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.

ELASTIC－PLASTIC CONSTITUTIVE MODELS BASED ON THE MULTIPLICATION PROCESSES OF DEFORMED GRAINS

According to the characteristics of micro-deformation of polycrystalline metal,the author divides grains intothree kinds and proposes a new conceplion of deformed grains.multiplication,from which some explicit elastic-Plastic constitutive equations can be deduced and some experimental results can be explained quantitativelv,It shows that the macro-yield,rate-correlativity work hardening and other phenomena are all closely related to the kinetic process of grains deformation.

Constitutive Laws for Visco-plastic Porous Medium Shaped by Regularly Distributed Circular Particles

A numerical study is presented,using a homogenization technique to consider the plain strain problem of visco-plastic porous medium shaped by regularly distributed circular particles. Based on a rigid plastic material,the paper derives the macroscopic constitutive laws for homogenous equivalent medium. By changing the shape parameter of circular particles,the effect of pore shape on macroscopic constitutive laws is explored. Yield surfaces with different pore shapes are obtained. About voids,a two-scale conception is introduced,which regards main void as macroscopic scale and secondary cavities as microscopic scale. The macroscopic potential involving main and secondary voids is achieved. The proposed macroscopic constitutive law taking microscopic features as influence factors is helpful for exploring the macroscopic mechanical properties of porous medium when numerical simulation is required.

On the yield functions in Lagrangian stress space of elastic-plastic materials with internal constraints

In the present paper it is shown that the elastic range in the second Piola-Kirchhoff stress space can be chosen in a hyperplane which is through the origin of Lagrangian stress space and perpendicular to the normal of the constraint manifold at the plastic configuration, if the determinate stress response of the elastic-plastic material with simple internal constraints with some condition is correctly chosen, otherwise, it is in general in a hypersurface and the normal flow rule by Ⅱ yushin＇s postulate will have an indeterminate part. The choice of deterrninate stress response is probable because of its indeterminacy. Therefore the yield function should be a function of the second Piola-Kirchhoff stress lying in the hyperplane so that it is more simple and the back stress as the geometric center of the elastic range in general is inside the elastic range. Finally some examples are concerned.

Contact dynamics of elasto-plastic thin beams simulated via absolute nodal coordinate formulation

Under the frame of multibody dynamics, the contact dynamics of elasto-plastic spatial thin beams is numerically studied by using the spatial thin beam elements of absolute nodal coordinate formulation（ANCF）. The internal force of the elasto-plastic spatial thin beam element is derived under the assumption that the plastic strain of the beam element depends only on its longitudinal deformation.A new body-fixed local coordinate system is introduced into the spatial thin beam element of ANCF for efficient contact detection in the contact dynamics simulation. The linear isotropic hardening constitutive law is used to describe the elasto-plastic deformation of beam material, and the classical return mapping algorithm is adopted to evaluate the plastic strains. A multi-zone contact approach of thin beams previously proposed by the authors is also introduced to detect the multiple contact zones of beams accurately, and the penalty method is used to compute the normal contact force of thin beams in contact. Four numerical examples are given to demonstrate the applicability and effectiveness of the proposed elasto-plastic spatial thin beam element of ANCF for flexible multibody system dynamics.

Study on the Constitutive Model of Marble Based on the Conventional Triaxial Compression Test

The RMB-150B rock mechanics test system was employed to obtain the complete stress-strain test curves under confining pressures of 0-30MPa for marble samples from Ya'an ,Sichuan province. On the basis of former study and the convention triaxial pressure test results ,the complete procedures curves which described the relationships between yielding strength、 peak strength、 residual strength and confining pressure was obtained. Taking the strain softening of rock into account, the bilinear elastic-linear softening-residual perfect plasticity four-linear model was put forward in this paper on the basis of the test results and theory of plasticity. This model was adopted to describe the behaviors of marble in different phases under triaxial compression with the constitutive equation of strain softening phase as focus. The results indicated that the theoretic model fitted in well with the test results.

STUDY ON THE GENERALIZED PRANDTL-REUSS CONSTITUTIVEEQUATION AND THE COROTATIONALRATES OF STRESS TENSOR

In this paper, the generalized Prandtl-Reuss (P-R) constitutive equations of elastic-plastic material in the presence of finite deformations through a new approach are studied. It analyzes the generalized P-R equation based on the material corotational rate and clarifies the puzzling problem of the simple shear stress oscillation mentioned in some literature. The paper proposes a modified relative rotational rate with which to constitute the objective rates of stress in the generalized P-R equation and concludes that the decomposition of total deformation rate into elastic and plastic parts is not necessary in developing the generalized P-R equations. Finally, the stresses of simple shear deformation are worked out.

东庄拱坝基础加固措施效果分析

拱坝基础加固是保证坝肩稳定和拱坝安全的重要工程措施,以东庄拱坝坝基加固措施为研究对象,系统模拟坝肩岩体中断层、夹泥裂隙、宽大裂隙和相应的加固措施,采用弹塑性本构对其坝基加固效果进行了有限元分析。计算结果表明:基础加固措施对坝体位移和应力的最大值影响很小,但在一定程度上使坝体以及建基面的屈服区减小,改善了坝体受力;基础加固措施对拱坝坝体的塑性区影响不大,但是基础加固后建基面屈服区明显减小,基础加固措施明显改善了坝基的受力状态,基础加固措施对于断层f5和夹泥裂隙Rnj3的屈服区体积影响相对较小,对于宽大裂隙L22的屈服区体积影响较为显著。东庄拱坝基础加固措施改善了坝体和坝基受力、提高了坝基的稳定性。

热熔焊接工艺参数对聚乙烯燃气管道焊接残余应力的影响

高密度聚乙烯(PE-HD)管道具有韧性高、抗腐蚀等优点,广泛应用于输水输气、核工业和氢能等领域。受加工工艺和焊接技术的限制,PE-HD管道系统存在生产残余应力和焊接残余应力。残余应力的存在,会加速管道内部裂纹的萌生和扩展,显著降低了管道的使用寿命。因此,研究残余应力对准确评价PE-HD管道可靠性具有重要意义。分别采用开口圆环法和盲孔法测得了PE-HD管基材和热熔接头的环向残余应力,并基于弹塑性本构建立了温度-位移耦合的热熔焊接有限元模型,探究了热熔焊接接头残余应力的分布及焊接工艺参数对温度场和残余应力的影响。结果表明:盲孔法和开口圆环法测量结果近似相等;与传统的黏弹性模型相比,建立的弹塑性热熔焊接有限元模型计算结果更接近实验测量值;熔融层厚度随焊接温度和加热时间的增加而增大,延长加热时间可导致热熔接头长度增加;焊缝和熔合区的残余应力为拉应力,且内壁的拉应力大于外壁的拉应力,距离焊缝5 mm处残余应力由拉应力转变为压应力,焊接温度升高和加热时间延长会使残余应力数值增大。

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。

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。

采用SPH方法的黏土切削特性分析

黏土在切削破坏过程中力学特性复杂。为较精确地描述黏土切削破坏过程与预估切削阻力,该研究基于弹塑性力学本构,建立了光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)框架下的黏土剪切破坏模型和GradyKipp张拉损伤破坏模型,并进一步将其耦合得到混合破坏模型。为验证该混合破坏模型开展了简单的黏土切削破坏试验,切削破坏变形的试验结果与模拟结果展示了良好的一致性,裂纹发展方向和裂纹形状有着良好的对应关系。在土-切削部件互作模型的基础上,进一步预测了黏土切削破坏过程中切削部件的切削阻力演化过程,并分析了切削深度及切削部件摩擦系数对黏土切削破坏形态和切削阻力的影响。结果表明,切削深度为0.01、0.02和0.03 m时对应的切削阻力峰值分别为7.89、9.90和11.07 N,切削阻力随切削深度的增加呈增大趋势。切削部件摩擦系数为0.1时对应的波动平缓后的切削阻力最小,为6.1 N。研究可为优化农业机械刀具的结构参数、运动参数,降低作业功耗,减少切削阻力,实现更好的黏土耕作效果提供参考。

考虑地震应变率效应的木材三维弹塑性损伤本构模型及其数值实现

木结构在服役过程中可能遭遇地震作用,木材表现出明显的地震应变率敏感性,需要建立考虑地震应变率效应的木材非线性本构模型。文章系统梳理已有研究中木材在不同地震应变率水平、不同纹理方向的试验结果,分析其不同纹理方向考虑应变率影响的强度与弹性模量绝对值统计规律性,建立木材考虑地震应变率效应的强度与弹性模量地震应变率影响系数表征模型。在此基础上,基于连续介质损伤力学建立考虑地震应变率效应的木材三维弹塑性损伤本构模型,编写相应的UMAT子程序,并将其嵌入ABAQUS有限元软件中。采用所建立的弹塑性损伤本构模型对木材进行顺纹与横纹受压加载模拟,模型结果与试验结果吻合较好,验证了所建本构模型及UMAT子程序的正确性。研究成果可为木结构的抗震分析与评估提供更符合实际的本构模型支持。

基于分段步进式弹塑性格构模型的混凝土破坏过程细观模拟

经典格构模型理论假设单元服从完全脆性的线弹性本构关系,忽略了砂浆基体的延性,导致预测的混凝土荷载-位移曲线延性不足。针对该问题,基于分段步进式方法描述砂浆单元弹塑性本构关系,通过序列线性理论模拟试件受荷损伤破坏过程及力学响应。基于混凝土单轴拉伸和压缩试验对模型进行了校验,发现该模拟方法可以精确模拟混凝土的开裂及荷载-位移曲线。同时,该模型可用于模拟混凝土受拉开裂的尺寸效应问题,以及受压破坏时受力端横向约束程度和试件长细比对开裂行为的影响,为研究混凝土的断裂行为提供了新的理论方法和途径。

一种基于Willam-Warnke模型的钢纤维混凝土单轴损伤本构模型

通过选取Willam-Warnke五参数模型作为屈服函数,基于等效应变假定和损伤准则,并将钢纤维含量特征值与屈服函数、损伤准则相联系,建立了增量型式单轴弹塑性损伤本构模型。根据已有钢纤维混凝土单轴拉伸与压缩试验结果,应用该模型进行了验证,验证结果表明,模型计算结果与试验结果吻合较好,能够很好地反映出钢纤维掺量对峰后曲线的影响。同时,应用该模型对在单轴下的拉伸循环、压缩循环以及、拉压循环进行了验算,验算结果表明,该模型能够模拟计算单轴复杂加载路径下的应力-应变关系。

FINITE ELEMENT NUMERICAL SIMULATION OF LAND SUBSIDENCE AND GROUNDWATER EXPLOITATION BASED ON VISCO-ELASTICPLASTIC BIOT'S CONSOLIDATION THEORY

The land subsidence due to groundwater exploitation has an obvious hysteretic nature with respect to the decrease of the under groundwater level, and the uneven settlement often causes ground fissures. To study these important features, a visco-elasticplastic constitutive relationship with consideration of the coupling of seepage and soil deformation is proposed, and a finite element model with variable coefficients based on the Biot＇s consolidation theory is built. With the groundwater exploitation and the land subsidence control in Cangzhou City, Hebei Province as an example, the variations of the under groundwater level and the deve- lopment of the land subsidence due to the groundwater exploitation are simulated and ground fissures are predicted by the horizontal displacement calculation. The results show that the lag time between the land subsidence and the under groundwater level descent is about a month, and the simulated results of fissures agree well with the observed data. The model can well reveal the characterization of the interaction between the land subsidence and the groundwater exploitation.

Derivation of the Orthotropic Nonlinear Elastic Material Law Driven by Low-Cost Data(DDONE)

Orthotropic nonlinear elastic materials are common in nature and widely used by various industries.However,there are only limited constitutive models available in today's commercial software(e.g.,ABAQUS,ANSYS,etc.)that adequately describe their mechanical behavior.Moreover,the material parameters in these constitutive models are also difficult to calibrate through low-cost,widely available experimental setups.Therefore,it is paramount to develop new ways to model orthotropic nonlinear elastic materials.In this work,a data-driven orthotropic nonlinear elastic(DDONE)approach is proposed,which builds the constitutive response from stress–strain data sets obtained from three designed uniaxial tensile experiments.The DDONE approach is then embedded into a finite element(FE)analysis framework to solve boundary-value problems(BVPs).Illustrative examples(e.g.,structures with an orthotropic nonlinear elastic material)are presented,which agree well with the simulation results based on the reference material model.The DDONE approach generally makes accurate predictions,but it may lose accuracy when certain stress–strain states that appear in the engineering structure depart significantly from those covered in the data sets.Our DDONE approach is thus further strengthened by a mapping function,which is verified by additional numerical examples that demonstrate the effectiveness of our modified approach.Moreover,artificial neural networks(ANNs)are employed to further improve the computational efficiency and stability of the proposed DDONE approach.

混凝土面板坝面板动力损伤有限元分析

联合采用混凝土塑性损伤模型和堆石料弹塑性本构模型,建立了面板堆石坝弹塑性动力分析方法,研究了地震荷载作用下混凝土面板的损伤发生和发展过程。计算结果表明:地震时,在0.65H(H为坝高)附近顺坡向拉应力最大,面板首先在该部位出现损伤,同时由于鞭稍效应,0.85H面板附近也出现损伤;采用损伤模型,损伤部位的面板出现软化,应力得到释放,计算结果比线弹性模型更加合理;采用塑性损伤模型可以反映混凝土面板渐进破坏过程,通过损伤变量可以清晰地了解面板的损伤分布和薄弱环节。此研究成果可以为进一步开展混凝土面板堆石坝极限抗震能力及抗震措施分析提供有效手段。

菜籽与菜籽仁的非线性粘弹塑性本构模型

在菜籽与菜籽仁流变试验的基础上,采用模型理论与经验模型相结合的方法建立菜籽与菜籽仁非线性粘弹塑性本构模型,并运用改进模拟退火计算方法对模型参数反演。结果表明,非线性粘弹塑本构模型能较好地模拟菜籽与菜籽仁流变特性。

水力压裂支撑剂嵌入深度计算方法

针对水力压裂支撑剂嵌入问题,基于支撑剂嵌入岩体的力学过程,建立支撑剂嵌入岩体的本构方程,并结合岩体-支撑剂体系的接触应力分析,提出考虑弹塑性变形的支撑剂嵌入深度计算方法,基于该方法分析了嵌入深度的影响因素。相对于弹性模型,新方法计算结果更接近于实验测量结果,预测更加可靠,且更便于进行理论计算和分析。研究表明:支撑剂嵌入岩体的过程主要发生弹塑性嵌入;支撑剂单层铺置条件下铺置浓度越高嵌入深度越小,多层铺置条件下增大支撑剂铺置浓度不会改变嵌入深度;支撑剂嵌入比例越大,承压支撑剂越多,支撑剂嵌入深度越小;高闭合应力情况下支撑剂嵌入更加显著,流体压力下降会显著增大支撑剂嵌入深度;增大支撑剂粒径或岩石与支撑剂弹性模量比值,会减小支撑剂嵌入深度。