Schallamach waves

Figure 8.22. (a) Schallamach waves at rubber/glass interface (b) pull-out of smooth fiber from polymer (c) low angle peeling of film. 

Friction - adhesion aspects A D ROBERTS Influence of adhesion on friction Schallamach waves... 

Figure 2. The classical distinction of friction modes. The contact mechanical work, or friction, leads to adhesive and cohesive deformations in the contact. This produces deformations which can be elastic, plastic or brittle in nature. Heat is produced. The scheme does not show the friction processes associated with Coloumbic (ratchet) friction or the Schallamach wave phenomena. The two-term non interaction model of friction considers the adhesive and cohesive (ploughing) to be separate and non-interacting.

Stick-Slip Phenomenon and the Schallamach Waves for Elastomers... 

Figure 5 Various forms of the adhesion experiment suitable for studying elastomers in contact with rigid substrates (a) peel test (b) and (c) growth of a crack in tension (d) blister test (e) rolling (f) the tackometer (g) rebound (h) Schallamach waves and (i) propagation of a macro dislocation in ironing. The rigid substrate is shaded (adapted from ref. 59)...

The values of Gj v) as measured from Schallamach wave propagation are similar to those obtained by more conventional means " see Figure 5. 

Perhaps the major weakness of all these theories is that they are too much concerned with getting the right answer and too little concerned with what actually happens at the interface. This is brought out most clearly by Schallamach s recent paper in which he described an optical study of the contact between a rubber hemispherical slider and a transparent perspex flat. He shows that adhesion between the surfaces causes buckling of the rubber and generates waves of detachment" which traverse the contact area at a high speed from front to rear. The energy dissipation process must be very different from that proposed in most of the past theories. These waves of detachment are observed with hard, as well as with soft rubbers (Courtel ), but whether they always occur and under what conditions is not yet established. Evidently we need a new look, literally, at the problem. 

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