STUDY ON THE PARAMETER VALUE DOMAIN OF MACRO-MICRO CONSTITUTIVE MODEL

宏微观耦合本构模型的参数识别往往通过反分析方法进行,为了使参数识别结果具有高的置信度,需要确定合适的参数取值范围. 基于动态再结晶过程的微观机理以及相应本构方程的数学特征,提出一个确定参数取值范围的方法. 首先详细给出考虑动态再结晶的黏塑性本构模型,并根据模型构造物理机理,提出通过6 步确定该模型参数取值范围的方法;其次,对300M 低合金钢进行不同温度、应变速率下的热变形试验,测试宏观的流动应力-应变数据及微观的组织数据;然后应用提出的方法,依据试验数据,确定参数取值范围;最后,基于确定参数取值范围中获得的知识,对模型进行局部修改,使模型模拟结果更接近实验结果.     

Bammann-Chiesa-Johnson粘塑性本构模型材料参数的一种识别方法

粘塑性本构模型能否成功模拟金属高应变率大应变变形过程依赖于材料参数识别结果的好坏。由于BCJ模型考虑了应变率、温度与材料硬化之间的耦合效应以及应变率、温度历史效应,同时模型中包含了多个材料参数,因此很难通过试验直接识别模型的材料参数。本文针对BCJ模型中的耦合效应和历史效应,基于对模型中材料参数物理涵义的界定,给出了一种对材料参数解耦、分离并进行估计的方法,获得了模型材料参数估计公式,估计了材料参数的取值范围。在此基础上,编制了BCJ模型应力积分径向返回算法和粒子群优化算法的计算程序,应用重新设计了BCJ模型耦合效应和历史效应的反分析方法,在参数取值范围内对材料参数进行了优化识别。以OFHC Cu为例,应用提出的识别方法对BCJ模型的材料参数进行了识别,计算结果和试验结果符合较好。     

立式瓦楞复合纸板的平面压缩本构模型

研究了立式瓦楞复合纸板静态和动态缓冲性能,提出其静态和动态本构模型。对A楞立式瓦楞复合纸板试样进行了静态压缩和动态冲击试验,得到其应力-应变曲线;提出立式瓦楞复合纸板静态本构方程,并利用静态压缩试验数据对静态本构方程进行了参数识别;研究应变率对本构方程的影响,进而提出动态本构方程,并通过动态冲击试验对动态本构方程进行了验证。结果表明:静态压缩和动态冲击试验中,立式瓦楞复合纸板的压缩过程均包括弹性阶段、屈服阶段、平台阶段、密实化阶段;静态本构模型的拟合误差为4.79%,动态本构模型的拟合误差为2.65%,都能较好地表示立式瓦楞复合纸板在压缩过程中的应力-应变情况。所提出的立式瓦楞复合纸板静态和动态本构模型为该新型材料的性能评价提供了理论支持,对其在缓冲包装中的推广应用具有重要参考价值。     

基于爆炸切割试验的有机玻璃本构模型参数反演

为了获取爆炸切割数值模拟中有机玻璃（PMMA）的材料本构模型参数,建立了一种基于神经网络的有机玻璃Johnson Holmquist ceramics (JH-2)本构模型参数反演方法：基于从爆炸切割试验和现有研究得到的JH-2本构模型经验参数,确定本构模型参数的调整区间;使用LS-DYNA数值模拟软件对2.5 mm宽爆炸切割索切割14 mm PMMA平板过程进行数值模拟并收集平板损伤数据集;建立PMMA平板本构模型参数与损伤数据之间的神经网络模型;通过训练完成的神经网络模型对PMMA平板的JH-2本构模型参数进行反演。为验证通过反演参数的可靠性,进行了4.2 mm宽爆炸切割索切割19 mm PMMA平板试验和有限元数值模拟,计算结果中的平板损伤情况与实验结果相差较小,表明通过反演获得的JH-2本构模型参数能较好地应用于PMMA平板爆炸切割数值模拟。传统材料参数获取方法,该参数反演方法相较于可以通过较少的试验及测试,获得比较准确的材料本构模型参数。     

DH-36钢的塑性流动统一本构关系研究

通过对DH-36钢动态应变时效的规律和试验数据进行系统分析, 发展和建立了描写第3种动态应变时效的本构模型. 然后基于热激活物理概念本构模型和塑性流动应力组合原理, 加入对第3种动态应变时效的描述, 获得了统一本构模型. 该模型不仅可以描写第3种动态应变时效, 还可以预测DH-36钢在温度77K~1000K, 应变率0.001s^{-1}~3000s^{-1}范围内的塑性流动应力,通过比较发现统一本构模型预测结果与试验结果吻合很好.      

考虑围压效应的冻结砂土动态本构模型研究

为描述主动围压作用下冻结砂土的动态力学特性,通过在朱-王-唐模型的非线性体上串联塑性体,建立了能够考虑围压效应的冻结砂土动态损伤本构模型;分析了损伤参数对应力-应变曲线特征、屈服点、峰值应力和峰值应变的影响规律,基于冻结砂土动力学试验数据确定了模型参数;通过将模型和试验数据进行对比,并对不同试验条件下模型的预测误差进行分析,验证了模型的适用性和准确性。结果表明,损伤参数对应力-应变曲线弹性阶段和屈服点无明显影响,而对塑性阶段和破坏阶段的影响较为显著,本构模型预测的应力-应变曲线与试验结果具有较好的一致性。模型能够预测围压引起冻结砂土塑性阶段占比大和屈服点明显的特征,且能够描述围压对冻结砂土动态强度的增强效应;不同负温和主动围压条件下,模型对峰值应力和屈服强度的预测效果优于峰值应变和屈服应变。     

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基于群体与适应度的概念，应用改进的PSO算法，从随机解出发，提出了基于PSO 算法的本构模型参数识别方法. 该方法解决了橡胶类材料大应变时硬化现象的本构模型参数 的确定这一难题. 首先通过单轴拉伸本构模型实验，在针对硬化实验曲线存在拐点的情 况下，应用PSO算法进行拟合，最后利用简单剪切实验进行验证. 结果表明该方法科学可行， 且具有速度快、精度高、易于收敛等优点. 并且有效地解决了本构模型参数识别的困难，可 广泛应用于各种复杂材料.     

帘线/橡胶复合材料各向异性黏-超弹性本构模型

帘线/橡胶复合材料广泛应用于轮胎等重要工程领域,为了描述其在服役条件下的大变形、非线性、各向异性和高应变率等材料力学行为,基于纤维增强复合材料连续介质力学理论,提出了一种考虑应变率效应的帘线/橡胶复合材料各向异性黏-超弹性本构模型. 该模型中单位体积的应变能被解耦为便于参数识别的基体等容变形能、帘线拉伸变形能、剪切应变能和黏性应变能四部分. 给出了模型参数的确定方法,并通过拟合文献中单轴拉伸、偏轴拉伸实验数据,得到了模型参数. 利用该模型预测了不同加载和变形条件下的力学行为,并将预测结果与实验结果对比分析. 结果表明, 考虑黏性模型和不考虑黏性模型对不同应变率变形条件下的预测结果相差很大,且考虑黏性模型的预测结果与实验结果吻合很好. 因此,与不考虑黏性模型相比,所提出的各向异性黏-超弹性本构模型能更好地表征帘线/橡胶复合材料在大变形、高应变率条件下的力学特性.      

基于机器学习软骨细胞的时间依赖性力学行为及本构参数反演

探究软骨细胞机械负载下的力学特性对于理解软骨细胞的正常和病理状态以及骨性关节炎的病因至关重要. 基于软骨细胞有限元计算模型的力学响应与其本构参数之间的高度复杂非线性, 本文提出了分别利用双向深度神经网络TW-Deepnets模型和随机森林RF模型并结合有限元方法来识别软骨细胞本构参数的两种反演方法. 首先, 建立了软骨细胞的无侧限压缩实验有限元模型, 收集MSnHS本构参数空间点与对应的有限元计算模型的压缩反作用力响应数据集. 其次, 结合贝叶斯超参数优化算法搭建了用于软骨细胞本构参数反求的TW-Deepnets模型和RF模型, 对有限元收集的数据进行训练, 并利用单个软骨细胞受到50%压缩程度下的实验数据对软骨细胞的MSnHS本构参数进行了反求. 最后, 通过与实验曲线的对比验证了所提出的反演方法的有效性, 并引入决定系数R2对两种模型的预测准确性进行了对比评估, 检验了模型对各本构参数的预测性能, 分析了MSnHS本构模型中各参数影响软骨细胞力学响应的重要性占比. 结果表明, 本研究提出的本构参数反演方法能够有效获取软骨细胞的本构参数值, 从而准确描述软骨细胞的时间依赖性力学特性, 该方法也可进一步推广到生物细胞在静态或动态负载条件下的复杂参数反演问题.      

混凝土材料动态本构参数的分阶段计算反求技术

基于不同应变率下的分离式Hopkinson压杆实验,提出了一种混凝土材料动态本构参数的分阶段反求方法。该分阶段反求方法中,结合不同的实验模型对未知参数进行敏感性分析,并依据敏感程度对参数进行分类,每类参数对应于1组实验,再利用反求方法分阶段确定各类参数,在每一类参数反求时均将上一次反求结果作为已知条件。结果表明,该分阶段反求方法充分利用所有实验的测量响应信息,能快速获取混凝土本构中较难确定的关键参数,为参数的确定提供了一种有效的途径。     

Some improvements in visco-plastic model considering dynamic recrystallization

Some improvements in Jin‘s thermal visco-plastic constitutive model considering dynamic recrysytallization is presented in this paper. By introducing the influence of the strain rate on the mobility of dynamic recovery, the improved model can be more smoothly applied to numerical simulation of material flow behaviour and microstructure prediction during hot working. Another improvement is to consider the accumulated dislocation energy in the newly recrystallized grains as a resistance to the driving force of dynamic recrystallization volume. This improvement makes the predicted results of dynamic recrystallization progress agree better with the actual physical process.Finally, some numerical examples are given to show the advantages of the improved model and the ability to predict the dynamic recrystallization.     

Amplitude dependence of filler-reinforced rubber: Experiments,constitutive modelling and FEM – Implementation

The focus of the present paper is the experimental investigation, the constitutive representation and the numerical simulation of the amplitude dependence of filler-reinforced elastomers. A standard way to investigate the dynamic properties of viscoelastic materials is via the dynamic modulus which is obtained from stress signals due to harmonic strain excitations. Based on comprehensive experimental data, an amplitude-dependent constitutive model of finite viscoelasticity is developed. The model is based on a modified Maxwell chain with process-dependent viscosities which depend on additional internal state variables. The evaluation of this thermodynamically consistent model is possible in both the time domain, via stress-time signals, and in the frequency domain, via the dynamic modulus. This property is very profitable for the parameter identification process. The implementation of the constitutive model into the commercial finite element code ANSYS with the user-programmable feature (UPF) USERMAT for large deformations in updated Lagrange formulation is presented. This implementation allows simulating the time-dependent behaviour of rubber components under arbitrary transient loading histories. Due to physical and geometrical nonlinearities, these simulations are not possible in the frequency domain. But, transient FEM computations of large loading histories are sometimes not possible in an acceptable time. In the context of the parameter identification the fundamental ideas are presented, how this problem has been solved. Transient FEM simulations of real rubber components are also shown to visualize the properties of the model in the context of the transient material behaviour.     

基于应变能法的单搭接螺栓剪切模型

为了简化复杂结构在冲击数值分析中的大量螺栓连接,可用等效的载荷位移模型代替复杂的螺栓连接关系,本文中针对单搭接螺栓连接在剪切载荷下建立了连接本构关系。首先通过对有预紧力的单搭接螺栓进行实验和精细有限元模拟,揭示了螺栓剪切载荷位移曲线的特征并针对不同特征阶段进行了相应的物理机理分析。在此基础上对于载荷位移曲线的界面黏结、部分滑移、整体滑移阶段提出了连接本构模型的基本形式和各阶段的参数估算方法。在部分滑移阶段考虑了4个方面的刚度贡献,其中部件对螺栓的支撑刚度是三维非轴对称变形问题,理论求解非常困难,本文中通过应力分布研究,采用应变能法解决了螺栓的支撑刚度的估算问题。提出的单搭接螺栓剪切模型物理含义明确,参数估算简单,准确度高。     

A modified Stillinger–Weber potential-based hyperelastic constitutive model for nonlinear elasticity

The Stillinger–Weber (SW) potential, which is a combination of the two- and three-body interaction, states that the bond energy is not only related to the distance between atoms, but also related to the bond angles subtended by this given bond and other bonds. The bond energy mechanism presented by the SW potential is different from that by the classical potentials, such as the Lennard–Jones, Tersoff and Embedded Atom potentials. Different micro energy mechanism reveals different micro fracture mechanism. The original SW potential takes the ‘ideal’ tetrahedral angle as the reference value of each bond angle in the current configuration, which makes it only applicable to the silicon materials. However, the micro fracture mechanism revealed by the SW potential should not be confined to the silicon materials. To extend the SW potential to a wider range of materials, the value of the bond angle in the reference configuration, not the ‘ideal’ tetrahedral angle, is taken as the reference value of this bond angle in the current configuration. Based on this modified SW potential, a constitutive model is developed. By this way, the micro fracture mechanism invoked by the SW potential is incorporated into the constitutive relation. Through this proposed constitutive model, it is found that the Hookean matrix derived from the SW potential matches that of a linear elastic continuum, which suggests that there exists a corresponding relationship between the micro physical parameters of SW potential and the macro material constants. The corresponding micro–macro parameter relationship is derived in this paper. To examine the application of this method to other materials, it is used to simulate the mixed fracture growth in concrete under static and dynamic load. The simulation results suggest that the present method can capture the characters of fracture growth in the quasi-brittle materials. It suggests that the constitutive model based on the modified SW potential can be applied to materials other than silicon. Because the interatomic potential-incorporated constitutive model makes the fracture criterion as the intrinsic property of a constitutive relation, it presents many advantages in fracture simulation. This paper enriches the constitutive relation with the micro fracture mechanism presented in SW potential, providing a new micro constitutive model for materials. Besides this, it also provides a feasible approach to calibrating the parameters of the SW potential for a certain material.     

Parameter identification for improved viscoplastic model considering dynamic recrystallization

The successful application of viscoplastic model considering dynamic recrystallization depends on how well the parameters are identified. However, it is difficult to obtain satisfactory parameters using conventional parameter identification methods. The reasons are due to difficulties in obtaining homogeneous deformation, high complexity of physical process described by the model and large number of parameters. In this paper, the material parameters are identified by inverse analysis. Global information on objective function is firstly studied by an improved uniform random sampling method; secondly, a hybrid global optimization method, which combines the genetic algorithm, the Levenberg–Marquardt algorithm, the augmented Gauss–Newton algorithm and the flexible tolerance method, is constructed and an inverse analysis numerical procedure, which combines the proposed optimization method with the finite element analysis, is proposed; at last, a set of satisfactory material parameters for 26Cr2Ni4MoV is obtained by the proposed inverse analysis numerical procedure.     

基于砼SHPB试验数值分析的HJC模型参数研究

为了研究混凝土HJC本构模型的参数取值及其参数对混凝土动态性能的影响,本文基于HJC模型原始参数,运用有限元软件ANSYS/LS-DYNA对混凝土SHPB试验进行了数值模拟,结果显示数值计算结果与试验结果存在一定的差异。据此根据模型中参数的物理意义确定出可能影响混凝土动态性能的关键参数,通过保持其他参数不变、改变关键参数的方法对混凝土SHPB试验进行数值分析,得到了各关键参数对混凝土动态性能的影响规律,并基于该分析结果对HJC模型的原始参数进行了修正。数值模拟结果表明,采用本文修正参数的计算结果与试验结果吻合良好,能较准确地反映混凝土的动态性能。     

ANALYSIS OF NONLINEAR DYNAMIC RESPONSE FOR VISCOELASTIC COMPOSITE PLATE WITH TRANSVERSE MATRIX CRACKS

I. INTRODUCTION The composite material and the composite structure are liable to generate damage during manufactureand under load, which will lead to a decrease of the material and structure’s mechanical properties.It is accepted that there exist four…     

Vibration analysis of linear coupled thermoviscoelastic thin plates by a variational approach

According to the integral type constitutive relation of linear coupled thermoviscoelasticity, a mathematical model of thin plates is set up by the introduction of “structural functions” and “thermal functions” in the sense of the Kirchhoff’s hypothesis. The corresponding integral type variational formulations are presented by means of modern convolution bilinear forms as well as classical Cartesian bilinear forms. The Ritz method in the spatial domain and the differentiating method in the temporal domain are used to approximate the mathematical model in a system of rectangular Cartesian coordinates. By properties of inequality and parabola, the structure of dynamic solution to vibration of a thermoviscoelastic thin plate under a harmonic thermal load is studied in the space splayed by material parameter and loading parameter. The influences of thermal excitation frequency, mechanical relaxation time and thermal relaxation time on amplitude and phase difference of steady-state vibration of a square plate are investigated by amplitude-frequency analysis and phase-frequency analysis. Double-peak resonance vibration of thermoviscoelastic plates exists for given parameters.     

高温条件下混凝土墙体的非线性分析研究

本文建立了一个弹塑性-损伤耦合本构模型用于数值模拟高温下混凝土的真实破坏过程。导出了一个利用Newton-Raphson迭代的一般的直接应力返回映射算法。同时求解应力向量和塑性、损伤的内状态变量。并推导了用于化学-热-湿-力学耦合分析的全局守恒方程Newton-Raphson迭代过程的一致性切线模量矩阵。建议了一个用于弹塑性-损伤耦合分析的两级求解过程。给出的数值例题结果显示了所提出的数法和公式的正确性,表明了所发展的弹塑性-损伤耦合本构模型在模拟高温下混凝土墙体中复杂破坏过程的能力。