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Mechanical Systems: Condition Monitoring, Reliability Analysis, Bearings, and Lubrication

  1. What are the 8 main steps in the generic procedure for implementing a condition monitoring programme which are outlined in BS ISO 17359:2011? (4 marks)

  2. With the aid of a block diagrams, outline the main elements of any twoof the following systems:

Active condition monitoring system. Vibration analysis system

PC based acoustic emission monitoring system (5 marks)

  1. Answer the following questions about condition monitoring techniques, according to your experience during the module. (Each is worth 2 marks)
  • Name twomaintenance strategies that apply condition monitoring techniques.
  • Name threevibration analysis methods used to analysis vibration signals.
  • Name twoAcoustic Emission (AE) monitoring features that are used in AE monitoring; based on the signal types.
  • Name twoapproaches used in oil debris analysis.
  • Identify the twomain elements of a structural health monitoring system architecture for an aircraft application. Provide examples of the typical systems or components to be found in each element.
  • For the bearing shown in Figure 1.c-6, which position (A, B, C or D) is suitable to monitor the condition of the shaft and bearing? Why?

Figure 1.c - 6.

  • Name threecommon mounting methods used to mount Accelerometers.
  • Based on the BS ISO 13373-3, ‘condition monitoring and diagnostics of machines’, name the fourexpected defect frequencies of a typical cylindrical roller bearing.

An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate force in the form of torque applied on the motor's shaft. Figure Q2 below shows the cut-away view of an electric motor.

Figure Q2. Cut-away view of an electric motor

  1. To determine if the transmission system design will meet the reliability requirements, reliability modelling is required. This modelling requires reliability data, however, as this is a new transmission system no specific historical data is available yet. Despite this, there are several sources of data that may be used until better data becomes available. Using a suitable source, justify the validity of the method. (4 marks)

  2. FMEA is a technique that can critically evaluate the reliability of preliminary designs, which makes it is critical to system reliability. Explain what is meant by the FMEA acronym. Using suitable examples, discuss advantages/disadvantages of FMEA. (6 marks)

  3. Perform an indicative 3-level system break down describing the electric motor, identify ONLY 4 failure modes (at least two different modes for one component) and perform FMEA to prioritise risks. Justify what the difference between FMEA and FTA. 15 marks)

The brakes are an important part of any bicycle. Figure Q3 below shows some rim brakes. When the brake lever on the handle bar is squeezed the cable is pulled up and the brake pads close on the rim of the bicycle wheel. Imagine a bicycle that has a braking system consisting of two braking sub-systems (one on the front wheel and one on the back).

Figure Q3. Bicycle brake lever and rim brakes with table of part reliabilities.

  1. Assuming that only one brake subsystem (either front or back) is required for safe operation. In order to make the bicycle more reliable, Designer A is suggesting for redundancy at the system-level (or high-level), while Designer B is suggesting for redundancy at the component-level (or low-level). Draw the reliability block diagrams (RBD) for the whole brake system according to these two Designers.(6 marks)

  2. Using the two reliability block diagrams drawn in part a, calculate the reliability of the braking system, respectively. And recommend the better design.(9 marks

  3. List at least FOUR possible physical causes of failure for the brakes system shown in Figure Q3.(4 marks)
  1. On average each brake cable fails once every five years. Assuming that the failure pattern is random.
  2. What is the probability that one cable will last for 1 year?
  3. What is the probability that both cables (in series configuration) will last for 2 years?
  1. A dry bearing is to be designed to support a shaft of 30 mm outer diameter and 20 mm inner diameter that rotates at 5 Hz. The load on the bearing will be a steady one of 1200 N. The radial wear of the bearing should be no more than 250 µm after 3000 hours of operation. Express the wear coefficient, k, in terms of bearing width, b in metres. Suggest some type of wear mechanisms the bearing may experience in service(5 Marks)

  2. Discuss four limitations of liquid lubricants as opposed to solid lubricants. Give two examples for solid and liquid lubricants. What happens to density and kinematic viscosity of the liquid lubricant with an increase in temperature?(5 Marks)

  3. Two spherical roller bearings are in mutual contact. Both the spherical roller bearings, Bearing A and Bearing B are made up of 80 mm diameter that rotates at 250 rpm. The load on the bearings is a steady one of 300 N. The wear volume in Bearing A is 8.5 x 10-7 m3 and Bearing B is 6.75 x 10-8m3 after 2500 hours of operation. Calculate the specific wear rate or wear coefficient, ‘k’, for both the Bearings A and B in m2N-1. What happens to the wear volume with increase in load and speed of the operation?(5 Marks)

  4. A hard steel cone having a semi angle of 85 degrees is drawn across the surface of a soft carbon plate, having a hardness of 1200 MPa under a constant normal load of 50 N. Estimate the width of the scratch, the coefficient of friction and the volume of material displaced in unit sliding distance.

  5. What happens if the semi angle and hardness of the material is changed to 80 degrees and 1400 MPa respectively under the same normal load. Justify your answers with supporting evidence?

  6. What happens to width of the scratch, coefficient of friction and the volume of material displaced in unit sliding distance with an incremental increase of the load in multiples of 30 N till 200 N while the cone semi angle and hardness of the materials are 80 degrees and 1400 MPa under a constant normal load of 50 N. Explain with help of a simple sketch the variation in scratch width and volume of material displaced with an incremental load.(10 Marks)

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