We systematically study the low cycle fatigue behavior and its dependence of specific surface area ([Formula: see text]) for nanoporous copper (NPC) under ultrahigh strain rate ([Formula: see text] s[Formula: see text]) cyclic shear loading by conducting large-scale molecular dynamic simulation and small-angle x-ray scattering analysis. With an increase in [Formula: see text], NPC undergoes a transition from the first excellent anti-fatigue property ([Formula: see text]) to the subsequent easy-to-fatigue capacity ([Formula: see text]). 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 [Formula: see text], 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 [Formula: see text].

In this paper, molecular dynamics simulation is conducted to study the relationship between the surface and dislocation of nanoporous copper under cyclic shear loading. The results show that the dislocation and the surface have both mutual promotion and competition relationship. On one hand, the surface becomes rough owing to reconstruction caused by cyclic shear, which promotes the dislocation activities, while the dislocation activities also accelerate the process of surface reconstruction. On the other hand, there is a competition between surface reconstruction and dislocation activities: in the early cycles, the dislocation density is low, and surface reconstruction dominates stress release; in the late cycles, the surface tends to be stable, and then, the dislocation activities dominate.