Question 1:

(a). Brass (CW614N - CZ121) has a Young's modulus of 97GPa and a Poisson's ratio of 0.34.Calculate the effective modulus at the interface when two brass plates are loaded together.

(b) Copper has a modulus of 140 GPa and a hardness of 150MPa. Estimate the elastic strain in copper at the yield stress.

Question 2:

A steel shaft with a R_a value of 0.4μm is rotating in a brass bush with a R_a value in its inner diameter of 0.7μm. The shaft and bush are immersed in oil and, during operation, an oil film thickness of 5μm is developed. In which lubrication regime is the sliding interface operating? Your answer should be supported by suitable examples and references.

Question 3:

Using appropriate examples or references discuss four limitations of liquid lubricants.

Question 4:

It is found that a polymer-based bearing supporting a rotating steel shaft has a depth wear rate of 0.25mm in 1000 hours both at a bearing pressure of 10MPaand speed of 10^-1ms^-1, and at a pressure of 1 MPa and a speed of 1ms^-1.

(a) Show that the bearing is operating in the range where the specific wear rate is constant.

(b) Calculate the time taken to reach a wear depth of 0.25mm if the pressure and speed were 2 MPa and 0.2 ms^-1.

(c) Given this information, decide if you could safely calculate the wear rate at a pressure of 10MPa and a speed of 1ms^-1, and give reasons for your decision.

(d) The test results were obtained using a polished steel shaft in a laboratory environment and at room temperature. Suggest changes in these conditions that could cause the specific wear rate to be different.

Question 5.

"To reduce wear on a steel component, a hard wear resistant ceramic coating is applied"

(a) Explain using suitable examples, what is meant by this statement.

why using ceramic coatings

(b) With the aid of diagrams, illustrate three different techniques by which this could be done. Explain why a ceramic coating and discuss the advantages of the three techniques. You may use appropriate examples and references.

Question 6:

A Tungsten carbide ball 50mm in diameter is loaded under an increasing normal force against a stainless steel plate with a hardness of 200 GPa, as shown below.

At what force does the material of the plate first yield; what is the corresponding contact width; what are the mean and maximum pressures in the contact zone; and what are the magnitude and the location of the maximum shear stress?The relevant Hertz equations for this contact are:

Radius of the circle of contact, a = (3PR/4E*)^1/3 (equation 1)

Maximum pressure, p₀ = 3P/2πa²

                              = (6PE^*2/π³R²)^1/3 (equation 2)

Where P is the normal load, R is the radius of the ball and E* is the composite modulus at the contact.