Railway industry invests considerable resources to manage low adhesion caused by the build-up leaves, despite these efforts, adhesion issues still have a significant safety and financial impact on the industry and society. The current process of treating railheads to resolve the issue has less than 20% efficiency. The treatment plan is based on a set of assumptions and operator's experience, but actual adhesion enhancement levels are not considered as they are unknown. Low adhesion is estimated to cost the UK industry £345m per annum and leads to costly delays as well as safety issues due to the loss of traction, potentially leading to uncontrolled condition and in the worst-case collisions. Rail Standard Safety Board (RSSB) has developed the ADHERE research programme to strategically tackle this challenge. However, the lack of fundamental understanding of the fundamental physics at the rail-wheel interface presents a barrier to progress. The rail-wheel interface is a multi-scale, multi-phase problem which has a highly transitory condition and it is exposed to open operating environments that can produce a variety of contaminations. Understanding the physical and chemical interactions at the interface is challenging, but it is essential and the only route to tackle the problem. In this project, a predictive computational model to simulate adhesion enhancement using sand particles in the rail-wheel interface will be a deliverable. This tool will be calibrated using experimental data at the micro-scale and validated using a full-scale rail-wheel set-up in collaboration with Prof Roger Lewis at the University of Sheffield. Running computational parametric simulations will lead to underscoring the crucial role of particle characteristics to assess the current assumptions stated in the RSSB standard catalogue GMRT2461. I hypothesise that tailoring particle characteristics (such as shape) will enhance 'self-steering' and 'self-entraining' of particles in rail-wheel interface, therefore it reduces particle ejections and increases efficiency. The outcomes of this project will be disseminated to stakeholders at an event hosted by RSSB, in addition to usual academic dissemination routes, i.e. conferences and journals. The main impact of this research work will be: In the short term: developing an understanding of the role of particle characteristics in adhesion enhancement; engagement with public and industry. In the mid-term: informing planning and decision-making models, design engineers and consultants; amendment of standard. In the long term: increased network capacity, reduced carbon, lower costs and improved customer satisfaction.

Friction plays a central role in life; in transport, in manufacturing, in process engineering, in medical devices and in everyday human activities. Friction has commanded the attention of Amontons, Coulomb and Da Vinci and their simplistic, empirical laws have been the cornerstone of friction theory. At the conceptual and theoretical levels the vast modern day friction literature has revealed the enormous complexity of even the simplest processes and the limitations of the early friction laws. Friction is intimately linked to both adhesion, contact geometry and wear and all require an appreciation of the highly non-equilibrium and non-linear processes occurring over multiple length scales. The challenge presented is that friction in realistic engineering contacts cannot be predicted. Understanding the physical and chemical processes at contacting interfaces is the only route to cracking the tribological enigma. The research gap addressed in this Programme Grant is linked to the development of accurate experimental and numerical simulations of friction. We appreciate that the search for a unified model for friction prediction is futile because friction is system dependent. However, the goal to predict friction is achievable. We have identified 4 key areas where there are current challenges in understanding the origins of friction because of different complexities as outlined below: - Reactive surfaces; in many systems the frictional contact brings about chemical reactions that can only be described by non-equilibrium thermodynamics. We need accurate kinetic rate data for reactions which can only be provided by advanced in-situ chemical analysis - Extreme interfaces; these can be described as any interfaces that are inducing high strain rate material deformation and combined with electrochemical or chemical reactions. Simulation and sensing are key to improving the understanding. - Non-linear materials; in engineering and in biological systems we see the evolution of "soft" materials for tribological applications. Predicting friction in these systems relies on understanding the rheology/tribology interactions. - Particles and 2nd phase materials; for materials processing or for understanding the transport of wear particles in a contact we need to understand particle-particle friction in complex contact conditions where fracture/deformation are occurring.