Creep, rubber-toughened

The same techniques were used in the present work to study the effects of orientation and rubber content upon the creep behavior of rubber-toughened SAN polymers at room temperature. As in previous work, the tests were conducted at low strain rates and were terminated at longitudinal strains between 5 and 6%. 

The loss of modulus caused by crazing becomes less pronounced as the draw ratio is increased, especially in tests carried out at lower stress levels. This observation supports earlier conclusions drawn from creep studies on other rubber-toughened plastics (6) if the specimen can reach a strain of 5% largely or entirely by shear mechanisms, the loss of modulus resulting from the creep and recovery program is quite small if, on the other hand, crazing is the dominant mechanism, the loss in modulus is large. 

The creep of a rubber-toughened polypropylene at TXfC can be fitted to the equation... 

It should be mentioned that even when rubber toughening is successful there are compromises which must be made, such as reduced modulus, yield strength, creep resistance and, in some cases, glass transition... 

The yield stress (Luder s band formation) vs. creep to yield time from Eig. 11.12 is shown in Eig. 11.16 and compared to Eq. 11.35. The constants A, B and C in Eq. 11.35 were determined from the creep to yield data. Poisson s ratio was assumed to be 0.4 and all other parameters were determined for the modified Bingham model. A similar procedure was used to obtain the creep to yield behavior of a rubber-toughened adhesive (Brinson, et ah, (1975)). 

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