Failure in a soft gel: Delayed failure and the dynamic yield stress

A soft thermo-reversible protein gel was studied with respect to failure. Flow curves recorded at constant shear-rates revealed a dynamic yield stress σy, seen as a stress plateau below about 10 s−1. When a shear stress below σy was applied to fractured gels, they reformed after a time that increased with increasing stress and diverged at σy. Application of shear stress to fresh gels led to an initial elastic response followed by creep. Following this creep regime, the strain stagnated below the dynamic yield stress σy, while for σ > σy failure was observed after a time that increased with decreasing stress and diverged at σ = σy. The time-to-failure dependence on the stress for σ > σy, with two distinct exponential scaling regimes, agrees with existing proposed theories for the fracture of colloidal strands.

Figure optionsDownload as PowerPoint slideHighlights
► Soft thixotropic protein gel studied with respect to delayed failure.
► Strain stagnation below and delayed fracture above dynamic yield stress.
► Time-to-failure had two exponential scaling-laws at different stress regimes.
► Gel reformation observed below dynamic yield stress.
► At static yield stress, time-to-failure tf = 0; at dynamic yield stress tf = ∞.