The University of Sheffield
Department of Mechanical Engineering

Dr David Fletcher

BEng, PhD

Dr David Fletcher

Senior Lecturer in Mechanical Engineering

Department of Mechanical Engineering
Sir Frederick Mappin Building
Mappin Street
Sheffield
S1 3JD
UK

Telephone: +44(0)114 22 27760
Fax: +44(0)114 2227890

email : d.i.fletcher@sheffield.ac.uk

Profile

Dr David Fletcher is a graduate of Leeds University where he studied Mechanical Engineering and worked with his sponsoring company CarnaudMetalbox Packaging. He was awarded a PhD in Mechanical Engineering from the University of Sheffield, and went on to conduct research in a range of areas including railway engineering, forming tool design and development of assistive tools for cataract surgery. From 2004 to 2009 he conducted research with Newcastle University focusing particularly on full scale railway engineering testing, before returning to Sheffield. He has been awarded several prizes for research in the railway area, including the prize for best paper addressing system interaction issues at the World Congress on Railway Research, Korea 2008, the Institution of Mechanical Engineers Railway Division, TA Steward-Dyer / F H Trevithick Prize, 2005, and the Institution of Mechanical Engineers Tribology Trust, Tribology Bronze Medal, 2000.

Areas of Research

Dr Fletcher's research interests are in engineering design and in performance of materials. The majority of his work has application in the railway sector, and combines experimental and modelling approaches. Major themes include:

Railway rail-wheel interface

The rail-wheel interface subjects the rail and wheel to extreme loading, often leading to high maintenance requirements. Dr Fletcher's research has developed new understanding of the interaction between rolling contact fatigue, surface crack initiation, crack growth and wear, linking these to the metallurgy of the steels involved. The research has combined experimental approaches including small and full scale trials to investigate crack growth, with modelling based on both fracture mechanics and contact energy, to understand and find solutions to the damage mechanisms involved.

Recent work has focused on adhesion at the rail-wheel contact, and development of new understanding of the creep-adhesion relationship. This is linked to earlier work on chemical approaches to prevention of low adhesion, and research into the performance of a range of lubricants and friction modifiers.

In 2009 Dr Fletcher revisited the Japanese Railway Technical Research Institute (RTRI), Tokyo, to continue a collaboration begun in 2006 on modelling crack growth in rail steel. This was originally supported through a short fellowship undertaken at RTRI funded by the Japan Society for the Promotion of Science.

Tribology

Research on the rail-wheel interface and its contact mechanics is a specialist area of tribology, and Dr Fletcher also applies tribological understanding to a range of wider industrial problems. Most recent work has looked at the railway overhead line to pantograph contact that can suffer extreme heating and wear problems due to the high sliding speeds, electric current and variable forces involved. The investigation was conducted by developing a wear testing machine capable of up to 200kph sliding speed, replicating in the laboratory the wear of copper overhead line and pantograph contact strips to better understand their performance.

Rail system design for safety and security

Over recent years European rail systems have been subject to terrorist attack, and their crowded and open nature makes them difficult to protect. Dr Fletcher is conducting research through UK and EU projects aiming to design resilience into stations and vehicles, thereby lowering the risk and impact of attack, and making recovery faster. Knowledge of rail system design and understanding of performance of materials under extreme loading links this area of work with the more conventional engineering aspects of Dr Fletcher's research. An essential aspect of this work is the acceptability to travellers and operators of any change in the design of stations or rail vehicles, and linking design decisions to risk assessment.

Professional Activity

Major Research Grants and Projects

PhD Students:

PhD research opportunities are available in any of my research areas - please contact me for discussion.

Prizes

Teaching

Dr Fletcher is module leader for the first year module Mechanical Engineering Design Skills (MEC131). He also teaches Mechanical Engineering in Railways to fourth year MEng and MSc students and is part of the team organising the 3rd year BEng/MEng group design project (MEC307).

Selected publications

 Selected refereed journal papers:

Selected refereed conference papers: