基于代表性体积单元的双模铝基复合材料性能拟实研究

目的 研究双模铝基复合材料连续区(Continuous Region,CR)和非连续区(Discontinuous Region,DR)力学性能对材料整体力学性能的影响规律,以深入了解双模铝基复合材料的强韧化机理。方法 基于Abaqus模拟软件,以双模CNT/Al为研究对象,建立了构型尺度的代表性体积单元(RVE)模型,采用GTN(Gurson-Tvergaard-Needleman)模型来描述双模CNT/Al中CR和DR的变形力学行为,通过定义力学性能参数来简化描述CR和DR复杂的力学性能。针对双模CNT/Al的CR和DR,分别设定力学性能参数HC和HD,并进行一系列的拉伸载荷模拟,研究HC和HD对双模复合材料整体力学性能的影响规律。通过与真实双模CNT/Al的力学性能进行对比,得到双模CNT/Al中CR和DR力学性能与均匀材料力学性能的差异,最后对双模CNT/Al在变形过程中的应力分布情况和断裂后的形貌进行分析。结果 当HC小于4时,双模CNT/Al的抗拉强度随HD的增大而下降;当HC大于5时,双模CNT/Al的抗拉强度随HD的增大而增大;双模CNT/Al的屈服强度随着HD和HC的增大而增大,延伸率随着HD和HC的增大而降低。当HD或HC一定时,在HC=HD时,模型材料的延伸率最大。典型双模CNT/Al由“粗晶铝合金+CNT/超细晶Al复合材料”构成,与均匀结构的粗晶铝合金相比,其构型中粗晶铝合金的强度显著提升、塑韧性显著下降;与均匀结构的CNT/超细晶Al相比,其构型中的CNT/超细晶Al复合材料的强度小幅降低、塑韧性小幅提升。当HD大于HC时,裂纹优先在DR产生;当HD小于HC时,裂纹优先在CR区产生;当HD和HC接近时,裂纹产生的区域更加分散。结论 建立了一种双模铝基复合材料的有限元模型,从数值上说明了双模CNT/Al复合材料微区与均匀材料的力学性能存在显著差异,为双模铝基复合材料的设计提供了参考。     

Representative volume: Existence and size determination

The concept of the representative volume element (RVE) is analysed in the present paper. For elastic materials the RVE exists and one can determine the size of the RVE. However, for other applications, such as the case of softening materials, the RVE may not exist. In the present work the RVE has been investigated for different stages of the material response, including pre- and post-peak loading regimes. Results were based on a statistical analysis of numerical experiments, where tests have been performed on a random heterogeneous material.     

粘弹阻尼结构动态性能的有限元分析

考虑到阻尼材料的频率依赖性,提出了一种研究粘弹阻尼结构动态力学性能的迭代有限元模拟分析方法。用这种迭代算法计算了几种典型阻尼结构 悬臂梁和压筋板的模态参数,计算结果与试验模态分析结果或理论解析计算的结果基本一致。此外,还探讨了有限元模拟单元的类型对计算结果的影响。     

水泥基材料的微观结构与离子传输性能

采用水泥基材料孔结构和界面过渡区逐渐优化的方法,设计了普通混凝土(Ordinary Concrete,简称OC)、高性能混凝土(High Performance Concrete,简称HPC)、低渗透混凝土(Low Permeability Concrete,简称LPC)、普通砂浆(Ordinary Mortar,简称OM)、无细观界面过渡区水泥基复合材料(Meso-interfacial transition zone-free cement-based materials,简称MIF)等5种水泥基材料,其抗离子渗透性能排列顺序为:LPC>HPC>OC,OM>OC,MIF>OM,MIF>LPC,其孔隙率、最可几孔径、孔径≥50nm的孔含量的排列顺序均为:LPC相似文献   

Numerical Simulation of the Mechanical Properties of Sintered and Bonded Perforated Hollow Sphere Structures (PHSS)

This paper investigated the uniaxial mechanical properties of a new type of hollow sphere structures. For this new type, the sphere shell was perforated by several holes in order to open the inner sphere volume and surface. The mechanical properties, i.e. elastic properties and initial yield stress of perforated hollow sphere structures (PHSS) in a primitive cubic arrangement were numerically evaluated for different hole diameters and different joining techniques of the hollow spheres. The results are compa...     

A crystal plasticity study of cyclic constitutive behaviour, crack-tip deformation and crack-growth path for a polycrystalline nickel-based superalloy

Crystal plasticity has been applied to model the cyclic constitutive behaviour of a polycrystalline nickel-based superalloy at elevated temperature using finite element analyses. A representative volume element, consisting of randomly oriented grains, was considered for the finite element analyses under periodic boundary constraints. Strain-controlled cyclic test data at 650 °C were used to determine the model parameters from a fitting process, where three loading rates were considered. Model simulations are in good agreement with the experimental results for stress–strain loops, cyclic hardening behaviour and stress relaxation behaviour. Stress and strain distributions within the representative volume element are of heterogeneous nature due to the orientation mismatch between neighbouring grains. Stress concentrations tend to occur within “hard” grains while strain concentrations tend to locate within “soft” grains, depending on the orientation of grains with respect to the loading direction. The model was further applied to study the near-tip deformation of a transgranular crack in a compact tension specimen using a submodelling technique. Grain microstructure is shown to have an influence on the von Mises stress distribution near the crack tip, and the gain texture heterogeneity disturbs the well-known butterfly shape obtained from the viscoplasticity analysis at continuum level. The stress–strain response near the crack tip, as well as the accumulated shear deformation along slip system, is influenced by the orientation of the grain at the crack tip, which might dictate the subsequent crack growth through grains. Individual slip systems near the crack tip tend to have different amounts of accumulated shear deformation, which was utilised as a criterion to predict the crack growth path.     

Automatic finite element meshing of planar Voronoi tessellations

The concept of Voronoi tessellation has recently been extensively used in materials science, especially to model the geometrical features of random microstructures like aggregates of grains in polycrystals, patterns of intergranular cracks and composites. Solution of the underlying field equations usually requires use of numerical methods such as finite elements.The framework for automatic generation of quadrilateral finite element meshing of planar Voronoi tessellation is proposed in the paper, resulting in a powerful set of tools to be used in the rather wide field of micromechanics. As far as feasible, the implementation of features built in commercially available mesh generators was pursued. Additionally, the minimum geometric requirements for a “meshable” tessellation are outlined.Special attention is given to the meshes, which enable explicit modelling of grain boundary processes, such as for example contact (closure of cracks) or friction between grains. This is inline with numerical examples, which are oriented towards the fracture mechanics, in particular to the development of intergranular microcracks and/or their impact on the effective behaviour of the polycrystal.The examples were evaluated using the commercially available general-purpose finite element code abaqus. The usual continuum mechanics based numerical methods and boundary conditions were safely applied to aggregates of randomly oriented polycrystals with anisotropic elastic material behaviour as computational domains.     

硬泡沫塑料的力学性能分析:压缩弹性模量分析与计算机摸拟

对包装行业中常用的一类包装材料—硬泡沫塑料的压缩弹性模量的估算方法进行了探讨，发展了以力学模型为基础的随机模拟方法。以PUR发泡硬泡沫塑料为例，将此方法的计算结果与试验数据进行了比较。本方法既反映泡沫塑料的结构的力学性质，又体现了结构参数的随机特征，并且算法简单，编程容易，耗机时小，利于工程应用。     

Microstructure and mechanical properties of AZ31 alloy ring processed by hot forging

AZ31 alloy ring was successfully processed by hot forging. The effects of effective strain and temperature distributions on the microstructure and the relationship between microstructure and mechanical properties of the ring were investigated. The effective strain distribution at the centre region is relatively uniform, while the temperature in or near the flash region is higher than the other regions. A refined but inhomogeneous microstructure is obtained in the ring. It shows that the larger the accumulated strain and the lower the temperature are, the finer and more homogeneous the microstructure will be achieved. The mechanical responses of the ring from different tensile directions differ greatly. The radial direction sample shows the lowest yield strength and the largest fracture elongation.     

聚乙烯包装薄膜形变性能与微观结构的研究

采用拉伸实验，研究形变速率对聚乙烯包装薄膜力学性能的影响。采用Ｘ射线衍射方法，分析聚乙烯薄膜形变后微观结构的变化，得到了形变后材料内部的微晶尺寸和点阵畸变值。     

Mechanical response of cellular solids: Role of cellular topology and microstructural irregularity

Rapid advance in additive manufacturing techniques promises that, in the near future, the fabrication of functional cellular structures will be achieved with desired cellular microstructures tailored to specific application in mind. In this perspective, it is essential to develop a detailed understanding of the relationship between mechanical response and cellular microstructure. The present study reports on the results of a series of computational experiments that explore the effect topology and microstructural irregularity (or non-periodicity) on overall mechanical response of cellular solids. Compressive response of various 2D topologies such as honeycombs, stochastic Voronoi foams as well as tetragonal and triangular lattice structures have been investigated as functions of quantitative irregularity parameters. The fundamental issues addressed are (i) uniqueness of mechanical response in irregular microstructures, and effects of (ii) specimen size, (iii) boundary morphology, (iv) cellular topology, and (v) microstructural irregularity on mechanical response.     

元胞自动机模型方法及其在材料组织结构模拟中的应用

元胞自动机是复杂体系的一种理想化模型 ,它对处理那些难以用数学定量描述的复杂动态体系问题如材料的组织结构演变问题有独到之处 ,并且特别便于计算机模拟实施。本文介绍了元胞自动机的基本思想、分类与特征 ,并综述了元胞自动机模型方法在材料的凝固结晶、再结晶和晶粒长大以及相沉淀和相分解的模拟研究中的应用。     

Estimation of residuals for the homogenized solution: The case of the beam with random Young's modulus

In this paper the estimation of residuals for the homogenized solution in elastic problem is taken into account. The case of the beam with Young's modulus randomly varying along the axis is considered. The analysis is performed by means of numerical simulation which is validated by comparison with particular solutions reported in the literature. The convergence to the homogenized solution and the behavior of the residuals are studied in terms of the parameter ɛ, which represents the ratio between the microscopic and the macroscopic scale. After validation with the literature results, the procedure is used to analyze the influence on the convergence of the correlation law of Young's modulus with log-normal distribution. Moreover the particular case of the two-phase beam is considered. The effect of different boundary conditions is also investigated.     

Comparison of Cellular Automaton and Phase Field Models to Simulate Dendrite Growth in Hexagonal Crystals

A cellular automaton (CA)-finite element (FE) model and a phase field (PF)-FE model were used to simulate equiaxed dendritic growth during the solidification of hexagonal metals.In the CA-FE model,the conservation equations of mass and energy were solved in order to calculate the temperature field,solute concentration,and the dendritic growth morphology.CA-FE simulation results showed reasonable agreement with the previously reported experimental data on secondary dendrite arm spacing (SDAS) vs cooling rate.In the PF model,a PF variable was used to distinguish solid and liquid phases similar to the conventional PF models for solidification of pure materials.Another PF variable was considered to determine the evolution of solute concentration.Validation of both models was performed by comparing the simulation results with the analytical model developed by Lipton-Glicksman-Kurz (LGK),showing quantitatively good agreement in the tip growth velocity at a given melt undercooling.Application to magnesium alloy AZ91 (approximated with the binary Mg-8.9 wt% Al) illustrates the difficulty of modeling dendrite growth in hexagonal systems using CA-FE regarding mesh-induced anisotropy and a better performance of PF-FE in modeling multiple arbitrarily-oriented dendrites growth.     

活化元素Co对Mo-Cu合金组织和性能的影响

采用机械合金化制备Mo-18Cu复合材料,利用SEM、XRD和万能试验机研究了Co含量对Mo-18Cu合金的相对密度、力学性能、断口形貌组织、导热和导电性能的影响。试验结果表明,活化元素Co的添加降低了Mo-18Cu合金的烧结致密化温度100℃,增加了合金的相对密度、抗弯强度及硬度,但导电和导热性能降低。含Co 2.0wt%Mo-18Cu合金在1250℃烧结2h获得较好的综合性能,合金的相对密度、抗弯强度、硬度、电阻率和热导率分别为99.1%,960 MPa,69 HRA,2.06×10-7Ωm和142 W.m-1.K-1。显微组织为均匀细小的网络结构。     

纳米材料结构与性能的计算机模拟研究

先进的理论和计算技术结合计算机的威力，提供了在原子层次上了解纳米材料及其演化过程细节的可能性，具有无先例的准确性，使纳米材料设计和性能预测成为可能。本文首先概送了计算机模拟的理论方法和作用，扼要地综述了计算机模拟在纳米材料的微观结构、力学、热学、电磁学等性能的研究进展，最后阐述了纳米材料结构和性能的计算机模拟研究所面临的问题。