Nicholas Morris | Loughborough University (original) (raw)

Journal Papers by Nicholas Morris

Tribology International, 2018

This paper investigates the frictional performance of a PECVD hydrogenated undoped DLC coating an... more This paper investigates the frictional performance of a PECVD hydrogenated undoped DLC coating and the alternative super-finished gear steel surface pairs. A tribometer replicates the conditions found in the conjunction of a performance racing transmission spur gear pair. In mixed and boundary regimes of lubrication the DLC contact is shown to have a lower coefficient of friction despite having comparable surface topography when measured using optical interferometry. To determine the mechanisms responsible for improved friction of DLC coated tribo-pairs atomic force microscopy is used. It is shown that the nanoscale surface topography of the investigated PECVD DLC coated pairs reduces the real asperity contact area formed at the same load carrying capacity. This highlights a contributing mechanism for improved friction with the DLC coating.

Journal of Fluids Engineering, 2019

The parasitic drag losses incurred by wet clutches, used in transmission systems, can significant... more The parasitic drag losses incurred by wet clutches, used in transmission systems, can significantly affect vehicular powertrain efficiency. This paper presents a novel implicit solution for hydrodynamic parasitic drag losses of disengaged clutches. These are generated by conjunctional friction, taking into account lubricant film separation during co-directional and counter-directional disc pair rotations. Lubricant film rupture is considered through application of incipient reverse flow boundary condition, which is representative of lubricant film separation. The results point to the operating conditions at which significant power losses occur. In particular, the time efficient model is able to represent the small losses incurred during co-directional rotation of disc pairs.

http://fluidsengineering.asmedigitalcollection.asme.org/article.aspx?articleid=2747813

Proc IMechE Part D: J Automobile Engineering, 2019

Multi-disc wet brake packs are commonly used for off-highway applications. Unfortunately, when di... more Multi-disc wet brake packs are commonly used for off-highway applications. Unfortunately, when disengaged, these components can generate significant levels of unwanted parasitic losses. This article presents a novel, validated model to predict the parasitic losses in disengaged multi-disc wet brake packs. The model employs pertinent boundary conditions to determine the position of the free boundary created by oil film separation. The experimental and analytical results demonstrate the significance of wet disengaged brake losses at a range of angular velocities, typically found in operation. The improved understanding accrued by the expounded time-efficient methodology presents significant opportunity to develop predictive tools for the whole driveline system efficiency calculations and component design optimisation for off-highway vehicles.

The lubricant-surface system is complex in nature and can significantly affect the frictional per... more The lubricant-surface system is complex in nature and can significantly affect the frictional performance of high-performance transmission systems. The complexity stems from the coupled mechanical and chemical phenomena that occur at the inter-facial tooth conjunctions. A combined analytical and precision experimental approach is presented to analyse the salient parameters of the lubricant-surface system. A multiscale procedure comprising topographical measurement, pin-on-disc tribometry, atomic force microscopy in lateral force mode, X-ray photo-electron spectroscopy and continuum contact mechanics analysis under mixed non-Newtonian thermo-elastohydrodynamics is used to describe the formation of a tribo-film, as well as wear and frictional characteristics of the lubricant-surface system. The contribution of chemisorbed and physisorbed bonded tribo-film on the boundary coefficient of friction is ascertained at different physical scales. Therefore, the paper presents a novel multiscale analysis, promoting improved understanding of the complex interactions between mechanisms of friction, wear and surface chemistry. Keywords Gear · Tribo · Film · Additive · ZDDP · AFM · Atomic force microscopy · Wear · Friction

This paper investigates the effect of surface texturing in a partial pad journal bearing through ... more This paper investigates the effect of surface texturing in a partial pad journal bearing through a series of controlled experiments at operating conditions, promoting mixed or boundary regimes of lubrication. Improvements to load carrying capacity are observed under certain operating conditions. A comprehensive computational finite volume multiphase fluid dynamics analysis, including vapour transport equation and modified finite‐size cavity Rayleigh‐Plesset model, is used to study the effect of indented surface textures in the microscale contact domain and within the individual textures themselves. The results show improved conditions with a textured journal through promotion of micro‐hydrodynamic effect, delaying the effect of lubricant rupture, thus extending the effective load bearing region. A very good agreement is obtained between measurements and predictions.

Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2017

The current study uses Reynolds equation and the cross-film flow velocity profile to analytically... more The current study uses Reynolds equation and the cross-film flow velocity profile to analytically determine pertinent locations for texture feature positioning in sliding hydrodynamic contacts. The position of textures is shown to have a significant effect on the lubricant film thickness, thus the load carrying capacity and generated friction and power loss. It is shown that textures, residing after the inlet lubricant recirculation boundary and prior to the position of maximum contact pressure enhance film thickness and reduce friction in the contact of real rough sliding surfaces. The methodology is applied to partial surface texturing of a thin compression ring of a high performance race engine, with the predicted results confirming the utility of the expounded analytical technique and its conformance to the findings of others reported in literature. The time-efficient analytical and fundamental approach constitutes the main contribution of the paper to furtherance of knowledge.

Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 1999

The primary function of the piston compression ring is to seal the combustion chamber from the bo... more The primary function of the piston compression ring is to seal the combustion chamber from the bottom end of the engine. As a result, its conformance to the cylinder liner surface is of prime importance. This close-contact contiguity results in increased friction, making this contact conjunction responsible for a significant proportion of energy losses. The frictional losses can be as much as 2–6% of the expended fuel energy, which is quite significant for such a diminutive contact. Under these conditions, the geometrical profile, the surface topography and the inertial properties of the ring assume significant importance. The paper presents an integrated mixed-hydrodynamic analysis of the compression ring– cylinder liner contact with multi-parameter optimisation, based on the use of a genetic algorithm. The multi-objective functionality includes minimisation of the parasitic energy loss, reduction in the incidence of asperity level interactions as well as minimisation of the ring mass. Both cold running engine conditions and hot running engine conditions in line with the New European Drive Cycle were considered. Hitherto, such an approach has not been reported in the literature.

Tribology International, 2017

Choosing in-cylinder surfaces is complex. A well-chosen surface has low friction and wear. Conver... more Choosing in-cylinder surfaces is complex. A well-chosen surface has low friction and wear. Conversely, poor oversight often leads to premature failure through wear and scuffing. Typically cylinder bore surfaces are selected experientially. This paper demonstrates the use of Atomic Force Microscopy in LFM mode, characterising typical cylinder bore materials and coatings. The approach uses integrated LFM with continuum contact mechanics. It evaluates the real contact area and effective elastic modulus of the surface, including the effect of any reactive surface film. Surface energy and shear strength, as well as the coefficient of friction in nanoscale interactions are also determined. These properties are measured for 6 cylinder bore materials, including for composite Nickel-Silicon Carbide and DLC, used for high performance engines.

Surface topography is important as it influences contact load-carrying capacity and operational e... more Surface topography is important as it influences contact load-carrying capacity and operational efficiency through generated friction, as well as wear. As a result, a plethora of machining processes and surface finishing techniques have been developed. These processes yield topographies, which are often non-Gaussian, with roughness parameters that alter hierarchically according to their interaction heights. They are also subject to change through processes of rapid initial running-in wear as well as any subsequent gradual wear and embedding. The stochastic nature of the topography makes for complexity of contact mechanics of rough surfaces, which was first addressed by the pioneering work of Greenwood and Williamson, which among other issues is commemorated by this contribution. It is shown that their seminal contribution, based on idealised Gaussian topography and mean representation of asperity geometry should be extended for practical applications where surfaces are often non-Gaussian, requiring the inclusion of surface-specific data which also evolve through process of wear. The paper highlights a process dealing with practical engineering surfaces from laboratory-based testing using a sliding tribometer to accelerated fired engine testing for high performance applications of cross-hatched honed cylinder liners. Such an approach has not hitherto been reported in literature.

Machine downsizing, increased loading and better sealing performance have progressively led to th... more Machine downsizing, increased loading and better sealing performance have progressively led to thinner lubricant films and an increased chance of direct surface interaction. Consequently, mixed and boundary regimes of lubrication are prevalent with ubiquitous asperity interactions, leading to increased parasitic losses and poor energy inefficiency. Surface topography has become an important consideration as it influences the prevailing regime of lubrication. As a result a plethora of machining processes and surface finishing techniques have emerged. The stochastic nature of the resulting topography determines the separation at which asperity interactions are initiated and ultimately affect the conjunctional load carrying capacity and operational efficiency. The paper presents a procedure for modelling of asperity interactions of real rough surfaces, from measured data, which do not conform to the usually assumed Gaus-sian distributions. The model is validated experimentally using a bench top reciprocating sliding test rig. The method demonstrates accurate determination of the onset of mixed regime of lubrication. In this manner, realistic predictions are made for load carrying and frictional performance in real applications where commonly used Gaussian distributions can lead to anomalous predictions.

Special Issue Paper on Surface Texturing, Nov 17, 2014

Reciprocating and low-speed sliding contacts can experience increased friction because of solid b... more Reciprocating and low-speed sliding contacts can experience increased friction because of solid boundary interactions. Use of surface texturing has been shown to mitigate undue boundary friction and improve energy efficiency. A combined numerical and experimental investigation is presented to ascertain the beneficial effect of pressure perturbation caused by micro-hydrodynamics of entrapped reservoirs of lubricant in cavities of textured forms as well as improved micro-wedge flow. The results show good agreement between numerical predictions and experimental measurements using a precision sliding rig with a floating bed-plate. Results show that the texture pattern and distribution can be optimised for given conditions, dependent on the intended application under laboratory conditions. The translation of the same into practical in-field applications must be carried out in conjunction with the cost of fabrication and perceived economic gain. This means that near optimal conditions may suffice for most application areas and in practice lesser benefits may accrue than that obtained under ideal laboratory conditions.

This article provides solution for isothermal mixed hydrodynamic conjunction of the compression r... more This article provides solution for isothermal mixed hydrodynamic conjunction of the compression ring to cylinder liner. This is obtained using the average flow model representation of Reynolds equation based on pressure- and shear-induced flow factors. In particular, the effects of compression ring axial profile along its face-width and surface topography of contiguous solids are investigated. It is shown that ring geometry may be optimized to improve lubrication, whilst care should be taken in order to avoid oil loss or degradation resulting from any loss of sealing. In predicting friction, it is shown that appropriate surface parameters should be used in-line with the state of wear of the ring. For a new ring against a plateau honed liner, boundary friction contribution during the initial running-in wear phase should be predicted according to the average asperity peak heights protruding above the plateau, whilst the plateau height also takes into account the valleys within the surface roughness or grooves created by any cross-hatch honing would be the appropriate measure of topography for worn rings. The main contributions of the article are in providing an analytic solution as well investigation of ring face-width geometry and effect of wear upon friction. However, it is acknowledged that generated heat, inlet boundary starvation and circumferential non-conformity of ring to the bore surface would affect the film thickness and exacerbate generated friction accordingly. These further considerations would require a numerical solution, rather than an analytical one presented here.

Fuel efficiency is the main IC engine attribute, with the compression ring-bore contact consuming... more Fuel efficiency is the main IC engine attribute, with the compression ring-bore contact consuming nearly 5% of the fuel energy. Analyses are often idealised, such as isothermal condition and smooth surfaces, the former being particularly contrary to practice. An analytic solution to the average flow model is presented for this contact with a new analytical thermal model. The generated contact temperatures, particularly at the inlet result in thinner films than the idealised analyses. For the simulated city driving condition the power loss is mainly due to viscous shear under cold engine condition, whilst for a hot engine boundary friction dominates.

Often the effect of interactions at nano-scale determines the tribological performance of load be... more Often the effect of interactions at nano-scale determines the tribological performance of load bearing contacts. This is particularly the case for lightly loaded conjunctions where a plethora of short range kinetic interactions occur. It is also true of larger load bearing conjunctions where boundary interactions become dominant. At the diminutive scale of fairly smooth surface topography the cumulative discrete interactions give rise to the dominance of boundary effects rather than the bulk micro-scale phenomena, based on continuum mechanics. The integration of the manifold localized discrete interactions into a continuum is the pre-requisite to the understanding of characteristic boundary effects, which transcend the physical length scales and affect the key observed system attributes. These are energy efficiency and vibration refinement. This paper strives to present such an approach. It is shown that boundary and near boundary interactions can be adequately described by surface topographical measures, as well the thermodynamic conditions.

Reciprocating and low-speed sliding contacts can experience increased friction because of solid b... more Reciprocating and low-speed sliding contacts can experience increased friction because of solid boundary interactions.
Use of surface texturing has been shown to mitigate undue boundary friction and improve energy efficiency. A combined
numerical and experimental investigation is presented to ascertain the beneficial effect of pressure perturbation caused
by micro-hydrodynamics of entrapped reservoirs of lubricant in cavities of textured forms as well as improved microwedge
flow. The results show good agreement between numerical predictions and experimental measurements using a
precision sliding rig with a floating bed-plate. Results show that the texture pattern and distribution can be optimised for
given conditions, dependent on the intended application under laboratory conditions. The translation of the same into
practical in-field applications must be carried out in conjunction with the cost of fabrication and perceived economic gain.
This means that near optimal conditions may suffice for most application areas and in practice lesser benefits may accrue
than that obtained under ideal laboratory conditions.

Minimisation of parasitic losses in the internal combustion engine is essential for improved fuel... more Minimisation of parasitic losses in the internal combustion engine is essential for improved fuel efficiency and reduced emissions. Surface texturing has emerged as a method palliating these losses in instances where thin lubricant films lead to mixed or boundary regimes of lubrication. Such thin films are prevalent in contact of compression ring to cylinder liner at piston motion reversals because of momentary cessation of entraining motion. The paper provides combined solution of Reynolds equation, boundary interactions and a gas flow model to predict tribological conditions, particularly at piston reversals. The results of the analyses are validated against measurements using a floating liner for determination of in-situ friction of an engine under motored condition. Very good agreement is obtained. The validated model is then modified to include the effect of surface texturing which can be applied to the surface of the liner at compression ring reversals under fired engine conditions. The predictions show that some marginal gains in engine performance can be expected with laser textured chevron features of shallow depth under certain operating conditions.

The use of advanced measurement techniques such as the digital holography method described in thi... more The use of advanced measurement techniques
such as the digital holography method described in this
paper improves the understanding of the cavitation phenomenon
in tribological contacts such as the sliding contact
of the piston ring–cylinder liner conjunction. The paper
describes the use of digital holography measurement
technique to measure cavitation bubble formation and
thickness. The position of observed lubricant film rupture
preceding the cavitation region is compared with some
commonly predicted boundary often used with Reynolds
equation. The experimental results indicate that the Reynolds
and Elrod boundary conditions are the most suitable
for the investigated sliding contact conditions.

Tribology International, 2018

Journal of Fluids Engineering, 2019

http://fluidsengineering.asmedigitalcollection.asme.org/article.aspx?articleid=2747813

Proc IMechE Part D: J Automobile Engineering, 2019

Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2017

Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 1999

Tribology International, 2017

Special Issue Paper on Surface Texturing, Nov 17, 2014

Reciprocating and low-speed sliding contacts can experience increased friction because of solid b... more Reciprocating and low-speed sliding contacts can experience increased friction because of solid boundary interactions.
Use of surface texturing has been shown to mitigate undue boundary friction and improve energy efficiency. A combined
numerical and experimental investigation is presented to ascertain the beneficial effect of pressure perturbation caused
by micro-hydrodynamics of entrapped reservoirs of lubricant in cavities of textured forms as well as improved microwedge
flow. The results show good agreement between numerical predictions and experimental measurements using a
precision sliding rig with a floating bed-plate. Results show that the texture pattern and distribution can be optimised for
given conditions, dependent on the intended application under laboratory conditions. The translation of the same into
practical in-field applications must be carried out in conjunction with the cost of fabrication and perceived economic gain.
This means that near optimal conditions may suffice for most application areas and in practice lesser benefits may accrue
than that obtained under ideal laboratory conditions.

Poor lubrication can occur under reciprocating motion where the momentary cessation of sliding le... more Poor lubrication can occur under reciprocating motion where the momentary cessation of sliding leads to a lack of lubricant entrainment into the contact. This condition occurs in many applications including piston-cylinder systems at and near the top and bottom reversal points. However such surfaces contain larger-scale features than the typical surface roughness features mainly produced through honing or cross-hatching of the cylinder liner. A development in modelling large scale roughness and surface features could lead to improvements in engineering the contacting surfaces. A combined numerical and experimental approach for the solution of a 2D average flow model, originally proposed by Patir and Cheng [1-2], is presented in the current study. The numerical approach is aimed at predicting the lubrication in an in-house reciprocal sliding test rig. The test rig is designed to simulate reciprocal motion of the piston compression ring in an internal combustion engine near the reversals. The study considers the effects of created large scale surface features, such as cross-hatching and honing marks, on the flow factors which represent the surfaces in real engine applications. To obtain the problem-specific flow factors, which take into account the larger surface features, a larger set of areas are chosen for statistical analysis. Surfaces representing typical real engine components were created and topographically measured in detail. The flow factors and the associated numerical approach were then verified through comparison with the friction results from the sliding test rig. The proposed approach indicates a better agreement with the experimental results compared with the cases in which the conventional flow factor proposed by Patir and Cheng were used [1-2]. References: [1] Patir, N. and Cheng, H.S., 1978, " An average flow model for determining effects of three-dimensional roughness on partial hydrodynamic lubrication " , J.

5th World Tribology Congress (WTC 2013), Torino, Italy, September 8-13, 2013

Surface texturing has been used to enhance the tribological properties of a variety of machine el... more Surface texturing has been used to enhance the tribological
properties of a variety of machine elements. Piston rings, face
seals and journal bearings have all shown improved tribological
performance due to introduction of surface textured features. A
multitude of texture geometries, shape, locations and
manufacturing techniques have been investigated in an attempt
to optimize the texture features imparted on to the surface.
A parameter which is commonly neglected during the
investigation and application of textured features is on which
surface (stationary or entraining) the textured feature should
reside. The choice of which surface to texture is often
influenced by the constraints of the available manufacturing
process, material and expected wear of the contiguous surfaces.
In some application the decision is less constrained and the
speed of surface that the texture is applied to should be
considered.
A computational fluid dynamic analysis is conducted to
investigate the influence of textures on the stationary and
moving surface. The Navier-Stokes and continuity equations
for multi-phase flow conditions are solved using a finite
volume method. A vapour transport equation is also included to
ensure continuity of flow in the cavitation region for the
multiple phases as well as Rayleigh-Plesset to take into account
the growth and collapse of cavitation bubbles.
The results indicate that the position of surface texture
features on either the stationary or entraining surface is a
parameter worthy of consideration. It is recognized by the
authors however that that this is not always possible due to
manufacturing constraints, material choices and wear rates of
surfaces.

3rd European Conference on Tribology (ECOTRIB 2011), Vienna, Austria, June 7-9, 2011

Internal Combustion Engine Division Spring Technical Conference, ICEDSTC, May 6-9, 2012, Torino, Italy, Paper No. ICES2012-81201, 6pp, 2012

Both the piston ring and cylinder bore experience wear throughout their life cycle. Therefore cha... more Both the piston ring and cylinder bore experience wear throughout their life cycle. Therefore change occurs in the geometrical profile and topography of the ring. In addition, coating on the ring is also subject to wear, thus altering the physical/mechanical property of the contacting surface. These changes affect the tribological performance of the ring-bore conjunction. Geometrical changes often alter the ring contacting profile, which affects the entrainment of the lubricant into the conjunction. This can affect the regime of lubrication, thus mechanisms that contribute to friction. Wear of surfaces also plays some role in boundary friction in terms of topographical changes as well as surface properties such as hardness and asperity shear strength. Most analysis does not take into account changes in tribological conditions which occur as the result of these salient changes in practice. The paper intends to bridge this gap in the fundamental knowledge and provide explanations for some in-field experiences noted with wear of a compression ring in a typical engine test. The method of solution used is based on the average flow factors which are indicative of entrainment of the lubricant through the rough ring-bore conjunction. This approach was initiated by Patir and Cheng, for which realistic topographical parameters according to the stage of the wear process is included. Changes in friction and fuel energy consumed are predicted.

The paper describes the use of a white light interformeter to measure the cavitation bubble and o... more The paper describes the use of a white light interformeter to measure the cavitation
bubble and oil film thickness in a tribological contact and compares the results to theory. It is
found that oil film thickness is best predicted by the theory proposed by Coyne and Elrod.

A simple partial tilting pad journal-bearing rig is developed. The journal diameter to pad width ... more A simple partial tilting pad journal-bearing rig is developed. The journal diameter to pad width is so chosen as to render a short width bearing. The attitude angle is recorded by reading from a graduated scale.........

The piston compression ring-bore contact accounts for 5-6% of input fuel energy [1]. This is sign... more The piston compression ring-bore contact accounts for 5-6% of input fuel energy [1]. This is significant for such a small conjunction. With ever-increasing costsand stricter emerging legislation much attention is directed towards reducing the parasitic losses.The piston ring is one of the most challenging tribological contacts on account of transient nature of the regime of lubrication during a typical engine cycle [2]. High friction occurs at piston reversals at the top and bottom dead centres, with highest friction at the beginning of the power stroke, where high pressures act behind the inner rim of the ring and with low piston sliding speed, inducing some Boundary interactions [2].
Laser texturing is used to reduce friction [3-7].This paper comprises direct measurement of friction from a reciprocating slider bearing test rig. It also presents numerical prediction of the same. The combined approach enables the study of possibleimprovements in tribological conditions similar to ring reversals in a piston system, but at a more fundamental level. It further reduces a plethora of other effects such as ring dynamics [8] and thermal distortions which make measurements difficult in an operating engine.

Journal of Tribology, 2015