Page 343 - Fiber Fracture

FRACTURE OF NATURAL POLYMERIC FIBRES 325

used when considering the strain energy associated with a screw dislocation in a crystal
(Cottrell, 1953): a small volume around the dislocation line is assigned a ‘core energy’
that is not calculated explicitly.
Eq. 13 can be rearranged to give

So xUf is an increasing function of tan& the fibre is shortest, promoting the most
effective use of reinforcing material, if the taper is gradual. This is precisely what sea
cucumbers and sea urchins do.

ACKNOWLEDGEMENTS

Fruitful collaborations with Professors M. Elices and J. Pkrez-Rigueiro (Departa-
mento de Ciencia de Materiales, Universidad Politkcnica de Madrid) are acknowledged
gratefully, as is the British Council for supporting that collaboration through an Ac-
cidn Integrada. Professor J. Trotter (University of New Mexico School of Medicine)
provided the stimulus for the section ‘Echinoderm Collagens: Fibre Optimisation in
Smart Composites’, and kindly faxed reprints of his publications at short notice. Fraser
Bell (Department of Chemistry, Heriot-Watt University, Edinburgh) provided the images
used in Fig. 6. The sea cucumber and sea urchin illustrations used in Fig. 7 were
provided by Dr. Lisa Gilliland.

REFERENCES

Alberts, B., Bray, D., Lewis, J., Raff, M., Roberts, K. and Watson, J.D. (1989) Molecular Biology efthe
Cell. Garland, New York, NY.
Augsten, K., Muhlig, P. and Herrmann, C. (2000) Glycoproteins and skin-core structure in Nephila clavipes
spider silk observed by light and electron microscopy. Scanning, 22(1): 12-15.
Banister, K.E. and Campbell, A.C. (Eds.) (1985) The Encyclopedia ofAquatic Life. Equinox, Oxford.
Billmeyer, F.W. (1984) Textbook of Polymer Science. Wiley, New York, NY.
Brown, D. and Viney, C. (1999) New materials. In: Biotechnology: The Science und the Business (2nd
ed.), pp. 351-366, D.G. Springham, V. Moscs and R.E. Cape (Eds.). Harwood Academic Publishers,
Amsterdam.
Chittick, J. (1913) Silk Manufacturing and its Problems. James Chittick, New York, NY.
Chou, T.-W. ( 1992) Microstructural Design of Fiber Composites. Cambridge University Press, Cambridge.
Cottrell, A.H. (1953) Didocutions and Plastic Flow in Crystals. Oxford University Press, Oxford.
Cottrell, A.H. (1975) An Introduction to Metallurgy. Edward Arnold, London.
Cunniff, P.M., Fossey, S.A., Auerbach, M.A. and Song, J.W. (1994) Mechanical properties of major
ampullate gland silk fibers extracted from Nephila clavipes spiders. In: Silk Polymers: Materials Science
and Biotechnology, pp. 234-251, D. Kaplan, W.W. Adams, B. Farmer and C. Viney (Eds.). American
Chemical Society, Washington, DC.
Derby, B., Hills, D.A. and Ruiz, C. (1992) Materials for Engineering: A Fundamental Design Approach.
Longman Scientific and Technical, Harlow.
Dunaway, D.L. (1 994) Mechanical Property and Diameter Evaluation of Epoxide-Treated Silk Fibers. MSE
Thesis, University of Washington, Seattle, WA. (Copies available from University Microfilms, 1490
Eisenhower Place, P.O. Box 975, Ann Arbor, MI 48106.)