ME 417
Advanced Materials Engineering
Assignment 5
1. a) Sketch the Volume-Temperature diagrams for a fully amorphous material, a fully crystalline material, and a partly crystalline material. b) Label the melting and glass transition temperatures on the graphs in a) c) At room temperatures which of the following are above their glass transition temperature (polyethylene, polypropylene, PMMA, Nylon (PA))
2. a) Define Creep. b) Define Stress Relaxation
3. How is the definition of yield strength different for polymers than it is for metals?
4. What is the Secant Modulus and why is it used for polymers?
5. According to Ticona, what is the effect of weld line on the strength of Celcon?
6. We plan to use a Delrin 100 as a housing (short term loads/displacements) in an indoor application with a safety factor of 3 on the Tensile Strength. Estimate the design stress and describe how you arrived at that number.
7. Fig 11 of the Delrin graphs you are given show Isochronous Stress Strain curves. Use the information in that graph to create a Strain-Time creep curve. Plot creep curves for 10, 15, and 20 MPa.
8. Suppose you have a Delrin gear you wish to press fit onto a 1 inch diameter steel shaft. a) determine the inside diameter of the gear such that there is a 5000 psi stress at the ID of the gear immediately after pressing. b) Suppose we are worried about stress relaxation causing a reduction in the force at the joint which may result in slipping of the gear on the shaft. How long will it take for the force at the joint to drop by 50%?
9. Suppose you are doing a failure analysis of what you believe to be a glass reinforced Celcon polymer. Define each of the following and, for this particular polymer, state the useful information you get from each. a) FTIR b) TGA c) DSC d) TMA
10. a) Describe the differences would you expect to see between brittle and ductile fracture in polymers? b) How would you distinguish fatigue failure from other fracture modes?
11. When selecting a viscoelastic material for use in a structural application, what information about the loading environment must be collected (other than the material properties or behavior)
12. a) Describe crazing in polymers, especially how it differs from simple cracking. b) Describe the difference between shear and crazing in polymers. c) In compression, would polymers more likely fail in shear or crazing? Why?