In part I, cracked Cu single crystals made out of diffusion bonding were 3-point bend tested. Specimen surfaces near crack tips were examined by optical microscope and stylus profilometer, and in the inner parts of specimens plastic deformation around the crack tip was investigated through dislocation etch pit method.
As the result of slip line observation at specimen surfaces, the plastic zone developed as assembled fan-shaped sectors, the details of which depends on the crystal slip lines, and operations of slips on coplanar slip planes(CSP) were mutually orientation. A sector is often characterized by a family of dominant exclusive, but operations between CSP and non-coplanar slip planes(NSP) were not so.
On the other hand, from dislocation etch pit experiments, each CSP sector boundary kept the position from crack tip constant along the direction of thickness from specimen surface. This fact means that the activity of CSP is constant irrespective of the distance from specimen surface. However, the activity of (NSP) decreased as the distance from surface increases. Also, operations of slips on NSP were mutually exclusive, which could not be detected from the observation of slip lines at specimen surface.
The above experimental results about near crack tip plasticity in Cu single crystals can be predicted by the combination of latent hardening effect and resolved shear stress for each slip system calculated under the assumption of an isotropic continuum.
Also, scratch lines at surface and through-thickness displacement changed gradually across sector boundaries but not its gradient, suggesting a constant plastic strain within a sector but the drastic change of strains across sector boundaries. Degrees of necking depend mostly on the operation of slips on non-CSP, but operation of CSP caused either local necking or protrusion depending on the crystal orientation.
If only the dominant slip line be activated within each sector, plastic compatibility condition at the sector boundary will not be satisfied. Therefore, the activation of secondary slip systems is needed to satisfy this condition. Though secondary slip lines are not observed at surfaces, however, the multiplication of secondary dislocations of which glide distance is short is observed from the experimental result of dislocation etch pit.
In part II, several kinds of Cu and Cu-Bi bicrystals in compact tension shape are investigated similarily to the experimental method of part I. Here also, the plastic zone developed as assembled fan-shaped sectors, the details of which depends on the crystal orientation of bicrystal. A sector is often characterized by a family of dominant slip lines. This result can be also explained by applying for the interpretation method in part I.
In case of Cu-Bi bicrystals, the extent of brittleness and the variation of fracture surface morphology with crystal orientation are studied.
