基于有限元分析的松原震群与日本大地震的关系探讨

日本3·11大地震之后,我国松原地区发生了多次4级以上地震,两者之间存在的关系是本文探讨的重点。利用有限元方法,构造两个有限元模型,从库仑应力变化的角度研究日本3·11大地震对位于郯庐断裂带北段第二松花江断裂的影响。模拟结果表明,日本大地震对我国东北部地区影响大,第二松花江断裂带的位移最大达到20 mm。整个研究区的静态库仑应力均为正值,表明该断层处于危险阶段。考虑到实际地壳介质对应变传递的延迟效应,日本3·11大地震对我国东北地区的实际影响会有一个滞后,因此松原震群与日本3·11大地震存在密切相关性。

基于断裂力学的老龄钢桥剩余寿命与使用安全评估

提出了基于断裂力学评估老龄铆接钢桥剩余寿命与使用安全的基本方法。根据铆接构件的疲劳破坏特征,建立了铆接钢桥简化断裂分析模型。鉴于简化断裂分析模型的不足,建立了铆接构件断裂分析模型,该模型可合理计入铆接构造、钉载等对疲劳裂纹扩展的影响。运用板壳断裂力学有限元程序,经计算回归得到了铆接构件断裂分析模型的几何修正因子公式。按铆接构件简化断裂力学模型和构件断裂力学模型,计算了浙江路桥主要杆件的剩余寿命,结果表明:按后者计算的剩余寿命均比前者降低约35%,可见钉载、钉孔应力集中等的影响是显著的。为保证正常使用功能,简化断裂分析模型和构件断裂分析模型的超声波探测间隔分别为4、2 a;若按保证主桁结构承载安全,则探测间隔已超过100 a,这样的探测间隔在一般情况下已无须考虑。

基于断裂力学的高拱坝底缝稳定性分析

采用三维断裂有限元及三维K判据分析了小湾高拱坝底缝扩展的稳定性。结果表明,该缝基本稳定,但中间坝段的底缝深度需作调整,以提高安全度。

多因素作用下预应力混凝土简支空心板梁的裂缝评价

以断裂力学及断裂有限元相关理论为基础,用ANSYS有限元软件建立完整梁和带裂缝梁并对其进行静力分析.在不同荷载作用下,比较完整梁和带裂缝梁的挠度、拉应力、压应力和切应力等受力变化.在标定荷载作用下,分析裂缝长度、深度及宽度对主梁受力的影响,计算不同裂缝尺寸下的应力强度因子.结果表明:相同荷载条件下,带裂缝梁由于裂缝尖端存在应力集中,混凝土所受拉应力比同一完整梁明显变大;在常量荷载作用下,随着裂缝尺寸的增加,裂缝尖端应力场强度增大,应力强度因子增大,发生断裂的可能性增大;对于本文中带裂缝20m预应力混凝土简支梁来说,当裂缝宽度为0.25mm时,会发生脆性断裂,因此要控制裂缝宽度小于0.25mm.

数值方法确定海底隧道最小岩石覆盖厚度研究

目前国内正在修建或拟修建多条海底隧道,其中最小岩石覆盖厚度直接制约着海底隧道的安全和造价。本文根据国内外有关文献资料,探讨了利用数值方法确定海底隧道最小岩石覆盖厚度的方法,应用断裂损伤有限元和国际通用数值分析软件,根据隧道在同一剖面处不同底板线位置,隧道上方同一个点的位移收敛情况,建立了确定海底隧道最小覆盖厚度的位移收敛法。通过对国内2条海底隧道开展的研究,其中一条已开始施工,总结出了数值方法确定最小岩石覆盖厚度的思路和过程。为定量确定海底隧道最小岩石覆盖厚度建立了数值分析基础,最后应用数值方法确定某海底隧道最小岩石覆盖厚度。

广义参数有限元法计算应力强度因子

应力强度因子是结构断裂分析中的重要物理量。工程应用中常采用奇异单元,利用裂尖奇异区内特定直线上的其他物理量间接计算,并拟合裂尖处应力强度因子的值。该文在改进Williams级数位移场的基础上,根据广义参数有限元法建立了含有裂尖广义应力强度因子作为待定参数的Williams宏单元(简称W单元),导出了奇异区单元的广义参数位移模型和W单元计算格式,并据此直接计算裂尖处的应力强度因子。结合算例分析了W单元的径向离散比例因子、径向离散网格数和级数项数等重要参数对计算精度的影响,并给出了它们的建议值。算例表明:断裂分析的广义参数W单元与通常使用的奇异单元相比,不仅简便实用,而且计算精度高、收敛快。

Numerical simulation and optimization of process parameters in fineblanking process

Fineblanking process is a typical large localized plastic deformation process. Based on its forming characteristics, a numerical model is established and an elasto-plastic simulation is performed using the finite element method （FEM）. The re-meshing method is used when the severe element distortion occurs to facilitate further computation and avoid divergence. The McClintock fracture criterion is adopted to predict and determine the time and site of crack initiation and propagation. Based on this numerical model, the distribution and developing trend of the stress and strain in the shearing zone are predicted. Furthermore, the influence of several process parameters, such as punch-die clearance, edge radius of punch and die, V-ring force, counter force, etc., on the blanked quality is analyzed. The discipline is in accordance with the actual manufacture situation, which can be a guidance to optimization of process parameters.

Fatigue fracture analysis of gear teeth using XFEM

Gear teeth in gear transmission systems suffer seriously from fatigue failure during service. In this work, a 2 D double-tooth model was constructed with periodic boundary conditions. The fatigue fracture behavior of gear teeth was analyzed using the extended finite element method(XFEM), with emphases on the impacts of initial crack geometries and cyclic load factors. The results suggested that the shortest fatigue life is expected for 0° orientation cracks initiating at the maximum principal stress. Cracks that initiate closer to the bottom land of gear tooth are relatively safe. Moreover, to evaluate the fatigue load conditions, load ratio, load range, and mean load should be all taken into considerations. Further XFEM simulation for material selection was performed to guide the gear design. Among various material parameters, the material constant C and tensile strength are the most significant ones in determining the fatigue life.

Fracture properties of epoxy asphalt mixture based on extended finite element method

Crack is found to be a major distress that affects the performance of the epoxy asphalt pavement.An extended finite element method was proposed for investigating the fracture properties of the epoxy asphalt mixture.Firstly,the single-edge notched beam test was used to analyze the temperature effect and calculate the material parameters.Then,the mechanical responses were studied using numerical analysis.It is concluded that 5℃ can be selected as the critical temperature that affects the fracture properties,and numerical simulations indicate that crack propagation is found to significantly affect the stress state of the epoxy asphalt mixture.The maximum principal stress at the crack surface exhibits different trends at various temperatures.Numerical solution of stress intensity factor can well meet the theoretical solution,especially when the temperature is lower than 5℃.

Stress based forming limit diagram for formability characterization of 6061 aluminum

Two numerical criteria of forming limit diagram（FLD） criterion and ductile fracture criterion（DFC） are presented for FLD prediction of 6061 aluminum. The numerical results are compared with the experimental FLD and also punch＇s load-displacement curve of experimental samples. Experimental FLD of this study is calculated using hemispherical punch test of Hecker. Experimental FLD is converted to FLSD and imported to the Abaqus software to predict necking of samples. Numerical results for FLSD prediction were compared with experimental FLSD. Results show that ductile fracture criterion has higher accuracy for FLD and FLSD prediction of 6061 aluminum. Comparison of numerical and experimental results for force-displacement curve of punch shows that numerical results have a good agreement with experiment.

Distribution of stress and strain between adjacent particles in particulate reinforced metal matrix composites

The distribution of stress and strain between adjacent particles in particulate reinforced metal matrix composites wasinvestigated using cohesive zone models. It is found that the strain of the composite is concentrated in the matrix, and there is aregion with higher strain along the loading path, which can promote the formation of a void near the particles pole. The stress andstrain in matrix near the particles gradually decrease with the increase of the distance between particles. And it is calculated that thereis a critical distance within which the stress and strain fields of the neighboring particles can influence with each other. This criticaldistance increases with the increase of particle size. It is also found that the angle between the tensile direction and the center line ofparticles plays an important role in the stress and strain distribution. The model with the angle of 0° has the greatest influence on thedistribution of stress and strain in the matrix, while the model with the angle of 45° has the least influence on the distribution of stressand strain in the matrix.

Origin of the regional stress field along the Liquine-Ofqui Fault Zone(LOFZ),Southern Chilean Andes by means of FE Simulation

The Liquine-Ofqui Fault Zone(LOFZ) of southern Chilean Andes is one of the largest active strike-slip fault zones.There is an ongoing debate regarding the origin of the stress field along the LOFZ due to its complex geometry.This paper represents a study of the origins of the LOFZ regional stress field.Stress fields are calculated by finite element(FE) analysis.The two possible stress origins, i.e., oblique plate convergence and ridge collision/indenter tectonics of Chile ridge against Peru-Chile trench, have been emphasized in the present study.Three types of boundary conditions for the three particular models have been applied to calculate stress fields.Models are assumed to be elastic and plane stress condition.Modeling results are presented in terms of four parameters, i.e., orientation of maximum horizontal stress(σ H max ), displacement vector, s train distribution, and maximum shear stress(τmax ) contour line within the model.The results of the first model with oblique plate convergence show inconsistency between the geometric shape of the LOFZ and the distribution of the four parameters.Although more realistic results are obtained from the second model with normal ridge collision, there are few coincident in the LOFZ geometry and regional stress field.The third model with normal and oblique ridge collision is reasonable in understanding the origin of stress field and geometrical condition in the lithosphere of the LOFZ.

Computational Fracture Analysis of an AFM-Specimen under Mixed Mode Loading Conditions

Fracture processes in ship-building structures are in many cases of a 3-D character. A finite element （FE） model of an all fracture mode （AFM） specimen was built for the study of 3-D mixed mode crack fracture behavior including modes Ⅰ,Ⅱ, and Ⅲ. The stress intensity factors （SIFs） were calculated by the modified virtual crack closure integral （MVCCI） method, and the crack initiation angle assessment was based on a recently developed 3-D fracture criterion--the Richard criterion. It was shown that the FE model of the AFM-specimen is applicable for investigations under general mixed mode loading conditions, and the computational results of crack initiation angles are in agreement with some available experimental findings. Thus, the applicability of the FE model of the AFM-specimen for mixed mode loading conditions and the validity of the Richard criterion can be demonstrated.

计算方法的进展

《大坝工程》编辑罗伯特·弗里尔着重叙述了大坝与水电工程软件方面的某些技术进展。

An Analysis on the Transmission Shaft Fracture of Screw Drill

The transmission shaft of the underground screw drill fractured when milling-shoe and grinding bridge plug was applied to the coiled tubes in a horizontal well of Sichuan province, but the position of this transmission shaft fracture did not occur at the minor-diameter retracting position and reducing position that were easy to fracture. An analysis of the transverse planes of the fracture found that the cause of the transmission shaft fracture surface was that the defects of the initial surface were propagating to cracks and gave rise to the fracture under torque load. To specifically know well the strength of the transmission shaft under damaging fracture, a statics analysis was conducted on the transmission shaft through ANSYS finite element simulation software, and the finite element models under no cracks, different-depth circumferential cracks, and similar situation of the transverse planes of fracture were established respectively. An analysis of the crack-free finite element model found that the fracture of the transmission shaft was really not caused by the self-structure of the transmission shaft; an analysis of circumferential crack finite element model found that strong stress concentration would appear in the tip of cracks, and the value of the stress would increase along with the increase of the circumferential crack depth, the stress of the entire crack top tended to fluctuate like waves, and also the strength of the transmission shaft was greatly impacted by the presence of cracks; an analysis of the similar crack finite element model found that stress concentration would appear in the tip of cracks, and the initial cracks always started to propagate from the tip of the external surface of the transmission shaft and would propagate inward until the propagating areas of two cracks overlapped, and finally reached the position of transient interruption, and then the transmission shaft fractured completely and the fracture strength was onlv 1/5 of that under no cracks.

冰劈效应对沥青路面表面裂缝的影响性分析

为研究冻融交替季节冰劈效应对沥青混凝土路面表面裂缝扩展的作用,基于断裂力学方法,采用ABAQUS有限元分析软件建立了路面结构模型,分别研究了路表裂缝在冰劈效应、温缩效应及二者结合作用下的应力强度因子随缝隙内积水深度、裂缝宽度以及裂缝长度等影响因素的变化规律及其相互之间的Pearson相关系数。研究结果表明:冰劈效应下,裂缝内少量积水便能够导致较大的应力强度因子,并且应力强度因子随着积水深度的增加而增长,但增长幅度逐渐放缓;同时较大的裂缝宽度能够导致裂缝更快的扩展,而裂缝长度对应力强度因子影响十分微弱;在冰劈与温缩的联合作用下,应力强度因子与冰劈效应作用下的应力强度因子的Pearson相关系数达到0.99以上,而由温缩效应所导致的应力强度因子相对于冰劈效应并不明显。因此在工程实践中,必须尽快修复路表裂缝,避免其在冻融交替季节受到冰劈效应的危害,从而保护路面的正常使用状况,延长路面使用寿命。

Fracture analysis of rock mass based on 3-D nonlinear Finite Element Method

Traditional fracture analysis is based on fracture mechanics and damage mechanics. They focus on the propagation of the fracture. However, their propagation criterions are not easily applied in practice and the current analysis is limited in planar problem. This paper presents a new theory that the occurrence of the unbalanced force (derived from the Deformation Reinforcement Theory) could be the criterion of the initiation of the fracture, and the distribution area and propagation of the unbalanced force could be the indication of the fracture propagation direction. By aggregate analysis with Stress Intensity Factor (SIF) criterion, the unbalanced force actually is the opposite external load that is the SIF difference incurred between the external loads and permitted by the structure. Numerical simulation and physical experiments on pre-fracture cuboid rock specimens proved that the occurrence of the unbalanced force could be the initiation of the fracture. Mesh size dependence was also considered by analysis of different mesh size finite element gravity dam models. Furthermore, the theory was applied to the feasibility analysis of the Baihetan arch dam together with physical experiments in order to evaluate the fracture propagation of dam heel. The results show that it is an effective way to use unbalanced force to analyze the fracture initiation and propagation when performing 3-dimensional nonlinear FEM calculation.

An Improved Ductile Fracture Criterion for Fine-blanking Process

In order to accurately simulate the fine-blanking process, a suitable ductile fracture is significant.So an evaluation strategy based on experimental and corresponding simulation results of tensile, compression, torsion and fine-blanking test is designed to evaluate five typical ductile fracture criteria, which are widely-used in metal forming process.The stress triaxiality and ductile damage of each test specimen are analyzed.The results show that none of these five criteria is sufficient for all tests.Furthermore, an improved fracture criterion based on Rice and Tracey model, taking the influence of both volume change and shape change of voids into account, is proposed.The characterization of this model for fine-blanking process is easily done by the tensile test and the prediction result shows good.