PPT Slide
Slip lines in bcc metals have a wavy appearance. This is due to the fact that slip occurs on several planes, {110}, {112}, {123} but always in the close-packed > direction which is common to each of these planes.
Dislocations can readily move from one type of plane to another by cross sip, giving rise to the irregular wavy slip bands.
If slip is assumed to occur by the translation of one plane of atoms over another, it is possible to make a reasonable estimate of the shear stress required for such a movement in a perfect lattice.