Formation of prismatic dislocation loops during unloading in nanoindentation

A team of researchers from Oxford's Materials and Engineering departments have developed a system of forming prismatic dislocation loops during nanoindentation of bcc iron with discrete dislocation plasticity: watch the film (click on the button (bottom left) to start or pause the film).

They noted the unloading phase of the test was crucial for prismatic loop formation (not the loading stage) when indenting a (001) crystal surface.  In this case, prismatic loops do not form during loading, but develop as the indenter is removed, in contrast to (111) indentation where prismatic loops are nucleated almost immediately upon loading.

You can read their paper in full in Volume 189 of Scripta Materialia.