1. R. J. Crawford, “Plastics Engineering” (Pergamon, Oxford, 1981) p. 105.
2. R. A. Horsley, “Applied Polymer Symposium 17” (Wiley, New York, 1971) p. 127.
3. P. C. Powell, “Engineering with Polymers” (Chapman and Hall, London, 1983) p. 153.
4. G. P. Marshall, “Plastics and Rubber International”, Vol. 7, 3 (1982) p. 146.
5. D. Broek, “Elementary Engineering Fracture Mechanics”, 4th edn (Martinus Nijhoff, Dordrecht, 1986).