Generating surface crack patterns

We present a method for generating surface crack patterns that appear in materials such as mud, ceramic glaze, and glass. To model these phenomena, we build upon existing physically based methods. Our algorithm generates cracks from a stress field defined heuristically over a triangle discretization of the surface. The simulation produces cracks by evolving this field over time. The user can control the characteristics and appearance of the cracks using a set of simple parameters. By changing these parameters, we have generated examples similar to a variety of crack patterns found in the real world. We assess the realism of our results by comparison with photographs of real-world examples. Using a physically based approach also enables us to generate animations similar to time-lapse photography.     

A hybrid finite element-scaled boundary finite element method for crack propagation modelling

This study develops a novel hybrid method that combines the finite element method (FEM) and the scaled boundary finite element method (SBFEM) for crack propagation modelling in brittle and quasi-brittle materials. A very simple yet flexible local remeshing procedure, solely based on the FE mesh, is used to accommodate crack propagation. The crack-tip FE mesh is then replaced by a SBFEM rosette. This enables direct extraction of accurate stress intensity factors (SIFs) from the semi-analytical displacement or stress solutions of the SBFEM, which are then used to evaluate the crack propagation criterion. The fracture process zones are modelled using nonlinear cohesive interface elements that are automatically inserted into the FE mesh as the cracks propagate. Both the FEM’s flexibility in remeshing multiple cracks and the SBFEM’s high accuracy in calculating SIFs are exploited. The efficiency of the hybrid method in calculating SIFs is first demonstrated in two problems with stationary cracks. Nonlinear cohesive crack propagation in three notched concrete beams is then modelled. The results compare well with experimental and numerical results available in the literature.     

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.     

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。     

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。     

高压引水隧洞混凝土衬砌开裂分析

为研究高压引水隧洞混凝土衬砌开裂问题,根据引水隧洞渗流场和应力场间的耦合作用,将隧洞衬砌作为透水介质;考虑渗透系数与体积应变的关系,建立渗透系数的动态演化模型;根据单裂缝宽度与等效渗透系数的关系确定裂缝开裂位置和裂纹宽度.将该方法应用于某二级水电站高压引水隧洞衬砌开裂分析,结果表明该方法能较好地判断裂缝分布和宽度.     

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.     

Numerical–experimental crack growth analysis in AA2024-T3 FSWed butt joints

This paper deals with a numerical and experimental investigation on the influence of residual stresses on fatigue crack growth in AA2024-T3 friction stir welded butt joints. The computational approach is based on the sequential usage of the Finite Element Method (FEM) and the Dual Boundary Element Method (DBEM). Linear elastic FE simulations are performed to evaluate the process induced residual stresses, by means of the contour method. The computed stress field is transferred to a DBEM environment and superimposed to the stress field produced by a remote fatigue traction load applied on a friction stir welded cracked specimen; the crack propagation is then simulated according to a two-parameter growth model. Numerical results have been compared with experimental data showing good agreement and evidencing the predictive capability of the proposed method. The obtained results highlight the influence of the residual stress distribution on crack growth.     

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.     

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.     

基于图像处理技术的混凝土路面裂缝检测方法

为了提高公路混凝土路面病害的检测效率,采用图像处理技术实现了路面裂缝的自动识别和病害参数的自动提取。首先通过阈值分割法检测出路面裂缝,根据线性和网状裂缝图像背景连通域数量的差异,采用区域标记法计算背景连通域的数量实现了裂缝分类;其次根据线性裂缝几何形态的差异性,通过投影法实现了横、纵和斜向裂缝的细分;最后对线性裂缝提取裂缝骨架并细化求出其长度、平均宽度等病害参数;对于网状裂缝通过求其最小外接矩形计算其破损面积。     

Pavement crack detection using hessian structure propagation

Pavement images are widely used in transportation agencies to detect cracks accurately so that the best proper plans of maintenance and rehabilitation could be made. Although crack in a pavement image is perceived because the intensity of crack pixels contrasts with that of the pavement background, there are still challenges in distinguishing cracks from complex textures, heavy noise, and interference. Unlike the intensity or the first-order edge feature of crack, this paper proposes the second-order directional derivative to characterize the directional valley-like structure of crack. The multi-scale Hessian structure is first proposed to analytically adapt to the direction and valley of cracking in the Gaussian scale space. The crack structure field is then proposed to mimic the curvilinear propagation of crack in the local area, which is iteratively applied at every point of the crack curve to infer the crack structure at the gaps and intersections. Finally, the most salient centerline of the crack within its curvilinear buffer is exactly located with non-maximum suppression along the perpendicular direction of crack. The experiments on large numbers of images of various crack types and with diverse conditions of noise, illumination and interference demonstrate the proposed method can detect pavement cracks well with an average Precision, Recall and F-measure of 92.4%, 88.4%, and 90.4% respectively. Also, the proposed method achieves the best performance of crack detection on the benchmark datasets among methods that also require no training and publicly offer the detection results for every image.     

基于曲率滤波和N-P准则的路面裂缝识别方法

针对沥青路面裂缝不连续问题,提出一种基于曲率滤波和N-P准则的裂缝识别方法。通过组合最小矩形切平面和最小三角切平面及修正正则能量项的改进型曲率滤波算法,消除随机噪声并平滑纹理。采取二次分割策略提取疑似裂缝目标和运用裂缝几何特性去除块状或点状噪声,实现裂缝定位和获取裂缝片段。在此基础上,融合裂缝片段的位置和方向信息,提出利用N-P准则连接裂缝片段的端点,从而获得完整裂缝数据。研究结果表明,提出的方法对横裂、纵裂、块裂及龟裂等裂缝都具有较好的检测效果和较高的检测精度,裂缝检测的完整性达到90.5%以上。     

Multi-scale boundary element modelling of material degradation and fracture

In the present paper a multi-scale boundary element method for modelling damage is proposed. The constitutive behaviour of a polycrystalline macro-continuum is described by micromechanics simulations using averaging theorems. An integral non-local approach is employed to avoid the pathological localization of micro-damage at the macro-scale. At the micro-scale, multiple intergranular crack initiation and propagation under mixed mode failure conditions is considered. Moreover, a non-linear frictional contact analysis is employed for modelling the cohesive-frictional grain boundary interfaces. Both micro- and macro-scales are being modelled with the boundary element method. Additionally, a scheme for coupling the micro-BEM with a macro-FEM is also proposed. To demonstrate the accuracy of the proposed method, the mesh independency is investigated and comparisons with two macro-FEM models are made to validate the different modelling approaches. Finally, microstructural variability of the macro-continuum is considered to investigate possible applications to heterogeneous materials.     

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...     

Automatic LEFM crack propagation method based on local Lepp–Delaunay mesh refinement

A numerical method for 2D LEFM crack propagation simulation is presented. This uses a Lepp–Delaunay based mesh refinement algorithm for triangular meshes which allows both the generation of the initial mesh and the local modification of the current mesh as the crack propagates. For any triangle t, Lepp(t) (Longest Edge Propagation Path of t) is a finite, ordered list of increasing longest edge neighbor triangles, that allows to find a pair of triangles over which mesh refinement operations are easily and locally performed. This is particularly useful for fracture mechanics analysis, where high gradients of element size are needed. The crack propagation is simulated by using a finite element model for each crack propagation step, then the mesh near the crack tip is modified to take into account the crack advance. Stress intensify factors are calculated using the displacement extrapolation technique while the crack propagation angle is calculated using the maximum circumferential stress method. Empirical testing shows that the behavior of the method is in complete agreement with experimental results reported in the literature. Good results are obtained in terms of accuracy and mesh element size across the geometry during the process.     

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.     

An Inverse Procedure for Crack Detection in Anisotropic Laminated Plates Using Elastic Waves

. This paper presents a computational inverse technique to detect the location and length of cracks in anisotropic laminated plates. The scattered elastic harmonic wave fields in the laminated plates with horizontal or vertical crack are calculated using the strip element method, whereby the anisotropic laminated plate is discretized into strip elements in the thickness direction. By applying the principle of virtual work, the governing differential equations of the wave propagation are derived for the field variables. These differential equations are solved analytically together with the vertical boundary conditions. The crack length and its location are then identified by minimizing an error function, which is defined as the difference between the scattered wave fields in plates with actual and searched parameters. A uniform micro-genetic algorithm is employed to search for the correct parameters that minimize the error function. Numerical examples are given to demonstrate the efficiency of the procedure in the detection of the location and the length of both horizontal and vertical cracks in composite laminates.