Corrigendum to “Thermodynamics of grease degradation” [Tribol Int 137 (2019) 433–445] (Tribology International (2019) 137 (433–445), (S0301679X19302798), (10.1016/j.triboint.2019.05.020))

Jude A. Osara, Michael D. Bryant

Research output: Contribution to journalComment/Letter to the editorAcademicpeer-review

Abstract

The authors regret to report the presence of high-frequency measurement noise in the (a) plots (NLGI 4 grease results) published in the original article. In Section 6. Results and data analysis, sampling rate is 0.1 Hz, rendering Δt = 10 s for use in numerical differentiation and integration of data. However, the (a) plots of the figures in the article present data and results at 1 Hz (10 times faster), thereby introducing the high-frequency transients, more easily observed in Figures 3(a) and 5(a). The fluctuations in the (b) plots, which use the correct Δt = 10 s, can be observed to be less closely packed (lower frequency) than the (a) plots transients. The thermocouples’ time constant was 5 s, rendering their output “too slow” for 1 Hz sampling rate and introducing unrealistic noise between actual data points. In this corrigendum, the high-frequency noise has been isolated and removed. Although accumulation values are not impacted given noise fluctuations were about a zero mean, plots of parameters that include temperature change rate dT/dt (e.g. MST entropy rate and phenomenological shear stress) show reduction in fluctuation amplitudes, revealing more observable overall trends. DEG domains (Figure 4 in the original article) and coefficients are not impacted by this error. Discussion of observed trends is not affected as high-amplitude fluctuations persist, albeit not as high as originally reported. Below are the corrected versions of the affected plots. Figure numbers and captions are from the original article which includes the (b) plots. Fig. 1. Monitored parameters during (a) 3-hr grease shearing of Aeroshell 14 NLGI 4 aircraft calcium grease (higher consistency) and (b) Valvoline NLGI 2 general multi-purpose lithium grease, at a constant shear rate of 28.8 s −1. Temperatures are on the right axes and instantaneous shear stresses on the left. [Figure presented] Fig. 2. Components of phenomenological Helmholtz entropy generation versus accumulated shear stress for (a) Aeroshell 14 NLGI 4 aircraft calcium grease and (b) Valvoline NLGI 2 general multi-purpose lithium grease. [Figure presented] Fig. 3. Phenomenological Helmholtz entropy generation rates over time during shearing of (a) #4 grease and (b) #2 grease. [Figure presented] Fig. 5. Measured and phenomenological shear stresses versus shearing time for (a) #4 grease and (b) #2 grease. [Figure presented] The authors would like to apologise for any inconvenience caused.

Original languageEnglish
Article number106369
JournalTribology international
Volume150
DOIs
Publication statusPublished - Oct 2020
Externally publishedYes

Keywords

  • Greases
  • Degradation
  • Shear stress
  • Lubrication

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