基于仿真和数据驱动的先进结构材料设计

先进结构材料近年来受到材料和结构设计领域的广泛关注, 这些材料一般通过多个尺度的结构设计实现各种卓越的性能. 在早期的材料设计中, 有的基于设计者的丰富经验, 从天然拓扑结构中抽象出合理的数学力学模型; 有的基于生物系统的结构和功能特点提取出仿生力学模型. 然而, 仅依靠经验性的巧妙设计很难得到最优的设计方案, 通过反复迭代设计和试验来遍历设计空间也不切实际. 为此, 拓扑优化方法被成功应用于声子晶体、元胞材料等先进结构材料的优化设计中, 但现有的拓扑优化方法在实现精准的反向设计方面尚存挑战. 基于数据驱动的机器学习方法擅长建立数据空间多维变量复杂关系, 能够揭示传统力学研究方法难以发现的更深层次的力学机理和规律, 成为力学领域崭新的研究热点. 本文系统地回顾先进结构材料设计方法的发展历程, 对比阐述各种主流设计方法, 结合本课题组的相关工作介绍数值仿真和数据驱动在先进结构材料的智能化设计方面的应用现状, 并对该领域的未来研究趋势进行探讨和展望.      

多尺度复合材料力学研究进展

多尺度复合材料力学是运用多尺度分析思想研究空间分布非均匀材料力学性能的学科, 近年来,多 组分、多层级先进材料的蓬勃发展和微纳米实验观测手段的不断进步,有力地推动了该学科的研究,论文围绕非均 匀材料力学性能的多尺度分析,首先从微纳米尺度到宏观尺度综述了常用的理论分析方法;接着分别针对非均匀 连续介质和离散体系介绍了常用的多尺度计算模拟方法;然后结合本课题组在纳米复合材料、抗冲击吸能材料、随 机网络材料和多层级自相似材料等方面的研究工作,举例说明了如何综合运用多种方法对各种复杂材料系统进行 多尺度分析;最后,展望了该领域还需进一步发展和完善的若干方向。     

Homogenization of the viscoelastic heterogeneous materials with multi-coated reinforcements: an internal variables formulation

In this work, a new homogenization method to estimate the effective behavior of viscoelastic heterogeneous materials with multi-coated reinforcements is presented. Unlike classical methods that are based on the Laplace transform, the present internal variables formulation operates directly in the time domain. Using the Green’s function techniques, the micromechanical approach is based on establishing a new integral equation adapted to scale transition methods. Using this integral equation, we apply a generalized self-consistent scheme to determine the local stress concentration equations and the effective behavior of multi-coated inclusion-reinforced materials. To assess the reliability of our model, some applications to the isotropic viscoelastic heterogeneous materials with homothetic spherical inclusions are given. The model is applied to the case of two-phase and three-phase materials, and the results are compared to exact solutions. Results for three-phase materials are presented regarding the influence of soft and stiff viscoelastic interphase on the effective behavior of heterogeneous materials.     

On Macrocrack–Microdefect Interaction

A review is given of studies devoted to problems and methods of evaluating the effective resistance to macrocrack growth in materials with microdamages and in materials reinforced with small rigid inclusions under mechanical and thermal loads. Also an analysis is made of the three-dimensional interaction of penny-shaped microcracks and macrocracks in isotropic and transversely isotropic materials. Related publications based on methods and models other than those used by the authors are reviewed.     

复合材料有效弹性性质分析方法eeeeee

建立复合材料的有效性质与微结构参数的关联,是复合材料优化设计的基础。本文具体针对有效弹性性质,重点介绍了建立有效性的基本思路 和主要分析方法。首先讨论了代表单元的概念,然后分别从复合材料有效性质的普适关系、界限理论和近似方法三个不同的视角较全面的介绍了建立非均质材料有效性质的方法、主要结果和最新进展。重点从构型的概念和微结构分布形式上分析了各种模型间及分析方法之间的联系与差别。最后还就建立非均质材料有效性质中存在的问题和研究热点做了简单的介绍。     

在材料研制中的连续介质细观力学有限元建模现状评论（译文）

评述了机械载荷下材料力学行为有限元模拟的先进技术.分析 了考虑材料微观及细观结构情况下，对材料变形、损伤、断裂进行模 拟时各种方法的优缺点及发展前景.阐述了对材料行为模拟方法的发 展，包括基本的及先进的方法，如体胞方法、真实结构模拟、粘结区 模型等.分析了在先进新材料的开发中运用有限元方法的可能性     

Physical Principles of Methods for Measuring Viscoelastic Properties

The main methods used to measure viscoelastic properties of materials in a wide range of frequencies from 10^?4 to 10⁶ Hz are reviewed. It is demonstrated that the accuracy of many experimental methods can be increased by taking into account the form factors, which depend on the specimen type. An example of the form factor for a cylindrical specimen is provided, which is determined numerically on the basis of a two-dimensional deformation model taking into account the specimen geometry and Poisson’s ratio. The importance of the precise determination of Poisson’s ratio for rubber-like and complex-structured materials is demonstrated. Requirements to such measurements and a setup satisfying these requirements are described. Two methods for measuring viscoelastic properties of living tissues (compliance and disturbance propagation velocity) are considered. Based on the developed method of measuring these parameters for materials with a fixed thickness, methods for the creation of a unified standard of measurements of viscoelastic characteristics of living tissues are proposed.     

On the methodologies of stress analysis of composite structures: Part 2: New experimental approaches

The rapidly increasing technological importance of composite materials and composite structures is leading to the development of new, more advanced models of their actual response to mechanical and thermal loads. This in turn results in the development of new experimental and analytical methods for determination of the mechanical and thermal responses of such structures and materials to various loads. In this respect the reliability and the predictive power of various methods and techniques of stress analysis become very important since all the analytical, experimental and numerical methods used for the determination, prediction and optimization of the actual mechanical responses of composite structures and materials are based on the concepts of strain and stress. Because of the inherently three-dimensional stress and strain states in composite materials and structures and the wide use of viscoelastic polymers as the matrix and some reinforcing fiber materials, a more rigorous type of modelling than had been common in the past is needed of all the involved physical phenomena which influence the strain and stress states at the local and global levels. Also, a more rigorous analysis of practical consequences of the physical and mathematical simplifications is required to assure reliability and accuracy of various methods of stress analysis. The influence of the above-mentioned factors on the reliability and applicability of analytical and experimental procedures is illustrated by examples of actual material responses.Part 2 of this paper presents theories and techniques of three new methods of strain/stress analysis which have been developed on the basis of comprehensive physical models of involved phenomena: the isodyne, strain gradient and thermoelastic effect methods. Presented examples illustrate the efficacy of these methods.     

功能梯度材料断裂行为实验研究

功能梯度材料作为一种新型材料在众多领域中有着重要的应用价值,其断裂问题是固体力学与材料科学共同关注的课题. 目前,功能梯度材料断裂力学研究工作主要集中在理论分析和数值模拟两方面,实验研究相对较少,其中的大部分实验工作只关注功能梯度材料的宏观断裂性能,而缺乏对其微观断裂机理的研究.本文对近10年来功能梯度材料断裂行为的实验研究的进展予以介绍和评述.首先介绍了可应用于功能梯度材料断裂行为研究的实验方法,然后介绍了相关实验工作的进展和取得的成果,最后分析了实验工作的不足之处,从实验研究角度提出了下一阶段功能梯度材料断裂行为的研究重点.      

Electron Moiré method

It is very important to measure local deformations for an in-depth understanding of mechanical properties and fracture mechanism of structural and functional materials. In this paper, different types of model grid fabrication methods and many types of electron Moiré methods using an electron beam drawing system, a scanning electron microscope or a focus ion beam are reported, together with their applications in the measurement of deformations occurring in various engineerings and materials science research.     

SPD纳米材料制备方法及其力学特性

剧烈塑性变形(severe plastic deformation, SPD)纳米化技术是近年来发展的一种力致材料纳米化方法.该方法克服了由粉体压合法带来的残余空隙、球磨法带来的杂质等不足,并且适用于不同形状尺寸的金属、合金、金属间化合物等,因此受到了越来越多的关注.介绍了SPD纳米材料的制备方法及相关纳米材料力学性能研究的现状,并展望了对SPD力致纳米材料的研究趋势.      

裂纹扩展量的检测技术

本文介绍能直接测量裂纹扩展量的涡流探头自动跟踪裂纹法及裂纹扩展计法。它们的共同特点是标定曲线与试件材料无关,并具有通用性。实践表明这些方法是有效和可靠的,且精度较高,也容易实现数据采集与处理自动化。     

负泊松比材料和结构的研究进展

负泊松比材料和结构具有特殊的力学性能,在单轴压力(拉力)作用下发生横向收缩(膨胀).其在抗剪承载力、抗断裂性、能量吸收和压陷阻力等方面比传统材料更有优势,因而负泊松比材料在医疗设备、传感器、防护设备、航空航海及国防工程等领域有广泛的应用前景,但目前负泊松比材料的应用与普及仍面临一些挑战.本文广泛讨论了国内外关于负泊松比材料的研究成果并介绍了负泊松比材料的最新进展,将负泊松比材料大体概括为以下4类:天然负泊松比材料、胞状负泊松比材料、金属负泊松比材料、多重和复合负泊松比材料.主要介绍了各种负泊松比材料的内部结构、负泊松比机理、力学性能以及在各行各业的新发明、新应用.针对目前负泊松比材料研究理论和实验成果多,而实际应用仍然较少的情况,指出了负泊松比材料的缺点及其推广所面临的挑战.目前负泊松比材料面临的主要问题是制造成本高、孔隙率大而承载力不足以及仅适用于小应变情况等.本文针对此情况详细介绍了金属负泊松比材料及其设计和制作的方法,改善负泊松比材料的不足并推广其应用.      

Extended multiscale finite element method for mechanical analysis of heterogeneous materials

An extended multiscale finite element method （EMsFEM） is developed for solving the mechanical problems of heterogeneous materials in elasticity.The underlying idea of the method is to construct numerically the multiscale base functions to capture the small-scale features of the coarse elements in the multiscale finite element analysis.On the basis of our existing work for periodic truss materials, the construction methods of the base functions for continuum heterogeneous materials are systematically introduced. Numerical experiments show that the choice of boundary conditions for the construction of the base functions has a big influence on the accuracy of the multiscale solutions, thus,different kinds of boundary conditions are proposed. The efficiency and accuracy of the developed method are validated and the results with different boundary conditions are verified through extensive numerical examples with both periodic and random heterogeneous micro-structures.Also, a consistency test of the method is performed numerically. The results show that the EMsFEM can effectively obtain the macro response of the heterogeneous structures as well as the response in micro-scale,especially under the periodic boundary conditions.     

压电材料中的Bueckner功共轭积分及和J积分M积分的关系

研究横观各向同性压电材料中裂纹问题,提出了Bueckner功共轭积分在这类材料中的表达式：并通过引出两类辅助的应力-位移-电位移-电势场,证明功共轭积分和这类材料中的J积分和M积分仍然存在简单的两倍关系由此,各类在脆性材料断裂问题中已广泛应用的权函数方法可顺理成章地推广到压电材料的研究中来．这对独立地确定电位移强度因子和经典的I、II型应力强度因子提供了有力的数学上的工具．进而通过计算机械应变能释放率对压电材料中裂纹的稳定做出判断．     

New integral formulation and self-consistent modeling of elastic–viscoplastic heterogeneous materials

Predicting the overall behavior of heterogeneous materials, from their local properties at the scale of heterogeneities, represents a critical step in the design and modeling of new materials. Within this framework, an internal variables approach for scale transition problem in elastic–viscoplastic case is introduced. The proposed micromechanical model is based on establishing a new system of field equations from which two Navier’s equations are obtained. Combining these equations leads to a single integral equation which contains, on the one hand, modified Green operators associated with elastic and viscoplastic reference homogeneous media, and secondly, elastic and viscoplastic fluctuations. This new integral equation is thus adapted to self-consistent scale transition methods. By using the self-consistent approximation we obtain the concentration law and the overall elastic–viscoplastic behavior of the material. The model is first applied to the case of two-phase materials with isotropic, linear and compressible viscoelastic properties. Results for elastic–viscoplastic two-phase materials are also presented and compared with exact results and variational methods.     

Shear modulus of transversely isotropic materials

A new and simple method is presented to determine the inde-pendent shear modulus of transversely isotropic material.Mathematical formulation,derivation and solution are given,and test apparatus and results are presented.The method wastested on one of such materials-Green River Formation oilshale.Comparisons wich other approximate results and acou-stical methods are made.Confirmation of the test methodwith materials having known shear moduli is also presented.     

正交异性动态光弹性方法的几个基本问题的研究

文章对适用于动态研究的正交异性光弹性复合材料进行了分析，详细说明了光弹性复合材料中残余双折射的确定方法；基于静态下Ｈｙｅｒ和Ｌｉｕ应力－光性定律，提出了正交异性动态应力－光性定律，并对正交异性材料的动态力学参数及动态光弹性常数给出了实用的标定方法；最后，利用三个单轴压缩试件（０°，９０°及４５°），采用动态应变测量方法，证实了单轴应力状态下正交异性动态应力－光性定律的正确性。     

复相材料中第二相的空间分布状况的描述方法综述

对复相材料二维截面中第二相的空间分布状况的多级判别的模式识别方法作了较全面的综述,并对第二相的三维空间分布状况的一些体视学观测研究方法,尤其是近年来发展的新方法作了较为系统的介绍．指出在实际材料微结构设计和性能预测的过程中,应针对所研究的具体的材料特点、具体的机械性能类型以及材料性能力学计算工作的需求来确定恰当的描述尺度,选择合适的描述方法,以确定夹杂物或第二相的空间分布对材料机械性能的定量影响,尤其应注意发挥体视学在其中的重要作用．     

五零能模式材料设计的非线性有限元计算方法

五零能模式材料是一种新型人工超材料,特征为其弹性模量矩阵的6个特征值中5个为零,可用等效体积模量来描述,表现出类似流体的性质,可被应用于声学隐声斗篷的设计中。然而,根据A.N.Norris[1]提出的理论,设计五零能模式材料时,与应用变换声学方法设计一般声学人工超材料不同,要求其满足一非线性偏微分方程约束。本文利用非线性有限元的完全拉格朗日方法,推导了这一偏微分方程的弱形式,并给出了相应的非线性有限元计算列式,以及迭代求解的具体算法。最后,给出了五零能摸式材料设计的二维和三维坐标变换数值算例。