韧性纳米胶体玻璃剪切流停止后的空间异质性弛豫动力学与可恢复应变演化
Spatially heterogeneous relaxational dynamics and the evolution of recoverable strain following flow cessation of a ductile nanocolloidal glass
浏览论文内容
中文总结 AI 辅助
本研究结合流变学与XPCS，揭示韧性纳米胶体玻璃在剪切流停止后，存在空间异质性弛豫动力学，明确了可恢复应变演化的微观机制，建立了内部动力学与宏观力学弛豫的关联。
中文摘要 AI 辅助
本研究结合流变学与X射线光子关联光谱（XPCS），探究韧性纳米胶体玻璃在剪切流停止后的结构与力学弛豫行为。将该玻璃在不同剪切速率下剪切至300%应变后保持固定应变，应力随保持时间呈现长期准对数衰减，且该衰减对初始剪切速率的依赖较弱。恢复流变学测量显示，此应力弛豫伴随可恢复应变的弹性分量呈对数下降，因此应力与可恢复应变的下降速率成正比。应力弛豫期间的XPCS测量揭示，动力学由类对流回流主导，该回流分为两个动力学截然不同的区域，表明存在带状运动：一个区域的流动可通过仿射应变建模，另一区域的玻璃则以塞体形式运动，同时经历缓慢的玻璃态弛豫。这些动力学的速率大致跟踪可恢复应变的损失速率，说明该运动是应力弛豫期间可恢复应变向不可恢复应变转化的主要微观机制。相比之下，应变恢复期间的XPCS测量显示纯仿射流动，无异质性证据，且应变率与流变测量定量一致。综上，这些结果提供了统一的微观图像，将韧性玻璃的演化内部动力学与其在流停止后的宏观力学弛豫关联起来。
英文摘要
We report a combined rheology and x-ray photon correlation spectroscopy (XPCS) study of the structural and mechanical relaxation of a ductile, nanocolloidal glass following the cessation of shear flow. After the glass is sheared to 300% strain at various shear rates and then held at fixed strain, the stress undergoes a protracted, quasi-logarithmic decay with hold time that depends weakly on the initial strain rate. Recovery rheology measurements reveal that this stress relaxation is accompanied by a logarithmic decrease in the elastic component of the recoverable strain; hence, the rates of decrease of the stress and recoverable strain are proportional. XPCS measurements during the stress relaxation reveal dynamics dominated by a convection-like backflow that is divided into two dynamically distinct regions indicative of banded motion. In one region, the flow can be modeled by an affine strain, while in the other region the glass moves as a plug while undergoing slow, glassy relaxation. The rates of these dynamics approximately track the rate of loss of recoverable strain, indicating this motion is the predominant microscopic mechanism driving the conversion of recoverable to unrecoverable strain during stress relaxation. In contrast, XPCS measurements during strain recovery reveal purely affine flow with no evidence of heterogeneity and with strain rates that agree quantitatively with the rheometry measurements. Together, these results provide a unified microscopic picture connecting the evolving internal dynamics of a ductile glass to its macroscopic mechanical relaxation following flow cessation.
