Research

Thermo-mechanical fatigue

Within the gas turbine engine, the high transient thermal stresses resulting from throttle movement from idle to high settings give rise to the phenomenon of thermo-mechanical fatigue (TMF). These effects have been widely explored for turbine blade materials, typically single crystal nickel alloys. More recently however, a combination of thinner disc rims and further increases in turbine entry temperature has lead to a situation where TMF in disc materials cannot be ignored. Turbine discs will usually be manufactured from polycrystalline nickel alloys, and as such it is now considered critical that TMF effects in this system of alloys is fully characterised. Research within the Institute of Structural Materials in collaboration with Roll-Royce plc leads the way in the development of modelling approaches to TMF through a range of cutting edge experimental techniques.

Modern creep lifing approaches

Traditional creep lifing techniques based on power law equations have shown themselves to be extremely limited, particularly in the prediction of long term data based only on short term experimental data. More recently, alternative approaches such as the Wilshire equations and hyperbolic tangent methods have been proposed which offer a new insight into the field. Ongoing research within the Institute of Structural Materials focuses on the development of the Wilshire equations in particular, their relationship with microscopic behaviour of engineering alloys and their application to a range of materials that currently includes copper, aluminium alloys, steels, titanium alloys, nickel superalloys and titanium aluminides.

Titanium alloys

Premature failure of titanium based engineering components in the 1970s brought to attention the phenomenon of dwell effects at low temperatures in these alloys, loosely termed ‘cold creep’, which are currently still a major concern for designers. Ongoing research at the Institute of Structural Materials seeks to address the issue through targeted mechanical testing and microscopic evaluation. The presence, extent and effect on mechanical properties of cold dwell related features such as ‘quasi-cleavage’ facets are investigated with the resultant effect on both creep and fatigue life also studied.

Selected publications

• R.J. Lancaster, M.T. Whittaker, S.J. Williams, A review of thermo-mechanical fatigue behaviour in polycrystalline nickel superalloys for turbine disc applications, Materials at High Temperatures, 2013, 30, 1, [ISSN:09603409], [DOI: 10.3184/096034013x13630238172260]
• Mark Whittaker, Microstructural Characterization of a Prototype Titanium Alloy Structure Processed via Direct Laser Deposition (DLD), Metallurgical and Materials Transactions B, 2012, 43, 2, [DOI: 10.1007/s11663-011-9599-x]
• Mark Whittaker, Advanced Procedures for Long-Term Creep Data Prediction for 2.25 Chromium Steels, Metallurgical and Materials Transactions A, 2012, [DOI: 10.1007/s11661-012-1160-2]
• Mark Whittaker, Long-Term Creep Data Prediction for Type 316H Stainless Steel, Materials Science and Engineering: A, 2012, [DOI: 10.1016/j.msea.2012.05.023]
• Mark Whittaker, Considerations in fatigue lifing of stress concentrations in textured titanium 6-4, International Journal of Fatigue, 2011, [DOI: 10.1016/j.ijfatigue.2011.05.001]
• Mark Whittaker, Variability in the mechanical properties and processing conditions of a High Strength Low Alloy steel, Procedia Engineering, 2011, [DOI: 10.1016/j.proeng.2011.04.020]
• Mark Whittaker, Microstructural Characterization of a Polycrystalline Nickel-Based Superalloy Processed via Tungsten-Intert-Gas-Shaped Metal Deposition, Metallurgical and Materials Transactions B, 2010, [DOI: 10.1007/s11663-010-9410-4]
• Mark Whittaker, Grain boundaries: their influence on creep strain accumulation, Materials Science and Technology, 2010, [DOI: 10.1179/026708309X12567268926605]
• Mark Whittaker, Modelling the behaviour of titanium alloys at high temperature for gas turbine applications, Materials Science and Engineering: A, 2010, [DOI: 10.1016/j.msea.2010.03.078]
• Mark Whittaker, The effect of prestrain on low and high temperature creep in Ti834, Materials Science and Engineering: A, 2010, [DOI: 10.1016/j.msea.2010.07.008]
• Mark Whittaker, The effect of microstructure and texture on mechanical properties of Ti6-4, International Journal of Fatigue, 2009, [DOI: 10.1016/j.ijfatigue.2009.02.014]
• Mark Whittaker, Effect of prestrain on the fatigue properties of Ti834, International Journal of Fatigue, 2009, [DOI: 10.1016/j.ijfatigue.2009.03.008]
• Mark Whittaker, Plain and notched fatigue in nickel single crystal alloys, International Journal of Fatigue, 2009, [DOI: 10.1016/j.ijfatigue.2009.03.010]
• Mark Whittaker, The role of grain boundaries in creep strain accumulation, Acta Materialia, 2009, [DOI: 10.1016/j.actamat.2009.05.009]
• P HURLEY, M WHITTAKER, S WILLIAMS, W EVANS, Prediction of fatigue initiation lives in notched Ti 6246 specimens, 2008, pp.none, [ISBN:0142-1123], [DOI: 10.1016/j.ijfatigue.2007.05.013]
• Mark Whittaker, Shaped Metal Deposition of a Nickel Alloy for Aero Engine Applications, 2008, pp.none, [ISBN:0924-0136], [DOI: 10.1016/j.jmatprotec.2007.10.051]
• M WHITTAKER, W EVANS, P HURLEY, D FLYNN, Prediction of notched specimen behaviour at ambient and high temperatures in Ti6246, 2007, pp.1716-1725, [ISBN:0142-1123], [DOI: 10.1016/j.ijfatigue.2007.02.006]
• P HURLEY, M WHITTAKER, P WEBSTER, W EVANS, A Methodology for Predicting Creep/Fatigue Crack Growth Rates in Ti6246, 2007, pp.1702-1710, [ISBN:0142-1123], [DOI: 10.1016/j.ijfatigue.2007.01.014]
• MT Whittaker, No title, 0, [DOI: 10.3390/ma6031118]
• MT Whittaker, No title, 0, [DOI: 10.1016/j.intermet.2013.02.003,]
• MT Whittaker, No title, 0, [DOI: 10.1016/j.msea.2013.02.070]
• MT Whittaker, No title, 0, [DOI: 10.1016/j.msea.2013.03.030]

Teaching

• EG-283 - Mechanical Deformation in Structural Materials (12/13)
• EGA306 - Mechanical Properties of Materials 2 (12/13)
• EG-397 - Propulsion (12/13)

Research theses supervised

PhD

• 2012 - Constitutive behaviour in turbine disc alloys (2nd Supervisor: Professor David Worsley)
• 2011 - Constitutive relationships and the prediction of notched specimen behaviour under TMF loading (2nd Supervisor: Professor David Worsley)
• 2010 - Characterisation of novel titanium alloys for future aero-engine rotative components (2nd Supervisor: Professor Martin Bache)
• 2008 - Establishing the conditions for facet formation in a titanium alloy (2nd Supervisor: Professor Valerie Randle)
• 2006 - Fourth Generation Single Crystal Superalloys and Advanced Lifing Methodologies (2nd Supervisor: Professor Martin Bache)
• 2004 - The Notch Sensitivity and Crack Propagation of Fourth Generation Single Crystal Alloys (2nd Supervisor: Professor Martin Bache)

EngD

• 2011 - Effects of bulk inelastic strain and stress concentrations on fatigue nucleation lives and dwell crack growth rates (2nd Supervisor: Professor David Worsley)
• 2011 - Effects of loading proportionality on fatigue life (2nd Supervisor: Professor David Worsley)
• 2011 - Lifing Methods Against Rotor Overspeed Failure in Disc Alloys (2nd Supervisor: Professor Stephen Brown)
• 2011 - Impact of wear damage on the fatigue performance of disc alloys in gas turbine (2nd Supervisor: Professor Stephen Brown)
• 2010 - Influence of Joining Technique on the Fatigue Performance of Novel Chassis/Suspension Design (2nd Supervisor: Professor David Worsley)
• 2010 - TMF and bithermal crack growth (2nd Supervisor: Professor Stephen Brown)
• 2010 - Improved creep models for nickel based disc alloys (2nd Supervisor: Professor Stephen Brown)
• 2010 - Titanium Alloy Developments for Vision 10 Fan Disc Applications (2nd Supervisor: Professor Martin Bache)
• 2008 - Minimising variability in steel/weld fatigue data and developing robust durability design for automotive chassis (2nd Supervisor: Professor David Worsley)
• 2007 - Multi-axial and thermo-mechanical loading effects in nickel-based disc superalloys (2nd Supervisor: Professor Martin Bache)
• 2006 - Characterisation of steel cut edges for improved fatigue property data estimations and enhanced CAE durability (2nd Supervisor: Professor David Worsley)
• 2005 - Reliable Durability Assessment of Welded Yellow Goods Equipment. (2nd Supervisor: Dr. David Isaac)
• 2004 - Thermo-mechanical fatigue in nickel based disc alloys (2nd Supervisor: Professor Martin Bache)

MRes

• 2010 - Fatigue resistant AHSS grades development (2nd Supervisor: Dr. Karen Perkins)
• 2009 - Applying the Wilshire Equations to Grades 22, 23 and 24 Steel (2nd Supervisor: Professor Hamilton Mcmurray)
• 2006 - The effects of waveform, mean stress and environment on fatigue crack growth in high temperature disc alloys (2nd Supervisor: Dr. David Isaac)

MSc

• 2011 - 'Creep Lifing of High Performance Alloys by using Wilshire equation'
• 2008 - Detailed Assessment of the effects of Thermo-Mechanical Fatigue in an Advanced Nickel Alloy

Measures of esteem

• Board member of Institute of Materials Structure and Properties of Materials Committee.(2011-present)
• Invited contribution to book (single author) – Gas Turbines (ISBN 978-953-307-324-8.) – Chapter title – Titanium in the Gas Turbine engine.
• Invited speaker – Power plant cycling conference, North Carolina, 2012
• External examiner at PhD and MRes levels for The University of Birmingham
• Co-author of invited papers (Fatigue 2007, Grain Boundaries at High Temperatures 2009)
• Act as an international consultant on titanium alloys and creep lifing
• Reviewer for 5 major international journals - International Journal of Fatigue, Journal of Materials Science, Metallurgical & Materials Transactions A, Fatigue & Fracture of Engineering Materials & Structures
• Awarded Chartered Physicist status, 2007
• Awarded RCUK Research Fellowship 2007

Conferences

Conferences, invited papers

• Use of Wilshire Equations for Life Assessment from Limited Ex-Service Creep and Creep-Fatigue Materials Data, M T Whittaker, W J Harrison, B Wilshire, Power plant cycling conference, Charlotte, North Carolina, 2012

Conferences

1. WJ Evans, RW Evans, MT Whittaker, W Voice, “Texture, microstructure and mechanical properties in Ti6-4”, Ti 2003 Science & Technology 3, pp 1759-1766 (2004)
2. PJ Hurley, MT Whittaker, S Williams, WJ Evans, “Prediction of LCF initiation lives in DEN specimens based on strain control testing of plain Ti6246 specimens”, 9th International Fatigue Congress, Atlanta 2006, Published on CD-ROM
3. WJ Evans, MT Whittaker, “Prediction of notched specimen behaviour in textured Ti-6Al-4V”, 9th International Fatigue Congress, Atlanta 2006, Published on CD-ROM
4. WJ Evans, MT Whittaker, JP Jones, “Torsion fatigue in near alpha and alpha titanium alloys”, 11th International titanium conference, Kyoto, June 2007
5. WJ Evans, MT Whittaker, JP Jones, D Rugg, T Jackson, “Effect of prestrain on ambient and high temperature creep in Ti834”, 11th International titanium conference, Kyoto, June 2007
6. WJ Evans, D Davies, MT Whittaker “Characterisation of stress concentration features in the +  titanium alloys” 11th Portuguese conference on fracture, February 2008
7. MT Whittaker, WJ Evans, W Harrison, “Time Dependent Fracture of Titanium Alloys” 12th International Conference on Fracture, Ottawa, Ontario, Canada July 12-17, 2009
8. MT Whittaker, WJ Evans, W Harrison, “Fracture mechanisms due to Fatigue, Creep and Environmental damage in titanium alloys” 12th International Conference on Fracture, Ottawa, Ontario, Canada July 12-17, 2009
9. JM Brear, MT Whittaker and B. Wilshire, “Creep fracture of centrifugally-cast HK40 tube steel”, ECCC creep conference, Zurich 2009
10. M.T. Whittaker, C. Pleydell-Pearce, M.R. Bache “Fatigue life variation due to microstructure in Ti6-4” 12th World conference on Titanium, Beijing, 2011
11. M. Whittaker, B.Wilshire, W. Harrison “The Wilshire Equations for Long-Term Creep Life Prediction”, Creep 2012, Kyoto, May 2012
12. Z Abdallah, M Dixon, MT Whittaker, MR Bache, “High Temperature Creep Behaviour of Gamma Titanium Aluminides (-TiAl)” Creep 2012, Kyoto, May 2012
    
    

Full publications in refereed journals

1. WJ Evans, JP Jones, MT Whittaker, “Texture effects under tension and torsion loading conditions in titanium alloys”, International Journal of Fatigue, Vol 27 (10-12) pp 1244-1250, 10.1016/j.ijfatigue.2005.06.045
2. D Clark, MR Bache, MT Whittaker, “Shaped Metal Deposition of a Nickel Alloy for Aero Engine Applications”, Journal of Materials Processing Technology, Vol 203, 2008, pp 439-448 10.1016/j.jmatprotec.2007.10.051
3. PJ Hurley, MT Whittaker, PJ Webster, WJ Evans, “A Methodology for Predicting Creep/Fatigue Crack Growth Rates in Ti6246”, International Journal of Fatigue, Vol 29 (9-11) pp 1702-1710, 10.1016/j.ijfatigue.2007.01.014 
4. MT Whittaker, PJ Hurley, WJ Evans, D Flynn, “Prediction of notched specimen behaviour at ambient and high temperatures in Ti6246”, International Journal of Fatigue, Vol 29 (9-11) pp 1716-1725, 10.1016/j.ijfatigue.2007.02.006  
5. PJ Hurley, MT Whittaker, SJ Williams, WJ Evans, “Prediction of fatigue initiation lives in notched Ti 6246 specimens”, International Journal of Fatigue, Volume 30, Issue 4, April 2008, pp 623-634, 10.1016/j.ijfatigue.2007.05.013
6. WJ Evans, D Davies, MT Whittaker “Characterisation of stress concentration features in the +  titanium alloys” Sociedade Portuguesa de Materials "Ciencia e Tecnologia de Materiais" 2008
7. M.T. Whittaker, W.J. Evans, R. Lancaster, W. Harrison, P.S. Webster, “The effect of microstructure and texture on mechanical properties of Ti6-4”, International Journal of Fatigue, November-December 2009, Pages 2022-2030,  doi:10.1016/j.ijfatigue.2009.02.014  
8. M.T. Whittaker, W.J. Evans “Effect of prestrain on the fatigue properties of Ti834”, International Journal of Fatigue, November-December 2009, Pages 1751-175, doi:10.1016/j.ijfatigue.2009.03.008   
9. W.J. Evans, R. Lancaster, A. Steele, M. Whittaker, N. Jones, “Plain and notched fatigue in nickel single crystal alloys”, International Journal of Fatigue, November-December 2009, Pages 1709-1718,  doi:10.1016/j.ijfatigue.2009.03.010  
10. B. Wilshire and M.T. Whittaker, “The role of grain boundaries in creep strain accumulation”, Acta Materialia, Volume 57, Issue 14, August 2009, Pages 4115-4124, doi:10.1016/j.actamat.2009.05.009
11. MT Whittaker, JP Jones, C Pleydell-Pearce, D Rugg  and SJ Williams, “The effect of prestrain on low and high temperature creep in Ti834” Materials Science and Engineering: A Volume 527, Issues 24-25, 25 September 2010, Pages 6683-6689  doi:10.1016/j.msea.2010.07.008 
12. M. T. Whittaker and B. Wilshire “Long term creep life prediction for Grade 22 (2.25Cr–1Mo) steels” Materials Science and Technology, 642-647. In Materials Science and Technology 27 (3), 2011 doi: 10.1179/026708310X520529   
13. B. Wilshire and M. T. Whittaker “Grain boundaries: their influence on creep strain accumulation” Materials Science and Technology 2010 Vol. 26 No. 7 pp793-796 doi: 10.1179/026708309X12567268926605   
14. D. Clark, MT Whittaker, MR Bache “Microstructural Characterization Of A Polycrystalline Nickel-Based Superalloy Processed Via Tungsten-Inert-Gas-Shaped Metal Deposition” Metallurgical and Materials Transactions B, 2010, vol. 41, no.6, pp. 1346-1353  doi: 10.1007/s11663-010-9410-4
15. M.T. Whittaker, W. Harrison, P.J. Hurley and S. Williams “Modelling the behaviour of titanium alloys at high temperature for gas turbine applications” Materials Science and Engineering: A Volume 527, Issues 16-17, 25 June 2010, Pages 4365-4372
     doi:10.1016/j.msea.2010.03.078  
16. M.T.Whittaker and B.Wilshire “Creep and creep fracture of 2.25Cr–1.6W steels (Grade 23)” Materials Science and Engineering: A Volume 527, Issues 18-19, 15 July 2010, Pages 4932-4938  doi:10.1016/j.msea.2010.04.033   
17. D.J. Thomas, G.W. Bright, M.T. Whittaker and Y. Gao   “The influence of mechanical and CO2 laser cut-edge characteristics on the fatigue life performance of high strength automotive steels” Journal of Materials Processing Technology, Volume 211, Issue 2, 1 February 2011, pp 263-274  doi:10.1016/j.jmatprotec.2010.09.018   
18. D.J. Thomas, Y. Gao, A. Blowey  and M.T. Whittaker  “Reliable cut-edge fatigue CAE durability predictions for high strength steel automotive chassis and suspension applications” Engineering Integrity Society Journal, September 2010   
19. M.T. Whittaker “Considerations in fatigue lifing of stress concentrations in textured titanium 6-4”, International Journal of Fatigue, Vol.33, Iss 10, October 2011, pp 1384-1391, doi 10.1016/j.ijfatigue.2011.05.001
20. D. Clark, M.T. Whittaker, M.R. Bache “Microstructural characterisation of a functional prototype titanium alloy structure processed via Direct Laser Deposition (DLD)” Accepted for publication in Metallurgical and Materials Transactions B, June 2011.
21. G.W.Bright, J.I.Kennedy, F. Robinson, M.Evans, M.T.Whittaker, J.Sullivan, Y. Gao  “Variability in the mechanical properties and processing conditions of a high strength low alloy steel”, Procedia Engineering, Vol 10, 2011, pp 106-111. doi 10.1016/j.proeng.2011.04.020
22. M.T. Whittaker, B. Wilshire “Advanced Procedures for Long-Term Creep Data Prediction for 2.25 Chromium Steels”, Submitted to Metallurgical and Materials Transactions A, In Press, 2012
23. R.J. Lancaster (RO), M.T. Whittaker, S.J. Williams (IC) “A Review of Thermo-Mechanical Fatigue behaviour in Polycrystalline Nickel Superalloys”, Materials at High Temperature, In Press 2012
24. M.T. Whittaker, M. Evans, B. Wilshire, Long-Term Creep Data Prediction for Type 316H Stainless Steel, Materials Science and Engineering A, In Press 2012

Invited Book Chapter

1. MT Whittaker “Titanium in the Gas Turbine Engine” Ed.E. Benini, Publ. INTech (ISBN 978-953-307-324-8).

Conferences

• WJ Evans, RW Evans, MT Whittaker, W Voice, “Texture, microstructure and mechanical properties in Ti6-4”, Ti 2003 Science & Technology 3, pp 1759-1766 (2004)
• WJ Evans, MT Whittaker, “Prediction of notched specimen behaviour in textured Ti-6Al-4V”, 9th International Fatigue Congress, Atlanta 2006, Published on CD-ROM
• PJ Hurley, MT Whittaker, S Williams, WJ Evans, “Prediction of LCF initiation lives in DEN specimens based on strain control testing of plain Ti6246 specimens”, 9th International Fatigue Congress, Atlanta 2006, Published on CD-ROM
• WJ Evans, MT Whittaker, JP Jones, D Rugg, T Jackson, “Effect of prestrain on ambient and high temperature creep in Ti834”, 11th International titanium conference, Kyoto, June 2007
• WJ Evans, MT Whittaker, JP Jones, “Torsion fatigue in near alpha and alpha titanium alloys”, 11th International titanium conference, Kyoto, June 2007