ENGR 240 - 10.1.07

ENGR 240 - 10.1.07 - Terms used with tensile testing •...

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ENGR 240 – October 1, 2007 Crystallinity – o More Less Linear Cross-linked Simple Complex Slow Cooled Fast Cooled PE PMMA Less bulky side group Bulkier side groups Two Models for Crystalline Polymer Structure o Lamella Chains fold back on themselves forming stacks of folded chains o Spherulites Aggregates of lamella that form a spherical shape Plastic Types (1-7) o PETE/PET: polyethylene terephthalate Form of polyester Water and soda bottles o HDPE: high density polyethylene Milk bottles, detergent, oil bottles o V: vinyl, polyvinyl chloride (PVC) Food wrap, some car products o LDPE: low density Polyethylene Some plastic bags, shrink wrap o PP: Polypropylene Bottle tops, some refrigerated containers o PS: Polystyrene Throw-away utensils/cups/plates, meat packing o Other Layered or mixed plastics Recyclable plastic types o PETE (1), HDPE (2) o Some LDPE (4) o Do not recycle others Can’t, don’t know how, not efficient End Exam 2 Information Mechanical Properties o
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Unformatted text preview: Terms used with tensile testing • Applying a tensile force (i.e. pulling on it) Engineering Stress (σ) • σ = (applied force perpendicular to the cross-sectional area) h (initial cross-sectional area) • σ = F/A psi, Pa, N/m 2 • Common tensile Specimens – dog-bone specimens o A = (π/4)(d ) 2 where d is in the very center Engineering Strain (ε) • ε = change in length = Δℓ initial length ℓ • ℓ is the original length of specimen were all of the deformation will take place o Compression not as common • more difficult than tensile • not as informative for structural applications o Hooke’s Law E = σ/ε • E modulus of elasticity, young’s modulus Stress and strain are linearly proportional Typical values of the modulus for metals • 40-400 GPa stiffer materials have larger modulus (smaller ε, stretches less)...
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ENGR 240 - 10.1.07 - Terms used with tensile testing •...

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