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arXiv 1809.04239cond-mat.soft
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接触力网络的全局拓扑:对剪切增稠悬浮液的新认识

Global topology of contact force networks: new insight into shear thickening suspensions

Lance E. Edens, Sidhant Pednekar, Jeffrey F. Morris, Gregory K. Schenter, Aurora E. Clark, Jaehun Chun

摘要:

高度浓缩或“致密”的颗粒悬浮液在施加应力下可经历粘度的急剧增加或剪切增稠。了解导致稠密悬浮液中这种流变变化的基本特征对于优化流动条件或设计用于浆料加工的流动改性剂至关重要。虽然在施加的剪切下颗粒环境的局部变化可能与粘度的变化有关,但更广泛地需要将剪切增稠过渡与导致长程组织的颗粒相互作用力的基本组织联系起来。特别是,在高体积分数的颗粒,最近的证据表明接触颗粒之间的摩擦力是重要的。在此,摩擦接触力的网络内模拟的二维剪切增稠悬浮液进行了分析。研究了两种拓扑度量来表征接触力网络(CFN)在不同剪切应力下的响应。的度量,测地线指数和空隙参数,反映互补方面的CFN:一个是连通性的接触网络,第二个是分布的空间区域没有粒子-粒子接触。考虑到粘度的变化,拓扑度量表明,网络均匀地增长,在大尺度上,但与许多局部地区缺乏接触,清楚地表明应力链的增长中的作用,导致在剪切增稠过渡的流变学响应的大的变化。

英文摘要:

Highly concentrated or 'dense" particle suspensions can undergo a sharp increase in viscosity, or shear thickening, under applies stress. Understanding the fundamental features leading to such rheological changes in dense suspensions is crucial to optimize flow conditions or to design flow modifiers for slurry processing. While local changes to the particle environment under an applied shear can be related to changes in viscosity, there is a broader need to connect the shear thickening transition to the fundamental organization of particle-interaction forces which lead to long-range organization. In particular, at a high volume fraction of particles, recent evidence indicates frictional forces between contacting particles is of importance. Herein, the network of frictional contact forces is analyzed within simulated two-dimensional shear thickening suspensions. Two topological metrics are studied to characterize the response of the contact force network (CFN) under varying applied shear stress. The metrics, geodesic index and the void parameter, reflect complementary aspects of the CFN: one is the connectedness of the contact network and the second is the distribution of spatial areas devoid of particle-particle contacts. Considered in relation to the variation of the viscosity, the topological metrics show that the network grows homogeneously at large scales but with many local regions devoid of contacts, indicating clearly the role of stress chain growth in causing the large change in the rheological response at the shear thickening transition.

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