About a quarter of the world’s energy consumption comes from tribological contact to overcome its effect or remanufacture worn parts. For almost all complex structures, these friction interfaces can be found and they are at the origin of nonlinear vibrational behaviors and uncertainties leading to poor predictability and reliability. The current modeling approaches for these friction interfaces are mainly based on macroscopic contact laws and parameters. It cannot effectively capture the uncertainties arising from microscopic interfaces due to surface roughness and wear. The workshop aims to bring together researchers working in this field across Europe and share the knowledge and challenge on this interesting topic to have a scientific discussion and form a consortium for the future research project.

1:00 - 1:15 Workshop introduction

1:15 - 2:00 Daniel Muvihill, Glasgow University, UK, Tribology of Triboelectric Nanogenerators: the Importance of Contact Area

2:00 - 2:45 Davendu Kulkarni, Rolls-Royce plc, Derby, UK, Current practices in modelling and assessment of friction interfaces for turbomachinery component

2:45 - 3:15 Coffee break

3:15 - 4:00 Anas Batou, Liverpool University, An Isogeometric analysis based method for frictional elastic contact problems with randomly rough surfaces

4:00 - 4:45 Rafael Teloli, FEMTO-ST, France, Experimental investigations on the functionalization of contact interfaces

4:45 - 5:00 Closing of the day

6:00 - 10:00 Dinner for the speakers

Conference room 4, Technology & Innovation Centre (TIC), University of Strathclyde 

Address: 99 George St, Glasgow G1 1RD, UK

Time: 1pm to 5pm,  8th June 

Daniel Muvihill, Glasgow University, UK

Tribology of Triboelectric Nanogenerators: the Importance of Contact Area

Triboelectric nanogenerators are a promising energy harvesting technology receiving significant global attention at present. This talk will explore some of the key tribology and mechanics of TENGs. For example, results published in the literature have indicated that TENG electrical output appears to be very sensitive to contact pressure and surface roughness. We demonstrate that the contact pressure and roughness dependence of TENG output arises because of the role that both contact pressure and roughness play in governing the real contact area at the active TENG interface [1-3]. 

[1] Kumar C., Perris J., Bairagi S., Min G., Xu Y., Gadegaard N. and Mulvihill D.M. (2023) ‘Multiscale in situ quantification of the role of surface roughness and contact area using a novel Mica-PVS triboelectric nanogenerator’, Nano Energy, 107, 108122.
[2] Min G., Xu Y., Cochran P., Gadegaard N., Mulvihill D.M. and Dahiya R. (2021) ‘Origin of the contact force-dependent response of triboelectric nanogenerators’ Nano Energy, 83, 105829.
[3] Xu, Y., Min G., Gadegaard N., Dahiya R. and Mulvihill D.M. (2020) ‘A unified contact force-dependent model for triboelectric nanogenerators accounting for surface roughness’ Nano Energy, 76, 105067.

Davendu Kulkarni, Rolls-Royce plc, Derby, UK
Current practices in modeling and assessment of friction interfaces for turbomachinery component

The mechanical systems of gas turbine engines incorporate multiple friction interfaces that lead to the non-linear interactions between their components. The understanding of these friction interfaces and their interactions are important as they determine the structural and aeromechanical behaviour of the mechanical systems. This presentation provides an overview of the current practices in modelling of friction interfaces and performing non-linear structural analyses for turbomachinery blades and vanes. It particularly focuses on the validation studies conducted for core compressor blade-root friction damping predictions, development of a method for generating friction damping characteristic curves and the integration of friction damping predictions into the aeromechanical assessments of a compressor outlet guide vane (OGV). The presentation also provides a view on the future work.

Anas Batou, Liverpool University, UK

An Isogeometric analysis based method for frictional elastic contact problems with randomly rough surfaces

The problem addressed in this presentation concerns the frictional contact between an elastomer and a rigid body with randomly rough surfaces. The work is accomplished on the basis of two crucial elements: a framework for generating random geometries and a robust frictional contact algorithm, both of which are realised in the approach of Isogeometric analysis (IGA) for its high accuracy and robustness. For the former, a new Isogeometric framework for random geometry modelling is proposed, which combines the random field generation based on Karhunen–Loeve expansion theory with Non-Uniform Rational B-Spline (NURBS) interpolation method. For the latter, a mortar-based frictional contact algorithm in 2D large deformation regime is adopted incorporating a modified closest point projection method for detection of contact. Numerical experiments are conducted with several settings such as ‘rough–smooth’, ‘smooth–rough’ and ‘rough–rough’ contact, depending on which side of the contact pair the randomly rough surface belongs to. The ratio of the global coefficient of friction to the prescribed local one and the ratio of true contact area to the nominal contact area are characterised under these settings, and factors like the root mean square roughness and correlation length of the random surface and the external traction are discovered to have a significant influence on the two ratios.

Rafael Teloli, FEMTO-ST, France
Experimental investigations on the functionalization of contact interfaces

This presentation focuses on the functionalization of contact interfaces in assembled structures to harness the potential of nonlinear dissipative phenomena for enhancing structural damping in vibrating systems. The study explores two innovative solutions in this context. The first solution, the Orion beam, is a lap-joint structure comprised of three contact patches. One bolt is dedicated to ensuring structural integrity, while the other two facilitate dissipative functions. By strategically designing the joint, the Orion beam exploits nonlinear damping mechanisms to effectively manage vibrations. This benchmark is also used for structural health monitoring purposes, which applications will be briefly introduced in the presentation. The second solution revolves around the concept of magneto-friction, which introduces a novel approach to assembled structures. The system incorporates a magnetoelastic core and ferromagnetic skins (MAE). Through magnetization of the MAE, the skins are attracted to the core, enabling assembly without the need for glue or other traditional fixation methods. The magnetic forces induced by the MAE generate normal loading at the contact interfaces between the skins and core, while forced vibrations applied to the sandwich beam induce tangential loading. By investigating these solutions through experimental investigations and numerical simulations, this presentation aims to shed light on their behavior, performance, and potential applications. The focus is on comprehending the intricate dynamics of these systems, particularly in the presence of frictional interfaces. 

The workshop is organised by J. Yuan (Strathclyde University, Glasgow, UK) and E. Denimal Goy (Inria, Rennes, France) in the context of the RSE Saltire Facilitation Awards UNIFY on the topic of multi-scale and uncertain dynamics of structures with friction interfaces.

Dr. Jie Yuan is currently a Lecturer at the Aerospace Centre of Excellence at the University of Strathclyde. His research interests are mainly on nonlinear dynamics and control with main applications to aerospace structures. He obtained his Ph.D. degree in aerospace dynamics from the Rolls Royce Composite UTC at Bristol. Before joining Strathclyde in 2020, he had worked as a research associate at Rolls Royce Vibration Technology Centre at Imperial College London.

Dr. Enora Denimal is currently a permanent researcher in the I4S team at Inria, which is the French national research institute in computer sciences. Her research is focused on the development of advanced numerical methods for uncertainty quantification and optimisation of nonlinear dynamics systems and large complex systems. Before joining Inria in 2020, she worked as a research associate at Rolls Royce Vibration Technology Centre at Imperial College London.