The low-cyclic fatigue response and its dependence of specific surface area for open-cell nanoporous Cu

We systematically study the low cycle fatigue behavior and its dependence of specific surface area ( ζ) for nanoporous copper (NPC) under ultrahigh strain rate ( γ ˙ ≈ 10 9 s − 1) cyclic shear loading by conducting large-scale molecular dynamic simulation and small-angle x-ray scattering analysis. With an increase in ζ, NPC undergoes a transition from the first excellent anti-fatigue property ( ζ < 1.24 nm − 1) to the subsequent easy-to-fatigue capacity ( ζ ≥ 1.24 nm − 1). Two different mechanisms are governing fatigue: (i) smooth nucleation and propagation of dislocations for the former and (ii) nanopore compaction/coalescence for the latter by prohibiting the activities of dislocations. For NPC with ζ = 0.42 nm − 1, fatigue contributes to a surprising superelasticity, prompted by the entanglements and reversed disentanglements of longer dislocations. Surface reconstruction contributes to the fatigue tolerance of NPC by facilitating local surface roughening and the emission of dislocation slips, and it becomes more pronounced with decreasing ζ.