Materials, Tribotechnology and Surface Engineering
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Module Code: MP 3702
Materials, Tribotechnolgy and Surface Engineering
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Using CES Edupack at level 2, are the fracture toughness, K1c, of the common polymers Polyethylene terephthalate (PET), Polyamides (Nylons, PA), or Polyethylene (PE)
larger or smaller than the engineering ceramic zirconia, ZrO2? Are their toughness G1c = (K1c)2 / E larger or smaller? Discus the apparent contradictions and explain
Hint A K1c E chart will help.
A composite material consists of 35% parallel carbon fibres of Youngs modulus 400GPa in a matrix of epoxy resin with a Youngs modulus of 3GPa.
Calculate the Youngs modulus of the composite in the directions parallel and perpendicular to the direction of the fibres.
Aluminium 6061 is widely used in the aircraft industry and high tech industry. With the suitable heat treatment can be used in welded structures as bicycle frames. In
the laboratory some probes of Aluminium 6061T6 are going to be tested against fatigue failure. Two experiments have been performed already, the probe have failed after
107 cycles and 105 cycles at 90 MPa and 110 MPa stress range respectively.
a)Applying Basquins law, estimate the stress range that will make the probe fail at 104 cycles.
b)Applying Goodmans rule, estimate the stress range that will make the probe fail at 107 cycles if the probe is subjected to a mean continuous tensile stress of 70
MPa. (TS=0.25 GPa)
Explain, with aid of a diagram, the physical failure of a bolt under, evaluate the accuracy of the assumptions you take for the calculations:
a)Single shear where the forces are parallel and opposing and applied at right angles to the longest axis.
b)Double shear where the forces are parallel and opposing and applied at right angles to the longest axis.
Hint You will need to assume and estimate the area of possible failed sections.
A bearing pad, shown in Figure 2.3 and consisting of two steel plates bonded to an artificial rubber, is subjected to a shear force F = 12 kN during a static test. The
pad has dimensions of a =170 mm and b = 250 mm and the artificial rubber has a thickness t = 60 mm. When the force F equals 12 kN, the top plate is found to have moved
laterally by 8 mm with respect to the bottom plate. What is the shear modulus of elasticity, G, of the artificial rubber?
The figure below shows the copper-antimony Cu-Sb phase diagram.
Figure 1: copper-antimony Cu-Sb phase diagram
a) Find the chemical formula for the compound marked X (atomic weights of Cu and Sb are 63.54 and 121.75 respectively).
b) The Cu-Sb system contains 2 eutectics, 1 eutectoid, 1 peritectic and 1 peritectoid. Mark them all on the figure, write down the temperature and composition of each
point, and identify the phases involved in each reaction, on cooling.
c) An alloy containing 95 wt% Sb is cooled slowly to room temperature from the melt.
Explain the phase changes that occur during cooling, using schematic sketches of
the microstructure at key temperatures to illustrate your answer.
d) Sketch a temperature-time curve for the 95 wt% Sb alloy over the range 650 to 450oC and account for the shape of the curve.
Total Marks 27
Dislocations are the underlying cause of plasticity in most metals and alloys. As such, they play an important role in determining the mechanical behaviour of many
a) Draw a left-hand screw (LHS) dislocation and give the shear stress that will move it to the left on the page. Do this graphically.
Use your knowledge of dislocations to explain each of the following observations about material properties.
b) Ceramics are generally very strong when loaded in compression but fail in a brittle manner at relatively low stresses when loaded in tension.
c) Many materials, like low C steel, exhibit a fatigue limit. What is a fatigue limit and how is it related to dislocations?
d) Why is the fracture toughness of aircraft grade titanium alloys greater than that of armour grade silicon carbide?
e) Explain why BCC metals exhibit a Ductile-Brittle Transition Temperature while FCC metals do not.
The strengthening mechanisms that are available for improving the strength of commercial alloys are also related to dislocations. Here, the name of the game is slowing
down or impeding the dislocations. In each of the following cases identify the obstacles that are used to slow down the dislocations.
f) Almost all FCC metals are stronger after cold rolling or forging why?
g) An Al alloy with 3% Cu that is solutionized, quenched, and heat-treated or aged at a moderate temperature has a strength that at first increases with heat-treat
time and then decreases if the alloy is over-aged. Why?
h) The room temperature yield strength of a pure metal that is heat-treated such that the grain size of the material increases from 10 microns to 40 micron will
decrease by a
factor of 2 why?