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Engineering and the Environment

Professor Fabrice Pierron PhD

Professor of Solid Mechanics

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Professor Fabrice Pierron is Professor of Solid Mechanics within Engineering and the Environment at the University of Southampton.

Current position
I am currently Professor of Solid Mechanics at the University of Southampton (since May 2012). I belong to the Structures and Solid Mechanics theme and have strong connections with the engineering materials, bioengineering, fluid-structure interaction and ISVR research groups.

Honours, Awards and Esteem

Publications (March 2017)


Career history
I graduated from ENSEM in Nancy, France, in 1989, with a major in mechanical engineering. During my degree, I was an exchange student in mechanical engineering at the University of Bath (UK) as a third year undergraduate. I then embarked on a PhD programme partly funded by the EU programme BRITE/EURAM and shared between the University of Bath and the Ecole Nationale Supérieure des Mines de St-Etienne (ENSM.SE, France). I got my PhD from Claude Bernard University in Lyon in 1994 (to which ENSM.SE was affiliated for postgraduate studies).

After a short post-doctoral period at ENSM.SE, I was awarded a lectureship there (1994-1999). During this period, I continued my collaboration with Professor Alain Vautrin and started seminal work on the Virtual Fields Method (see project pages) with Professor Michel Grédiac and initiation to optical methods with Dr Yves Surrel. I was awarded an ‘Habilitation à Diriger les Recherches’ (HDR) in 1999 from Clermont-Ferrand University (to which ENSM.SE was also affiliated), the French degree to access professorial rank.

I then moved on to my first full professor position in 1999 at Ecole Nationale Supérieure d’Arts et Métiers (ENSAM, France), Châlons-en-Champagne campus, at the age of 33, one of the youngest full professors in mechanical engineering in France at the time. I was tasked to create a research laboratory (LMPF) from scratch, which I did, hiring researchers, attracting funding to buy equipment and obtaining recognition from the French Ministry of Higher Education and Research in 2001. I led LMPF for 6 years, after which I stepped down to lead one of the two research groups until my departure to Southampton in 2012. I was promoted to first class professor in 2006, again one of the youngest in France at the time. In 2004-2005, I spent a year at the University of Bristol on a sabbatical, funded by the EPSRC.

Research

Publications

Teaching

Contact

Research interests

My research interests lie in the general area of the mechanics of deformable solids. Solids deform everywhere around us, which unfortunately sometimes leads to failure of engineering systems. Understanding, modelling and testing this behaviour is therefore of primary importance to many engineering areas like transportation, health (biomechanics), infrastructure, microelectronics etc. My research deals with a very wide range of materials, from engineering metals (including welds) to polymers, composites, wood, foams, concrete, tissues etc. My research is methodological in nature, mainly experimental and underpins the design, simulation and validation of engineering systems at large.

I started my research career in the development of mechanical test methods for fibre composite materials. At the time, this was based on local strain measurements using strain gauges. Because the amount of experimental information was limited (a few local or global strain values), strong limitations existed on the test design (uniform stress state etc.). Early work on the Iosipescu shear test (or the double V-notched shear test, ASTM D5379, Figure 1) and the 10° off-axis tensile test led to several articles that have become references in this area and have attracted tens of cites [1-5].

The Iosipescu fixture redesigned by F. Pierron [6]
Fig. 1.

I was introduced to optical full-field deformation measurement methods in the mid 1990’s, when such measurement techniques were still confined to a few specialist groups worldwide. In particular, I came across the so-called ‘grid method’ (also known now as ‘sampling moiré’), which is based on capturing images of a grid (set of contrasted regular lines) bonded onto the test specimen. The images are processed numerically to produce a map of deformation (see Video 1 below: Deformation maps showing surface cracks appearing at the surface 45o ply in a carbon/epoxy composite open-hole tensile teset [7, 8]).

Such techniques have become more popular now and many commercial systems are available on the market, in particular for ESPI (an interferometric technique, use for the FSW study below) and the extremely popular Digital Image Correlation (or DIC, www.matchid.org) which relies on a random pattern or speckle as opposed to a regular grid. These techniques are very powerful, providing maps of deformation at a great number of points, which make them look as if they were continuous, hence the term ‘full-field’.

The availability of such powerful full-field measurement techniques has led to novel developments of mechanical testing procedures for materials. Indeed, when only a few strain measurement points are available, the determination of the material parameters (also called ‘identification’) like stiffness, yield stress etc. relies on the a priori knowledge of the stress distribution within the specimen. As a consequence, these tests require simple specimen geometry and well-controlled loading. Even when performed rigorously, these tests cannot address the complexity of the deformation scenario in the video above (FSW weld). Therefore, a new generation of mechanical tests is currently under development combining full-field deformation measurements and inverse mathematical tools to ‘read’ these maps for materials mechanical parameters.

I have been instrumental in developing and establishing this new paradigm in mechanical testing. My early interactions with Professor Michel Grédiac, now at Blaise Pascal University in Clermont-Ferrand, France, led to the development of the so-called Virtual Fields Method [10]. This technique is a direct competitor to the more general Finite Element Model Updating (FEMU) technique. It is fully adapted to full-field measurements and as a result, much more computationally efficient than FEMU. The VFM is currently receiving increasing interest from the international scientific community and gradually establishing itself as a reference tool. My research activities are entirely dedicated to furthering the VFM in order to establish it as a standard engineering tool within the next 5 to 10 years.

 

Video 2: maps showing spectacular deformation concentrations in the nugget of a friction stir weld on magnesium plates [9]

References
1. Pierron, F. and A. Vautrin, Accurate comparative determination of the in-plane shear modulus of T300/914 by the iosipescu and 45° off-axis tests. Composites Science and Technology, 1994. 52(1): p. 61-72.http://eprints.soton.ac.uk/210711/
2. Pierron, F., A. Vautrin, and B. Harris, The losipescu in-plane shear test: validation on an isotropic material. Experimental Mechanics, 1995. 35(2): p. 130-136.http://eprints.soton.ac.uk/210709/
3. Pierron, F. and A. Vautrin, The 10 ° off-axis tensile test: a critical approach. Composites Science and Technology, 1996. 56(4): p. 483-488.http://eprints.soton.ac.uk/210707/
4. Pierron, F., Saint-Venant effects in the Iosipescu specimen. Journal of Composite Materials, 1998. 32(22): p. 1986-2015.http://eprints.soton.ac.uk/210695/
5. Pierron, F. and A. Vautrin, Measurement of the in-plane shear strengths of unidirectional composites with the Iosipescu test. Composites Science and Technology, 1998. 57(12): p. 1653-1660.http://eprints.soton.ac.uk/210705/
6. Pierron, F., New Iosipescu fixture for the measurement of the in-plane shear modulus of laminated composites: design and experimental procedure. 1994, École Nationale Supérieure des Mines de Saint-Étienne
7. Pierron, F., B. Green, and M.R. Wisnom, Full-field assessment of the damage process of laminated composite open-hole tensile specimens. Part I: methodology. Composites Part A: Applied Science and Manufacturing, 2007. 38(11): p. 2307-2320.http://eprints.soton.ac.uk/210641/
8. Pierron, F., et al., Full-field assessment of the damage process of laminated composite open-hole tensile specimens. Part II: experimental results. Composites Part A: Applied Science and Manufacturing, 2007. 38(11): p. 2321-2332.http://eprints.soton.ac.uk/210639/
9. Commin, L., et al., Identification of shear bands in wrought magnesium alloy friction stir welds and laser beam welds. Materials Science and Technology, 2009. 25(10): p. 1215-1221.http://eprints.soton.ac.uk/210615/
10. Pierron, F. and M. Grédiac, The virtual fields method. Extracting constitutive mechanical parameters from full-field deformation measurements. 2012: Springer New-York. 517.http://eprints.soton.ac.uk/346980/

Research group

Engineering Materials

Research project(s)

Imaging the mechanical properties of welds

Welding is a very important industrial joining technique.

Imaging materials deforming really fast

New ultra-high speed cameras enable to record a great number of images at very high frame rates.

The Virtual Fields Method

The Virtual Fields Method (VFM) is a method to extract mechanical parameters from full-field deformation maps obtained by imaging.

Seeing the deformations inside solids

While most of the deformation imaging techniques deal with surface information, some new methods enable to provide deformation inside solids.

Strain through the looking glass

This projects aims at using an unusual but very powerful technique to image the surface deformation of mirror-like structures.

Articles

Conferences

Fabrice currently teaches the following modules:

FEEG1002 Mechanics, structures and materials

This module consists of six (6) inter-dependent, to some extent, parts, covering topics of Statics, Dynamics and Materials.

SESG6031 Experimental mechanics

This module aims to:

  • provide an in-depth understanding of experimental mechanics approaches
  • introduce students to testing procedures
  • provide detailed knowledge of the application of point measurement techniques such as electrical resistance strain gauges and optical fibre sensors
  • provide a detailed knowledge of modern full field techniques such as Thermoelastic Stress Analysis (TSA), Digital Image Correlation (DIC), Electronic Speckle Pattern Interferometry (ESPI).
  • help students understand how the data from experimental techniques are manipulated to validate numerical models
Professor Fabrice Pierron
Professor Fabrice Pierron Engineering and the Environment University of Southampton Highfield Southampton SO17 1BJ Telephone: +44 (0)23 8059 2891 Internal extension: 22891

Room Number:13/3061


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