452 Prakt. Met. Sonderband 30 (1999) 
Glass fiber 
| an 0 
— 7h s0 
Tim 
«15% a0 4 25.21810 
SE oN 
— 25%) /. 
— 30 [%] 17 
etn 35%) a 
® mean; 
values 
of. 40 
10 oT 5 \ 
; EL 50 
50 40 30 0 0 
Cellulose fiber Aramid fiber 
Fig. 3: Composition (in vol. %), detected wear of investigated samples and calculated isowear contours. 
Samples with high enough content of Kevlar and low enough content of glassy phase in bulk are typified by 
formation of a continuous friction layer (Fig. 4a). This friction layer is composed of deformed Kevlar fiber, 
which forms a basis (matrix) of the layer, and friction debris represented by fragments of bulk and products of 
ongoing chemical reactions. As apparent from Fig. 4a, the well-developed friction layer is able to catch 
fragments of glassy fibers and wear debris. Since the samples with well-developed friction layers exhibited the 
lowest wear rate, it is evident that this friction layer prevents excessive wearing. However, if the glassy fiber 
content is high enough and Kevlar content low enough, the friction layer may be easily destroyed. Accumulation 
of glassy fiber in the bulk is responsible for excessive wear of samples with higher than optimum content of 
glassy fiber. As shown in Fig. 4b, phenolic resin does not wet glassy fiber sufficiently and formation of 
relatively big holes on the friction surface due to fiber pullout was detected. Free fragments of glassy phase, 
which came from the bulk material to locate between the rubbing surfaces, are very probably responsible for 
destroying the Kevlar-based friction layer. On the other hand, it can be expected that the well-developed friction 
layer, which covers the surface of specimen (see Fig. 4a) diminishes the abrasive effect of glass by making the 
edges less sharp and the friction surface smoother. This was documented using profilometry [3]. 
Fig. 4: Friction layer covering the surface of sample #151 (a) and flaking out of accumulated and poorly wetted 
glassy phase (b)