Crystal microstructure evolution under straining at rate x50. In this simulation a crystal containing dislocations sources (loops) was subjected to uniaxial compression along the axis at a constant true straining rate. The simulation volume contains about 33 million atoms of tantalum. This video sequence progresses through extension of the initial loops, to nucleation of embryonic twins on screw dislocations, to rapid propagation and growth of twinning particles. The outer surfaces bounding the twins are colored light gray whereas the insides of twin particles are colored red, yellow, purple or cyan depending on each twin's rotational variant.