在非晶态固体中，“剪切转变”（Shear Transformation, ST）是被广泛认可的 结构弛豫和塑性流动的基本载体。ST 描述了在弹性介质约束下，原子或粒子以 集团模式发生的局域、不可逆重排，同时在周围介质中产生 Eshelby 弹性场。但 是，ST 事件在非晶态原子或分子体系中，由于时空尺度限制极难实现实时原位 观察。为此，本论文以微米尺度硬球构成的胶体玻璃为非晶态固体模型体系，研 究 ST 介导的结构弛豫与塑性流动。 本论文从剪切主控的 ST 事件及其剪胀（自由体积产生）特性角度，开展了 热激活的结构弛豫实验以及简单剪切应变加载实验，取得了以下几个方面的研究 进展： （1）从动力学（均方位移）和结构（自由体积）两个方面解析了非晶态固 体弛豫过程，证实了非晶态固体老化弛豫过程中自由体积的非单调下降过程。随 着时间增长，弛豫过程分别经历β弛豫、α弛豫和扩散三个阶段。基于粒子振动 均方位移的时间不变性以及扩散运动均方位移-时间的线性相关性，定量确定了 粒子振动、跳跃、协同运动三种动力学模式在结构弛豫各个阶段的贡献。在β弛 豫阶段，粒子以在近邻构成的笼子中的振动为主。但在β弛豫后期，发生不可逆 跳跃重排（即热激活 ST 事件）的粒子数逐渐增加，从而引起更大结构尺度的α 弛豫。在此过程中，伴随着体系自由体积的增加。随后，参与协同运动的粒子数 逐渐增加，体系自由体积开始下降，最终发生协同运动主导的扩散弛豫。 （2）根据解析的粒子振动位移获取完整的三维振动信息，找出最优低频振 动模态与跳跃重排的强关联。通过位移协变矩阵法获取了真实的三维胶体玻璃振 动信息，并在求解过程中解决了振动态密度拖尾和空间参与度在高频处不收敛的 问题。利用三维胶体玻璃的低频振动模态理解并预测弛豫重排事件，低频振动模 态贡献大的粒子在α弛豫初期发生了跳跃（STs），即发生在能量较低处。探究不 同低频模态对重排的预测作用，找出最优振动模态，最优模态与重排之间相关性 最高，但这个最优模态不一定是最低频模态。 （3）在低应变率简单剪切实验中，提供了非晶微观塑性流动过程实验证据， 发现应变剪胀、应力剪胀弹性场核心尺度始终大于应变、应力相关的全场尺度体 系未能形成剪切带。做出 STs 的剪应变、剪应力、应变剪胀、应力剪胀的空间自 相关场随加载时间的演化。通过量化场的空间衰减，发现剪应变、剪应力的空间 相关都表现出两级衰减：强相关核心不随加载时间变化；外场则随加载时间增长 衰减速率减慢，空间关联性增强。应变剪胀、应力剪胀的空间相关则只捕捉到一 级衰减：强相关核心不随加载时间变化。在加载过程中，弹性响应场相互竞争。（4）在不同应变率条件下开展简单剪切实验，提供了受应变率控制的 STs 形成剪切带的实验证据，进一步通过分析弹性场的率相关性，提出剪切带失稳的 弹性准则。研究发现，随着应变率提高，固体变形呈现从均匀到剪切带模式的非 均匀转变。计算了粒子尺度剪切应变和自由体积的空间自相关的弹性剪切场和体 胀场，这两种弹性场在空间上可解耦为强关联的核心区和弱关联的外场：前者服 从指数衰减，而后者服从幂律衰减。通过分析弹性场的率相关性，提出剪切带失 稳的弹性准则：当且仅当体胀场的强关联尺度小于剪切全场的关联尺度时，剪切 带才能从无序结构中涌现。该弹性准则表明，只有当 ST 产生的自由体积被束缚 在其弹性剪切场范围内，这些 ST 事件才有机会以类似雪崩的方式自组装形成剪 切带；否则，ST 事件将在空间上均匀成核并最终贡献均匀变形。这些实验发现 协调了自由体积的局域效应和剪切转变的非局域效应，从而统一了历史上关于非 晶态固体剪切带的两种经典模型。

In amorphous solids, ‘Shear Transformation’ (ST) is a widely recognized fundamental carrier for structural relaxation and plastic flow. ST describes the local irreversible rearrangement of particles in a group mode under the constraint of an elastic medium. STs generates non-local Eshelby shear fields in space. However, ST events in amorphous atomic or molecular systems are extremely difficult to be observed in situ in real time due to spatio-temporal scale limitations. Therefore, in this dissertation, the structural relaxation and plastic flow mediated by ST are studied by using colloidal glass composed of micron scale hard spheres as amorphous solid model system. In this dissertation, from the perspective of ST events controlled by shear and their dilatancy (free volume generation) characteristics, thermally induced structural relaxation experiments and simple shear strain loading experiments are carried out, and several advances have been achieved in the following: (1) Resolving the amorphous relaxation dynamics in terms of dynamics (the mean square displacement) and structure (free volume). With aging time increasing, the structural relaxation process goes through three stages, β relaxation, α relaxation and diffusion. Based on the time invariance of mean square displacement of particle vibration and the linear correlation between mean square displacement of diffusion motion, the contributions of particle vibration, hop and cooperative motion in each stage of structural relaxation are determined quantitatively. In the β relaxation, the particles are dominated by vibrations in a cage formed by neighbor particles. However, in the late phase of β relaxation, the number of particles with irreversible hop rearrangement (i.e. thermally induced ST events) gradually increases, which leads to α relaxation at a larger structural scale. In this process, the free volume of the system is increased. With the progress of α relaxation, the number of particles participating in the cooperative motion gradually increases, and the free volume of the system begins to decrease, and finally the diffusion relaxation dominated by the cooperative motion occurs. These findings demonstrate for the first time the non-monotone decline of free volume in the aging relaxation process of amorphous solids. (2) According to the relaxation analysis results, the particle vibration displacement is decomposed. And the complete three-dimensional vibrational modes are obtained by the Displacement covariant matrix method, and the correlation between low frequency vibrational modes and structural relaxation is calculated. The vibrational information of three-dimensional colloidal glass is obtained for the first time. In the process, the dynamic density trailing and the spatial participation do not converge at high frequency are also solved. The relaxation rearrangement events are understood and predicted by using the low-frequency vibration. After the end of β relaxation, the particles with high contribution of low-frequency vibrational modes hop (STs) at the initial stage of α relaxation, that is, the particles hop at the lower energy first. The prediction effect of different low-frequency modes on rearrangement is explored, and the optimal mode is found. The correlation between the optimal vibrational mode and rearrangement is the highest, but this optimal mode is not necessarily the lowest frequency mode. (3) Experimental evidence of a microplastic flow process in low strain rates simple shear is presented for the first time. The evolution of spatial autocorrelation fields of shear strain, shear stress, strain dilatancy and stress dilatancy of STs with loading time is obtained. By quantifying the spatial decay, experimental results have shown that the spatial correlation of strain and stress both show two-order decay: the core of strong correlation does not change with loading time; however, as the loading time increases, the decay rate of the external field decreases and the spatial correlation increases. The spatial correlation of shear dilatancy and stress dilatancy only show first-order decay: the core of strong correlation does not change with loading time. In loading process, the elastic response fields at different times constantly compete, but the shear banding fails to form because that the strain dilatancy and stress dilatancy core scales are always larger than the strain and stress full-field correlation scales. (4) Simple shear experiments under different strain rates provide the first experimental evidence of avalanche shear bandings in STs controlled by strain rates. It is found that with the increase of strain rate, the solid deformation presents a non-uniform transition from uniform to shear band mode. The spatial autocorrelation of the elastic shear field and the dilatancy field of the particle scale shear strain and free volume is calculated. The two elastic fields can be spatially decoupled into a strongly correlated core region and a weakly correlated external field: the former is subject to exponential decay, while the latter is subject to power law decay. By analyzing the rate correlation of the elastic field, the elastic criterion of shear banding instability is proposed: only if the strong correlation scale of the dilatancy field is smaller than the correlation scale of the shear field, the shear banding can emerge from the disordered structure. This elastic criterion shows that only when the free volume generated by ST is bound within its elastic shear field, these STs have the opportunity to self-organize to trigger shear banding in a manner similar to avalanche; Otherwise, STs will uniformly nucleate in space and eventually contribute to uniform deformation. These experimental findings harmonize the local effects of free volume and the non-local effects of shear transformation, thus unifying the two classical models of shear bands in amorphous solids.