1. Faculty of Engineering, Machining and Condition Monitoring Research Group, Manufacturing and Process Technologies Research Division, The University of Nottingham, University Park, Nottingham NG7 2RD, UK e-mail:
2. Professor Faculty of Engineering, Machining and Condition Monitoring Research Group, Manufacturing and Process Technologies Research Division, The University of Nottingham, University Park, Nottingham NG7 2RD, UK e-mail:
3. Professor Faculty of Engineering, Materials, Mechanics and Structures Research Division, The University of Nottingham, University Park, Nottingham NG7 2RD, UK e-mail:
4. Manager, New Technologies, Element Six Ltd., Berkshire SL5 8BP, UK e-mail: