The chemical and microstructural changes occurring during braking simulatio
n tests at the surface of a conventional brake pad material were investigat
ed mainly by scanning and transmission electron microscopy and surface anal
ytical techniques. It can be shown that patches of a third body material de
velop, comprising a compositional mix of all constituents of the pad and ir
on oxides from the disk. Milled debris particles still have the crystal str
ucture of barite, the major phase of the pad material, but the grain size i
s reduced drastically to the nanometer scale. The major wear mechanism is d
elamination of filler particles from the organic binder, supported by local
degradation of the phenolic resin during asperity heating. Quartz crystals
are preserved thereby adopting the function of primary contact areas. (C)
2001 Elsevier Science B.V. All rights reserved.