Particle Modeling Based on Interatomic Potential and Crystal Structure: A Multi-Scale Simulation of Elastic-Plastic Deformation of Metallic Material

We formulate a macroscopic particle modeling analysis of metallic materials (aluminum and copper, etc.) based on theoretical energy and atomic geometries derivable from their interatomic potential. In fact, particles in this framework are presenting a large mass composed of huge collection of atoms and are interacting with each other. We can start from cohesive energy of metallic atoms and basic crystalline unit (e.g. face-centered cubic). Then, we can reach to interparticle (macroscopic) potential function which is presented by the analytical equation with terms of exponent of inter-particle distance, like a Lennard-Jones potential usually used in molecular dynamics simulation. Equation of motion for these macroscopic particles has dissipative term and fluctuation term, as well as the conservative term above, in order to express finite temperature condition. First, we determine the parameters needed in macroscopic potential function and check the reproduction of mechanical behavior in elastic regime. By using the present framework, we are able to carry out uniaxial loading simulation of aluminum rod. The method can also reproduce Young’s modulus and Poisson’s ratio as elastic behavior, though the result shows the dependency on division number of particles. Then, we proceed to try to include plasticity in this multi-scale framework. As a result, a realistic curve of stress-strain relation can be obtained for tensile and compressive loading and this new and simple framework of materials modeling has been confirmed to have certain effectiveness to be used in materials simulations. We also assess the effect of the order of loadings in opposite directions including yield and plastic states and find that an irreversible behavior depends on different response of the particle system between tensile and compressive loadings.

Study of elastic-plastic damage model of cement consolidated soil with high organic content

On the basis of elastic-plastic damage model of cement consolidated soil,the authors took organic contents into reasonable damage variable evolution equation in order to seek relation between the organic contents and parameters in the equation,and established the elastic-plastic damage model of cement consolidated soil considering organic contents.The results show that the parameters change correspondingly with difference of the organic contents.The higher the organic contents are,the less the valves of the parameters such as elastic modulus(E),material parameters(K,n) and damage evolution parameter(ε) become,but the larger strain damage threshold value(εd) of the sample is.Meanwhile,the calculation results obtained from established model are compared with the test data in the condition of common indoors test,which is testified with reliability.

Elastic-plastic contact force history and response characteristics of circular plate subjected to impact by a projectile

A new elastic-plastic impact-contact model is proposed in this paper. By adopting the principle of minimum acceleration for elastic-plastic continue at finite deformation, and with the aid of finite difference method, the proposed model is applied in the problem of dynamic response of a clamped thin circular plate subjected to a projectile impact centrally. The impact force history and response characteristics of the target plate is studied in detail. The theoretical predictions of the impact force and plate deflection are in good agreements with those of LDA experimental data. Linear expressions of the maximum impact force/transverse deflection versus impact velocity are given on the basis of the theoretical results.

ELASTIC-PLASTIC CONSTITUTIVE RELATION OF PARTICLE REINFORCED COMPOSITES

In this paper, a systematic approach is proposed to obtain the macroscopic elastic-plastic constitutive relation of particle reinforced composites (PRC). The strain energy density of PRC is analyzed based on the cell model, and the analytical formula for the macro-constitutive relation of PRC is obtained. The strength effects of volume fraction of the particle and the strain hardening exponent of matrix material on the macro-constitutive relation are investigated, the relation curve of strain versus stress of PRC is calculated in detail. The present results are consistent with the results given in the existing references.

Harten-Lax-van Leer-contact(HLLC)approximation Riemann solver with elastic waves for one-dimensional elastic-plastic problems

A Harten-Lax-van Leer-contact （HLLC） approximate Riemann solver is built with elastic waves （HLLCE） for one-dimensional elastic-plastic flows with a hypo- elastic constitutive model and the von Mises＇ yielding criterion. Based on the HLLCE, a third-order cell-centered Lagrangian scheme is built for one-dimensional elastic-plastic problems. A number of numerical experiments are carried out. The numerical results show that the proposed third-order scheme achieves the desired order of accuracy. The third-order scheme is used to the numerical solution of the problems with elastic shock waves and elastic rarefaction waves. The numerical results are compared with a reference solution and the results obtained by other authors. The comparison shows that the pre- sented high-order scheme is convergent, stable, and essentially non-oscillatory. Moreover, the HLLCE is more efficient than the two-rarefaction Riemann solver with elastic waves （TRRSE）

An elastic-plastic analysis of short-leg shear wall structures during earthquakes

Short-leg shear wall structures are a new form of building structure that combine the merits of both frame and shear wall structures. Its architectural features, structure bearing and engineering cost are reasonable. To analyze the elastic-plastic response of a short-leg shear wall structure during an earthquake, this study modified the multiple-vertical-rod element model of the shear wall, considered the shear lag effect and proposed a multiple-vertical-rod element coupling beam model with a new local stiffness domain. Based on the principle of minimum potential energy and the variational principle, the stiffness matrixes of a short-leg shear wall and a coupling beam are derived in this study. Furthermore, the bending shear correlation for the analysis of different parameters to describe the structure, such as the beam height to span ratio, short-leg shear wall height to thickness ratio, and steel ratio are introduced. The results show that the height to span ratio directly affects the structural integrity; and the short-leg shear wall height to thickness ratio should be limited to a range of approximately 6.0 to 7.0. The design of short-leg shear walls should be in accordance with the ＂strong wall and weak beam＂ principle.

Elastic-Plastic Behavior and Failure Analysis of Pipe-on-Pipe Impact

The elastic-plastic behavior and failure of pipe-on-pipe impact(p-o-p-i)problem is studied through analytical model and numerical simulation in this paper.The impact of a whipping pipe with one end hinged and the other end free on a simply-supported target pipe at its midpoint is considered.The analytical model based on tubular beam theory is proposed in the study of the deformation and plastic collapse behavior of pipes impacted on different positions and therefore to obtain the various failure modes depending on the material and structural parameters of the pipes.Numerical simulations using the finite element code MSC-Marc are performed and the results are coincident with the theoretical predictions.

基于统一强度理论的扰损围岩巷道脆塑性解答

钻爆法施工常造成岩质巷道扰损区围岩性能劣化。针对扰损围岩、扰损外围岩的弹塑性状态下不同的扰损围岩巷道力学模型,采用统一强度理论、弹-脆-塑性模型和非关联流动法则,建立扰损围岩巷道有关应力、位移和塑性区半径的脆塑性解答,探讨巷道力学模型的转换路径及判定方法,并将结果进行对比、验证,获得各因素的影响规律。研究表明:提出的巷道脆塑性解答合理反映了中间主应力、围岩扰损范围和峰后强度、剪胀特性的综合影响,通过参数组合变换可退化为多种解答并得到正确性验证,具有重要的理论意义和应用前景;巷道力学模型判定与中间主应力、围岩扰损范围密切相关,显著影响巷道应力-位移分布和围岩特征曲线;支护压力和巷道稳定变形随着围岩峰后强度下降、剪胀特性参数增加而明显增大。

基于修正力磁模型的混凝土结构压磁疲劳模拟

为了通过混凝土梁内钢筋在力磁效应下的磁信号来定量分析混凝土梁的疲劳状态,整合几种力磁模型的优缺点和适用范围,提出了适用于铁磁性材料弹塑性阶段的力磁本构模型,并通过ANSYS定量模拟分析了混凝土梁在弹性和弹塑性阶段的磁化特征;对混凝土结构在拟动力和疲劳加载过程中的力磁效应进行了有限元模拟,得到了测点处磁感应强度的时变曲线,并与试验和隐式微分模型所得结果进行对比。结果表明:修正后的力磁模型在弹性阶段的应用能够准确反映试验观察到的3个阶段变化规律,即梁开裂前的平直段、开裂后的迅速磁化段和加载后期的磁化饱和段;该模型的磁场模拟结果还能反映箍筋、纵筋的相对位置和梁的受载情况;在疲劳阶段,模拟结果与试验观察的规律一致,精度较高,并与试验结果在同一数量级;该修正力磁模型不仅具有应力与磁学属性的直观映射关系,而且相较于隐式微分模型更易于应用,可作为力磁效应的定量化研究工具。

上海浦东足球场整体模型分析与计算

上海浦东足球场整体结构由一层地下室结构、地上钢结构看台和大跨度钢结构屋盖三部分组成,地上看台结构采用钢框架+屈曲约束支撑体系,屋盖采用轮辐式张拉体系。屋盖和下部结构单独分析,不能体现上下结构之间的相互影响。为更可靠合理进行整体结构设计,采用了整体模型分析作为单体模型分析的重要且必要的补充。整体模型分析工作主要包括多遇地震、设防地震下的弹性分析,罕遇地震下的弹塑性时程分析,以及超长混凝土结构应力分析。结果表明:单体分析存在局限性,整体模型的足球场结构受力安全。

基于三剪能量屈服准则的岩石弹塑性耦合模型

为建立能够准确描述岩石变形过程中能量演化规律的力学模型,提出利用三剪能量屈服准则和弹性剪应变能获取岩石黏聚力与内摩擦角,以及基于三剪能量塑性势函数获取剪胀角的方法,依据所提方法和岩石循环加卸载试验数据,得到了各级围压下不同塑性累积阶段岩石的弹性模量、黏聚力、内摩擦角及剪胀角等参数,发现随着塑性变形的增大,弹性模量呈负指数关系减小,黏聚力峰前线性增大而峰后呈负指数减小,内摩擦角满足比例参数为1、形状参数为1.5的Weibull函数,剪胀角线性减小;随着围压的增大,弹性模量和黏聚力均呈线性关系增大而剪胀角呈线性减小。建立岩石三剪能量弹塑性耦合力学模型,实现了模型在有限差分软件中的二次开发并编写了能量演化监测程序。模拟岩石室内试验,结果表明所建模型能较准确地描述岩石后继屈服过程中的硬化软化、剪胀、围压效应以及能量演化等力学行为。研究成果可为从能量角度研究岩体失稳提供理论支撑和现实手段。

考虑强弱轴影响的矩形钢管网壳结构弹塑性稳定性分析

在单层网壳结构中,存在强弱轴的矩形钢管较圆钢管、方形钢管在结构受力合理性、材料性能充分利用上存在优势。首先通过一组算例对比分析了圆钢管、H型钢、方形钢管和矩形钢管四种杆件形式在网壳结构曲面内外承受双向压弯的稳定性差异,随后将矩形钢管带入装配式节点的弹簧单元有限元模型,对比刚接模型进行研究,得到了节点域、节点刚度、初始缺陷幅值、矢跨比等参数对结构稳定承载力的影响规律。结果表明,矩形钢管的稳定应力在两个方向上可以达到平衡,且在强轴方向的稳定应力要低于同截面面积的圆钢管和方形钢管的稳定应力;对于截面存在强、弱轴且在截面两个方向材料充分运用的杆件,其弱轴方向抗弯刚度的影响不可忽视。

汽轮机部件多轴蠕变-疲劳寿命评估方法

汽轮机汽缸、转子等高温部件运行中受到疲劳损伤和蠕变损伤,二者的损伤机制会互相影响,有必要对疲劳损伤和蠕变损伤以及二者的耦合作用进行评估。在Ohno-Wang循环塑性模型基础上进行了拓展,提出了一种统一黏弹塑性循环材料本构模型,在ABAQUS平台上采用UMAT用户子程序开发了多轴蠕变-疲劳耦合分析程序。采用该程序对1 000 MW超超临界机组高温转子进行了多轴蠕变-疲劳寿命评估,结果显示损伤最大的位置出现在第1级动叶叶根轮槽位置。研究成果可为汽轮机高温部件的寿命评估提供技术支撑。

利用黏-弹-塑性模型对磁流变阻尼器动力学性能预测与分析

为了建模合适的参数模型来描述阻尼器的动态输出特性,发挥磁流变阻尼器工程应用中的半主动控制优势。本文的研究在激励频率和振幅为5 Hz和10 mm条件下,利用振动系统测试磁流变阻尼器在不同激励电流下得到动态输出特性,在此基础上利用黏-弹-塑性参数模型,采用果蝇优化算法对所有电流下的实测结果进行预测并对其结果展开分析讨论。研究结果表明该阻尼器的输出力能够跟随外部位移随时间变化情况;阻尼力随激励电流增大表现出先缓慢增大后显著增大的特性,这表明该阻尼器具有依赖输入电流的可控性,为实现工程应用中的半主动控制提供条件。并讨论了产生这种现象的原因在于不同电流下颗粒于基体间的相互作用。预测结果表明利用果蝇优化算法,黏-弹-塑性参数模型能够很好的描述实测结果。

基于弹塑性模型的某舰炮抽壳力仿真计算

舰炮射击后药筒贴膛力对抽壳初速存在重要影响,贴膛过程药筒表现出弹塑性大变形特性,且沿口部至底部贴膛极不均匀,简化的二维模型及薄壁圆筒解析模型已经不能满足定量的分析需求。建立了基于弹塑性抽壳过程动力学仿真模型,采用Johnson-Cook本构模型描述药筒弹塑性大变形行为,通过仿真计算获取药筒及炮膛动态应力应变、接触力及摩擦力等参量,分析了药筒动态贴膛规律及受力特性。仿真结果表明,舰炮射击过程药筒经历贴闩、径向自由膨胀至贴膛、贴膛后与炮膛协同变形及回弹至平衡态四个阶段,平衡状态后抽壳阻力不再变化,保持在13320N左右,抽筒子作用于药筒后抽壳初速最高达到18.9m/s,该抽壳初速满足了舰炮高速连发的设计性能要求。

泡沫金属经典本构模型表征三轴拉伸和拉压组合条件下宏观力学性能的研究

泡沫金属在实际工程应用中往往承受多轴拉伸、拉压组合和压缩等复杂应力状态,且拉伸和压缩性能差异显著,而现有的本构关系理论模型基于多轴压缩实验构建,能否描述多轴拉伸和拉压组合条件下泡沫金属宏观弹塑性力学性能存疑。本文采用数值模拟的方法开展多轴加载数值仿真实验,基于数值模拟结果检验泡沫金属两个经典模型:D-F模型与汤立群等提出的理论模型(以下简称Tang模型),在三轴拉伸和拉压组合工况下的合理性。结果表明,D-F模型的椭圆度参数显著影响模型的预测精度,基于三轴拉伸、压缩和拉压组合屈服面拟合计算的椭圆度预测效果最优,结合单轴拉伸应力应变曲线,D-F模型能较好地表征泡沫金属三轴拉压组合条件下力学性能,但存在无法描述塑性耗散功大于单轴拉伸破坏时对应的塑性耗散功的力学行为的缺陷;该模型不能准确描述三轴拉伸力学性能。Tang模型分别描述三轴拉伸和拉压组合破坏前的力学行为,等效应力和应变曲线均具有良好的一致性,但确定等效应力和应变的四个参数均不同且不同于三轴压缩对应的参数;综合考虑三轴拉压组合和三轴压缩工况时,等效应力和应变曲线的一致性很差。

Theoretical model and testing method for ball indentation based on the proportional superposition of energy in pure elasticity and pure plasticity

For a homogeneous,continuous,and isotropic material whose constitutive relationships meets with the Ramberg-Osgood law(R-O law),the energy in the elastoplastic indentation with a ball indenter was theoretically analyzed,and the proportional superposition of energy in pure elasticity and pure plasticity during indentation was considered based on the equivalence of energy density.Subsequently,a Proportional Superposition-based Elasto Plastic Model(PS-EPM)was developed to describe the relationships between the displacement and the load during the ball indentation.Furthermore,a new test method of Ball Indentation based on Elastoplastic Proportional Superposition(BI-EPS)was developed to obtain the constitutive relationships of R-O law materials.The load–displacement curves predicted using the PS-EPM model were found to agree closely with the Finite Element Analysis(FEA)results.Moreover,the stress vs.strain curves predicted using the BI-EPS method were in better agreement with those obtained by FEA.Additionally,ball indentation was performed on eleven types of metal materials including five types of aluminum alloys and six types of steel.The test results showed that the stress vs.strain relationships and the tensile strength values predicted using the proposed BI-EPS method agreed well with the results obtained using conventional uniaxial tensile tests.

An elastic-plastic contact model for line contact structures

Although numerical simulation tools are now very powerful,the development of analytical models is very important for the prediction of the mechanical behaviour of line contact structures for deeply understanding contact problems and engineering applications.For the line contact structures widely used in the engineering field,few analytical models are available for predicting the mechanical behaviour when the structures deform plastically,as the classic Hertz’s theory would be invalid.Thus,the present study proposed an elastic-plastic model for line contact structures based on the understanding of the yield mechanism.A mathematical expression describing the global relationship between load history and contact width evolution of line contact structures was obtained.The proposed model was verified through an actual line contact test and a corresponding numerical simulation.The results confirmed that this model can be used to accurately predict the elastic-plastic mechanical behaviour of a line contact structure.

Numerical Study of the Plastic Behaviour of a Low Alloy Steel during Phase Transformation

Phase transformations in steels play a major role on the generation of residual stresses and distortions during thermal processes such as welding and heat treatments. In this paper, we focus on the influence of phase transformations on the plastic behaviour of a low-alloy steel. It is now well known that the plastic strain rate can then be decomposed as the sum of two terms. The first one corresponds to classical plasticity while the second one is due to the evolution of the transformation and is usually referred to as corresponding to transformation induced plasticity. A theoretical approach of the problem has been achieved ([1][2][3]] and a macroscopic model has been proposed in the case of ideal-plastic phases. The theoretical approach has been assessed and completed using micromechanical numerical simulations but these were based on rather coarse 3D meshes due to limited computer capabilities in the 80’s. This paper presents new finite element micromechanical calculations using refined meshes to analyse the classical plastic behaviour and transformation induced plasticity. The results of the computations are discussed and compared with the calculations initially performed. Finally improvements of the macroscopic model are proposed.

An Earth multi-body system elasticity and plasticity dynamics model

Research on the elasticity and plasticity dynamics of the Earth multi-body system, including the Earth multi-body system stratum-block's equivalent inertia force system and generalized inertia force, the Earth multi-body system stratum-block's equivalent inertia force system expressed with partial velocity and partial palstance, and Earth multi-body system generalized inertia force expressed with partial velocity and partial palstance. This research provides a theoretical foundation for further investigation of Earth multi-body dynamics.