Molecular dynamics studies on energy dissipation and void collapse in graded nanoporous nickel under shock compression

•Total energy dissipation is dependent on porosity, but not on void size gradient.•There is an upper limit of total energy dissipation, corresponding to a critical porosity.•Competition between plasticity mechanism and internal jetting mechanism is revealed.•Earliest dislocations nucleation is depend on void size gradient and position of void.•Effects of shock intensity on energy dissipation rate and void collapse rate are presented.