含损伤演化的TM耦合数值模型及其应用研究

基于生物力学中的Wolff法则，发展了一种连续体拓扑优化的新方法. 有待优化的结构 被看作是一块遵从Wolff法则生长的骨骼，把寻找其最优拓扑的过程比拟为骨骼的重建/生 长过程. 采用骨骼的重建/生长规律作为准则更新材料分布，直至达到一个平衡状态并由此 获得结构的最优拓扑. 算例表明了所提出方法的有效性.     

A multi-scale enriched model for the analysis of masonry panels

A multi-scale model for the structural analysis of the in-plane response of masonry panels, characterized by periodic arrangement of bricks and mortar, is presented. The model is based on the use of two scales: at the macroscopic level the Cosserat micropolar continuum is adopted, while at the microscopic scale the classical Cauchy medium is employed. A nonlinear constitutive law is introduced at the microscopic level, which includes damage, friction, crushing and unilateral contact effects for the mortar joints. The nonlinear homogenization is performed employing the Transformation Field Analysis (TFA) technique, properly extended to the macroscopic Cosserat continuum. A numerical procedure is developed and implemented in a Finite Element (FE) code in order to analyze some interesting structural problems. In particular, four numerical applications are presented: the first one analyzes the response of the masonry Representative Volume Element (RVE) subjected to a cyclic loading history; in the other three applications, a comparison between the numerically evaluated response and the micromechanical or experimental one is performed for some masonry panels.     

Integrated numerical–experimental analysis of interfacial fatigue fracture in SnAgCu solder joints

In ball grid array (BGA) packages, solder balls are exposed to cyclic thermo-mechanical strains arising from the thermal mismatch between package components. Thermo-mechanical fatigue crack propagation in solder balls is almost always observed at the chip side of the bump/pad junction. The objective of the experimental part of this study is to characterize the bump/pad interface under fatigue loading. Fatigue specimens are prepared by reflowing Sn3.8Ag0.5Cu lead-free solder alloy on Ni/Au substrates. Obtained results show that fatigue damage evolution strongly depends on the microstructure. Applied strain and solder volume both have an influence on the fatigue damage mechanism. In the numerical part of the study, fatigue experiments are modeled using the finite element technique. A cohesive zone approach is used to predict the fatigue damage evolution in soldered connections. Crack propagation is simulated by an irreversible linear traction–separation cohesive zone law accompanied by a non-linear damage parameter. Cohesive zone elements are placed where failure is experimentally observed. Damage evolution parameters for normal and tangential interaction are scrutinized through dedicated fatigue tests in pure tensile and shear directions. The proposed cohesive zone model is quantitatively capable of describing fatigue failure in soldered joints, which can be further extended to a numerical life-time prediction tool in microelectronic packages.     

On the thermo-mechanical coupling in austenite–martensite phase transformation related to the quenching process

The present contribution considers modeling and simulation of the quenching process, presenting an anisothermal model formulated within the framework of continuum mechanics and the thermodynamics of irreversible processes. The energy equation thermo-mechanical coupling terms due to internal and thermal couplings are exploited. In order to analyze the importance of these terms, three different models are considered. The first one is an uncoupled model in the sense that these terms are neglected, corresponding to the rigid body energy equation. In second model, these couplings are represented through the incorporation of a source term in the energy equation associated with the latent heat released during the austenite–martensite phase transformation. Finally, the third model considers all thermo-mechanical coupling terms of the proposed model. Progressive induction hardening of a long cylindrical body is considered as an application of the proposed general formulation. Numerical simulations analyze the effect of the thermo-mechanical coupling terms, comparing the three proposed models.     

含热冲击预损伤的陶瓷基复合材料损伤本构模型

陶瓷基复合材料结构在服役过程中不可避免地经受热冲击(较高的热应力梯度)而产生热机械损伤, 因此, 建立含循环热冲击预损伤材料的损伤本构模型, 以描述材料在热机械载荷作用下的力学行为, 对材料结构损伤容限设计与结构完整性评估非常重要. 本文首先对经历了循环热冲击的材料进行单调拉伸损伤实验, 发现对于含循环热冲击预损伤的材料, 其弹性模量的下降与所施加的应变直接相关. 然后在连续介质损伤力学的框架下, 基于平面应力假设, 建立了含循环热冲击预损伤材料的损伤演化模型, 该模型所涉及的参数可通过一个偏轴(45$^\circ$)以及两个正轴(平行于两个主方向)的单调拉伸试验获得. 最后, 采用经典塑性理论对由基体损伤引起的非弹性应变进行了描述. 本文所提出的应变损伤宏观模型可以描述陶瓷基复合材料在热机械载荷作用下的损伤演化, 同时弥补了含预损伤的陶瓷基复合材料在机械载荷下损伤本构模型在理论及实验研究方面的不足.      

考虑晶体滑移面分解正应力的细观损伤模型

材料内部的解理、滑移面剥离等细观损伤是引起宏观失效的根源,从细观尺度研究损伤的发生和发展有助于深入认识材料的变形和失效过程.本文基于晶体塑性理论,从滑移系的受力和变形出发研究材料的细观损伤,建立了考虑滑移面分解正应力的细观损伤模型,为晶体材料解理断裂的分析提供了新方法.首先,在晶体弹塑性变形构型的基础上引入损伤变形梯度...     

多轴随机载荷下的疲劳寿命估算方法

现代工业的发展使得更多的构件承受着复杂的载荷形式, 将单轴疲劳模型应用到多轴载荷情况已不能满足现代工业的设计要求, 多轴随机载荷下的疲劳寿命计算日益引起人们的重视. 多轴随机载荷的寿命预测中, 如何计算载荷循环次数是其基础,目前广泛使用的是雨流计数方法, 现在已能成功的应用于多轴载荷的情况. 累积的疲劳损伤分析在各种构件和结构的载荷历史中都起着重要的作用. 自从线性损伤律提出以来已发展了数十种损伤律, 变幅载荷引起的疲劳损伤可以由许多不同的累积损伤律来计算, 虽然发展了许多损伤模型, 由于问题的复杂性, 每个模型的应用范围也是随具体情况而定. 线性损伤律方法尽管有很多不足之处, 但在设计使用中仍占有重要的位置. 两载荷水平及模式下的损伤累积以及损伤与物理机制的关系在本文中也做了介绍. 针对近年来提出的描述多轴随机载荷下疲劳寿命估算方法进行了详细的评述, 对各模型的应用范围和预测能力进行了讨论, 并对今后的工作提出了建议.      

A damage model for the blistering of polyvinylidene fluoride subjected to carbon dioxide decompression

Semicrystalline polymers (SCPs) used in complex petroleum structures are subjected to high variations of temperature and gas pressure, which induce some damage. For this reason, the Representative Volume Element (RVE) of a SCP evolving in a gaseous environment is modelled using a phenomenological approach based on the porous media theory. SCPs are in fact two-phase materials at the scale of the spherolite. One phase is crystalline (skeleton), and the other corresponds to a mixture (fluid) of gas and free amorphous medium (the latter is considered penetrable by gas). The modelling is described within the framework of the thermodynamics of irreversible processes with internal variables by considering the above RVE. An elastoviscoplastic model with cavity growth is proposed within the framework of general diffuso-mechanical continuum media. The aim is to predict the evolution of ductile damage observed during decompression. This two-phase diffuso-elastoviscoplastic-damage model is implemented in Abaqus^® software via a user subroutine. This numerical tool allows us to study the damage of polyvinylidene fluoride SCP during a rapid decompression test.The influence of the decompression rate on the evolution of initial cavities is discussed. Comparison with experiments shows the relevance of the proposed model as far as blistering is concerned. We hope that the present model can help understanding the occurrence of damage mechanisms during decompression.     

Study on cyclic deformation and fatigue of thermal and magnetic shape memory alloys

形状记忆合金(包括热致和磁致形状记忆合金)由于其特有的超弹性和形状记忆效应, 一直以来受到学者和工程界人士广泛关注, 且已有诸多成功的工程应用案例.为了进一步拓展该类合金的工程应用范围, 对其热--力和磁--力耦合循环变形和疲劳失效行为的宏微观实验观察和理论模型研究成果进行了综述. 总结了NiTi和NiTiX两类合金材料的温度诱发(即热致)的热--力耦合循环变形和疲劳失效行为研究的最新成果; 对以NiMnGa合金为代表的磁场诱发(即磁致)的磁--力耦合循环变形和疲劳失效行为的研究现状进行了评述; 提出并预测了未来的研究方向及发展趋势.     

热致和磁致形状记忆合金循环变形和疲劳行为研究

形状记忆合金(包括热致和磁致形状记忆合金)由于其特有的超弹性和形状记忆效应, 一直以来受到学者和工程界人士广泛关注, 且已有诸多成功的工程应用案例.为了进一步拓展该类合金的工程应用范围, 对其热--力和磁--力耦合循环变形和疲劳失效行为的宏微观实验观察和理论模型研究成果进行了综述. 总结了NiTi和NiTiX两类合金材料的温度诱发(即热致)的热--力耦合循环变形和疲劳失效行为研究的最新成果; 对以NiMnGa合金为代表的磁场诱发(即磁致)的磁--力耦合循环变形和疲劳失效行为的研究现状进行了评述; 提出并预测了未来的研究方向及发展趋势.      

Tension-Torsion High-Cycle Fatigue Life Prediction of 2A12-T4 Aluminium Alloy by Considering the Anisotropic Damage:Model,Parameter Identification,and Numerical Implementation

To consider the anisotropic damage in fatigue, an improved boom-panel model is presented to simulate a representative volume element(RVE) in the framework of continuum damage mechanics. The anisotropic damage state of the RVE is described by the continuity extents of booms and panels, whose damage evolutions are assumed to be isotropic. The numerical implementation is proposed on the basis of damage mechanics and the finite element method. Finally,the approach is applied to the fatigue life prediction of 2A12-T4 aluminium alloy specimen under cyclic loading of tension-torsion. The results indicate a good agreement with the experimental data.     

Model for 28CrMoV5-8 steel undergoing thermomechanical cyclic loadings

An anisothermal elastoviscoplastic three-dimensional model is proposed in order to predict the response of brake discs used in the French T.G.V. (high speed train). The brake disc is subjected simultaneously to mechanical and thermal cyclic loadings by the application of brake pads to the friction surface. This anisothermal law is based on the internal thermodynamic variables and takes into account the non-linear kinematic hardening, isotropic hardening (to describe cyclic softening) and plastic strain memory effect. Cyclic viscoplastic behavior under in-phase changes of temperature and strain is analysed by using this elaborate anisothermal model with its material constants determined from isothermal experiments. Good agreement is obtained between the predictions and experiments.     

疲劳损伤状态的试验研究

从疲劳过程中材料显微组织结构的变化特征、疲劳损伤的非线性效应等方面进行分析与论证，提出了不存在一般意义上的“等效损伤状态”的观点，采用高－低和低－高两组循环载荷下的损伤累积试验，对传统意义上的“等效损伤状态”下的剩余寿命试验进行了验证。     

Transformation-induced plasticity in high-temperature shape memory alloys: a one-dimensional continuum model

A constitutive model based on isotropic plasticity consideration ispresented in this work to model the thermo-mechanical behavior ofhigh-temperature shape memory alloys. In high-temperature shapememory alloys (HTSMAs), both martensitic transformation andrate-dependent plasticity (creep) occur simultaneously at hightemperatures. Furthermore, transformation-induced plasticity isanother deformation mechanism during martensitic transformation. Allthese phenomena are considered as dissipative processes to model themechanical behavior of HTSMAs in this study. The constitutive modelwas implemented for one-dimensional cases, and the results have beencompared with experimental data from thermal cycling test foractuator applications.     

A thermodynamic model for electrical current induced damage

Electromigration-induced damage, which is in principal an irreversible mass diffusion under high current density, has been a concern for VLSI design for a long time. Miniaturization of electronic device sizes down to nano-scale will make electromigration a concern for all conducting components. This paper uses thermodynamics, statistical mechanics and mass transport (diffusion) principals to propose a model for electromigration process and a damage evolution model to quantify the degradation in microelectronics (and micro electromechanical system) solder joints subjected to high current densities. Entropy production in the system is used as a damage metric. The irreversible thermodynamic damage model utilized in this work has previously been successfully applied to thermo-mechanical fatigue of microelectronic solder joints. In this paper we extend this model to electromigration-induced degradation.Electromigration process is modeled by the atomic vacancy flux (mass diffusion) process. The proposed unified model is compared with several existing analytical and empirical models. A comparison of the damage evolution model proposed in here agrees well with empirical models proposed in the literature.     

A penny-shaped cohesive crack model for material damage

A novel micromechanics based damage model is proposed to address failure mechanism of defected solids with randomly distributed penny-shaped cohesive micro-cracks (Barenblatt–Dugdale type). Energy release contribution to the material damage process is estimated in a representative volume element (RVE) under macro hydrostatic stress state. Macro-constitutive relations of RVE are derived via self-consistent homogenization scheme, and they are characterized by effective nonlinear elastic properties and a class of pressure sensitive plasticity which depends on crack opening volume fraction and Poisson’s ratio. Several distinguished features of the present model are compared with Gurson model and Gurson–Tvergaard–Needleman (GTN) model, showing that the proposed model can better capture material degradation and catastrophic failure due to cohesive micro-crack growth and coalescence.     

Numerical simulation of thermo-mechanical fatigue properties for particulate reinforced composites

In this paper, a two dimensional Voronoi cell element, formulated with creep, thermal and plastic strain, is applied for the numerical simulation of thermo-mechanical fatigue behavior for particulate reinforced composites. The relation between mechanical fatigue phases and thermal fatigue phases influences the thermo-mechanical fatigue behavior and cyclic creep damage. The topological features of micro-structure in particulate reinforced composites, such as the orientation, depth-width ratio, distribution and volume fraction of inclusions, have a great influence on thermo-mechanical behavior. Some related conclusions are obtained by examples of numerical simulation.The project supported by the Special Funds for the National Major Fundamental Research Projects (2004CB619304), the National Natural Science Foundation of China (10276020 and 50371042), the Key Grant Project of Chinese Ministry of Education (0306)     

Strength of damaged polycarbonate after fatigue

A fatigue damage model is proposed to establish a predictive formula for the fatigue service life of polycarbonate (PC) materials. A damage variable is introduced in terms of remaining fracture strain, and a new fatigue damage evolution relation is derived to characterize the extent of fatigue damage after a certain number of loading cycles. Fatigue tests were conducted to construct the stress amplitude versus the fatigue life curve. After different numbers of cycles of fatigue, the new damage variable for PC materials was measured by pulling damaged specimens to fracture under monotonic loading. Experimental results on damage evolution and fatigue life have a good agreement with those predicted by the proposed damage model.     

基于介观力学信息的颗粒材料损伤——愈合与塑性宏观表征

本文在二阶计算均匀化框架下提出了颗粒材料损伤--愈合与塑性的多尺度表征方法. 颗粒材料结构在宏观尺度模型化为梯度Cosserat连续体,在其有限元网格的每个积分点处定义具有离散颗粒介观结构的表征元. 建立了表征元离散颗粒系统的非线性增量本构关系. 表征元周边介质作用于表征元边界颗粒的增量力与增量力偶矩以表征元边界颗粒的增量线位移与增量转动角位移、当前变形状态下表征元离散介观结构弹性刚度、以及凝聚到表征元边界颗粒的增量耗散摩擦力表示. 基于平均场理论与Hill定理,导出了基于介观力学信息的梯度Cosserat连续体增量非线性本构关系. 在等温热动力学框架下定义了表征颗粒材料各向异性损伤--愈合和塑性的损伤、愈合张量因子与综合损伤、愈合效应的净损伤张量因子和塑性应变. 此外,定义了损伤和塑性耗散能密度与愈合能密度,以定量比较材料损伤、愈合、塑性对材料失效的效应. 应变局部化数值例题结果显示了所建议的颗粒材料损伤--愈合--塑性表征方法的有效性.