Effect of Loading Rate on Mechanical Properties and Fracture Morphology of Spider Silk

Spider silks have been shown to have impressive mechanical properties. In order to assess the effect of extension rate, both quasi static and high rate tensile properties were determined for single fibers of major (MA) and minor (MI) ampullate single silk from the orb weaving spider Nephila clavipes. Low rate tests have been performed using a DMA Q800 at 10(-3) s(-1), while high rate analysis was done at 1700 s(-1) utilizing a miniature Kolsky bar apparatus. Rate effects exhibited by both respective silk types are addressed, and direct comparison of the tensile response between the two fibers is made. The fibers showed major increases in toughness at the high extension rate. Mechanical properties of these organic silks are contrasted to currently employed ballistic fibers and examination of fiber fracture mechanisms are probed via scanning electron microscope, revealing a globular rupture surface topography for both rate extremums.