Repeated Stressing Dynamic Crack Propagation

FIGURE 10.19 Crack growth step, A/, per stress application versus energy, G, available for fracture, for a natural rubber vulcanizate. (From Lake and Lindley (1965).) 

G Gq no crack growth occurs by tearing, but only by chemical (ozone) attack. 

The transitional value of G between one crack growth law and another, denoted G above, is found to be about 400 J/m. No explanation has yet been advanced either for the form of these experimental growth laws or for the transition between them. They must therefore be regarded for the present as empirical relations for the growth step. A/, per stress application. 

In practice it is customary to approximate crack growth over a wide range of G values (but greater than the threshold value, Gq) by a Paris Law relation that can be put in the form  

Crack growth in natural rubber compounds is brought about only by imposing the deformation if the deformation is maintained, the crack does not grow 

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