Lecture34-Notes - ME 382 Lecture 34 EFFECT OF TEMPERATURE...

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ME 382 Lecture 34 1 E FFECT OF TEMPERATURE ON ELASTIC MODULUS OF POLYMERS Below T g Above T g Thermoplastics Only secondary bonds between chains Modulus dictated by energy Large strains cause fracture Thermoplastics No bonding between chains Modulus dictated by entropy Large strains permanent deformation as chains slide over each other Thermosets Extensive covalent cross-links & secondary bonds between chains Modulus dictated by energy Large strains cause fracture Thermosets Extensive covalent cross-links between chains. Modulus dictated by energy Large strains involve bond rupture and yielding (permanent deformation) Elastomers A few covalent cross-links & secondary bonds between chains Modulus dictated by energy Modulus 1 GPa Elastomers A few covalent cross-links Modulus dictated by entropy Large strains recovered elastically because the few cross-links provide memory of unstrained state. Modulus increases with extent of cross linking, chain size and side groups E FFECTS OF TIME ON D EFORMATION OF P OLYMERS Chain motion impeded by tangles activation energy needs to be overcome 50 100
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ME 382 Lecture 34 2 Molecules and atoms vibrate with a frequency
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This note was uploaded on 09/08/2011 for the course MECHENG 382 taught by Professor Thouless during the Fall '08 term at University of Michigan.

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Lecture34-Notes - ME 382 Lecture 34 EFFECT OF TEMPERATURE...

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