Grooves in scratch testing
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Lev Rapoport, Yakov Soifer, and Armen Verdyanb) Department of Sciences, Holon Institute of Technology, 58102 Holon, Israel
Yakov Soifer Department of Sciences, Holon Institute of Technology, 58102 Holon, Israel; and Department of Physical Electronics, Faculty of Engineering, Tel Aviv University, 69978 Tel Aviv, Israel (Received 16 December 2006; accepted 12 April 2007)
For a number of polymers with a variety of chemical structures and different properties, we have performed scratch-resistance tests and investigated the profiles of the grooves formed using a profilometer. Three main kinds of material response are seen: plowing; cutting; and densification. The cross-sectional areas of the grooves include the groove and side top-ridge areas. The latter are smaller than the former, an indication of densification at the bottom and the sides of the groove; the effect can be connected to molecular dynamics simulations of scratch testing. The sum of the groove and top-ridge areas is the highest for Teflon, thus providing another measure of its poor scratch resistance. The Vickers hardness of the polymers was also determined. An approximate relationship exists between the hardness and the groove area. An unequivocal relationship between the hardness and the total cross-sectional area of the material displaced by the indenter is found. The resulting curve can be represented by an exponential decay function.
I. INTRODUCTION
The economic well-being of industry is dependent on material wear, as argued eloquently by Rabinowicz.1 As noted in an earlier article of ours,2 the problem is particularly serious for relatively soft polymer surfaces. Wear has been defined as the loss of solid material from the rubbing surface due to mechanical interaction at asperities.1 However, material displacement on the surface without any changes in weight or volume also occurs.3 Such displaced material can either mitigate subsequent wear by material transfer, by blunting of the asperities, or else by becoming a part of the later more pronounced wear. It is generally recognized that the most common types of wear of polymers are those caused by abrasion, adhesion, or fatigue.4 There is ongoing work on mitigating wear by a variety of means; for a review of polymer tribology see Ref. 5. As an example, both ␥-irradiation and the addition of
a)
Address all correspondence to this author. e-mail: [email protected] b) Deceased. DOI: 10.1557/JMR.2007.0307 J. Mater. Res., Vol. 22, No. 9, Sep 2007
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carbon black as a filler have been used to achieve lower friction and higher sliding wear resistance.6 Another line of work aims at an improved understanding of wear mechanisms. The surface-damage-maps approach developed by Briscoe and coworkers7 belongs to this category. Important here is the fact, analyzed by Maeda et al.,8 that for hard solid sliding over a soft material (polymer) the damage occurs concurrently with energy dissipation. Our work belongs to the second category defined above: an understand
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