Grain boundaries (GBs) are not static structures during shock loading

despite the short timescales. We present a mechanistic explanation for why non-coherent Σ 3 GBs are particularly mobile

due to their consisting of coherent twin boundaries every third (111) glide plane

separated by incoherent twin boundary segments with three Shockley partial dislocations that can readily glide into either grain. Asymmetric GBs with such structures can thus move in response to the elastic driving force provided by uniaxial compression. We present large-scale molecular dynamic simulations that illustrate this mechanism

which explains the Σ 3 GB faceting recently observed in shock-recovered copper multi-crystals.