SILKWORM SILK AS AN ENGINEERING MATERIAL

While silk exhibits high values of tensile strength and stiffness, the se properties are compromised by their poor reproducibility. We presen t the results of experiments aimed at characterizing the variability o f tensile properties exhibited by cocoon silk from Bombyx mori silkwor ms. Scanning electron microscopy is used to measure an average diamete r for individual test specimens; the interspecimen variability of diam eter is quantified and found to be inadequately represented by standar d deviation. When load-extension data are converted into stress-strain curves, a marked improvement in reproducibility is realized if each s pecimen cross-section is calculated hom diameter measurements specific to that specimen. Nevertheless, a significant variability in fracture stress remains; a Weibull analysis reveals that silkworm silk has a f ailure predictability comparable with that of glass and nonengineering ceramics. Unloading/reloading tests demonstrate that stiffness is not significantly affected by cumulative deformation, and the stress-stra in relationship is not sensitive to strain rate. (C) 1998 John Wiley & Sons, Inc.