粘弹塑性统一本构模型理论

文章在已有的统一本构模型的基础上,将粘弹性变形引入到统一本构模型之中,成功地改善了材料过渡段的变形模拟情况。通过Hastelloy-X的变形模拟及与其它统一本构模型的变形模拟比较,证明了粘弹塑性统一本构模型的合理性。     

一种黏弹塑性统一本构模型

经过对大量有关统一本构模型的文献资料分析，指出了现有统一本构模型存在的问题，并通过对材料实验数据的分析，指出了黏弹性现象在实验中的表现，并据此将黏弹性引入到弹性黏塑性统一本构模型之中，建立了黏弹塑性统一本构模型，通过模型的数值模拟证明：模型计算结果无论在变形趋势上，还是在数值精度上都与实验数据符合得很好，克服了此前统一本构模型存在的问题。黏弹塑性统一本构模型的产生将统一本构模型的产生将统一本构理论的内涵扩大到黏弹性范围，进而构造了一个黏弹塑性理论的新框架。     

基于统一强度理论的岩石弹塑性本构模型及其数值实现

基于弹塑性力学理论，以统一强度准则为屈服准则，建立了考虑硬化/软化行为和应变率效应的岩石弹塑性本构模型；采用Fortran语言通过LS-DYNA的用户自定义材料接口(Umat)对该弹塑性本构模型进行编程，并把该程序生成求解器以达到对该模型进行应用的目的；通过岩石的单轴压缩实验和SHPB实验对所建的弹塑性本构模型进行验证，结果表明，该弹塑性本构模型能够反映岩石在准静态和动态下的力学行为。     

广义双剪粘弹塑性本构模型在渤海海冰动力学中的应用

在连续介质力学基础上建立了一个广义双剪粘弹塑性海冰动力学本构模型。该模型在海冰屈服前采用Kelvin-Vogit粘弹性模型,考虑中间主应力和静水压力对海冰屈服的影响选用广义双剪应力屈服准则作为海冰屈服判据,屈服后采用相关联的正则流动法则。采用该本构模型对渤海海冰动力过程进行了48小时数值模拟,讨论了辽东湾海冰的厚度、密集度、冰速和主应力的分布规律,其中海冰厚度分布与卫星遥感资料符合良好,从而有效地验证了该广义双剪粘弹塑性本构模型在海冰动力学中的可靠性。     

粘弹塑性本构理论及其应用

本文综述粘弹塑性材料力学行为的研究概况和近期进展,探讨粘弹塑性本构关系的研究途径和表达形式,阐述粘弹塑性理论研究的重要意义和广阔的应用前景。      

经典弹塑性力学体系下岩土材料的本构方程

剑桥模型,修正剑桥模型以及近年来出现的适用于砂土和黏土的统一硬化模型在岩土工程中有重要的科研和实用价值．在经典弹塑性力学框架下重新推导了以上这些岩土材料本构方程,对岩土工程中常用的本构模型和经典弹塑性理论框架下的岩土本构模型进行了对比,将两个体系下的相关量建立了联系．     

SnPb钎料合金的粘塑性Anand本构方程

采用统一型粘塑性本构 Anand方程描述了电子封装焊点 Sn Pb钎料合金的非弹性变形行为 ,基于 Sn Pb 合金的弹塑性蠕变本构方程和实验数据 ,确定了6 2 Sn36 Pb2 Ag、6 0 Sn40 Pb、96 .5 Sn3.5 Ag和 97.5 Pb2 .5 Sn四种钎料合金 Anand方程的材料参数 ,验证了粘塑性 Anand本构方程对 Sn Pb合金在恒应变速率和稳态塑性流动条件下应力应变行为的预测能力。结果表明 ,Anand方程能有效描述 Sn Pb钎料的粘塑性本构行为 ,并可应用于电子封装 Sn Pb焊点的可靠性模拟和失效分析     

本构模型对复合材料中X射线热击波数值模拟结果的影响

以碳酚醛靶中的一维应变热击波为例,讨论本构模型对热击波数值模拟结果的影响.数值模拟采用3种本构模型,即各向同性理想弹塑性本构模型、各向异性理想弹塑性本构模型及各向异性动态弹塑性本构模型.结果表明:与各向同性理想弹塑性、各向异性理想弹塑性本构模型相比,利用各向异性动态弹塑性本构模型获得的热击波应力峰值较小、应力峰值衰减较...     

非饱和土力学理论的研究进展

回顾了非饱和土有效应力的发展,目前普遍认同采用两个应力变量来建立本构模型,且对基质吸力中毛细和粘吸两部分作用进行了阐述。分析了非饱和土强度问题,包括抗剪强度和抗拉强度。讨论了非饱和土的本构模型问题,包括基于净应力和基质吸力的弹塑性模型,基于Bishop有效应力和基质吸力的水力力学耦合弹塑性模型,以及双孔隙结构的模型。最后探讨了热力学方法和多孔介质理论在非饱和土中的应用,基于多孔介质理论在多场耦合条件下土体复杂的行为是当前值得研究的问题。     

304不锈钢室温单轴循环棘轮行为的粘塑性本构描述

在统一粘塑性循环本构模型的框架下对循环硬化的304不锈钢的单轴棘轮行为进行了本构描述。模型中通过随动硬化背应力演化和各向同性变形阻力演化对304不锈钢在非对称应力循环下的循环附加硬化和循环流动特性进行了分析，同时考虑了加载历史对循环棘轮行为的影响。将模型应用于304不锈钢室温单轴循环棘轮行为及其对加载历史依赖性的描述中，预言结果与实验结果吻合较好。     

The unified elastic-viscosic-plastic theory of solids

1ThePostulatesandillustrationsofUnifiedElastic-Viscosic-PlasticTheoryWhenthesolidsareundertyleexternalexcitations,theresponseswillexistintheinterior.Inthesolid,therearethreemainstates:elastic,plasticandviscosic.Itisimpossibletostudythesebehavioursbymolecularmethod,butthesebehaviourscanberesearchedfromthepointofviewoflargescale.Inthispaper,weconsidertheexcitationbyexternalworkonly,theresponsesarestrainenergyandtheheatwasted,asinFig.1.InFig.1(a),theworkratebyexternalforceisW,onepartofwhichis…     

Two-dimensional numerical analysis of non-isothermal melt spinning with and without phase transition

A model and simulation method are developed for two-dimensional non-isothermal melt spinning of a visco elastic melt. The visco elastic stress is evaluated from a non-isothermal Giesekus constitutive equation developed by application of the pseudo-time method to the isothermal form of the model [J. Non-Newt. Fluid Mech. (2001)]. The crystallization kinetics is described with the model proposed by Nakamura et al. [J. Appl. Polym. Sci. 17 (1973) 1031], whereas the crystallization rate, which is a function of both temperature and molecular orientation, is evaluated according to the equation proposed by Ziabicki [Fundamentals of Fiber Formation, Wiley, New York, 1976]. The set of non-linear governing equations is solved by using the DEVSS-G/SUPG finite element method. Melt spinning is simulated for two different polymers: amorphous polystyrene and fast-crystallizing Nylon-6,6. The analysis demonstrates that although the kinematics in the thread-line are approximately one-dimensional, the radially non-uniform thermal history, caused by the leading order variation of the temperature gradient ∂T/∂r, gives rise to radially non-uniform visco elastic stresses. This stress gradient results in radially non-uniform molecular orientation and a strong radial variation in crystallinity for Nylon-6,6. The radially non-uniform stress profiles obtained from the simulations are in good agreement with experimental results for melt spinning of polystyrene. Simulations of Nylon-6,6 show that the thermally-induced crystallization depends strongly on the choice of the Avrami index n, and a sharp increase in crystallinity due to stress-induced crystallization is predicted only when the molecules are highly oriented in the drawing direction at high drawing speeds. The significant influences of visco elasticity, air drag, and operating conditions on non-isothermal melt spinning dynamics also are predicted.     

Some basic issues in traditional Eulerian formulations of finite elastoplasticity

In traditional Eulerian formulations of finite elastoplasticity, there are some basic issues that still need clarification and further investigation. Among them are the characterization of initial anisotropy for scalar- and tensor-valued constitutive functions, plastic consistency conditions involving time differentiation of anisotropic yield functions, a unified loading criterion for hardening, softening, and perfectly plastic behaviour, etc. Sometimes, it is thought that a satisfactory and complete treatment for these issues could not be achieved within a framework of traditional Eulerian formulation. In this work, efforts are made towards explaining and clarifying these basic issues. Introducing the notion of an Eulerian type rotation-conjugate group of the initial material symmetry group, we show that consistent Eulerian formulations of scalar- and tensorvalued constitutive functions may be achieved for any given type of initial anisotropy. With such consistent Eulerian formulations, we derive plastic consistency conditions in a corotating frame associated with the foregoing rotation-conjugate group. As to the loading conditions for hardening, softening, and perfectly plastic behaviour, we recall and study the unified criterion proposed by Hill [J Mech Phys Solids 6 (1958) 236]. It is pointed out that the tangential elastic stiffness tensor in this unified criterion has to fulfill rather complicated integrability conditions for the elastic rate equation with an objective stress rate. It appears to be far from being a simple or even trivial matter to give an explicit form of the tangential elastic stiffness tensor meeting these conditions. It is indicated that this issue may be resolved by using the logarithmic stress rate. With this rate, an explicit form of Hill's unified loading criterion, together with an explicit form of tangential elastic stiffness tensor, is presented in terms of a general complementary hyperelastic potential.     

Displacement of surrounding rock in a deep circular hole considering double moduli and strength-stiffness degradation

The problem of cavity stability widely exists in deep underground engineering and energy exploitation. First, the stress field of the surrounding rock under the uniform stress field is deduced based on a post-peak strength drop model considering the rock's characteristics of constant modulus and double moduli. Then, the orthogonal non-associative flow rule is used to establish the displacement of the surrounding rock under constant modulus and double moduli, respectively, considering the stiffness degradation and dilatancy effects in the plastic region and assuming that the elastic strain in the plastic region satisfies the elastic constitutive relationship. Finally, the evolution of the displacement in the surrounding rock is analyzed under the effects of the double modulus characteristics, the strength drop, the stiffness degradation, and the dilatancy. The results show that the displacement solutions of the surrounding rock under constant modulus and double moduli have a unified expression. The coefficients of the expression are related to the stress field of the original rock, the elastic constant of the surrounding rock, the strength parameters, and the dilatancy angle. The strength drop, the stiffness degradation, and the dilatancy effects all have effects on the displacement. The effects can be characterized by quantitative relationships.     

不同排水条件下非饱和土中柱孔扩张问题的解析分析

现有的圆柱孔扩张理论已可为诸如石油工程中井筒稳定性鉴定、 及旁压和圆锥贯入实验分析等提供理论依据, 但在非饱和地基压力注浆, 复合地基处理等实际工程问题中却鲜有应用. 基于弹塑性理论和非饱和土力学原理, 采用统一强度理论, 对非饱和土中柱形小孔扩张问题进行了解析研究. 首先将柱孔周围土体分为弹性区和塑性区, 并考虑在弹性区遵循小应变理论, 在塑性区遵循大应变理论, 同时考虑了中间主应力及粒间吸力对非饱和土体强度的影响. 其次应用有效应力表示的统一强度准则, 在本构关系、几何方程、动量平衡方程等基本方程的基础上, 结合相应的边界条件, 最终获得了不同排水条件下柱孔扩张时周围弹塑性区域内的应力场、应变场、位移场及极限扩孔压力的解析表达式. 通过数值算例和参数分析, 在与现有的饱和及非饱和土中柱孔扩张理论进行退化验证的同时, 分析了吸力、剪胀参数、中主应力效应参数及初始径向有效应力等对弹塑性区域内的应力场、应变场及位移场的影响规律, 验证了本文理论的正确性及有效性, 以期为实际工程问题提供合理的理论依据.      

Orthotropic elastic–plastic material model for paper materials

Paper and paperboard generally exhibit anisotropic and non-linear mechanical material behaviour. In this work, the development of an orthotropic elastic–plastic constitutive model, suitable for modelling of the material behaviour of paper is presented. The anisotropic material behaviour is introduced into the model by orthotropic elasticity and an isotropic plasticity equivalent transformation tensor. A parabolic stress–strain relation is adopted to describe the hardening of the material. The experimental and numerical procedures for evaluation of the required material parameters for the model are described. Uniaxial tensile testing in three different inplane material directions provides the calibration of the material parameters under plane stress conditions. The numerical implementation of the material model is presented and the model is shown to perform well in agreement with experimentally observed mechanical behaviour of paper.     

基于显式有限元方法的两相介质弹塑性动力反应计算分析

针对增量形式的流体饱和两相多孔介质弹塑性波动方程组,运用基于显式逐步积分格式的时域显式有限元方法对该波动方程组进行求解,并应用基于SMP破坏准则的弹塑性动力本构模型描述两相介质的动力反应性质,对两相介质在输入地震波作用下的弹塑性动力反应进行计算和分析,将计算结果与相应的弹性动力反应的计算结果进行对比;对本文应用的弹塑性...