Understanding Leaf Chemistry and Effects on Low Adhesion

Lead Research Organisation: University of Sheffield
Department Name: Mechanical Engineering


Project summary:
The rail network in the UK is responsible for 4 million journeys daily (1), with this number predicted to double over the next 25 years. As the global drive for more sustainable and environmentally friendly travel continues, rail companies and operators are being put under more pressure to improve safety and reliability, as well as encourage commuters to switch to rail for their commute. Leaves create a problematic "Teflon like" coating which adheres to the railhead while severely reducing friction to the wheels which roll/slide over it (2).

Low adhesion in the wheel-rail interface can and does cause problems for braking and traction and significantly affects network performance in the Autumn period. The annual cost estimation of low adhesion to the whole of GB rail industry has been estimated to be in excess of £100 million (3). This cost is attributed to; refunds/compensation due to delays, incident investigation, maintenance repairs (wheelset re-profiling, replacing broken track), trackside vegetation management and more.

The main aim of the project is to widen the understanding of low adhesion caused by leaves to include effects of different leaf chemistries, times that particular leaves fall and related weather conditions. This data will then be used with other fundamental knowledge of low adhesion (from RSSB projects on oxides and small amounts of water) to develop an improved adhesion index prediction. This improved adhesion prediction could reduce incidents and delays in the autumn period as well as improve reliability and appeal rail as a more environmentally friendly means of mass transportation.

This work will expand the scope of the project currently under way by examining more leaves and bringing in the field side, i.e., friction assessment, effects of weather, information on leaf fall and entrainment of leaves and finally by helping to develop the prediction of adhesion problems.

The aims proposed for this project include;
Identify the main types of leaves present on UK rail track that cause low adhesion problems:
Research current literature regarding leaf contamination in the wheel-rail interface.
Investigate industry reports on railhead contamination, what are the more and less troublesome leaf species?.
Research most common types of trees in the UK (deciduous only).
To find operational data on the leaf problems and Key Performance Indicators (KPIs).
Collect data about autumn weather conditions and leaf fall.
Collect friction data throughout the autumn period to correlate with weather data.

To investigate the chemical analysis techniques regarding leaves:
Research the advantages and disadvantages of different chemical analysis techniques.
Research the chemical analysis used in the literature.
Find the ideal sample state for analysis techniques.

Prepare the leaves for testing:
Collect leaves and store safely until required.
Prepare samples using the same method found in the literature.

Carry out chemical analysis of the selected leaves:
Contact relevant members of staff for training on required machines such as; FT-IR (Fourier Transform-Infrared Spectroscopy), XPS (X-ray Photoelectron Spectroscopy) and LRS (Laser Raman Spectroscopy).
Carry out chemical analysis and collect data.

Carry out tribological tests of the different leaves and leaf layers:
Become trained on required rigs/machinery such as; SUROS (Sheffield University ROlling Sliding) rig, UMT (Universal Machine Tribometer), FSR (Full-Scale Rig) and Pendulum rig.
Carry out tribological tests comparable to those in the literature.

1.Passengers - Network Rail. [online]. [Accessed 12 February 2018]. Available from: https://www.networkrail.co.uk/communities/passengers/
2.FULFORD, C. F. Review of low adhesion research. 2004.
3.AWG, RSSB. Adhesion Manual Edition 6.0 [online]. 2018. [Accessed 29 May 2018]. Available from: https://www.rssb.co.uk/rgs/oodocs/rdg-awg ma

Planned Impact

The impact of the Centre will be manifest itself in four ways; by the number and quality of skilled PhD graduates it produces, by the reach and significance of the research that is generated during their studies, by the contribution to the research base in tribology, and through the broader societal impact of improved machine efficiency and energy utilisation.

The number and quality of PhD graduates. iT-CDT plans, in the steady state, to graduate 12 PhD students per year. We expect these students to enter industry as research leaders or academia as RAs then lecturers. UK and EU industries are desperately short of PhD graduates, and they are in demand. We expect to have impact on UK industry with a stream of PhD graduates who will enter for example, the automotive sector (e.g. designing more fuel efficient engines), the rail sector (e.g. increasing network capacity and reducing cost through improved track and vehicle components), the oil industry (e.g. developing new lubricants for increased fuel efficiency), aerospace sector (e.g. tribology needs in jet engines), the power industries (e.g.developing and maintaining more efficient transmissions). PhD students may also commercialise technology or consultancy in the form of a spin-out activity. We have a track record of past PhD students achieving all these things. The iT-CDT plans to extend and broaden that record, will facilitate synergy across the discipline.

The transformative PhD research. During their studies, PhD students will be conducting research on an industry led project. These projects will also have elements of generic application therefore have wide impact. The students will be closely involved with both the sponsoring organisation and other industrial partners. This means that there will be a direct route for technology transfer.

Contribution to the Research Base in Tribology. The iT-CDT is a grouping of the two leading universities in tribology in the UK. It will form the largest critical mass of academics, RAs, and PhD students in the EU. A team of industrial partners will steer the research so that it is relevant and has real routes to impact. This platform will lead to a growth in the research base in tribology for the UK and will impact both industry, with improved products and processes, and academia with the supply of new technology and analytical methods.

Societal Impact. The development of new tribological processes, and engineers skilled in their conception and implementation, will have broader societal impact with machines and process that run with lower friction, higher energy efficiency and have greater durability. In the shorter term, we also plan as part of the iT-CDT for public engagement events using PhD students as the agents of delivery.


10 25 50
Description The focus of my project (railway based) has had a slight shift due to the effects of the pandemic and lockdown. I was able to obtain some data through a contact I met while giving a feedback presentation to my industrial sponsors industry research group (Adhesion Research Group (ARG)) back in May of 2020. I was given industry data on low adhesion incidents and WSP activation, and as a result had shifted my focus to investigating the locations of the low adhesion incidents primarily using Google Maps, along with and various other industry reports and data sources.
Exploitation Route Research projects that started after mine may be able to take my findings and apply them to their own research to further the understanding of what causes leaf layers to build on the railhead, and what the differences are between leaf layers of different species.
Sectors Transport

Title Autumn Supertram leaf fall and weather data 
Description For the time periods 05/09/2018 - 20/12/2018 and 03/09/2019 - 20/12/2019, leaf fall rates and weather conditions (ambient temperature, pressure and humidity and railhead temperature) were monitored at 12 locations on the Sheffield Supertram network. there were 27 collection dates in 2019 and 18 collection dates in 2018. The leaf fall rates were monitored by means of photographs taken of specific trees/groups of trees in order to compare the density of leaves on the tree vs on the ground between collection dates. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
Impact Noteable impacts have not currently been reached using the data collected for this database.