Page 245 - Fiber Fracture

STRENGTH AND FRACTURE OF METALLIC FILAMENTS 229

Fig. 43. Left: extrusions and open crack perpendicular to the stress direction in a 20 Fm thick Cu foil
fatigued for 7 x IOh cycles at 5.5 MPa. Right: same as left but viewed from the edge of the foil after
1 .S x lo4 cycles at 60 MPa. (From Judelewicz, 1993.)

Fig. 44. Typical fatigue fracture in a rolled and annealed Cu foil. This 20 prn thick sample failed after
1.8 x lo5 cycles at 77 MPa. (Judelewicz, 1993.)

fragility. Metallic glasses are somewhere in between crystalline metals and inorganic
glasses. They have a disordered structure but metallic bonds and this combination asserts
then still a certain ductility. In other words, the isotropic bonds allow short-range atomic
rearrangements but the lack of periodicity does not allow mobile dislocations, at least
not in the sense of crystalline metals. The typical shape of metallic glass ribbons, their
production and effects of macroscopic defects on fracture have already been discussed
in pp. 195 and following. Here we return to intrinsic mechanical behavior.

Elastic Behavior of Metallic Glasses

In common with all other solids, metallic glasses behave in an essentially elastic manner
at low temperatures and low stresses. The elastic constants of amorphous metals are,