Abstract
From the first observation of moving dislocations to the latest developments of piezo-actuated sample holders and direct electron sensing cameras in modern transmission electron microscopes (TEM), in situ mechanical testing has brought an unequaled view of the involved mechanisms during the plastic deformation of materials.
In this talk, I would like to survey our recent research activity in this field with the emphasis on the important role of in-situ straining experiments in probing elementary relaxation mechanisms in small scaled metals.
Metals with one (whiskers, fibers), two (thin films) or three (small grained materials) reduced dimensions indeed demonstrate a clear trend that their strength scales as a power-law of their size. The identification of elementary plastic deformation mechanisms involved in small scale materials are not very well documented, mainly because of the difficulty to assess the dislocation activity in such small confined areas. To that respect, in-situ transmission electron microscopy (TEM) has rapidly appeared in the last years as the adequate experimental tool to probe these mechanisms at the pertinent length and time scales.
In the last years, our research work has concentrated on different micro- or nano-structured materials like  nanocrystalline metals (Cu, Al) obtained by electrodeposition (freestanding thin films or films inserted in Micro Electro Mechanical Systems (MEMS) equipped with stress/strain gauges), bulk ultra fine grained (UFG) materials (Ni, Al) obtained by severe plastic deformation or monocrystalline sub-micron fibers.
Our efforts were more specifically focused on the understanding of the plastic relaxation mechanisms caused by the motion of grain boundaries (GB) under stress (so-called shear-migration coupling)[1-3], the dislocation mechanisms in ultrafine-grained metals (anelastic effect, dislocation/grain boundary interactions, dislocation emission from GB)[4] and the role of dislocation sources in sub-micron fibers [5].

[1] Mompiou, F., Caillard, D., Legros, M., Grain boundary shear-migration coupling–I. in situ  TEM straining experiments in Al polycrystals, Acta Mater. 57, 2198 (2009).
[2] Rajabzadeh, A., Legros, M., Combe, N., Mompiou, F., Molodov, D. A., Evidence of grain  boundary dislocation step motion associated to shear-coupled grain boundary migration, Phil.  Mag. 93, 1299 (2013).
[3] Rajabzadeh, A., Mompiou, F., Legros, M., Combe, N., Elementary mechanisms of shear- coupled grain boundary migration, Phys. Rev. Lett. 110, 265507 (2013).
[4] Mompiou, F., Caillard, D., Legros, M., Mughrabi, H., In situ TEM observations of reverse dislocation motion upon unloading in tensile-deformed UFG aluminium, Acta Mater. 60, 3402  (2012).
[5] Mompiou, F., Legros, M., Sedlmayr, A., Gianola, D. S., Caillard, D., Kraft, O., Source-based  strengthening of sub-micrometer Al fibers, Acta Mater. 60, 977 (2012).

CV :
I'm research scientist since 2006 at Centre d’Élaboration de Matériaux et d’Études Structurales (CEMES) a laboratory of the french National Center of Scientific Research CNRS , located in Toulouse, France. I obtained my PhD from Toulouse University in 2004 and was Guest Researcher at the Dept. Material Science, NIST (Gaithersburg, MD, USA), in 2005-2006. My research interests concern mainly mechanical properties of nanostructured materials that i investigate with the use and development of in situ Transmission Electron Microscopy (in-situ TEM) technique. I have published 35 papers in international peer-reviewed journal (available at http://mompiou.free.fr).