ENGINEERING PROPERTIES OF SPIDER SILK Frank K. Ko 1, Sueo Kawabata 2 , Mari Inoue 3 , Masako Niwa 4 , Stephen Fossey 5 and John W. Song 6 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 KEYWORDS: Spider silk, tensile modulus, compressive modulus, shear modulus, micromeasurement instrument, anisotropic properties, combined strength and toughness. 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