Abaqus/CAE高级实用技巧

Abaqus新提出的扩展有限元法（ExtendedFiniteElementMethod,XFEM）在解决裂纹扩展问题时有何优点？如何在Abaqus／CAE中设置？对于裂纹扩展问题,传统的有限元法一般采用预先埋设裂纹路径或网格重新划分的方法,让其沿网格扩展,这对模型网格的要求非常高．XFEM能克服以上弊端,在应力集中或裂纹尖端等高应力区域自动将每个单元剖分为2个单元,在模拟裂纹生长时无须重新剖分网格．     

基于XFEM和正交实验法的裂纹参数对扭杆强度影响的分析

为研究裂纹对扭杆安全运行的影响,采用扩展有限元法（eXtended Finite Element Method, XFEM）对其进行裂纹扩展分析,并结合正交实验法研究裂纹参数对扭杆强度的影响.结果表明：裂纹的长度对扭杆强度影响最大,裂纹的形状对扭杆强度影响最小.该数值分析方法可应用于扭杆的设计和检修中.     

ALOF——新一代三维疲劳裂纹扩展分析软件

针对当前亟需开发能分析和评估含缺陷工程结构及装备的专业商业软件的现况,基于成熟的扩展有限元法(eXtended Finite Element Method,XFEM)和自主研发的虚节点法(Virtual Node Method,VNM),推出具有完全自主知识产权的三维疲劳裂纹扩展分析软件ALOF(Analyses Laboratory of Fracture).介绍ALOF求解断裂问题的流程及其特点:可以方便地导入完整的CAD模型及多种形式的裂纹模型,可以自动生成疏密合理的二维和三维裂纹扩展分析网格;具有丰富的失效准则库;能自动分层加密裂尖区域网格;能全自动地进行裂纹扩展计算等.与同类软件相比,ALOF更简单、更精准、更高效和更专业.利用ALOF进行的3个实际工程案例表明,ALOF能准确、高效评估任意复杂缺陷体的剩余强度和疲劳寿命.     

基于XFEM的折弯片断裂仿真

采用Abaqus的XFEM功能对折弯片的断裂问题进行仿真,断裂区为转角处的过渡区域.转角处圆弧的半径影响裂纹的开裂时间.裂纹的扩展路径具有任意性,细化网格下裂纹扩展方向不稳定,会超出断裂区.1阶单元和1阶减缩积分单元的分析结果比较接近.通用静态分析比动态隐式分析效率更高一些.在端部压力的作用下,折弯片约在1 ms内开裂,8 ms完全断开.Cohesive element算法的裂纹路径较LEFM方法更平滑一些.     

基于二次插值重构有限元法的动态裂纹扩展模拟

基于二次插值重构有限元法（Twice interpolation Finite Element Method, TFEM）分析动态断裂力学问题并进行数值实验,考察TFEM在裂纹动态扩展模拟中的准确性和可靠性.由于TFEM保证节点处梯度场的连续性,因此裂尖附近的应力场可以得到较好的逼近.把该算法成功移植到自主开发的三维裂纹扩展仿真软件（ZonCrack）中.利用ZonCrack进行的裂纹扩展,分析结果表明：TFEM得到裂尖应力强度因子（Stress Intensity Factor, SIF)与解析解基本一致;裂纹扩展的模拟结果与实验值吻合良好.     

孔边角疲劳裂纹的扩展仿真及分析

给出了一种利用有限元技术模拟周期性张力载荷作用下孔边角裂纹扩展过程的方法。首先利用一系列点定义裂纹前沿,据此形成包含奇异单元的二维有限元网格,再扩展为三维网格．然后利用有限元法进行应力应变分析,最后使用Paris定律计算局部扩展增量．以此来更新裂纹的形状和尺寸。该方法还能够自动地重复执行扩展仿真。文中还对三个不同半径的四分之一椭圆形边角裂纹扩展过程进行了仿真和分析比较,以此来取得裂纹在扩展过程中的形状变化特征和不同方向上扩展的特征。     

基于神经网络的裂纹扩展过程预测

提出基于神经网络的裂纹扩展过程实时预测方法,其计算效率比近场动力学(peridynamic,PD)模型提高.使用PD算法获取裂纹扩展过程中的损伤云图,构建裂纹扩展数据集.基于数据集构建生成对抗网络(generative adversarial networks,GAN)模型,根据不同加载条件实时生成损伤云图,从而快速预测裂纹的扩展过程.将PD模型计算得到的损伤云图中的RGB值与相应位置处的损伤值结合,构建多层前馈神经网络模型的数据库,并使用多层前馈神经网络模型分析GAN模型产生的损伤云图,得到相应的损伤值.通过数值算例证明该方法的效率和准确性.     

基于概率断裂力学的管道疲劳寿命分析

采用奇异单元模拟裂纹尖端应力场的奇异性,计算裂纹尖端的应力强度因子和张开应力.以概率论为基础,结合确定性疲劳断裂力学估算方法,考虑参数的不确定性和随机性,应用蒙特卡洛模拟法分析管道的疲劳寿命.结果表明：通过J积分计算得到的裂纹尖端张开应力与计算得到的管道工作应力基本相等.采用蒙特卡洛模拟法进行的一定可靠度和置信度下的疲劳寿命预测能反映评定参数的不确定性,较传统的断裂力学计算结果更安全.     

半椭圆表面裂纹前缘应力强度因子的计算

在断裂力学中,如何求取应力强度因子一直是一个重要的课题.该文通过MSC.Marc提供的断裂力学模块,采用三维J积分法计算含有半椭圆表面裂纹前缘应力强度因子.首先通过MSC.Marc.Mentat建立特定裂纹体有限元模型,假设裂纹前缘处在平面应变状态下.由MSC.Marc计算出裂纹前沿的J积分,再由J积分计算出裂纹前缘的应力强度因子值.最后将计算结果与经验公式得到的结果进行了比较.仿真结果表明,通过MSC.Marc采用三维J积分法计算的应力强度因子具有较高的准确性和可靠性.     

圆柱形部件表面疲劳裂纹扩展仿真及分析

给出了一种利用有限元技术模拟周期性张力载荷作用下圆柱形部件内裂纹扩展过程的方法。首先利用一系列点定义裂纹前沿，据此形成包含奇异单元的二维有限元网格，再扩展为三维网格，然后利用有限元法进行应力应变分析，最后使用Paris定律计算局部扩展增量，以此来更新裂纹的形状和尺寸。该方法还能够自动地重复执行扩展仿真。文中还对具有不同半径比的椭圆形和具有不规则形状的初始裂纹的扩展过程进行了仿真和分析比较，以此来取得裂纹在扩展过程中的形状变化特征。     

基于扩展有限元法的黏聚性裂缝模型的混凝土梁断裂过程模拟

为研究混凝土梁的断裂过程,提出用基于二维扩展有限元法（eXtended Finite ElementMethod,XFEM）的黏聚性裂缝模型模拟混凝土简支梁在集中载荷作用下的断裂过程.推导考虑近裂尖奇异性的基于XFEM的黏聚性裂缝模型,得出裂缝开度随裂缝长度的变化曲线;对上述模型与相关文献用有限元结合节点释放技术对相同时间的裂缝扩展的计算结果进行比较,二者结果吻合良好,并与实际裂缝扩展过程相符.计算结果证实基于XFEM的黏聚性裂缝模型能有效进行混凝土梁的断裂过程模拟.     

Shape optimization for 2-D mixed-mode fracture using Extended FEM (XFEM) and Level Set Method (LSM)

Weight and service life are often the two most important considerations in design of structural components. This research incorporates a novel crack propagation analysis technique into shape optimization framework to support design of 2-D structural components under mixed-mode fracture for: (1) maximum service life, subject to an upper limit on volume, and (2) minimum weight subject to specified minimum service life. In both cases, structural performance measures are selected as constraints and CAD dimensions are employed as shape design variables. Fracture parameters, such as crack growth rate and crack growth direction are computed using extended finite element method (XFEM) and level set method (LSM). XFEM employs special enrichment functions to incorporate the discontinuity of structural responses caused by the crack surfaces and crack tip fields into finite element approximation. The LSM utilizes level set functions to track the crack during the crack propagation analysis. As a result, this method does not require highly refined mesh around the crack tip nor re-mesh to conform to the geometric shape of the crack when it propagates, which makes the method extremely attractive for crack propagation analysis. An accurate and efficient semi-analytical design sensitivity analysis (DSA) method is developed for calculating gradients of fracture parameters. Two different approaches—a batch-mode, gradient-based, nonlinear algorithm and an interactive what-if analysis—are used for optimization. An engine connecting rod example is used to demonstrate the feasibility of the proposed method.     

基于Zencrack的岸边集装箱起重机圆管构件疲劳裂纹扩展分析

由于二维裂纹扩展模式不能非常全面地反映岸边集装箱起重机结构件的疲劳裂纹扩展行为,以岸边集装箱起重机圆管构件为研究对象,利用Zencrack三维裂纹分析软件,详细分析未穿透裂纹与穿透裂纹的裂纹扩展关系,以及初始裂纹大小和载荷幅值对未穿透裂纹的疲劳裂纹扩展寿命的影响,对岸边集装箱起重机结构的抗疲劳设计及裂纹管理具有一定的参考价值。     

Numerical modeling of crack reorientation and link-up

The FRANC3D/BES software system has been used to simulate the reorientation and link-up of hydraulic fractures in three-dimensional (3D) problems. The adopted technique only needs to discretize the body surface and the crack surface. The crack propagation direction is determined using the minimum strain energy criterion. Crack propagation amount is calculated using the mode I stress intensity factor. In hydraulic fracturing, the number of multiple cracks for a given number of perforations depends on the resulting interaction of the cracks. The interaction may be expressed by the fracture stiffness which has been obtained for 3D problems in this paper.     

Three-dimensional analysis of a cohesive crack coupled with heat flux through the crack

This paper presents an algorithm for coupling cohesive crack modeling with non-stationary heat flow. Firstly, the nonlinear system of equation, based on global formulations, for such a computational model is derived. The nonlinearity here comes from nonlinear relations in the crack. The relations refer to cohesion forces and to heat flux which both depend of crack opening and additionally are dependent of temperature difference between both sides of the crack. In the paper the discontinuities of displacement field and temperature field are both approximated using XFEM. All the analysis concerning crack surface is performed using local coordinate systems for each integration point. The local coordinate system is two-dimensional for both 2D and 3D analysis. The paper is illustrated with non-stationary thermo-mechanical examples for a domain with propagating crack.     

Simulation of three-dimensional fatigue crack propagation using enriched finite elements

A three-dimensional methodology for simulation of fatigue crack propagation is presented. The method is leveraged by the use of enriched crack tip elements to compute the mixed-mode stress intensity factors. The crack growth model used and the crack propagation life calculation are also described. As examples, fatigue crack propagation of a mode-I surface crack and crack advancements of mixed-mode surface cracks are simulated. The predicted results showed excellent agreement with experimental data from the literature. Thus, it is concluded that the crack propagation method developed allows efficient and accurate simulation of three-dimensional fatigue crack propagation problems.