Lab6-PolymerStrengthF06-1 - Laboratory 6 Polymers:...

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MatE 215 Lab 6: Polymer Tensile Testing (Fall 06) Page 1 of 11 Laboratory 6 Polymers: Structure-Property Relationships with Tensile Testing Goal: To relate how a polymer’s mechanical strength and ductility are linked to its molecular structure and to predict & explain the transition in strength above the glass transition temperature. Learning Objectives: 1. Define a polymer , and give some properties and applications of polymers. 2. Give situations or applications in which a polymer might be used to replace a metal or ceramic. 3. Discuss how the bonding within the molecular chains vs. between the chains can affect properties. 4. Sketch, model, and describe the molecular structure (e.g., bonding, pendant groups) of polyethylene, polycarbonate, and polystyrene. 5. Explain how the structure of a thermoplastic affects its mechanical properties . 6. Rank the relative mechanical properties (such as stiffness, strength and ductility) of different polymers, based on their structure. 7. Explain the changes that take place at and then above the glass transition temperature (T g ) for thermoplastic polymers. 8. Identify the elastic modulus , yield strength , and % elongation from tensile tests of materials.
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MatE 215 Lab 6: Polymer Tensile Testing (Fall 06) Page 2 of 11 Why Study Polymers? More and more engineering designs are using polymers to replace other materials. They have become vastly popular because of their low cost, ease of synthesis, low density, and their wide range of properties. In general, they have relatively low strengths and get weaker at high temperatures. You can find polymers that are slippery, providing non-stick surfaces (like Teflon used in cookware); you can find those that can take a lot of elastic strain without losing their elasticity (rubber used in bungee cords); you can find polymers that are excellent thermal and electrical insulators (Bakelite used for integrated circuit packages). There are a few naturally occurring polymers, such as rubber, but for the most part, they are chemically synthesized from petroleum products. Polymers are truly “engineered” materials. What Are Polymers Made Of? If you were to examine the chemical make up of polymers, you’d find that they are composed mostly of carbon (C), and hydrogen (H). Other elements, like oxygen (O), nitrogen (N), chlorine (Cl), fluorine (F), phosphorus (P), and sulfur (S) are added to obtain certain properties. Most of the elements are strung off a long chain made up of C atoms (the “carbon backbone”). Polymers are thus molecular chains (sort of like spaghetti), and thus do not have an ordered and periodic atomic arrangement like metals or ceramics. Thus, polymers tend to be noncrystalline . You can think of polymers in three categories:
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This note was uploaded on 04/02/2008 for the course MATE 215 taught by Professor Granados during the Spring '07 term at Cal Poly.

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Lab6-PolymerStrengthF06-1 - Laboratory 6 Polymers:...

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