MECHENG 382 Lecture Notes - Natural Rubber, Entropy, Epoxy

• School: U of M
• Department: Mechanical Engineering
• Course: MECHENG 382
• Professor: All

Document Summary

No unique set of properties: accurate data for design must be measured or obtained from supplier. Unlike metals, no standards or well-defined properties that can be looked up. Data-book values are approximate (even for modulus: general properties: (i) (ii) (iii) (iv) E 1-8 gpa (down to 1 mpa for an elastomer) Design often stiffness limited (because of low modulus) Properties sensitive to temperature (around room temperature) and time. Polymers are very sensitive to u/v radiation and o3 (become stiff & brittle: three types of polymers determined by nature of bonding between chains. Secondary bonding (hydrogen or van der waals) (i) (ii) (iii) chain entanglements. Thermoplastics: no covalent cross-links between chains, below glass transition temperature, tg, there is secondary bonding between chains. Lecture 33 - polymers: above tg secondary bonds melt leaving molecules free to slide over each other. Viscosity drops with increased temperature: thermoplastics can be melted and reformed.