Strain hardening in glassy polymers: Influence of network density on elastic and viscous contributions

In this study, the rate‐ and temperature‐dependent strain hardening and the Bauschinger effect is studied for three glassy polymers. It appeared that for all materials, an equal distribution of elastic and viscous hardening was necessary to accurately predict the Bauschinger effect, as well as the rate‐ and temperature‐dependent strain hardening response. As for the elastic contribution, the viscous contribution appears to increase with an increase in entanglement network density. Investigating the effect of temperature on the Bauschinger effect revealed that at elevated temperatures the model predictions are not accurately enough. It is shown that this is caused by the magnitude of the elastic hardening contribution; to improve the predictions, a temperature‐dependent elastic contribution is necessary. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1001–1013     

水饱和花岗岩本构模型及地下爆炸波的数值研究

采用广义自洽方法描述介质的细观几何结构,基于混合物理论建立了水饱和岩石含损伤弹塑性本构模型,提出了一个适用于爆炸波数值计算的饱和水体积分数演化方程,也即给出了本构关系中的闭合方程.使用Biot有效应力描述水压对岩石强度的影响,在有效应力空间里建立了水饱和岩石剪切屈服和破坏的强度准则,并引入了剪胀效应对强度的影响因子.对地下封闭核爆炸的力学效应开展了数值模拟,系统地研究了含水花岗岩中地下爆炸波的传播特征以及含水量对爆炸应力波传播规律的影响.     

Plastic spin associated with a non-normality theory of plasticity

A plasticity model using a vertex-type plastic flow rule on a smooth yield surface for an anisotropic solid has been proposed recently. This model is here completed by incorporating the effect of plastic spin. Simple shear with a large shear strain is one of the hardest tests on finite strain anisotropic plasticity models, and it is here shown which plastic spin expression is needed to avoid unrealistic oscillatory behavior of the shear stress under large shear strains. The idea of using non-normality with a smooth yield surface originates from a recent proposal of using an abrupt strain path change to determine the subsequent yield surface shape. For this method both polycrystal plasticity calculations and experiments have shown a vertex-type response on the apparently smooth yield surface.     

A Linear Theory of Porous Elastic Solids

The theory of porous elastic solids with large vacuous interstices, considered by Giovine like materials with ellipsoidal structure, includes, as a particular case, the nonlinear theory of Nunziato and Cowin of elastic materials with small spherical voids finely dispersed in the matrix.In this paper we propose appropriate constitutive relations and then specialize the basic balance equations of Giovine to the linear theory. Also, generalizing the developments of Cowin and Nunziato, we formulate boundary-initial-value problems and examine classical applications as responses to homogeneous deformations and small-amplitude acoustic waves.     

结构性黏土模型在FLAC中的二次开发及应用

FLAC软件广泛应用于岩石及岩土工程数值分析中,但内置材料模型库的不足影响了其应用范围及分析结果的精细化。本文基于FLAC程序提供的二次开发平台,以结构性黏土边界面模型为例,在FISH编译环境下实现了复杂本构模型的开发与应用。首先,介绍了FLAC的关键开发技术和具体实施方法;其次,给出了结构性黏土边界面模型的基本原理及应力积分方法;然后,通过FLAC单元测试与FORTRAN程序计算结果的对比,验证了FLAC二次开发在多种应力路径下的正确性;随后,通过FLAC排水平面应变剪切试验模拟剪切带的形成,测试了二次开发模型的多单元模拟能力,同时验证了其网格依赖性问题;最后,通过对土坡开挖的模拟,测试了结构性黏土模型FLAC二次开发的工程适用性。     

APPLICATION OP THE FINITE PART OF A DIVERGENT INTEGRAL IN THE THEORY OF ELASTICITY

Using the finite part of a divergent integral, we transform Kelvin’s solutions, Boussinesq’s solutions and Mindlin ’s solutions in the three-dimensional theory of elasticity into corresponding solutions in the two-dimensional theory. Besides, its application in plane problems is also given.     

Nonlinear constitutive law for ferroelectric/ferroelastic material and its finite element realization

The hysteresis phenomena of ferroelectric/ferroelastic material in polarization procedure are investigated. Some assumptions are presented based on the published experimental data. The electrical yielding criterion, mechanical yielding criterion and isotropic hardening model are established. The flow theory in incremental forms in polarization procedure is presented. The nonlinear constitutive law for electrical-mechanical coupling is proposed phenomenologically. Finally, the nonlinear constitutive law expressed in a form of matrices and vectors, which is immediately associated with finite element analysis, is formulated. In the example problem of a rectangular specimen subjected to a uniaxial electric field, the procedure from virgin state to fully polarized state is simulated. Afterward, a uniaxial compressive loading is applied to depolarizing the specimen. Results are in agreement with the experimental data.     

一种非经典滑移模型及其应用

采用由弹簧和塑性阻尼器构成的简单机械模型建立了不采用屈服判据的滑移本构方程,并利用KBW自洽理论和一种混合平均方案得到了多晶体弹塑性的分析方法.此法不采用屈服判据 ,无需对滑移系的开动和滑移方向进行搜索,使计算过程简化.分析了316不锈钢在拉压-剪切二维塑性应变空间中典型路径下的循环响应特性,得到了与实验较为一致的结果.     

一种横观各向同性强度准则及变换应力空间

考虑岩土介质在自然形成过程中产生的原生各向异性性质,将其简化为一种横观各向同性岩土材料.基于已提出的a强度准则,根据沉积面与有效滑移面在物理空间中位置的相互关系,采用两面的空间夹角作为度量岩土材料原生各向异性在加载条件下发挥强度作用的影响变量.并根据有效滑移面的物理概念,当沉积面与有效滑移面夹角越大,则摩擦特性潜力发挥的越充分,此时对应更高的强度应力比,反之则对应越小的强度应力比.基于上述思想,建立了考虑原生各向异性的强度应力比公式,将其用于修正a准则,进而得到了横观各向同性a准则公式.采用上述横观各向同性a准则公式向各向同性Von-Mises准则公式转换的变换思路,在横观各向同性a准则公式基础上,推导得到了变换应力公式,该公式可由横观各向同性应力空间转变为各向同性应力空间,利用所提出的变换应力方法,可方便的将传统的在偏平面上以Von-Mises准则为基础的二维模型转换为可考虑原生各向异性的三维模型.通过对岩土材料的强度以及真三轴条件下的应力应变关系试验数据预测,验证了所提的横观各向同性a准则及其变换应力公式的有效性及适用性.     

复杂加载条件下的砂土本构模型

试验表明,饱和砂土的应力应变关系具有显著的密度以及压力依存性,上述两点构成了描述砂土静力加载下变形特性无法忽视的因素. 此外,在循环加载等复杂加载作用下,砂土还会表现出明显的应力诱导各向异性以及相变转换特性. 基于在