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Michael Sutcliffe - Tribology Research

Tribology in Composites manufacturing - Active
Microscopic contact of composite
In many manufacturing processes, tribology plays a key role in controlling deformation and material properties. While the mechanics of surface contact in metal-forming operations is well understood, this is not the case for composites. The project, funded by EPSRC and in collaboration with the University of Nottingham, Jaguar Land Rover and Granta Design, explores the fundamentals of friction in composites forming via microscopic experiments and modelling, and aims to link this with macroscopic testing. The aim is both to understand the mechanics but also to guide testing which can better characterise friction performance in real applications. Recent work has shown how the true area of contact between a dry fibre composite and a coated glass surface varies with the contact area and fabric properties. The contact area can be directly linked to the measured frictional resistance via a characteristic shear strength of the interface. The work has been undertaken by Olga Smerdova and Daniel Mulvihill.

Tyre Tribology - Active
Tyre Tribology
Tyre tribology is an important subject in road vehicle research due to the fact that tyre/road interaction plays a vital role in defining the performance, comfort and safety of a road vehicle. A tread block contact mechanics model for free-rolling tyres has been developed to help in prediction of tyre noise and hub vibration. Analysis and experiments were carried out to model tread block contact forces for both smooth and rough road surfaces. Based on the FE and experimental findings, two simplified tread block contact models have been established including a discrete viscoelastic spring model for smooth roads and a viscoelastic indentation model for rough roads. The outcome of the research project will enable vehicle and tyre designers to predict unsteady hub forces generated by a tyre rolling on any road surface. Tyre wear work has focussed on measurements of the wear process in controlled laboratory tests. Work is now being undertaken to apply that to real rough roads and to relate the work to field tests. The tyre vibration work was undertaken by Feiyang Liu funded by EPSRC in collaboration with colleagues in the Engineering Department, LandRover Jaguar and Goodyear. The tyre wear work is being undertaken by MEng students in collaboration with the Cambridge Vehicle Dynamics Consortium project; a PhD application would be welcome.

Metal Rolling Tribology - Complete
Metal Rolling Tribology
Substantial effort has gone into understanding the mechanisms and to develop theoretical models for surface finish generation and friction in metal rolling. Work on aluminium rolling, sponsored by EPSRC, Alcan and ALSTOM, focused on modelling of friction in conventional rolling and the surface finish generation in pack rolling. Further work has considered the details of the roughness spectra found in practice: it is found that short wavelengths are difficult to eliminate. This tribological model has been coupled into a mechanical model for foil rolling, where the rolling load is particularly sensitive to friction. Work on stainless steel, sponsored by EPSRC, Corus and Avesta Sheffield, concentrated on modelling the elimination of pits of voids which arise from the shot blasting and pickling process used before the finishing passes. Substantial contributions to this work were made by Huirong Le and Rehan Ahmed.

Chemical Mechanical Polishing - Complete
Chemical Mechanical Polishing
Chemical mechanical polishing (CMP) is widely used in integrated circuit manufacture to achieve smooth surfaces. Integration of Cu and materials with a very low dielectric constant (ultra low-k) has been used recently to improve performance. However low-k materials generally have poor mechanical properties and are susceptible to delamination during CMP. Two sets of experiments were performed to examine the delamination mechanism of ultra low-k material during CMP: (i) a macro-scale polishing test using a metallographic polisher and (ii) a micro-scale scratch test on a micro-tribometer. Delamination was observed at higher pressures in both sets of experiments and the relationship between delamination rate and pressure established. Contact mechanics models were proposed to correlate results from the two sets of experiments, combining a Weibull model of failure with a statistical asperity contact model. Results confirmed the usefulness of the combined testing procedure in predicting safe polishing pressures during CMP. The project was undertaken by Feiyang Liu.

© 2015 Cambridge University Engineering Dept and Michael Sutcliffe.
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