巴西圆盘劈裂破坏的近场动力学建模与分析

基于非局部近场动力学（Peridynamics,PD）理论,对含预置裂纹的混凝土巴西圆盘劈裂破坏问题进行建模分析.将结构离散为包含混凝土材料信息的粒子,引入动态松弛、分级加载和失衡力守恒等粒子系统数值算法,构建可以自然模拟脆性裂纹扩展的PD算法体系.对含不同角度单预置中心裂纹巴西圆盘的裂纹扩展过程进行数值模拟,所得结果与试验结果吻合较好,验证所提出的模型和算法正确.进一步采用该方法模拟双预置裂纹巴西圆盘劈裂破坏过程中的裂纹扩展、交汇、贯通过程,通过将所得模拟结果与试验结果进行比较分析,探究该方法处理多裂纹扩展问题的可行性.     

基于近场动力学方法的水力压裂过程数值模拟

利用近场动力学方法便于处理多裂纹萌生、扩展和分叉的优点,将其应用于页岩水力压裂过程的数值模拟.结合页岩水力压裂机理提出在近场动力学中由破坏度跟踪裂纹扩展路径,并通过在新生成裂纹面法线方向施加水压载荷的裂纹追踪方法,成功模拟单射孔横剖面开裂水压实验以及单射孔和多射孔水平井纵剖面的水力压裂过程,得到压裂导致的裂纹缝网结构.数值结果还表明初始射孔裂纹会显著影响后续的水力压裂过程.     

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.     

考虑釉面膨胀系数的陶瓷表面微裂纹扩展模拟

考虑到釉面膨胀系数对陶瓷表面微裂纹的影响,研究设计了一种陶瓷表面微裂纹扩展模拟方法.将釉面视为陶瓷基体材料中包裹的球状颗粒,基于球状颗粒半径趋于无穷大的情形,计算陶瓷材料与界面垂直的表面微裂纹的应力强度因子,然后分析热膨胀系数差对应力强度因子的影响并构建数字模型,建立符合Weibull分布的陶瓷表征单元体.从热传导和热膨胀系数等角度出发,模拟陶瓷表面微裂纹扩展情况.实验结果表明:裂纹扩展长度与膨胀系数成正比,当膨胀系数为10时,陶瓷试件表面微裂纹扩展迅速;陶瓷试件的水平方向应力随着膨胀系数的增加而增加;陶瓷表面微裂纹的长度与宽度与应力强度因子数值成正比.     

XFEM在高压管道裂纹扩展计算中的应用

介绍XFEM的基本理论,针对常规有限元计算困难的三维裂纹,运用XFEM完成三维高压管道中的裂纹扩展计算.根据管道裂纹扩展的计算结果,总结得到管道裂纹扩展的规律,得到径向裂纹比轴向裂纹更严重的结论.     

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．     

基于分形的高聚物裂纹尖端温度场建模与仿真

研究高聚物材料加工问题,含缺陷高聚物在变形与破坏过程中,相当部分的能量消耗于材料的不可逆变形,以热的形式耗散掉,形成温度场.结合分形断裂力学和含缺陷物体流变学的基本理论,从理论上推导裂纹分形维数和断裂速度的关系,为解决上述问题,采用裂尖弹塑性边界的近似模型,合理地构造热源密度函数,得到裂尖温度场模型.采用Matlab软件对含缺陷高聚物裂纹尖端温度场进行仿真,仿真结果表明温度场模型符合实际,裂尖局部温升与裂纹分形维数密切相关,局部最高温升随裂纹分形维数的增大而增大.     

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。     

计算机在Ti-6Al-4V钛合金疲劳裂纹扩展曲线绘制中的应用

利用当前通用的计算机编程技术,以高级编程语言VB为制作工具,以Origin7.0为作图工具,绘制了铸造Ti-6Al-4V钛合金疲劳裂纹扩展曲线。采用该编程技术,实现了参数的随机输入和曲线的动态形成,真实地制作了不同应力比下的疲劳裂纹扩展速率（da/dn）与裂纹尖端应力强度因子（ΔK）的关系曲线。同时该方法极大地提高了数据处理的效率及准确性。     

Application of an interface failure model to predict fatigue crack growth in an implanted metallic femoral stem

A novel computational modelling technique has been developed for the prediction of crack growth in load bearing orthopaedic alloys subjected to fatigue loading. Elastic-plastic fracture mechanics has been used to define a three-dimensional fracture model, which explicitly models the opening, sliding and tearing process. This model consists of 3D nonlinear spring elements implemented in conjunction with a brittle material failure function, which is defined by the fracture energy for each nonlinear spring element. Thus, the fracture energy criterion is implicit in the brittle material failure function to search for crack initiation and crack development automatically. A degradation function is employed to reduce interfacial fracture properties corresponding to the number of cycles; thus fatigue lifetime can be predicted. Unlike other failure modelling methods, this model predicts the failure load, crack path and residual stiffness directly without assuming any pre-flaw condition. As an example, fatigue of a cobalt based alloy (CoCrMo) femoral stem is simulated. Experimental fatigue data was obtained from four point bending tests. The finite element model simulated a fully embedded implant with a constant point load. Comparison between the model and mechanical test results showed good agreement in fatigue crack growth rate.     

Modeling crack in viscoelastic media using the extended finite element method

In this paper,the problem of modeling crack in 2D viscoelastic media is studied using the extended finite element method.The paper focuses on the definition of enrichment functions suitable for cracks assessment in viscoelastic media and the generalized domain integrals used in the determination of crack tip parameters.The opening mode and mixed mode solutions of crack tip fracture problems in viscoelastic media are also undertaken.The results obtained by the proposed method show good agreement with the ana...     

材料中应变率力学性能测试数据处理与表征方法

针对材料的中应变率力学性能测试数据,为数据处理与本构表征设计专用的分析软件。给出了载荷测量和应变测量方法,梳理了从测试数据到本构参数所历经的数据处理流程和方法,按照逻辑程序和功能模块化设计,基于MATLAB GUI平台编制了数据处理软件。利用该软件处理了S580B合金钢的测试数据,得到3种动态本构模型对应的应变强化参数和应变率敏感性参数,结果表明,Johnson-Cook模型相对于Cowper-Symonds模型和塑性随动模型更适合反映S580B合金钢的动态力学性能,拟合曲线和试验结果较为吻合。利用该专用软件,处理手段和过程完整可追溯,本构参数更容易获得,很大程度地提高了中应变率动态力学性能测试工作的效率和规范性,为冲击动力学数值仿真提供了重要的数据支持。     

Meshless Animation of Fracturing Solids

We present a new meshless animation framework for elastic and plastic materials that fracture. Central to our method is a highly dynamic surface and volume sampling method that supports arbitrary crack initiation, propagation, and termination, while avoiding many of the stability problems of traditional mesh-based techniques. We explicitly model advancing crack fronts and associated fracture surfaces embedded in the simulation volume. When cutting through the material, crack fronts directly affect the coupling between simulation nodes, requiring a dynamic adaptation of the nodal shape functions. We show how local visibility tests and dynamic caching lead to an efficient implementation of these effects based on point collocation. Complex fracture patterns of interacting and branching cracks are handled using a small set of topological operations for splitting, merging, and terminating crack fronts. This allows continuous propagation of cracks with highly detailed fracture surfaces, independent of the spatial resolution of the simulation nodes, and provides effective mechanisms for controlling fracture paths. We demonstrate our method for a wide range of materials, from stiff elastic to highly plastic objects that exhibit brittle and/or ductile fracture.     

Determination and simulation of stable crack growth in ADINA

Stable crack growth was simulated by displacing and releasing the crack-tip nodes corresponding to the J-resistance curve or a discretionary measured displacement as a function of the crack elongation Δa. For the numerical determination of J-integral, use is made both of the line integral and of the method of virtual crack elongation.

The computer simulation of fracture mechanics experiments using two-dimensional models produced a satisfactory measure of agreement.     

A cohesive approach to thin-shell fracture and fragmentation

We develop a finite-element method for the simulation of dynamic fracture and fragmentation of thin-shells. The shell is spatially discretized with subdivision shell elements and the fracture along the element edges is modeled with a cohesive law. In order to follow the propagation and branching of cracks, subdivision shell elements are pre-fractured ab initio and the crack opening is constrained prior to crack nucleation. This approach allows for shell fracture in an in-plane tearing mode, a shearing mode, or a bending of hinge mode. The good performance of the method is demonstrated through the simulation of petalling failure experiments in aluminum plates.     

某型自润滑杆端关节轴承仿真分析

为分析某型自润滑杆端关节轴承的结构、制造工艺和疲劳寿命是否满足使用要求,基于Abaqus软件建立该轴承的有限元模型,通过对产品动态加载和轴承-杆端体过盈装配进行仿真分析和试验验证轴承结构的科学性,通过对外圈挤压和车削过程进行工艺优化仿真提高轴承的密合度,通过对轴承铆压固定和轴向推出过程进行仿真确保铆压固定性能满足要求.基于杆端体S-N曲线,计算轴承疲劳寿命,并通过磨损仿真获得轴承25000次摆动的磨损量,结果认为该轴承满足设计要求.仿真结果与试验结果吻合,证明仿真方法和结果可靠.