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Unformatted text preview: increase, decrease, or stay the same. a. in the rubbery region, increase the number of crosslinks b. in the rubbery region, increase the crystallinity c. in the glassy region, decrease the crystallinity d. in the leathery region, increase temperature e. in the leathery region, decrease the time at which you measure the stress relaxation modulus Continued on next page. 6. Using the figure below, estimate values for the stress relaxation modulus of PMMA under the following conditions: a. 120˚ C and 1000 hours b. 110˚ C and 1000 hours c. 110˚ C and 0.0001 hours d. 92˚ C and 10 hours e. 40˚ C and 10,000 hours 7. A polymer with a Tg of 50˚ C has a 2 hour creep compliance of 10-5 cm 2 /dyne at 80˚ C. At what time will it have the same creep compliance at 150˚ C? 8. The tensile strength of polystyrene is much less sensitive to strain rate than high density polyethylene. Explain why this is so....
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- Fall '10
- Materials Science, Stress relaxation modulus