Silkworm silk as an engineering material

TLDR

Silk exhibits high tensile strength and stiffness, but these properties suffer from poor reproducibility. The study characterizes the variability of tensile properties in Bombyx mori cocoon silk. The authors used scanning electron microscopy to measure specimen diameters and then calculated stress–strain curves using specimen‑specific cross‑sections, improving reproducibility. Despite improved reproducibility, fracture stress variability remains high, and Weibull analysis shows failure predictability comparable to glass and ceramics, while stiffness is unaffected by cumulative deformation and strain rate. © 1998 John Wiley & Sons, Inc., J Appl Polym Sci 70: 2439–2447.

Abstract

While silk exhibits high values of tensile strength and stiffness, these properties are compromised by their poor reproducibility. We present the results of experiments aimed at characterizing the variability of tensile properties exhibited by cocoon silk from Bombyx mori silkworms. Scanning electron microscopy is used to measure an average diameter for individual test specimens; the interspecimen variability of diameter is quantified and found to be inadequately represented by standard deviation. When load-extension data are converted into stress-strain curves, a marked improvement in reproducibility is realized if each specimen cross-section is calculated from diameter measurements specific to that specimen. Nevertheless, a significant variability in fracture stress remains; a Weibull analysis reveals that silkworm silk has a failure 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–strain relationship is not sensitive to strain rate. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2439–2447, 1998