dry contact conditions. Elemental mapping confirmed a patchy oxide film had developed and loose oxide wear debris became charged. Correlation is seen between surface charge maps and the patchy surface oxide films. A correlation was also found between the coefficient of friction and electrostatic charge, highlighting the potential of electrostatic sensors in detecting changing friction and wear levels. Negative charge signals were observed under starved sliding conditions using polyalphaolefin (PAO), primarily attributed to the degradation of PAO under high shear rates and tribo-charge mechanism. The charge progressively changed towards a more positive value, suggesting the progression of mild oxidational wear. Only very mild wear was measured at the end of the test (i.e. plastic flow of asperity material into valleys).

A map of real-time wear progression and measurement of instantaneous wear rate of oxidational wear and mild wear induced by partially lubricated contacts are presented. This advancement could significantly impact digital tribology, as the electrostatic sensing allows the surface chemistry to be better characterised. This allows for monitoring of the wear processes in action, allowing for better optimisation of predictive maintenance, as the information is real-time and the sensor is non-invasive.

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Identifiers

ORCID for Jo Grundy: orcid.org/0000-0003-2583-5680

ORCID for Robert Wood: orcid.org/0000-0003-0681-9239

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