Laboratoire Charles Coulomb (L2C), Université Montpellier, CNRS, Montpellier, France.
Phys Rev Lett. 2020 Dec 31;125(26):268006. doi: 10.1103/PhysRevLett.125.268006.
We investigate the delayed rupture of biopolymer gels under a constant shear load by simultaneous dynamic light scattering and rheology measurements. We unveil the crucial role of normal stresses built up during gelation: All samples that eventually fracture self-weaken during the gelation process, as revealed by a partial relaxation of the normal stress concomitant to a burst of microscopic plastic rearrangements. Upon applying a shear stress, weakened gels exhibit in the creep regime distinctive signatures in their microscopic dynamics, which anticipate macroscopic fracture by up to thousands of seconds. The dynamics in fracturing gels are faster than those of nonfracturing gels and exhibit large spatiotemporal fluctuations. A spatially localized region with significant plasticity eventually nucleates, expands progressively, and finally invades the whole sample, triggering macroscopic failure.
我们通过同时进行动态光散射和流变学测量来研究在恒定剪切负载下生物聚合物凝胶的延迟破裂。我们揭示了凝胶过程中产生的正应力的关键作用：所有最终断裂的样品在凝胶过程中都会自我减弱，这表现为伴随着微观塑性重排的爆发，正应力会部分松弛。在施加剪切应力时，在蠕变阶段，弱化的凝胶在其微观动力学中表现出独特的特征，这些特征可以提前预测宏观断裂，最长可达数千秒。在断裂凝胶中的动力学比非断裂凝胶中的动力学更快，并且表现出大的时空涨落。具有显著塑性的局部区域最终会成核，逐渐扩展，并最终侵入整个样品，引发宏观失效。
