Non-classical scaling of strength with size in marine biological fibers

Intriguing physical phenomena observed in natural materials have inspired the development of several engineering materials with dramatically improved performance. Marine sponge glass fibers, for instance, have attracted interest in recent decades. We tested the glass fibers in tension and observed that the strength of these fibers scales inversely with their size. While it is expected that the strength of a material scales inversely with its size, the scaling is generally believed to be inversely proportional to the square root of the specimen dimension. Interestingly, we found that the marine sponge glass fibers' strength scaled much faster, and was inversely proportional to the square of the specimen dimension. Such non-classical scaling is consistent with the experimental measurements and classical linear elastic fracture mechanics. We hypothesize that this enhanced scaling is due to the flaw size decreasing faster than the size of the specimen. The tensile strength, as a result of non-classical, higher-order scaling, reached a value as large as 1.5 GPa for the smallest diameter specimen. The manufacturing processes through which the spicules are made might hold important lesson for further enhancing the strength of engineering materials.