1. G. Sachs:Principles and Methods of Sheet-Metal Fabricating, p. 103, Reinhold Publishing Co., New York, NY, 1966.
2. W. Schroeder:Trans. ASME, 1943, vol. 65, p. 817.
3. F. J. Gardiner:Trans. ASME, 1957, vol. 79, p. 1.
4. C. A. Queener and R. J. DeAngelis:Trans. ASM, 1968, vol. 61, p. 757.
5. J. C. Benedyk and J. A. Newham:J. Inst. Met., 1970, vol. 98, p. 97.