近日，中国科学技术大学的徐宁教授及其研究小组取得一项新进展。经过不懈努力，他们揭示了无序固体中的不连续不稳定性现象。
该研究团队报道了于折叠不稳定性不同的另一种异常的不稳定性，这种不稳定性是由“稳定键”的断裂引起的，它的移除会产生不稳定的振动模式。在通常研究的系统中，例如具有有限范围粒子间谐波相互作用的系统，这种“不连续不稳定性”不仅是不可避免的，而且往往主导着失效模式。稳定键是系统中所有键的一个子集，在无序固体中普遍存在。虽然它们不会在相互作用截止点刚度消失的系统中引发不连续不稳定，但它们是早期机械故障的局部指标。因此，稳定键不仅为不连续型的不稳定性，而且也为折叠型的不稳定性提供了准确的结构预测。
据悉，在足够大的载荷下，固体材料将通过重排流动，其中粒子改变邻居。这种可塑性最容易在零温度和无限小加载率的非热准静态极限中描述。只有当系统变得机械不稳定时才会发生重排。对于无序固体，标志着重排开始的不稳定性长期以来被认为是折叠不稳定性，其中能量势垒消失，正常振动模式的频率连续消失。
附：英文原文
Title: Discontinuous instabilities in disordered solids
Author: Xu, Ding, Zhang, Shiyun, Liu, Andrea J., Nagel, Sidney R., Xu, Ning
Issue&Volume: 2023-8-16
Abstract: Under a sufficiently large load, a solid material will flow via rearrangements, where particles change neighbors. Such plasticity is most easily described in the athermal, quasistatic limit of zero temperature and infinitesimal loading rate, where rearrangements occur only when the system becomes mechanically unstable. For disordered solids, the instabilities marking the onset of rearrangements have long been believed to be fold instabilities, in which an energy barrier disappears and the frequency of a normal mode of vibration vanishes continuously. Here, we report that there exists another, anomalous, type of instability caused by the breaking of a “stabilizing bond,” whose removal creates an unstable vibrational mode. For commonly studied systems, such as those with harmonic finite-range interparticle interactions, such “discontinuous instabilities” are not only inevitable, they often dominate the modes of failure. Stabilizing bonds are a subset of all the bonds in the system and are prevalent in disordered solids generally. Although they do not trigger discontinuous instabilities in systems with vanishing stiffness at the interaction cutoff, they are, even in those cases, local indicators of incipient mechanical failure. They therefore provide an accurate structural predictor of instabilities not only of the discontinuous type but of the fold type as well.
DOI: 10.1073/pnas.2304974120
Source: https://www.pnas.org/doi/10.1073/pnas.2304974120