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Materials Homework Chapter 16

Materials Homework Chapter 16 - This means that the sliding...

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Homework for Chapter 16 Lauren Beauchamp MSE 280-2B Due Thursday, November 18, 2010 Problems 16.2, 16.6, and 16.21 1. Define: a. Thermoplastic - Linear or branched polymers in which chains of molecules are not interconnected to one another. b. Thermosetting Plastics - polymers that are heavily cross-linked to produce a strong three dimensional network structure c. Elastomers - These are polymers (thermoplastics of lightly cross-linked thermosets) that have an elastic deformation >200% d. Thermoplastic Elastomers - Polymers that behave as thermoplastics at high temperatures, but as elastomers at lower temperatures. 1. Explain why low-density polyethylene is good to make grocery bags, however, super high molecular weight polyethylene must be used where strength and very high resistance is needed. a. The bonding within the chains is stronger in ultrahigh molecular weight polyethylene.
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Unformatted text preview: This means that the sliding in the chains is more difficult leading to higher strengths, higher stiffness, and high melting points. Because the stiffness is also affected it would not be ideal in grocery bags, because of the lack of flexibility. However, it is great for anything that requires high strength and resistance. 1. A stress of 1000 psi is applied to a polymer that operates at a constant strain: after 6 months the stress drops to 850 psi. For a particular application, a part made of the same stress of 900 psi after 12 months. What should be the original stress applied to the polymer for this application? a. Using the formula: i. σ=σ ℮(-t÷λ) 850=1000℮(26/λ) λ=26/(ln(0.1625) λ= 160 weeks 900=σ ℮(-52/160) 900=σ ℮(-0.325) 900=σ (0.723) σ =1246...
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