An edge dislocation interacting with a slightly wavy interface

The undulant interface of a bi-material, which is due to manufacturing or instability under high stress, may provide certain preferred places where microdefects accumulate. In the present paper, an edge dislocation near a slightly wavy interface is studied via a regular perturbation scheme. Stress investigation for the interaction between the edge dislocation and the wavy bi-material interface has been carried out. The Peach-Koehler force on the dislocation is calculated from the first perturbed solution of the stress fields. The influence of several key parameters, such as the Dundurs bi-material interface constants α, β, the distance of the dislocation to the interface, the wavy extent of the interface, etc., on the behavior of the dislocation has been analyzed. The numerical examples indicate that there are certain “equilibrium” points around which the dislocations are expected to be accumulated. In turn, microdefects, such as microcracks and microvoids, may be initiated near these sites. Results obtained can be applied to study crack initiation or delamination along bonded bi-material interfaces.     

Multiphase hybrid stress finite element analysis of heterogeneous media by simple mesh: One element with one interface

In this paper, a finite element method is proposed to analyze the microscopic and macroscopic mechanical behaviors of heterogeneous media with randomly distributed inclusions. A simple mesh partitioned the domain into regular quadrilateral or triangular elements, where one element may contain two phases. An assumed stress hybrid formulation is implemented in the finite element model and the functional is derived for an element containing two phases. Numerical examples were used to study the microscopic and macroscopic properties of the composites, such as the effective modulus, to validate of the proposed model. The results show that the proposed multiphase hybrid stress finite element model can accurately measure the stress fields of materials with arbitrary microstructural distributions and improve computational efficiency by about 30 to 1500 times in comparison with the traditional displacement based finite element method.     

Pulse propagation in finite elastic inhomogeneous media

The transfer matrix of a finite elastic bar is derived and the reflection and transmission functions are obtained. The matrix formalism is combined with Fourier component decomposition and applied to simulate acoustic pulse propagations in elastic inhomogeneous periodic and finite media. The numerical results are compared with experimental data to conclude about the validity of this method.     

Developments in ultrasonic modeling with finite element analysis

An overview is given of finite element analysis and its application to the modeling of ultrasonic nondestructive evaluation phenomena. Following a discussion of the underlying weighted residual methodology, a mass-lumping technique is described which results in an efficient computer implementation for 2D geometries. Code predictions are compared with both analytical and experimental results, and data from studies of attenuation, anisotropy, defect interactions, and surface waves are given. Initial results from a full 3D formulation are also shown.     

Stress analysis with arbitrary body force by boundary element method

Linear stress analysis without body force can be easily carried out by means of the boundary element method. Some cases of linear stress analysis with body force can also be solved without the domain integral. However domain integrals are generally necessary to solve the linear stress problems with complicated body forces. This paper shows that the linear stress problems with complicated body forces can be solved approximately without the domain integral. In order to solve these problems, the domain is divided into small areas using contour lines of body force. In these areas, the distributions of body force are assumed approximately to satisfy the Laplace equation.     

Stress analysis around crack tips in finite strain problems using the eXtended finite element method

Fracture of rubber‐like materials is still an open problem. Indeed, it deals with modelling issues (crack growth law, bulk behaviour) and computational issues (robust crack growth in 2D and 3D, incompressibility). The present study focuses on the application of the eXtended Finite Element Method (X‐FEM) to large strain fracture mechanics for plane stress problems. Two important issues are investigated: the choice of the formulation used to solve the problem and the determination of suitable enrichment functions. It is demonstrated that the results obtained with the method are in good agreement with previously published works. Copyright © 2005 John Wiley & Sons, Ltd.     

考虑位错密度和损伤的NiCoCrFe高熵合金晶体塑性有限元分析EI北大核心CSCD

结合实验和晶体塑性有限元方法研究准静态加载NiCoCrFe高熵合金有限变形过程中的宏观和微观力学响应、损伤行为以及微观结构演化。使用电子背散射衍射技术(EBSD)对拉伸实验变形前后NiCoCrFe的微观结构进行表征。通过修改强化模型和流动准则分别在CPFEM模型中引入位错密度内部状态变量和连续介质损伤因子,并结合拉伸实验应力-应变曲线确定NiCoCrFe相关的模型参数。结果表明:考虑位错密度和损伤的CPFEM模型可以有效地描述NiCoCrFe宏观和微观力学响应。CPFEM模型合理预测NiCoCrFe颈缩区域的变形形状和尺寸,其中实验获得的颈缩区域长度比预测结果小7%,CPFEM预测的颈缩区域宽度比实验结果大23%。CPFEM模型预测NiCoCrFe拉伸变形后的织构演化同EBSD表征结果大致相同,均表现为弱的(100)∥RD以及强的(111)∥RD纤维织构。在三维微观结构损伤分析中,CPFEM模型预测的损伤在应力集中以及位错密度集中的晶界处萌生,表现为晶间损伤机制,并且随着变形的增加损伤逐渐向晶粒内部扩展。     

A coupling extended multiscale finite element method for dynamic analysis of heterogeneous saturated porous media

A coupling extended multiscale finite element method (CEMsFEM) is developed for the dynamic analysis of heterogeneous saturated porous media. The coupling numerical base functions are constructed by a unified method with an equivalent stiffness matrix. To improve the computational accuracy, an additional coupling term that could reflect the interaction of the deformations among different directions is introduced into the numerical base functions. In addition, a kind of multi‐node coarse element is adopted to describe the complex high‐order deformation on the boundary of the coarse element for the two‐dimensional dynamic problem. The coarse element tests show that the coupling numerical base functions could not only take account of the interaction of the solid skeleton and the pore fluid but also consider the effect of the inertial force in the dynamic problems. On the other hand, based on the static balance condition of the coarse element, an improved downscaling technique is proposed to directly obtain the satisfying microscopic solutions in the CEMsFEM. Both one‐dimensional and two‐dimensional numerical examples of the heterogeneous saturated porous media are carried out, and the results verify the validity and the efficiency of the CEMsFEM by comparing with the conventional finite element method. Copyright © 2015 John Wiley & Sons, Ltd.     

基于有限元的异步电机电磁振动分析

电机的电磁振动是电机电磁场与机械结构耦合的结果,要研究电机的电磁振动,需要将电机的电磁场和结构振动分析结合起来。通过有限元软件,采用一种弱磁-固耦合的方法,对异步电机的电磁振动特性进行分析。首先利用ANSOFT有限元软件建立异步电机的二维有限元模型,计算电机的瞬态电磁场,得到电机在给定转速稳态运行状态下的磁场分布和作用在定子上时变的电磁力;其次用ANSYS有限元软件建立异步电机结构的三维有限元模型,将ANSOFT软件得到的时变电磁力进行频谱分析并校正,然后施加到电机上,计算出电机结构的电磁振动响应。基于对电机电磁振动特性的分析,可以对电机的电磁参数和结构进行改进和优化设计,以降低电机的电磁振动     

Elasto-plastic finite element analysis of a crack in an infinite plate

The elastic support method was recently developed to simulate the effects of unbounded solids in the finite element analysis of stresses and displacements. The method eliminates all the computational disadvantages encountered in the use of `infinite' elements or coupled finite element boundary element methods while retaining all the computational advantages of the finite element method. In this paper, the method is extended to the elasto-plastic analysis of fracture in infinite solids by using the load increment approach and including the effects of strain hardening. Numerical tests and parametric study are conducted by analysing a straight crack in an infinite plate. Present results for J integrals and plastified zones are compared, respectively, with analytical solutions and available results obtained by using the body force method. The agreement between the results is found to be very good even if the truncation boundary of the finite element model is located very close to the crack tip or the plastified zone.     

Micro-mechanical analysis and TEM study of crack initiation in dislocation free zone

Dislocation emission, dislocation-free zone (DFZ) formation and crack initiation in the DFZ and/or at the crack tip were analyzed by micromechanics. The results show that a DFZ is formed after dislocation emission under constant load. The DFZ size decreases with increase in the applied stress intensity factor K _Ia or lattice friction stress _f. There are two stress peaks ahead of the crack tip. The first one is located at the blunt crack tip and the second one in the DFZ. With increasing in the applied stress intensity factor K _Ia, the peak stress at the crack tip may decrease while the peak stress in the DFZ increases monotonically. Microcrack will initiate when the peak stress is equal to the cohesive strength. In situ tensile tests in a transmission electron microscope (TEM) show that microcrack initiates in DFZ or/and at a blunt crack tip after dislocation emitting and DFZ formation.     

Nonlinear finite element analysis of masonry wall strengthened with CFRP strips

In many experimental studies, it has been proved that unreinforced masonry (URM) brick walls have high strength against lateral forces acting in plane. However, out-of-plane strength of URM brick walls against lateral forces has found to be quite low. According to the experiences that were obtained from the major earthquakes, the low out-of-plane performance of URM brick walls resulted in excessive loss of human lives during an earthquake, hence the strengthening of URM brick walls with CFRP strips has been appeared to be a very important subject. However, very limited literature has been found. Especially, the data obtained from experimental studies must be increased for the true understanding of the behavior of strengthened brick walls under out-of-plane lateral forces. However, in most cases, this procedure required large number of expensive experiments. At this stage, numerical analysis can be an appropriate choice, thus in this paper a finite element model is presented for modeling URM brick walls that are strengthened with CFRP strips. The numerical results are compared with the experimental ones and consistent results are obtained from the finite element model. General purpose finite element analysis software ANSYS is used throughout this study. Contact elements are used along the masonry wall–CFRP strip interfaces for the investigation of the stress distribution and load – strain behavior.     

Modelling cracks in finite bodies by distributed dislocation dipoles

The method of continuous distribution of dislocations is extended here to model cracks in finite geometries. The cracks themselves are still modelled by distributed dislocations, whereas the finite boundaries are represented by a continuous distribution of dislocation dipoles. The use of dislocation dipoles, instead of dislocations, provides a unified formulation to treat both simple and arbitrary boundaries in a numerical solution. The method gives a set of singular integral equations with Cauchy kernels, which can be readily solved using Gauss–Chebyshev quadratures for finite bodies of simple shapes. When applied to arbitrary geometries, the continuous distribution of infinitesimal dislocation dipoles is approximated by a discrete distribution of finite dislocation dipoles. Both the stress intensity factor and the T -stress are evaluated for some well-known crack problems, in an attempt to assess the performance of the methods and to provide some new engineering data.     

车辆乘坐室声学泄漏分析的声振耦合有限元模型

提出了一种新的“声学泄漏边界条件” ,并将其引入到声振耦合分析的有限元模型中 ,使模型具备了对实际车辆乘坐室声学泄漏问题的处理能力。然后以SH76 0A型轿车乘坐室为对象给出了算例 ,并通过计算和测量结果的对比分析 ,验证了所提方法的正确性。     

Stress intensity factors of semi-elliptical surface cracks in pressure vessels by global-local finite element methodology

In the present study the problem of calculation of the stress intensity factors (SIF) of semi-elliptical cracks located in the stress concentration areas of a pressure vessel is numerically solved by advanced global-local finite element (FE) analysis. The common characteristic of the cases solved is that the stress field at the crack area varies along the axial, the circumferential, as well as, the through-the-thickness directions. SIF solutions for such problems are not available, neither analytically, nor numerically, as the currently existing solutions in the literature (numerical results, Newman-Raju empirical equations, weight function solutions, etc.) are only valid for uniform stress distribution along the axial and circumferential directions of the pressure vessel and allow variation only through-the-thickness. The crack locations considered are the intersection of the cylinder to a nozzle and the connection of the cylinder with its hemi-spherical ends. The stress intensity factors are presented in a suitable table format for various geometrical configurations of both the pressure vessel and the semi-elliptical crack, thus providing a useful tool for the fracture mechanics design of cracked pressure vessels. The modeling details of the sub-structuring methodology, employed in the analysis, are extensively discussed and the numerical approach is proven to be very efficient for the SIF calculation of pressure vessel semi-elliptical cracks.     

Stabilized finite element methods with reduced integration techniques for miscible displacements in porous media

The objective of this work is to study some techniques to increase computational performance of stabilized finite element simulations of miscible displacements. We propose the use of a reduced integration technique for bilinear quadrilateral elements in the determination of the pressure and concentration fields. We also study the evaluation of pressure gradient (Darcy's velocity) by differentiation at super‐convergent points. Numerical examples are shown to validate our approach, accessing its efficiency and accuracy. Copyright © 2003 John Wiley & Sons, Ltd.     

Dynamic analysis of fixed cracks in composites by the extended finite element method

This paper is dedicated to simulation of dynamic analysis of fixed cracks in orthotropic media using an extended finite element method. This work is in fact an extension to dynamic problems of the recently developed orthotropic extended finite element method for fracture analysis of composites. In this method, the Heaviside and near-tip enrichment functions are used in the framework of the partition of unity for modeling crack discontinuity and crack-tip singularities within the classical finite element method. In this procedure, elements that include a crack are not required to conform to crack edges. Therefore, mesh generation can be performed without any need to comply to crack edges and the method is capable of modeling the crack propagation without any remeshing. To determine the fracture properties, mixed-mode dynamic stress intensity factors (DSIFs) are evaluated by means of domain separation integral (J^′-integral) method. Results of the proposed method are compared with other available analytical and computational results.     

Progressive damage analyses of angle‐ply laminates exhibiting free edge effects using continuum damage mechanics with layer‐wise finite element method

Capability of continuum damage mechanics (CDM) to predict the damage mechanism evolution of composite laminates has rarely been carried out, and most of the previous CDM works mainly focused on the overall response of the laminates. In this paper, progressive damage and overall response of the composite laminates under quasi‐static, monotonic increasing loading are investigated using three‐dimensional (3D) CDM implementation in a finite element method that is based on the layer‐wise laminate plate theory. In the damage formulation, each composite ply is treated as a homogeneous orthotropic material exhibiting orthotropic damage in the form of distributed microscopic cracks that are normal to the three principal material directions. The progressive damage of different angle‐ply composite laminates under quasi‐static loading that exhibit free edge effects is investigated. It is shown that using CDM global behaviour and various damage mechanisms affected by the complex nature of free edges can be qualitatively well predicted.