1. 1) S. Shida: J. Soc. Mech. Eng., 73(1970), 315 (in Japanese).
2. 2) R.Hill: The Mathematical Theory of Plasticity, Oxford University Press, Oxford, (1950), 199.
3. 3) D.R. Bland and H. Ford: Proc. Inst. Mech. Eng., 159(1948), 144.
4. 4) R.B. Sims and D.F. Arthur: J. Iron Steel Inst., 168(1952), 285.
5. 5) M.P. Stone: Iron Steel Eng., 30(1953), 61.