Independent slip systems in crystals

Abstract The slip systems observed in a number of crystal structures common amongst metals and simple ceramic materials are examined to see whether they allow the crystal to undergo an arbitrary strain without change of volume. For most materials, other than f.c.c. and b.c.c. metals, there are insufficient independent slip systems. The condition under which cross slip can give rise to extra independent systems is stated. The results explain in a natural way recent experimental findings on the ductility of polycrystals with the sodium chloride structure.