1. E. O. Hall, Proc. Phys. Soc. B64 (1951) 747.
2. N. J. Petch, J. Iron Steel Inst. 174 (1953) 25.
3. R. Armstrong, in ?Yield flow and fracture of polycrystals?, edited by T. N. Baker (Applied Science Publishers Essex, 1983) p. 1.
4. N. Hansen, ibid., p. 311.
5. Idem., Met. Trans. 16A (1985) 2167.