Fatigue crack closure in submicron-thick freestanding copper films

Vacuum effects on fatigue crack growth in submicrometre‐thick freestanding copper films

“…In oxidising environments, oxide‐induced crack closure increases K op , especially in the near‐threshold region where the crack tip opening displacement becomes small and is comparable with the size of oxide on the crack wakes . Crack closure occurred even in thin films, and the dependence of stress ratio on the fatigue crack growth properties disappeared when Δ K eff was used . This indicates that oxide‐induced crack closure would be expected in Cu films as a cause of the environmental dependence.…”

“…In vacuum, the suppression of the oxidation on a fresh surface would enhance reverse slip at the fatigue crack tip and/or at intrusions/extrusions. Moreover, rewelding on the fresh surface at the crack wake just behind the crack tip would occur because crack closure occurred even in thin films, and rewelding would also occur at intrusions/extrusions. These mechanisms would reduce the fatigue damage accumulation rate at the crack tip and at the intrusions/extrusions ahead of the crack tip, leading to the reduction of d a /d N in vacuum.…”

“…10,[22][23][24] Crack closure occurred even in thin films, and the dependence of stress ratio on the fatigue crack growth properties disappeared when ΔK eff was used. 21 This indicates that oxide-induced crack closure would be expected in Cu films as a cause of the environmental dependence. In addition, the extent of plastic deformation and surface roughness on the fracture surface in air and vacuum was not the same (Figure 8).…”