Stress relaxation in network materials: the contribution of the network
Stress relaxation in network materials: the contribution of the network
复制标题
网络材料中的应力松弛：网络的贡献
DOI：
10.1039/d1sm01546j
复制
发表时间：
2022
期刊：
影响因子：
3.4
通讯作者：
Picu, R. C.
中科院分区：
文献类型：
--
作者：
Amjad, S. N.;Picu, R. C.
具有永久交联性的网络材料的应力松弛是由于流体在网络中的传输(孔弹性)、基质的粘弹性和网络的粘弹性。虽然与矩阵相关的松弛得到了广泛的研究，但网络的贡献仍未被探索。在这项工作中，我们考虑了含有粘弹性纤维的二维和三维随机纤维网络，并探索了应力松弛对网络结构的依赖关系。我们观察到弛豫有两个区域--一个初始的指数区域，然后是一个扩展的指数区域--类似于其他无序材料的情况。拉伸指数是密度、纤维直径和网络结构的函数，在网络行为的仿射和非仿射区域之间存在最小值。第一指数区的松弛时间常数与单根纤维的松弛时间常数相似，与网络密度和纤维直径无关。第二个伸展指数区的松弛时间常数是网络参数的弱函数。拉伸指数来自于松弛动力学在与网格大小相当的尺度上的异质性，非均质性越高，拉伸指数越小。在松弛时间常数取自一组均值分布的纤维复合网络中，拉伸指数随纤维时间常数分布的变异系数的增大而减小。与热玻璃成型体和胶体不同，在这些无热体系中，动态非均质性是由网络结构引入的，在松弛过程中不会演化。而在热力系统中，控制参数是温度，在这种非热的情况下，控制参数是描述网络的非亲和性程度的无量纲结构参数。
Stress relaxation in network materials with permanent crosslinks is due to the transport of fluid within the network (poroelasticity), the viscoelasticity of the matrix and the viscoelasticity of the network. While relaxation associated with the matrix was studied extensively, the contribution of the network remains unexplored. In this work we consider two and three-dimensional stochastic fiber networks with viscoelastic fibers and explore the dependence of stress relaxation on network structure. We observe that relaxation has two regimes – an initial exponential regime, followed by a stretched exponential regime – similar to the situation in other disordered materials. The stretch exponent is a function of density, fiber diameter and the network structure, and has a minimum at the transition between the affine and non-affine regimes of network behavior. The relaxation time constant of the first, exponential regime is similar to the relaxation time constant of individual fibers and is independent of network density and fiber diameter. The relaxation time constant of the second, stretched exponential regime is a weak function of network parameters. The stretched exponential emerges from the heterogeneity of relaxation dynamics on scales comparable with the mesh size, with higher heterogeneity leading to smaller stretch exponents. In composite networks of fibers whose relaxation time constant is selected from a distribution with set mean, the stretch exponent decreases with increasing the coefficient of variation of the fiber time constant distribution. As opposed to thermal glass formers and colloids, in these athermal systems the dynamic heterogeneity is introduced by the network structure and does not evolve during relaxation. While in thermal systems the control parameter is the temperature, in this athermal case the control parameter is a non-dimensional structural parameter which describes the degree of non-affinity of the network.