SESM6050B
Tribology for Future Mobility
SEMESTER 2 FINAL ASSESSMENTS 2021/22
Question 1
(i) For a traction load that is sufficient to induce sliding within an adhesive tribological contact, describe the surface stresses in the direction of sliding and the likely surface degradation mechanism. [4 marks]
(ii) A horizontal silicon carbide plate has a tensile strength (stress to fracture) of 950 MPa, a E = 450 GPa and v = 0.19. A 35 mm diameter silicon nitride ball, with the same mechanical properties, slides over the plate surface without rotation. Calculate the maximum pressure (pmax) and normal load (FL) that could be applied to the ball without risk of tensile fracture at the trailing edge of the contact if the coefficient of friction was: (a) 0.4; (b) 0.10; and (c) 0.0.
Comment on the benefits of lubricating sliding contacts between ceramic components. [10 marks]
(iii) Explain why running-in is potentially useful. [3 marks]
(iv) Discuss the mechanisms leading to friction and self-friction for a rolling-element bearing. [8 marks]
Question 2
(i) Describe the operational performance demands of electric vehicle (EV) motors and how these may influence the tribological design criteria. [10 marks]
(ii) An EV electric motor bearing (6205 single-row, deep-grooved ball bearing) is reported to be suffering from excessive vibration and noise. Describe the possible causes and consequences of bearing damage that could lead to the observed vibration and noise. [15 marks]
Question 3
(i) What is gear pitting failure and which stresses cause pitting failure? [5 marks]
(ii) What is the basis to decide the operational lubrication mechanism for a gearset? [4 marks]
(iii) A gear with 40 teeth meshes with a 16 tooth pinion. The gearset has a module of 2 mm and a pressure angle of 20。.
(a) Determine the circular pitch, the centre distance, and the base diameter for the pinion and the gear. [6 marks]
(b) If the centre distance is increased by 1 mm, find the pitch diameters for the gear and pinion and the pressure angle. [10 marks]
Question 4
(i) What are the important parameters when designing a journal bearing? [5 marks]
A journal bearing is used to carry 4500 N radial load. The shaft rotates at 1650 rpm and is 63 mm in diameter. The journal bearing has a diameter-to-width ratio of 1 and is lubricated with SAE 20 oil with an inlet temperature of 89。C. Assume the bearing design to have a characteristic number halfway between the minimum friction and maximum curves. Determine the following:
(ii) Mean temperature and temperature rise in the bearing; [5 marks]
(iii) Minimum film thickness and its location; [5 marks]
(iv) Maximum pressure and its location; [5 marks]
(v) Total and side-leakage flow rates. [5 marks]