Creep and fracture of a protein gel

Biomaterials such as protein or polysaccharide gels are known to behave qualitatively as soft solids and to rupture under an external load. Combining optical and ultrasonic imaging to shear rheology we show that the behaviour of a protein gel under creep is strongly reminiscent of brittle failure: after a power-law creep regime, fractures nucleate and grow logarithmically perpendicularly to shear up to sudden rupture. A single equation describing the temporal evolution of the strain rate during those two successive processes nicely captures the full rheological response. The failure time follows a robust decreasing power-law with the applied shear stress, which is known as the Basquin law in the literature of solids. Our results are in excellent agreement with recent fiber-bundle models that include damage accumulation on elastic
fibers and exemplify protein gels as model brittle-like soft solids.