Robert Paynter

University of Oxford, Engineering Science, Department Member

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I am an engineer working on the science that modern systems depend on. I have experimental experience of structures as small as 50nm (photo lithograpy of gratings) to 25m (fatigue testing of wind turbine blades).

I engauge with the fundamental theory and knowledge of the phenomema I am investigating as well as the the means of achieving those investigations; this has encompassed: chemistry, fluid dynamics, aucoustics, probability theory, radiation, stress analysis, wear, electrical power systems, electronics.
Contact mechanics forms the core of my current work, with residual stresses and fatigue as significant components.
My Doctorate entitled "Ring Dislocations and Analysis of Complete Contacts" encompassed theoretical analyses found in these themes.

I assist in teaching, having delivered lectures, undergraduate tutoring and demonstrating, and supporting post graduate experimental and theoretical work.

I am happy to be wrestling with a big spanner one minute and an integral equation the next.
Supervisors: Prof. David A Hills
Phone: 07806527267
Address: Department of Engineering Science,
University of Oxford,
Parks Road, Oxford, United Kingdom.
OX1 3PJ

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Papers by Robert Paynter

Prediction of fatigue crack initiation under biaxial loading

Frattura ed Integrità Strutturale, 2017

This investigation revisits biaxial fatigue experiments carried out with the nickel-based superal... more This investigation revisits biaxial fatigue experiments carried out with the nickel-based superalloy termed Waspaloy. Recently, yield criteria extended to multiaxial fatigue and stress based approaches were analysed and their performance to correlate the biaxial test data was evaluated. It was concluded that despite their reliable results, the parameters did not properly represent the physical behaviour of the material. In this context, an extension of this study was executed considering the strain based critical plane approaches proposed by Fatemi-Socie (FS) and Smith-Watson-Topper (SWT). The first parameter presented overly conservative predictions with large scatter of results. In contrast, more accurate predictions were obtained with the SWT parameter.

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The effect of path cut on Somigliana ring dislocations in a half-space

International Journal of Solids and Structures, 2009

This paper provides solutions for the stress and displacement fields induced in a half-space by a... more This paper provides solutions for the stress and displacement fields induced in a half-space by an edge dislocation of constant magnitude, where the dislocation line is a circular ring lying in a plane parallel with the free surface. Two types of edge dislocations are considered; the prismatic form with a displacement discontinuity vector normal to the surface and cases with radial dislocation vectors. The latter are not true Volterra dislocations and produce different results for different path cuts these effects are investigated in some detail. The primary application of these results is for analysis of axisymmetric problemsthe radial dislocations would be impossible in finite material.

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The effect of wear on nucleation of cracks at the edge of an almost complete contact

Wear, 2010

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Separation and slip at the edge of a complete contact: An asymptotic solution

International Journal of Solids and Structures, 2010

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The Use of a Second Harmonic Correlation to Detect Damage in Composite Structures Using Thermoelastic Stress Measurements

Strain, 2003

Abstract: A novel development of the thermoelastic stress measurement technique using the second ... more Abstract: A novel development of the thermoelastic stress measurement technique using the second harmonic of the load test frequency is presented. Clear identification of significant sub-surface damage is demonstrated using the new technique, and test results are presented from a small scale wind turbine blade test which indicate that some quantitative assessment of damage criticality might be possible from a single full-field measurement. A hypothesis is presented as to why the new technique is successful, based on complex ...

Simulation of Fretting Wear in Halfplane Geometries: Part 1—The Solution for Long Term Wear

Journal of Tribology, 2009

The final configuration of a cylindrical Hertzian contact, subject to oscillatory shear and under... more The final configuration of a cylindrical Hertzian contact, subject to oscillatory shear and undergoing wear, is studied. It is assumed that wear has proceeded for a long time, so that the final, modified contact is wholly adhered. It is shown that the extent of the final contact corresponds to that of the initial adhered region and the pressure distribution, and state of stress at the new contact edge are all derived, so that the environment in which cracks nucleate is well described.

A comparison of two and three-dimensional analyses of fatigue crack closure

International Journal of Fatigue, 2007

Plasticity-induced fatigue crack closure is an important mechanism in the reduction of the effect... more Plasticity-induced fatigue crack closure is an important mechanism in the reduction of the effective stress intensity factor range for a fatigue crack. A calculation of the level of reduction would allow more accurate predictions of fatigue crack growth rate. However, modelling plasticity-induced closure is not straightforward, particularly when the three-dimensional aspects of the problem are included. Some simplification is possible by reducing the problem to two dimensions, but it is not always clear how this can be achieved for practical ...

An overview of the quantification of fretting fatigue lives of complete contacts

Engineering Fracture Mechanics, 2012

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Blade surface pressure measurement on an operating wind turbine

Work, 1996

Engineers, Part C: Journal of Mechanical

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2009

Abstract: The state of stress induced by a shrink-fitted circular shaft in an elastically similar... more Abstract: The state of stress induced by a shrink-fitted circular shaft in an elastically similar half-space, positioned so that the end of the shaft is flush with the remainder of the free surface, is studied. At deep interior points the classical plane strain (Lamé) solution obtains, and the transition to the free surface state is found. It is found that a residual interfacial axial shear develops and the coefficient of friction needed to ensure adhesion along the interface is found. The effect of slip when a lower coefficient of friction is present is also found as a ...

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The influence of contacting Ni-based single-crystal superalloys on fretting fatigue of Ni-based polycrystalline superalloys at high temperature

Tribology International, 2014

ABSTRACT Fretting fatigue tests at high temperature were carried out with single-crystal and poly... more ABSTRACT Fretting fatigue tests at high temperature were carried out with single-crystal and polycrystalline alloys. The influence of the crystallographic orientation of contacting single-crystal pads on the lives of polycrystalline specimens is investigated. An analytical formulation of the contact problem between two anisotropic cylinders is used to study the changes in peak stress and contact width due to the orientation of the single-crystal. Finite element analysis is also used to study the variation of stress near the contact edge due to crystallographic orientation. An area averaging method is suggested to correlate fretting fatigue and plain fatigue curves. Using finite element analysis combined with the area averaging method, a better correlation was found between fretting fatigue results and plain fatigue.

The influence of contacting Ni-based single-crystal superalloys on fretting fatigue of Ni-based polycrystalline superalloys at high temperature

The Observation and Interpretation of Crack Closure under Plain Fatigue Conditions

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Remembering DuBois: The Struggle for Recognition at the W.E.B. Du Bois Boyhood Homesite

The potential of hydrogen and electricity production from wind power

... English | Nederlands. The potential of hydrogen and electricity production from wind power. (... more

Pressure measurement on a stall regulated wind turbine blade

Renewable Energy. A clean technology. A review strategy for SERC

ABSTRACT ERU Internal Report

Asymptotic analysis of an adhered complete contact between elastically dissimilar materials

The Journal of Strain Analysis for Engineering Design, 2014

A complete contact problem between elastically dissimilar materials is studied using an asymptoti... more A complete contact problem between elastically dissimilar materials is studied using an asymptotic analysis. A quarter plane wedge on a half-plane represents the contact edge geometry. Two eigenvalues are obtained for pairs of contacting materials, and their characteristics are classified on the Dundurs parallelogram. Generalized stress intensity factors, KI and KII, are derived to use a two-term stress equation of dimensionless form with developing a mode separation angle. It is found that the order of stress singularity increases as the wedge becomes more rigid than the half-plane. Slipping characteristics on the contact interface are investigated in detail, especially for the case of KI < 0 < KII that represents a typical adhesive complete contact condition. An example case is given using a finite element model to provide calibration of the stress intensities for a specific material, geometry and load combination.

Fatigue testing and NDE of a sectional wind turbine rotor blade

Contact analysis of a semi-infinite strip pressed onto a half plane by a line force

International Journal of Mechanical Sciences, 2014

ABSTRACT Receding contacts are a class of contacts that have received little attention. The first... more ABSTRACT Receding contacts are a class of contacts that have received little attention. The first studies carried out on the subject have shown that the area of contact decreases as a load is applied and is load independent. The simple plane problem of an elastic layer pressed onto an elastically similar half space by a line force is studied here. The problem is solved for several coefficients of friction using distributions of edge dislocations. The extent of the stick and slip zone are found and the lift-off angle of the strip is estimated from the resulting tractions distribution.