3.064 Quiz 3 – Sample Questions 1. Write out the 1-D form of the energy equation and explain the origin of the various terms. What are the units of the various material constants? 2. Derive expressions for the x-velocity in a narrow channel subjected to simple drag-plus-pressure gradient flow conditions. 3. Define and explain the significance in polymer processing of the Foucault , Reynolds and Damkohler (or Brinkman) numbers. Explain how consideration of the Foucault number leads to avoiding thick sections in polymer processing. 4. Consider the metering zone of a single-screw extruder (neglect temperature variations): a. Sketch the flow field and indicate the boundary conditions. b. Describe the influence of the die on this field. c. Describe how you would go about calculating the volumetric flow output of the extruder, and the power needed to drive it. d. Explain the graph: 5. Give three examples of (a) commodity plastics, (b) engineering plastics, (c) elastomers, (d) transparent plastics, (e) thermoset resins for composites. Include chemical formulas if you can. Give typical applications for these materials. 6. How does “tentering” produce biaxially oriented film or sheet? What effect does this orientation have on mechanical properties? 7. Sketch and describe the operation of a reciprocating-screw injection molder, and define the terms (a) nozzle, (b) freeze plug, (c) sprue, (d) runner, (e) gate, (f) part line, (g) knock-out pin. 8. What is “die swell?” How is it caused by fluid elasticity? 9. Write out a one-dimensional form of the transient heat transfer equation, and explain the physical meaning of the various terms. 10. Why is it usually possible to neglect the convective term in the momentum (velocity) equation for polymer melt flows, but not the corresponding term in the energy (temperature) equation? 11. Short answers: a. Why is polyethylene a good barrier against water transport but not for CO2? b. Why are some polymers transparent and some opaque or translucent? Why are some yellow?c. What is it about polystyrene that makes it a poor choice for children’s toys? d. How does compounding polystyrene with a suitable distribution of rubber particles improve its properties? e. Why is pressure applied during composite laminate cure? f. How are one-gallon milk bottles made? What material is used? Hood advertises that their “white” bottle is better at preserving milk quality; might this be true? g. Why does a short-fiber composite have inferior strengths and stiffnesses compared to continuous-fiber composites? h. Why might a plot of E vs. KIc be useful in materials selection? i. Why do molded polymer parts sometimes exhibit a nonuniform internal stress that varies from compression at the outer surfaces to tension in the interior. Why do injection-molded parts sometimes exhibit a stress distribution with tension on the outside and compression on the insider, especially near the gate? What are the consequences of such