橡胶材料弹性的一种新的螺旋管模型
A NEW HELICAL TUBE MODEL FOR THE ELASTICITY OF RUBBER-LIKE MATERIALS
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摘要: 建立统计力学模型正确描述材料微观结构与宏观力学特性之间的关系是软物质类材料的最大挑战之一, 已有的橡胶材料统计模型尚存在一些不足. 文章根据橡胶类材料宏观各向同性、连续均匀和不可压缩特性, 结合分子链的非高斯统计模型, 提出一种橡胶材料网络结构的力学特性模型. 该模型将代表体元上对应点之间的传力路径用一个类螺旋管区域约束的分子链子网络来描述, 螺旋管的表面随材料的宏观变形做仿射变形, 分子链子网络由方向和长度随机的分子链或链段首尾链接而成, 在此基础上由分子链的熵推导出描述材料宏观力学特性的本构关系. 通过大量的材料测试数据对本构模型进行拟合验证, 拟合结果表明该模型具有非常好的精度, 并且在采用两个参数时模型具有非常高的可靠性, 仅用单轴拉伸实验数据拟合模型就能准确预测全部3类实验数据. 该模型使用了仿射的弯曲管假设, 能从微观结构尺度上说明材料的不可压缩特性, 避免了直管模型的近似性, 为微观尺度的随机性和宏观的均匀性的联系提出一个新的模型.Abstract: One of the biggest challenges for soft materials is to establish statistical mechanical models to correctly describe the relationship between its microstructure and macroscopic mechanical properties, and the statistical models for rubber-like materials still have some imperfections. Based on the macroscopically isotropic, continuous uniform and incompressible properties of rubber-like materials, combined with a non-Gaussian statistical model for molecular chains, a new elastic model for rubber material is proposed. The force transfer path between the corresponding points on the representative volume element is described by a subnetwork constrained to a region as a spiral helical tube, whose surfaces all deform affinely with the macroscopic deformation. The sub-network consists of molecular chains or chain segments linked end-to-end with random orientation and length. Hence, the constitutive model describing the macroscopic mechanical characteristics of the material is derived from the entropy of the subnetwork. A large number of test data were used to fit the constitutive model, which show that the model has very good accuracy. Especially, the proposed model with two parameters show very high reliability that it gives good predictions of the three basic test with the parameters derived from data-fitting with uniaxial tension data only. With the proposed curved affine tube confinement, this model can explain the incompressible properties of the material from the microstructure scale, overcome the shortcoming of straight tube model, and build a new model for the correlation between the stochastic at the micro scale and the uniform at the macro scale.