1. E. Siebel and A. Pomp:Mitt. Kaiser-Wilhelm-Inst. Eisenforsch., 1927, vol. 9, p. 157.
2. N. H. Polakowski:J. Iron Steel lnst, 1951, vol. 169, p. 337.
3. D. C. Drucker and W. Prager:Quart. Appl. Math, 1952, vol. 10, pp. 157–65.
4. D. C. Drucker:Grenoble Symposium on Rheology and Soil Mechanics, J. Kravtchenko and P. M. Sirieys, eds., pp. 23–46, Springer-Verlag, Berlin, 1966.
5. W. Whitney and R. D. Andrews:J. Polymer Sci, 1967, vol. 16, pp. 2981–90.