Page 235 - Fiber Fracture

220 H.U. Kunzi

Fig. 36. Left: wire surface of a 95 km diameter Cu wire with bamboo structure showing extrusions
and micro-cracks that result from persistent glide bands (fatigued for 1.2 x IO' cycles). Right: surface
of annealed wire after 1.8 x IO4 cycles showing damaged grain boundaries that are characteristic for
intermediate grain sizes.

rolled foils having a thickness of 20 and 100 pm, Hong and Weil (1996) studied 25
pm thick electrodeposited foils, and Read (1998a) published results on freestanding
evaporated foils that were only 1.1 pm thick (see also Read and Dally (1995) for similar
A1 foils).
In as-rolled foils of 20 and 100 pm thickness that were not annealed prior to the
fatigue tests, Judelewicz (1993) and Judelewicz et al. (1994) find a marked difference
in fatigue life between samples that were cut parallel and perpendicular to the rolling
direction (Figs. 37 and 38). For thin samples the rolling imprints were found to play an
important role. Samples that were rolled perpendicular to the stress direction fail at a

Number of cycles to rupture +

Fig. 37. Fatigue curves for rolled Cu foils (99.99% purity) that were measured in the stress-controlled
tension-tension loading mode parallel and perpendicular to the rolling direction. Thickness 25 bm.