Nanoscratch and friction: An innovative approach to understand the tribological behaviour of poly(amide) fibres J. Cayer-Barrioz a, * , D. Mazuyer a , A. Tonck a , Ph. Kapsa a , A. Chateauminois b a Laboratoire de Tribologie et de Dynamique des Syste `mes, UMR 5513, Ecole Centrale de Lyon, 36 avenue Guy de Collongue—69130 Ecully, France b Laboratoire de Physique Chimie des Polyme `res et des Milieux Disperse ´s, UMR 7615, ESPCI, 10 rue Vauquelin—75231 Paris, France Available online 6 June 2005 Abstract The analysis of the wear resistance of polymeric fibres requires a better understanding of both their abrasive scratch behaviour and their frictional response. These aspects have been investigated at the nanometre scale using the resources of a modified surface force apparatus. In an attempt to simulate the abrasive wear losses, nanomachining experiments have been carried out which consists in the repeated scratching of a portion of the fibre surface by the rigid indenter. However, an analysis of the resulting surface topography indicated a significant plastic grooving of the fibre surface with no evidence of wear losses as it was observed at the macroscopic scale. Single pass nanoscratch experiments realised at various sliding speeds also allow discussing the relative contributions of both the material viscoplasticity and the tip/material local interactions on the frictional response. When the sliding speed was incrementally changed during a scratch experiment, it was observed that the associated friction variation was accommodated on a 50 nm distance, independently of the sliding speed. q 2005 Elsevier Ltd. All rights reserved. Keywords: Friction; Nanoscratch; Nanotribology; Poly(amide) fibre 1. Introduction Over the past years, the tribological behaviour of polymeric materials has drawn a considerable interest. Polymers’ tribological performance is particularly relevant in the field of textile applications, where friction and wear properties are important aspects during both fibre processing and end-using. Even if poly(amide) fibres have emerged as an interesting alternative to natural fibres (such as cotton and wool), their surfaces remain highly sensitive to scratches. Such damage shortens the fibre life, and there- fore, hinders their use for high performance textile structures. A detailed investigation [1,2] of the wear mechanisms of poly(amide) fibres was previously carried out using a tribometer simulating the fibre abrasion processes at the macroscopic scale. The damaged contact zone on the fibre presents numerous abrasive scratches which are aligned along the sliding direction, as shown in Fig. 1. At the macroscopic scale, very important volumetric wear losses are measured. The detailed analysis of such abrasive processes is, however, much complicated by the multiple dynamic asperity interactions involved in macroscopic contacts between the rough surfaces. In order to bypass these difficulties, indentation and scratching experiments have long been recognized as a potential route to mimic and characterize in a more controlled manner the deformation and failure modes involved in asperity engagements [3]. Most existing models describing the scratch properties of materials consider a moving hard tip grooving the surface, but they do not take into account the viscoelastic and/or viscoplastic effects which can be significant in the case of polymeric materials [4–6]. The early description of Bowden and Tabor [4] assumed that the tangential load necessary to move a grooving tip laterally under a constant normal load is the sum of two separate components, namely an interfacial shear component (often denoted to as the ‘adhesive’ component of friction) and a bulk ploughing term. As a first approximation, these two components were assumed to be non-interactive. Recent experiments using the resources of in situ visualization demonstrated, how- ever, that strong interactions between the interface and ploughing components can be involved during the scratch- ing of viscoelastic polymers [7]. Such effects are especially Tribology International 39 (2006) 62–69 www.elsevier.com/locate/triboint 0301-679X/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.triboint.2005.04.010 * Corresponding author. Tel.: C33 4721 86288; fax: C33 4784 33383. E-mail address: juliette.cayer-barrioz@ec-lyon.fr (J. Cayer-Barrioz).