粘弹塑性统一本构模型的参数评估

针对粘弹塑性统一本构模型参效众多的特点和传统评估参效方法的缺点,应用非线性最小二秉法与敏感系数分析方法相结合,提出了一个比较系统的对粘弹塑性统一本构模型的参数进行评估的方法。对铜合金在室温下不同加载速率的试验曲线进行参数适配,表明本方法的合理性与正确性。为粘弹塑性统一本构模型的工程应用奠定了基础。     

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。     

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。     

一种弹性粘塑性统一本构模型

在深入研究分析材料变形过程的基础上,对材料变形与选定描述材料变形内变量的问题进行探讨,在唯象法的基础上提出一种金属材料变形的粘塑性统一本构模型.用该模型对304不锈钢的变形过程进行模拟,其计算结果较Miller模型更接近实验结果.     

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。     

高分子材料粘弹塑性本构关系研究进展

总结和评述了高分子材料粘弹塑性本构关系的研究成果,并介绍了笔者利用模糊约束法建立的模糊随机高分子网络力学体系。     

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。     

基于物理变量的热粘塑性本构模型

在位错的运动和产生与塑性变形的一般关系及考虑到热激活与粘性阻尼效应的位错集体运动的统一理论基础上,通过对结构参量的演化规律的具体建议,提出了一种基于物理变量的热粘塑性本构模型。在此模型的基础上,讨论了金属材料动态力学行为的微观机理。     

弹塑性本构积分算法

本文运用模态应力,模态应变等概念,发展了一种本构积分中点算法。在简正坐标系下得到简单的算法公式。并对算法的精度和稳定性进行了计算验证和理论分析。本文算法的精度和稳定性比通用的屈服面校正方法——切线刚度—径向拉回方法要好。该法对复杂载荷情况下的弹塑性分析有一定的价值。     

大变形弹塑性本构理论的几个基本问题

本文对大变形弹塑性本构理论的变形、变形率的分解以及旋率等基本问题进行了评述,提出了变形率分解为弹性与塑性变形率所应满足的两个条件,提出采用变形率标架旋率来构造应力客观率,在单剪问題中可得到无剪应力振荡现象的结果。     

A quasi-flow constitutive model with strain-rate dependence

In this paper, the proposed is a quasi-flow constitutive model with strain-rate sensitivity for elastic plastic large deformation. The model is based on the Quasi-flow Corner theory, and is suitable for the sheet metal forming process simulation with a variable punch machine velocity. Uniaxial tensile tests and deep-drawing tests of a circular blank with square punch are carried out and numerically simulated. The consistency between the experimental and the numerically simulated results shows the validity of the present new constitutive model. The project supported by the Scientific Foundation of National Outstanding Youth of China (10125208), the National Natural Science Foundation of China (19832020), and the National Education Committee of China     

A constitutive model and elastoplastic analysis of structures under cyclic loading

A constitutive model for cyclic plasticity is briefly outlined. Then the model is implemented in a finite element code to predict the response of cyclic loaded structural components such as a double-edge-notched plate, a grove bar and a nozzle in spherical shell. Comparision with results from other theories and experiments shows that the results obtained by using the present model are very satisfactory.The Project Supported by National Natural Science Foundation of China.     

A constitutive model for creep-plasticity interaction based on dislocation dynamics

A glide-plus-climb micromechanism of dislocation evolution with the formation of subgrains is proposed for modelling of the creep-plasticity interaction (CPI). The long-range internal stress can be divided into the resistance for dislocation climb in subgrain boundaries and that for dislocation glide within grains or subgrains. Their evolution equations are then derived based on dislocation dynamics. Furthermore, a unified constitutuve model for CPI is developed from Orowan's formula. Theoretical calculations on the basis of this model show a very good agreement between the model prediction and experimental results of benchmark tests for 2 1/4 Cr-1 Mo steel at 600°C.     

A nonclassical constitutive model for crystal plasticity and its application

I.IntroductionTheresearchoncrystalplasticitycanbedatedbackto1930'sill.AherHill[=],HillandRicely]builtupaperfectsystemofthegeometryandkineticsofCrystalplasticity,itsapplicatiollbecolllesmoreandmoreattractive,especiallyintheallalysisofpolycrystallinelllaterialssubjectedtoInultiaxiallynonproportionalcyclicloading.Ithasalreadybeenrealizedthattileillll,ol'talltforthepracticalapplicationis:tofindal.ealisticalldeasilyapplicableof'ystallineconstitutiverelationandaneffectivenumericalapproach.Tilecon…     

An elasto-plastic damage constitutive theory and its prediction of evolution of subsequent yield surfaces and elastic constants

Based on pair functional potentials, Cauchy-Born rule and slip mechanism, a material model assembling with spring-bundle components, a cubage component and slip components is established to describe the elasto-plastic damage constitutive relation under finite deformation. The expansion/shrink, translation and distortion of yield surfaces can be calculated based on the hardening rule and Bauschinger effect defined on the slip component level. Both kinematic and isotropic hardening are included. Numerical simulations and predictions under tension, torsion, and combined tension-torsion proportional/non-proportional loading are performed to obtain the evolution of subsequent yield surfaces and elastic constants and compare with two sets of experimental data in literature, one for a very low work hardening aluminum alloy Al 6061-T6511, and another for a very high work hardening aluminum alloy annealed 1100 Al. The feature of the yield surface in shape change, which presents a sharp front accompanied by a blunt rear under proportional loading, is described by the latent hardening and Bauschinger effect of slip components. Further, the evolution law of subsequent yield surfaces under different proportional loading paths is investigated in terms of their equivalence. The numerical simulations under non-proportional loading conditions for annealed 1100 Al are performed, and the subsequent yield surfaces exhibit mixed cross effect because the kinematic hardening and isotropic hardening follow different evolution tendency when loading path changes. The results of non-proportional loading demonstrate that the present model has the ability to address the issue of complex loading due to the introduction of state variables on slip components. Moreover, as an elasto-plastic damage constitutive model, the present model can also reflect the variation of elastic constants through damage defined on the spring-bundle components.     

泰勒杆实验对材料动态本构参数的确认和优化确定

通过实验数据和数值模拟结果的对比,研究了泰勒杆实验在材料动态本构关系参数确认和优化方面的应用。以Johnson-Cook模型描述的oxygen-free high-conductivity（OFHC） copper材料为例进行了具体说明,并对实验中的部分不确定因素进行了分析。结果表明,利用该方法对材料本构模型参数进行确认和优化确定是合理的。     

Quasi-micromechanical constitutive theory for brittle damaged materials under tension

One of fundamental but difficult problems in damage mechanics is the formulation of the effective constitutive relation of microcrack-weakened brittle or quasi-brittle materials under complex loading, especially when microcrack interaction is taken into account. The combination of phenomenological and micromechanical damage mechanics is a promising approach to constructing an applicable damage model with a firm physical foundation. In this paper, a quasi-micromechanical model is presented for simulating the constitutive response of microcrack-weakened materials under complex loading. The microcracking damage is characterized in terms of the orientation domain of microcrack growth (DMG) as well as a scalar microcrack density parameter. The DMG describes the complex damage and its evolution associated with microcrack growth, while the scalar microcrack density factor defining the isotropic magnitude of damage yields an easy calculation of the effects of microcrack interaction on effective elastic moduli. Project supported by the National Natural Science Foundation of China (19891180).     

A constitutive theory for shape memory polymers. Part II: A linearized model for small deformations

A constitutive theory is developed for shape memory polymers. It is to describe the thermomechanical properties of such materials under large deformations. The theory is based on the idea, which is developed in the work of Liu et al. [2006. Thermomechanics of shape memory polymers: uniaxial experiments and constitutive modelling. Int. J. Plasticity 22, 279-313], that the coexisting active and frozen phases of the polymer and the transitions between them provide the underlying mechanisms for strain storage and recovery during a shape memory cycle. General constitutive functions for nonlinear thermoelastic materials are used for the active and frozen phases. Also used is an internal state variable which describes the volume fraction of the frozen phase. The material behavior of history dependence in the frozen phase is captured by using the concept of frozen reference configuration. The relation between the overall deformation and the stress is derived by integration of the constitutive equations of the coexisting phases. As a special case of the nonlinear constitutive model, a neo-Hookean type constitutive function for each phase is considered. The material behaviors in a shape memory cycle under uniaxial loading are examined. A linear constitutive model is derived from the nonlinear theory by considering small deformations. The predictions of this model are compared with experimental measurements.