CHARACTERIZATION OF STICKY DEBRIS GENERATED DURING SMEAR WEAR

Guangchang Wu; Paul Sotta; Menglong Huang; Lewis B. Tunnicliffe; James J. C. Busfield

doi:10.5254/rct-23.236012

Article Contents

ABSTRACT
INTRODUCTION
SMEAR WEAR
EXPERIMENTAL
RESULTS AND DISCUSSION
CONCLUSION
ACKNOWLEDGEMENTS
REFERENCES

Editorial Type:

Article Category: Research Article

Online Publication Date: 30 Dec 2023

CHARACTERIZATION OF STICKY DEBRIS GENERATED DURING SMEAR WEAR

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Page Range: 588 – 607

DOI: 10.5254/rct-23.236012

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ABSTRACT

Smear wear behavior has often been observed during rubber abrasion, especially under mild test severities. It generates degraded sticky rubber debris that often produces erratic measurements of abrasion weight loss. Various practical methods to avoid or remove the debris from the abrasion test surface have been reported, such as applying a drying powder lubricant. However, the detailed mechanism of smear wear behavior is still not clear. Various characterization techniques are applied to investigate the smear wear of both an unfilled NR model compound and a commercial carbon black (CB)–filled SBR tire tread compound obtained during blade abrasion testing. The debris showed lower molecular weight and higher oxygen content than the virgin materials. In addition, 75% of the smear wear was found to be de-crosslinked during smear wear, as detected by the double quantum-NMR technique. For the first time, it is demonstrated that both the polymer itself and crosslinking points are broken down during smear wear. The effect of the smear layer on friction and abrasion is also discussed.

Fig. 1.

Blade abrasion apparatus.

Fig. 2.

Cumulative weight loss at 20 N normal force.

Fig. 3.

Smeared rubber surface of NR0 tested under a normal force of 4N after 1000 wear cycles.

Fig. 4.

Fully developed abrasion pattern under 8, 12, 16, and 20 N normal force (from left to right) for NR0.

Fig. 5.

Abrasion surface of SBR50 under 20N normal force: (a) smear layer surface at 10000 cycles, (b) transition phase surface at 60000 cycles, and (c) abrasion pattern at 110 000 cycles. The arrow in (a) shows the sliding directions; this direction also applies to the other two figure panels.

Fig. 6.

Collected sticky debris during the smear wear: (a) NR0 collected during the test with a normal force of 4 N and (b) SBR50 collected during the test with a normal force of 12 N.

Fig. 7.

DSC trace of the smear wear and bulk materials for NR0.

Fig. 8.

TGA weight loss in nitrogen up to 700°C and in air from 700 to 1000°C of (a) NR0 and (b) SBR50.

Fig. 9.

TGA weight loss in air of (a) NR0 and (b) SBR50.

Fig. 10.

Normalized GPC trace of the rubber melt and smear wear of (a) NR0 and (b) SBR50.

Fig. 11.

(a) Fresh smear wear of SBR50 dissolved in toluene immediately after abrasion and (b) placed in toluene after a 24 h dwell time.

Fig. 12.

Reference and DQ signal (normalized to I_ref = 1 at zero evolution time) in uncured NR melt and NR0 sticky wear debris.

Fig. 13.

Reference signal subtracted DQ signal for uncured NR melt and NR0 smear wear. The long-time tail contribution is shown for each case.

Fig. 14.

Reference signals and DQ signals for unworn SBR80 and SBR80 smear wear. The long-time tail contribution, corresponding to so-called defects, or uncrosslinked material, is shown for each case. Inset is a zoom of the DQ signals at short DQ evolution time.

Fig. 15.

Normalized DQ curves for NR0 melt and NR0 smear wear.

Fig. 16.

Normalized DQ curves for unworn SBR80, unworn SBR80 manually cut into small pieces and SBR80 smear wear debris.

Fig. 17.

Friction profile during blade abrasion for SBR50 at 8 N normal force. Black line, the oscillating real time recorded data and red line, logarithmic trend of the data.