Losses and Negative Resistance Branch

Mullins(35) pointed out that viscoelastic losses at the crack tip are related to the frequency dependence of the loss modulus E (the imaginary part of Young s modulus). As a matter of fact, E varies as fof polyurethane at low frequency.(39) Such a correlation between 

FIGURE 8. Glass ball on polyurethane influence of withdrawal speed on the recorded force. (From Reference 38.) 

FIGURE 9. Schematic diagram of a logG-logv curve showing viscoelastic effects. 

FIGURE 10. Experimental G(v) curve for peeling an adhesive tape, with its two branches of stable crack propagation. (From Reference 52.) 

Inertial effects due to kinetic energy of the roller can be taken into account in a 

---