A Predictive Approach to Modelling Frictional Joint Performance (PAMFJP)

Lead Research Organisation: Imperial College London
Department Name: Dept of Mechanical Engineering


The proposed research aims to address the problems inherent in predicting the behaviour of frictional joints. Such joints are an important feature of a wide range of engineering products. Joint behaviour can be beneficial (e.g. by introducing frictional damping and controlling vibration amplitude) or detrimental (e.g. by inducing accelerated wear of fatigue failure). Whilst models now exist for some of these phenomena, it is at present difficult to predict the frictional behaviour of an interface in advance without making experimental measurements under representative conditions. Indeed, uncertainties associated with the behaviour of frictional joints are one of the remaining obstacles to reliable prediction of vibration amplitides and resulting component life.The proposed work addresses the difficulteis outlined above through a combined experimental and modelling programme undertaken by two leading groups in the traditionally separate areas of vibration and structural integrity. The work will be undertaken from a common standpoint and will result in a holistic approach which is valuable to both communities. Intitially, measurements will be made of joint performance using two standard geometries and two material pairs. Measurements will then be taken to characterise the surface topography, material properties, and interface behaviour at microstructural and asperity scales. These measurements will provide input for modelling of the contact, initially at the scale of a single asperity, but later generalised using statistical methods to provide predictions of overall contact behaviour. These predictions will be based on recent developments in the understanding of interface behaviour at the micro- and nano- scales.Finally, validation experiments will be carried out. These will be carefully chosen to give validation of the model in circumstances which differ significantly from the initial characterisation experiments. The overall output of the proposed work will be an enhanced understanding and predictive modelling approach for frictional joints in engineering assemblies such as gas turbine engines. The result will be increased confidence in joint (and therefore overall system) performance, and a reduction in the need for characterisation experiments.
Description (i) We performed a comprehensive set of experimental measurements of macroscopic load-displacement (hysteresis) response for two material pairs subjected to relative motion and a range of well-characterised surface topographies and developed a thorough understanding of teh frictional response of these pairs.
(ii) We compared and correlated existing approaches to the characterisation of frictional interfaces, which unifies the understanding currently held by the dynamics, tribology and structural integrity communities. A single coherent framework which can describe the interface appropriately in each of these areas was developed, highlighting the importance of surface oxides and material transformation during wear.
(iii) Development of an asperity-scale model of frictional contact which incorporates understanding of interface mechanics at the micro and nano-scale together with appropriate material behaviour.
(iv) We have conducted detailed studies of single asperieties and failure mechanisms and wear fundamentals, which have helped undertsanding the role of plasticity in contact problems.
(v) Development of a statistical model for real surfaces which have been generalised from the asperity-scale model to engineering surfaces and predict the effects of surface topography and material properties on interfacial frictional damping.
Exploitation Route The methodologies developed during this project have been used by industrial partners (Rolls-Royce and AWE) to improve the design of frictional interfaces in teh presence of vibratory loads. Research on fretting fatigue and damage has immensely benefited from our findings. Both the new experimental techniques and modelling methodologies we have developed can be used to study a range of systems and materials.
Sectors Aerospace, Defence and Marine,Energy,Manufacturing, including Industrial Biotechology,Transport

Description Both the numerical and experimental methodologies developed during this project have been used by Rolls-Royce to develop their next generation of underplatform dampers for turbine blades. Some of the techniques developed have also been used by AWE to optimise teh design of bolted connections in critical components. The investigator have also developed methods nos used to study teh energy dissipation in a variety of contacts involving rough dry surfaces in a number of industrial applications (with Element Six, Ford, Rolls-Royce and Bosch). This has strenghtened the links between the Vibration University Technology Centre at Imperial College and has also enable to establish a strong research stream in triboogy within Rolls-Royce.
First Year Of Impact 2009
Sector Aerospace, Defence and Marine,Energy,Manufacturing, including Industrial Biotechology,Transport
Impact Types Economic

Description EPSRC
Amount £1,021,359 (GBP)
Funding ID EP/G026114/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Description Element Six studentship
Amount £90,000 (GBP)
Organisation De Beers Group 
Department Element Six
Sector Private
Country Luxembourg
Start 10/2012 
End 09/2016
Description Engine Efficiency Benefits from Surface Texturing
Amount £130,000 (GBP)
Organisation Ford Motor Company 
Sector Private
Country United States
Start 01/2016 
End 01/2017
Description Platform Grant
Amount £1,024,467 (GBP)
Funding ID EP/G026114/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 01/2009 
End 12/2013
Title Fast Solver for Contact Models with Roughness and Adhesion 
Description A new methodology and algorithms to study contact mechanics of rough surfaces 
Type Of Material Improvements to research infrastructure 
Year Produced 2009 
Provided To Others? Yes  
Impact Now incorporated in a Research Software TriboSIM and made available to Ford, Rolls-Royce and BP for other projects 
Description AWE 
Organisation Atomic Weapons Establishment
Country United Kingdom 
Sector Private 
PI Contribution We made contributions to look at the fretting damage induced in bolted connections under vibratory load. Important studies emerged from looking at the effect of surface roughness.
Collaborator Contribution Contributed to materials and data to study bolted assemblies
Impact Maim outcomes: - New design tools for bolted assemblies and PhD research in this area
Start Year 2007
Description Rolls-Royce 
Organisation Rolls Royce Group Plc
Country United Kingdom 
Sector Private 
PI Contribution We helped developing methodologies to design underplaftorm dampers in turbine and fan blades
Collaborator Contribution They provided fudning to carry out specific work and now to design their next generation engines
Impact Main outcomes: - New design tools and methods for design of surfaces and dynamic resonse of systems - Strenghten teh links between the Imperial College Rolls-Royce Vibration Univesity Technology Centre, the Tribology Group at Imperial College and teh University of Oxford
Start Year 2007
Title TriboSIM 
Description A suite of tools put together by teh investigators to solve Tribological problems in teh presence of rough contacts 
Type Of Technology Software 
Year Produced 2011 
Impact Now a research tool used in teh Tribology Group at Imperila College with much potential for commercialisation and exploitation 
Description Company set to develop and license software for use by companies and academic institutions interested in tribological simulations. It alos provides services linked to the use of the software. 
Year Established 2018 
Impact So far engaged 3 oil and gas and automotive companies for licences and consultancy projects
Description Workshop on Frictional Joints 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact The aims of the workshop were as follows:

1. To communicate the results we have obtained so far on our current PAMFJP project and to understand how these can be applied in practical engineering situations.
2. To gain a fuller understanding of the range of contact issues experienced in industrial applications
3. To identify areas where the resources remaining on the current project could be applied to address more effectively these application-driven problems
4. To identify priorities for future research in this area (e.g. a new application for research council funding)

The workshop was attended by:
University of Oxford: D.A. Hills; D. Nowell; M.E. Kartal; D. Mulvihill
Imperial College: D.J. Ewins; D. Dini; A. Olver; S. Medina; C. Schwingshackl; D. Proprentner

Rolls-Royce plc: J. Schofield; J. Green; N. Banerjee
Jaguar/Land-Rover: A Harrison; L. Harper
Wärtsilä: C. Lönnqvist
Alsthom: S. Osgerby
Ferrari: M. Spuria
Vestas: C. Nielsen
MoD: A. Davis
Skoda/Doosan Babcock: D Mitchell; J. Kellner
GKN: S. Cragg; B. Mason

Three breakout groups addressed the following questions:

1. In what areas is our current understanding of frictional joint behaviour deficient?
2. What are the consequences of this lack of understanding?
3. What physical phenomena do we need to understand in order to make progress in this area?
4. Which of these are the most important?
5. In which of these areas are we most likely to make progress?
6. What are the priorities for research into frictional joint behaviour over the next 5 years or so?
7. To what extent do joints influence the dynamic behaviour of your structures
8. How much of a problem is it that joints vary from build to build and day to day
9. How can we quantify the consequences of better joint modelling capabilities (including economic aspects)?

The following is a brief summary of the discussions in each of the groups:

Group A

(i) Bolted joints were a significant area of uncertainty
(ii) There was appreciable variation between nominally similar joints due to manufacturing tolerances etc
(iii) Degradation of joints in service was a major issue (through wear etc). This needed more understanding, and better surface treatments
(iv) There was a need for a multi-scale modelling approach, bridging a detailed scientific understanding with higher level assessment tools

Group B

(i) There was a need to understand stiffness, damping, and friction coefficient, but these may not be the only relevant parameters
(ii) Wear has a big impact on performance
(iii) There would be benefit in moving towards more standardised tests for joints (how do we choose test parameters)
(iv) Joint variability was an issue
(v) Better understanding of coatings would be helpful

Group C

(i) Life prediction requires understanding of evolution over time - this is a fundamental feature of joints
(ii) Better understanding of wear is important
(iii) There was a need for guidelines on how to run tests (and how to choose representative parameters)
(iv) Joint evolution and variability represent significant uncertainties at present.
Year(s) Of Engagement Activity 2010