X-ray Moduli of Silk Fibers from <i>Nephila clavipes</i> and <i>Bombyx mori</i>

X-ray moduli were determined for silk fibers from the golden orbweaver spider Nephila clavipes and the domesticated silkworm Bombyx mori to provide insight into their physical properties. Differences between the respective moduli, 17 and 29 GPa, are discussed in terms of the lack of scaling with the basal area per molecule, the effect of the amorphous content and the stress history dependence. Both annealed and irradiated B. mori fibers yielded decreased X-ray moduli. All these results as well as the considerable difference between the experimental and computer modeled moduli raise questions regarding the applicability of the uniform stress assumption for the X-ray modulus calculation at room temperature conditions.