Morovati Vahid, Saadat Mohammad Ali, Dargazany Roozbeh
Department of Civil & Environmental Engineering, Michigan State University, East Lansing, Michigan, USA.
Phys Rev E. 2020 Dec;102(6-1):062501. doi: 10.1103/PhysRevE.102.062501.
In this study, a constitutive model is proposed to describe the necking behavior of double network (DN) gels based on statistical micromechanics of interpenetrating polymer networks. Accordingly, the constitutive response of DN gels in large deformations has been divided into three zones, i.e., prenecking, necking, and postnecking. The behavior of the DN gel is dominated by the behavior of the first and the second networks in each stage. In a previous study, we described how the destruction of the first network can govern the inelastic effects during the prenecking stage. Here, we elucidate the role of the second network to govern the material behavior in the necking and postnecking stages. To incorporate the effect of necking, the material behavior at each zone is described through the competition of three mechanisms that control the rearrangement of the two networks. Here, we challenge a general simplifying assumption in the modeling of DN gels, which considers the second network to be fully elastic. The recent experimental observations show the reduction of energy dissipation in the first network after necking initiation due to the localization of the damage in an active zone. Thus, we assumed that the chains of the second network contribute to the energy dissipation of the matrix by keeping the connection between the fragments of the first network. The proposed model has been validated in all three stages against different sets of experimental data on the uniaxial cyclic tensile behavior of DN gels. Moreover, the initiation and propagation of necking instability have been comprehensively illustrated through a finite-element implementation of the proposed model.
在本研究中，基于互穿聚合物网络的统计微观力学，提出了一个本构模型来描述双网络（DN）凝胶的颈缩行为。相应地，DN凝胶在大变形下的本构响应被分为三个区域，即预颈缩、颈缩和颈缩后。DN凝胶在每个阶段的行为由第一网络和第二网络的行为主导。在之前的一项研究中，我们描述了第一网络的破坏如何控制预颈缩阶段的非弹性效应。在此，我们阐明第二网络在控制颈缩和颈缩后阶段材料行为中的作用。为了纳入颈缩效应，通过控制两个网络重排的三种机制的竞争来描述每个区域的材料行为。在此，我们质疑DN凝胶建模中的一个普遍简化假设，即认为第二网络是完全弹性的。最近的实验观察表明，由于损伤在活性区域的局部化，颈缩开始后第一网络中的能量耗散减少。因此，我们假设第二网络的链通过保持第一网络片段之间的连接来对基体的能量耗散做出贡献。所提出的模型已在所有三个阶段针对关于DN凝胶单轴循环拉伸行为的不同组实验数据进行了验证。此外，通过所提出模型的有限元实现，全面阐述了颈缩不稳定性的起始和传播。
