Engineering Properties of Spider Silk
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ENGINEERING PROPERTIES OF SPIDER SILK Frank K. Ko1, Sueo Kawabata2, Mari Inoue3, Masako Niwa4, Stephen Fossey5 and John W. Song6 1 Fibrous Materials Research Center, Department of Materials Engineering, Drexel University, Philadelphia, PA 19104, USA 2, 3 Department of Materials Sciences, University of Shiga Prefecture, Shiga, Japan 4 Nara Women University, Nara, Japan 5, 6 US. Army Natick Research and Development , Engineering Center, Natick, MA. USA
ABSTRACT Motivated by the high level of strength and toughness of spider silk and its multifunctional nature, this paper reports on the engineering properties of individual fibers from Nephila Clavipes spider drag line under uniaxial tension, transverse compression and torsional deformation. The tensile properties were compared to the Argiope Aurentia spider silk and show different ultimate strength but similar traits of the unusual combination of strength and toughness characterized by a sigmoidal stress-strain curve. A high level of torsional stability is demonstrated. comparing favorably to other aramid fibers (including Kevlar fibers). INTRODUCTION Strength and toughness are usually considered mutually exclusive properties for materials. In spite of the progress made in the recent years in polymeric fiber science and technologies, the search for a truly strong and tough fiber continues. It is of practical and scientific interest to explore the limit of strength and toughness of fibrous materials; and to examine the factors which contribute to the development of a combination of strength and toughness in materials. The answers to these questions may be found in nature. In the world of natural fibers, spider silk has long been recognized as the wonder fiber for its unique combination of high strength and rupture elongation. An earlier study indicated spider silk has strength as high as 1.75 GPa at a breaking elongation of over 26%.[1,2]. With toughness more than three times that of aramid and industrial fibers, spider silk continues to attract the attention of fiber scientists and hobbyists alike. [3-13] Considering the remarkable mechano-chemical properties of spider silk and fueled by the recent progress in biotechnology, there is a revival of interest in using spider silk as a model for the engineering of high energy absorption fibers [14]. Because of the
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fineness of spider silk, on the order of 4 µm, the characterization of the mechanical properties of spider silks are limited to tensile mode. Little is known about the response of spider silks to other modes of deformation in the transverse direction and in torsion. Original data are presented on the tensile, transverse compression and torsional stressstrain properties of the spider silk from Nephila Clavipes spiders. This was made possible by using an ultra sensitive micromeasurement fiber testing system developed by Kawabata [15]. From these experimental data, the engineering properties: tensile modulus, transverse compressive modulus, and shear modulus of the spider silk was determined. TENSILE PROPE
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