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arXiv 2202.10657cond-mat.dis-nncond-mat.mtrl-sci
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非晶态固体中向剪切带转变的隐时空序列

Hidden spatiotemporal sequence in transition to shear band in amorphous solids

Zeng-Yu Yang, Yun-Jiang Wang, Lan-Hong Dai

摘要:

剪切带是非晶态固体中一种基本的非平衡现象。由于原子的剪切、膨胀和转动三种局域运动之间的内在纠缠,剪切带产生的精确物理过程至今仍是一个谜。为了揭开这一神秘面纱,我们首次制定了一个理论协议,涵盖仿射和非仿射变形组件,以解码这些高度纠缠的局部原子尺度事件。与广义的剪切转变区概念不同,塑性行为可以通过对剪切主导区(SDZ)、剪切变形主导区(DDZ)和旋转主导区(RDZ)的操作来全面地说明。它们的时空演化表现出一种从同步运动到剪切带开始时的分离分布的新的转变,这与流体动力学中从层流到湍流的转变有着惊人的相似之处。利用极值理论和渗流分析揭示了其内在机理。EVT分析表明,在初始塑性单元的胚胎阶段,扩张是主要的模式。逾渗分析点的临界幂律标度性质的过渡,从随机激活渗流的塑性区域。从而揭示了剪切带出现的全貌。首先,膨胀触发初始剪切和旋转在软区,导致胚胎的流动单元,这是其次是不均匀的类粘性图案表现为二次激活的旋转在相邻的硬材料。这种旋转激活有助于进一步扰动,并最终导致剪切带的形成。我们的研究结果也加强了在无序材料的塑性行为的讨论必须考虑仿射和非仿射分量变形。

英文摘要:

Shear banding is a fundamental non-equilibrium phenomenon in amorphous solids. Due to the intrinsic entangling of three local atomic motions: shear, dilatation and rotation, the precise physical process of shear band emergence is still an enigma. To unveil this mystery, we formulate for the first time a theoretical protocol covering both affine and non-affine components of deformation, to decode these highly entangled local atomic-scale events. In contrast to the broad concept of shear transformation zone, plastic behavior can be demonstrated comprehensively as the operative manipulation of more exact shear-dominated zones (SDZs), dilatation-dominated zones (DDZs) and rotation-dominated zones (RDZs). Their spatiotemporal evolution exhibits a novel transition from synchronous motion to separate distribution at the onset of shear band, which is in striking resemblance with the transition from laminar flow to turbulent flow in flow dynamics. The hidden mechanism is revealed with the help of extreme value theory (EVT) and percolation analysis. Analysis of EVT indicates dilatation is the dominant mode at the embryo of initial plastic units. The percolation analysis points towards the critical power-law scaling nature at the transition from stochastic activation to percolation of plastic regions. Then the comprehensive pictures of shear banding emergence are uncovered. Firstly, dilatation triggers initial shear and rotation in soft regions, leading to embryo of flow units, which is followed by the inhomogeneous turbulent-like pattern manifesting as the secondary activation of rotation in neighboring hard material. Such rotation activation contributes to further perturbation, and ultimately, leads to shear band formation. Our findings also reinforce that the discussion of plastic behavior in disordered materials must take into account both affine and non-affine component deformation.

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