How common is the steady-state? The implications of wear transitions for materials selection and design

Abstract

a b s t r a c tLike other forms of mechanical damage, wear may progress in stages, the length and severity of which depend upon the type of wear and the nature of the tribosystem. Wear rates, wear coefficients, and wear factors are commonly reported as normalized quantities whose units imply a linear relationship with variables such as sliding distance, number of repetitive cycles, elapsed time, and normal force. Unfortunately, such implied linearity can be misleading in design-specific material selection. Examples of non-linear wear characteristics are provided for erosive wear, abrasive wear, fretting wear, and nonabrasive (also known as 'adhesive') wear. The differences between a system-specific, linearized wear rate and the instantaneous wear rate will be discussed, as will the difference between sequential and simultaneous wear transitions. The practice of linear normalization ignores such phenomena as incubation periods, running-in, and post-steady-state transitions, leading to misleading dependencies of wear rates on the sliding distance and sampling interval. Some current ASTM testing standards, notably those on erosion testing, account for the non-linear behavior of wear, but others, such as tests for sliding wear, usually do not. This article discusses non-linear wear behavior of several kinds, how the data can be treated, how wear rate notation can be improved, and how recognizing certain non-steadystate behavior can improve the basic understanding, modeling, and testing of wear.

Improving rail wear and RCF performance using laser cladding

“…However, as shown in Figure 4, and discussed in great detail in [9], the wear rate is constantly changing as different wear mechanisms come to dominate due to shifts in wear transition. With reference to Figure 4 it seems as if 30,000 cycles was sufficient for most of the samples to transition into the "steady wear" regime as depicted in Figure 16.…”

In situ stylus profilometer for a high frequency reciprocating tribometer

“…The experimental conditions were such that this contact exhibited an incubation period followed by running-in and steady state [13]. The incubation period was accompanied by a friction coefficient of 0.3 and lasted until halfway through the second minute of sliding whereupon the friction coefficient doubled to 0.6.…”

“…In some cases run-in is proceeded by an incubation period, for example where an oxide film protecting one or both surfaces is gradually worn away, or where material is initially transferred between sliding surfaces before being removed from the contact [13], Figure 1. Figure 1: Two example sliding wear behaviours: run-in followed by steady state (blue) and incubation followed by run-in and steady state (yellow), adapted from [13].…”

“…Figure 1: Two example sliding wear behaviours: run-in followed by steady state (blue) and incubation followed by run-in and steady state (yellow), adapted from [13].…”

Tools for Imaging and Characterizing Worn Surfaces

“…Associating a specific type of wear and wear rate to a given tribosystem may be convenient for damage diagnosis and wear forecasting; the truth is that many, if not most, real engineering tribosystems do not operate under steady-state conditions [65]. As a result, wear damage can build up incrementally rather than smoothly and continuously.…”