Nigel M JENNETT

National Physical Laboratory, NPL Materials, Teddington, UK

Specialization: Determination the mechanical properties of materials

Dr Nigel Jennett is leading work to determine the mechanical properties of materials; ranging from the nano-scale to the macro-scale, and from super-hard to super-soft (including polymers and biomaterials). His interests include the effect of length scale on material properties and on test response, the performance of mechanical contacts, designing higher resolution test methods for testing of small volumes of material and for mapping surface properties, and methods to derive macro property information from nano-mechanical tests. Nigel is using validated nano-mechanical measurements to develop a better fundamental understanding of deformation as a function of length scale, temperature and time; an output being the ability to distinguish measurement effects from genuine material performance. This, for example, is providing design rules to enable material performance enhancement through length-scale engineering. Nigel has been involved in the standardisation of instrumented indentation from its beginning; he is working to extend the scope of current standards to include the measurement of the dimensions and mechanical properties of viscous materials and instrumented indentation at elevated temperatures.

Nigel is a chartered Scientist a Chartered Physicist and a member of the Institute of Physics (UK) and the Materials Research Society (USA).

Biography

Nigel M Jennett BSc(hons) (Physics), PhD (Physics), CSci CPhys MinstP has over 25 years experience of fabrication and characterisation of nano-structured materials and 20 years developing nano-mechanical test methods. He is an Associate Editor of Philosophical Magazine (and Philos. Mag. Letters), is the international chair of VAMAS Technical Working Area 22 “Mechanical properties measurement of thin films and coatings,” is a UK technical expert on the CIPM consultative committee working group for hardness (CCM-WGH), chairs the BSI indentation hardness committee and leads the UK delegation for a number of ISO working groups drafting standards for indentation-based test methods. Nigel has also served two terms (6y) on the European Commission Certification Advisory Panel for Physical and Physicochemical Properties.

A prize winning experimentalist (Bristol Physics Laboratory prize 1984 & 1986 and the Raychem prize 1985), Nigel spent 6 years researching magnetic multilayers at Bristol University (1990 PhD, 1991 Chartered Physicist), before moving to NPL in 1992 to work on developing traceable Scanned Probe Microscopy and nano-mechanical measurements.  In 1998 he created his own research group focussed on surfaces, coatings and nano‑mechanics. Awarded a Glazebrook Fellowship in 2003 and the NPL Rayleigh award in 2010, he is a seasoned leader of projects funded by Government, Industry and the European Commission and is a regular invited speaker at international conferences.

Selected Publications:

”In search of validated measurements of the properties of visco-elastic materials by indentation with sharp indenters”M. A. Monclus and N. M. Jennett, Philosophical Magazine, 91(7), 1308-1328, (2011)

Provides methods to compare results between oscillatory and static (indentation creep) methods of obtaining visco-elastic properties of materials by indentation.

”High resolution measurement of dynamic (nano) indentation impact energy: a step towards the determination of indentation fracture resistance.”
Nigel Jennett and John NunnPhilosophical Magazine,91(7), 1200-1220, (2011)
Describes the NPL devised method using fast data acquisition to measure the energy absorbed by fracture in a nano-impact with sub-pJ energy resolution and 50 µs time resolution. This method is now incorporated in commercial instrumented indentation equipment.

”Enhanced Yield Strength of Materials -The Thinness Effect”
N.M. Jennett, R. Ghisleni, J. MichlerAppl. Phys. Lett.95, 123102 (2009)
This paper shows that the strength of small structures is determined by ‘thinness', i.e. only by the smallest dimension of a structure. This is the first unambiguous confirmation that a modified slip distance theory explains plasticity size effects (smaller contacts or structures are ‘stronger’).

”Higher accuracy analysis of instrumented indentation data obtained with pointed indenters.” T. Chudoba and Nigel M. Jennett,J. Phys. D: Appl. Phys. 41,215407 (2008). 
This paper publishes a validated, improved analysis method that removes a ~10% systematic error hidden in current indentation results and is being used to inform revision of the current ISO standard for indentation.

”Study of the interaction between the indentation size effect and Hall-Petch effect with spherical indenters on annealed polycrystalline copper”

X.D. Hou, A. J. Bushby, and N. M. Jennett.J. Phys. D: Applied Physics 41(7),074006(2008).
This paper provides a clear demonstration that the elastic proportional limit depends on both contact size and grain size, providing a route to length scale engineering of components. Noticeable even at large length scales, size effects are a “show stopper” for Finite element modelling using continuum models of plasticity and invalidate calibration methods in hardness standards.

”Validated measurement of Young’s modulus, Poisson ratio and thickness for thin coatings by combining instrumented (nano)indentation and acoustical measurements.”N. M. Jennett, G. Aldrich-Smith, A. S. Maxwell, J. Mater. Res  19(1), 143-148 (2004).
Indentation and acoustical spectroscopy dispersion curve data are combined to derive non-destructively the mass density, thickness, Poissons ratio, and modulus of a coating; validated by cross sectional Scanning Electron Microscopy of coating thickness.

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