Fracture and friction is ubiquitous in Nature, technology and daily life. Deformation of the Earth's upper crust is brittle, i.e.\ the material fractures and there is repeated displacement on these fractures (earthquakes) controlled by friction. This has been the starting point of several experimental projects at PGP. One project probed into the time-dependent friction of a reactive interface~\cite{Renard2011a}, another into the precursors to stick slip friction~\cite{Scheibert2010a}.

Another starting point for the study of friction was a contract with Hydro Aluminum to study extrusion of aluminum. I found a class of organic crystals that are plastically deforming at room temperature, that can be alloyed and that are transparent. Extrusion dies made of glass, perspex or NaCl allowed high resolution imaging by visible light microscope or infrared camera~\cite{Dysthe2011c,aluiii,aluiv,aluv}. I used image correlation methods to determine the velocity field of the material inside the die, imaging and infrared interference contrast images were used to follow the dynamics of the slip line. Imaging in a polarimeter was used to measure the stress field of the material flowing in the die. The dies machined from single crystal NaCl were used to study dissipation at the extrudate/die interface by infrared imaging.

Crack growth driven by internal buildup of stress has been studied experimentally in situ by syncrotron microtomography~\cite{Panahi2011a,Kobchenko2011a} and by continuum modelling~\cite{Royne2011b}. The first process was driven by gas production on heating, the second by crystal growth. We are also in the process of studying the fundamental process of subcritical crack growth itself~\cite{Royne2011a}