3 064 Quiz 3 Sample Questions 1 Consider a unidirectionally reinforced fiber matrix composite a What elastic constants relative to the fiber and transverse directions are needed to describe this material b Describe how you would compute the elastic modulus in a direction inclined at an angle to the fiber direction c Explain why the tensile strength seems to increase when the stress is applied at a small angle to the fibers as seen in the figure below tensile strength sq GPa 1 5 0 5 0 0 30 60 90 angle q 2 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 3 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 4 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 e f How does compounding polystyrene with a suitable distribution of rubber particles improve its properties Why does a short fiber composite have inferior strengths and stiffnesses compared to continuous fiber composites Why might a plot of E vs KIc be useful in materials selection