Quasistatic and continuous dynamic characterization of the mechanical properties of silk from the cobweb of the black widow spiderLatrodectus hesperus

Abstract

Spider silks are among the strongest and toughest known materials, but investigation of these remarkable properties has been confined largely to orb-weaving spiders. We investigated the mechanical performance of silk from the cobweb-weaving spider Latrodectus hesperus. Both silk from the scaffolding region of the web and sticky gumfooted capture lines had material properties similar to the major ampullate silk that orb weavers use as the framework for their orb webs. Major ampullate fibers obtained from anaesthetized Latrodectus spiders were similar, but exhibited increased stiffness and reduced extensibility. Novel continuous dynamic analysis of the silks revealed that the loss tangent (tanδ) increased rapidly during the first 2-3% of extension and reached a maximum near the yield point of fibers. The loss tangent then rapidly declined at an ever-decreasing rate until failure. We suggest that these data support molecular models for the mechanics of spider silk. We also demonstrate that the addition of sticky aggregate glue to the ends of the gumfooted lines modulates their mechanical performance -reducing stiffness and increasing extensibility. The storage modulus of viscid regions of the gumfooted lines was much lower than dry regions. This may be explained by disruption of hydrogen bonding within the amorphous regions of the fibers due to hydration from the glue.

Unraveling the mechanical properties of composite silk threads spun by cribellate orb-weaving spiders

“…In addition to capture silk, we also collected samples of major ampullate silk from Deinopis and Uloborus by manually pulling dragline from spiders that had been secured to the stage of a stereo microscope (see Blackledge et al, 2005a;Blackledge et al, 2005c). These samples of silk were 21·mm in gage length.…”

“…This strain rate was chosen because it was also within the range of many other studies on spider silk mechanics (e.g. Blackledge et al, 2005b;Blackledge et al, 2005c;Swanson et al, 2006), maximizing comparability of results.…”

“…However, engineering stress can greatly underestimate the stress experienced by fibers at high extensions. Using true stress values facilitates comparison of the mechanical properties of different silks that vary in extensibility (Blackledge et al, 2005c).…”

Strain-dependent dynamic mechanical properties of Kevlar to failure: Structural correlations and comparisons to other polymers

“…We find that as the storage modulus of Kevlar is essentially equal to the Young's modulus, the measured quantitative relationships between storage modulus and strain can provide insights into the tuning of the mechanical properties of aramid materials for specific applications. On the other hand, the technique of continuous dynamic analysis (CDA) combines the advantages of dynamic mechanical analysis with those of the quasi-static tensile test to quantify the evolution of viscoelastic properties as a continuous function of strain [4]. This is achieved through application of a small harmonic (20 Hz) strain during the tensile deformation.…”

“…DMA tests can only be carried out at low harmonic displacements to ensure linear viscoelasticity, severely limiting the ability to characterize the viscoelastic response of materials past their yield point [3]. On the other hand, the technique of continuous dynamic analysis (CDA) combines the advantages of dynamic mechanical analysis with those of the quasi-static tensile test to quantify the evolution of viscoelastic properties as a continuous function of strain [4]. This is achieved through application of a small harmonic (20 Hz) strain during the tensile deformation.…”