Engineering materials

Engineering materials
1. Explain the term grain when used in connection with the structure of metals.
2. Explain what is meant by
a. the term alloy.
b. ferrous alloy and
c. non-ferrous alloy.
3. Name the three types of lattice structures of metals and identify how many atoms in each unit cell.
4. Explain hexagonal close packing and cubic close packing using diagrams if necessary.
5. Defined the term amorphous
6. How does the grain size in a metal affect its properties?
7. Describe the effects on the grain structure and properties of a metal of cold working.
8. Describe the effects on the properties of carbon steels of increasing the percentage of carbon in the alloy.
9. What types of structure (in terms of grains) might you expect for a metal which is (a) ductile and (b) brittle?
10. Define the terms ferrite, austenite and pearlite
11. A pure metal is formed into an alloy by larger atoms being forced into the spaces in its crystal structure. What changes
might be expected in the properties and why?
12. Describe how the mechanical properties of a cold-worked metal changes as its temperature is raised from room
temperature to about 0.6Tm where Tm is the melting point on the kelvin scale.
13. How does the temperature at which working is carried out determine the grain size and so the mechanical properties?
14. Why are the mechanical properties of a cold-rolled metal different in the direction of rolling from those at right angles to
this direction?
15. How does a cold-rolled product differ from a hot-rolled one?
16. Brasses have recrystallization temperatures of the order of 400oC. Roughly, what temperature should be used for the
hot extrusion of brass? Explain.
17. A brass, 65% copper and 35% zinc, has a recrystallization temperature of 300oC after being cold worked so that the
cross-sectional area has been reduced by 40%.
(a) How will further cold working change the structure and properties of the brass?
(b) To what temperature should the brass be heated to give stress relief?
(c) To what temperature should the brass be heated to anneal it?
(a) What is the maximum hardness possible with cold-rolled copper?
(b) Copper plate, already cold worked 10%, is further cold worked 20%. By approximately how much will the hardness
19. Compare the properties of low and high-density polyethylene and explain the differences in terms of structural
differences between the two forms.
20. Why are (a) stabilizers; (b) plasticisers and (c) fillers added to polymers?

21. Describe how the properties of PVC depend on the amount of plasticiser present in the plastic.
22. Explain how elastomers can be stretched to several times their length and still be elastic and return to their original
23. Calculate the tensile modulus of a composite consisting of 45% by volume of long aligned glass fibres, tensile modulus
76 GPa, in a polyester matrix, tensile modulus 4 GPa. In what direction does your answer give the modulus?
24. In place of the glass fibres referred to in problem 23, carbon fibres are used. What would be the tensile modulus of the
composite if the carbon fibres had a tensile modulus of 400 GPa?
25. Long boron fibres, tensile modulus 340 GPa, are used to make a composite with aluminium as the matrix, the
aluminium having a tensile modulus of 70 GPa. What would be the tensile modulus of the composite in the direction of
the aligned fibres if they constitute 50% of the volume of the composite?
26. How will the properties of composites differ if they are
a. made of long fibres all orientated in the same direction and
b. short fibres with random orientation?