Elasto-Plastic FEM Analysis of Residual Stress in Spun Tube

The residual stress distribution of Hastelloy C corrosion-resistant alloy tubes after power spinning was simulated with the elasto-plastic finite element method combining with the element birth and death technique, the influences of spinning parameters on the distribution of the residual stress were investigated in detail, and the formation mechanism of residual stress during tube spinning was discussed. Based on the calculation of the residual stress, the reasons for annealing cracks on the spun tube during interpass heat treatment were explored. The simulation results and the characteristics of annealing cracks show that the circumferential residual tensile stress is a main factor to cause the annealing cracks.

基于声学FEM-BEM的户内变电站噪声场计算

准确计算户内变电站大型、复杂的噪声场分布,进而评价可采用降噪措施的减噪效果,是解决户内变电站噪声污染的关键问题。为此,综合声学有限元法(finite element method,FEM)求解复杂声场收敛性好及精度高的优点,及声学边界元法(boundary element method,BEM)降维求解大型声场的优势,提出了一种基于声学FEM-BEM的户内变电站噪声场求解算法。首先,建立变电站内部声源声固耦合模型,采用声学FEM求解混响噪声作用下的声固耦合响应;然后,基于声学FEM-BEM耦合理论,求解内、外耦合边界处结构单元受声固耦合激励产生的位移及应力载荷;最后,根据声压及应力载荷激发的外场声波扩散模型,基于常规Gauss数值积分法,建立外部空间声域2维BEM声学积分方程,求解外部声场。该算法在湖南某110 kV户内变电站噪声场的求解分析中得到了成功应用,与实测值的相对误差为3.61%~4.87%。

基于DEM-FEM耦合方法的碎屑流对桥墩最大冲击力的影响因素研究

碎屑流是我国山区最危险的地质灾害之一,山区桥墩常受到碎屑流冲击而开裂、倾斜甚至倒塌,给山区桥梁建设、运营带来严重的安全隐患。采用离散元方法(discrete element method,DEM)和有限元方法(finite element method,FEM)耦合的三维数值模拟方法模拟了碎屑流对双柱式桥墩的冲击效应,并结合斜槽试验,验证了耦合方法的准确性,进一步分析了碎屑流冲击坡度、距离和体积密度对桥墩冲击力的影响规律。结果表明,最大冲击力与碎屑流冲击坡度、距离和体积密度分别呈幂函数(指数大于1)、幂函数(指数小于1)和线性正相关。冲击坡度、距离和体积密度对最大冲击力的敏感度值分别为3.012、0.202、0.804,在桥梁碎屑流灾害防治时需重视冲击坡度和体积密度的影响。将冲击力的数值模拟值与流体动力学模型预测值对比分析表明,流体动力学模型理论公式能较好地预测桥墩所受的最大冲击力,最大预测误差低于23.6%。相关研究结果可为山区桥梁碎屑流灾害防治与设计提供一定的参考依据。

饱和地基水泥土复合桩近场主动隔振的BEM-FEM耦合分析

人工振动污染是当前城市发展过程中面临的一个难题,单排或多排桩是人工振动污染防治的一种重要方式。传统基桩施工容易造成泥浆污染、振动等各种负面环境问题,而水泥土复合桩是一种低振动、低噪声、无挤土、少排泥浆的新型基桩,特别适合在城区构建排桩屏障。针对饱和地基中单排水泥土复合桩的近场主动隔振问题,建立了动力机器基础环境振动影响的半解析BEM方程;在此基础上,分别采用半解析BEM对饱和地基、FEM对水泥土复合桩进行建模,根据饱和地基-水泥土桩接触面的平衡和相容条件,建立了水泥土复合桩近场主动隔振的半解析BEM-FEM耦合方程,给出了耦合方程稀疏矩阵的存储策略,并对单排水泥土复合桩的近场主动隔振效果进行了计算分析。研究结果表明:单排水泥土复合桩能够有效地对动力机器基础引起环境振动进行隔振;等长芯桩复合桩的隔振效果要优于短芯桩。单排水泥土复合桩的隔振效果随着桩数的增加而逐渐提高;较小桩间距并不一定取得更好的隔振效果,建议相邻桩桩间净距取2.0~2.5λ_(R)(Rayleigh波波长)。随着单排水泥土复合桩距振源距离的增加,屏障隔振效果逐渐降低,但降低幅度相对较小。此外,对水泥土复合桩而言,当内插预制桩的外轮廓尺寸相同时,预制芯桩型式对水泥土复合桩隔振效果影响相对较小,可根据实际工程条件选择合适的芯桩类型。

Predicting impact strength of perforated targets using artificial neural networks trained on FEM-generated datasets

The paper considers application of artificial neural networks(ANNs)for fast numerical evaluation of a residual impactor velocity for a family of perforated PMMA(Polymethylmethacrylate)targets.The ANN models were trained using sets of numerical results on impact of PMMA plates obtained via dynamic FEM coupled with incubation time fracture criterion.The developed approach makes it possible to evaluate the impact strength of a particular target configuration without complicated FEM calculations which require considerable computational resources.Moreover,it is shown that the ANN models are able to predict results for the configurations which cannot be processed using the developed FEM routine due to numerical instabilities and errors:the trained neural network uses information from successful computations to obtain results for the problematic cases.A simple static problem of a perforated plate deformation is discussed prior to the impact problem and preferable ANN architectures are presented for both problems.Some insight into the perforation pattern optimization using a genetic algorithm coupled with the ANN is also made and optimized perforation patterns which theoretically enhance the target impact strength are constructed.

基于FEM与MBD的商用车驾驶室疲劳耐久性分析

为提高商用车驾驶室疲劳仿真与强化路耐久试验的关联性,以某(6×4)牵引车驾驶室为研究对象,提出一种将实测路谱与虚拟仿真相结合的疲劳耐久分析方法。在Hypermesh中建立含配重加载的驾驶室有限元模型,并应用惯性释放法获得其单位载荷下应力分布结果。采用Adams/car软件搭建驾驶室-车架刚柔耦合多体动力学模型,以试验场实车采集的驾驶室气囊悬置位移、加速度信号作为期望信号,通过Femfat-Lab虚拟迭代获取其疲劳分析载荷谱。基于Miner线性疲劳累积损伤理论在nCode中进行疲劳仿真分析,结果表明:导流罩支架等疲劳破坏部位与试验场路试结果基本一致,所提出的疲劳分析方法对研究汽车系统级疲劳耐久性具有重要的参考价值。

ELASTO-PLASTIC FEM ANALYSIS OF CYLINDER UPSETTING BETWEEN TWO FLAT PLATENS

A whole analysis model including forging and flat platens is built,which is used to analyse the process of upsetting a cylinder between flat platens.The influence of surface friction and transient temperature are comprehensively considered.By means of ANSYS software,the elasto plastic FEM analysis of the whole upsetting process is carried out.From the point of view of numerical calculation,the correctness of the centre region tension stress theory about upsetting a cylinder between flat platens is tested and verified.The concept of plasto nucleus is presented to explain the forming of double dumps.The efffect of temperature is inspected.The relation curves between the radial stress of the symmetry centre point and the relative pression ratio are given.

基于SPH-FEM耦合方法的泥石流冲击输电塔基础的动力分析

泥石流是我国西南山区常见的地质灾害。架空输电杆塔在泥石流的冲击下往往发生基础破坏甚至会造成杆塔倒塌。首先采用光滑粒子流体动力学(smoothed particle hydrodynamics,简称SPH)方法和有限元方法(finite element method,简称FEM)相耦合的三维数值方法模拟了泥石流对杆塔基础的冲击作用;在与相关模型试验结果验证的基础上,开展了不同泥石流密度、黏度系数及初始速度条件下对输电塔基础的冲击力作用的参数分析;研究结果表明:随着泥石流初始速度的增加,冲击力峰值会随之增大;前排基础的冲击力峰值均大于后排基础;泥石流冲击过程特性受到泥石流密度和黏度系数影响。与稀性泥石流相比:黏性泥石流冲击基础后,基础下游真空区相对要小;此外,将数值模拟结果与Kwan冲击力公式及铁二院推荐的冲击压力设计公式预测值进行对比分析可以发现:Kwan冲击力公式能较好地预测出基础所受泥石流冲击力的平均趋势,最大预测误差低于30%,铁二院公式预测的稀性和黏性泥石流的冲击压力平均偏低分别约17%和28%。相关研究结果有望为泥石流频发区域输电塔基础的设计和风险评估提供一定的参考依据。

基于FEM的汽车轮毂轴承动态特性及可靠性研究

采用Workbench软件对某型汽车轮毂面对面式双列圆锥滚子轴承进行基于力学仿真分析的动态可靠性研究。首先,简化轴承模型后采用SolidWorks建立其三维模型;然后,采用Workbench对轴承开展模态及谐响应分析,获取轴承空载与满载状态下的位移和等效应力云图,并分别提取空载前10阶与满载前6阶的振型和固有频率等动态性能参数,采用Workbench中的六西格玛分析模块对轴承进行可靠性分析;最后,加载增量载荷谱获取轴承的可靠度和可靠性灵敏度。研究结果与汽车轮毂轴承的实际情况基本吻合。汽车轮毂轴承在不同工况下的仿真及其可靠性研究可以为故障轴承运动学、动力学计算与分析提供一定的参考。

A Simple Elasto-Plastic Iterative Method by Fem for the Analysis of Plane Articulated Truss: Case of a 3-Bar Truss

This paper presents a simplified numerical simulation tool for the elasto-plastic calculation of plane articulated truss by the finite element method (FEM) in MATLAB. The simplified approach consists of linearizing isotropic strain-hardening (to obtain a bilinear material law). The numerical implementation is built on the basis of the incremental and iterative FEM algorithms. The numerical resolution technique used is based on the projection methods of the modified Newton-Raphson solution. The MATLAB program is developed for the application of a 3-bar truss under monotonous quasi-static loading. Different values of the approximation error of the convergence criterion are used to study its impact on the quality of the algorithm. Numerical simulations have shown the reliability and quality of our simplified approach regardless of the approximation error.

miR-511-5p/FEM1C轴通过激活自噬对乳腺癌细胞增殖和侵袭的影响

目的 探讨微小RNA-511-5p(miR-511-5p)对乳腺癌细胞的影响及其潜在调节机制。方法 通过实时荧光定量PCR(qPCR)检测乳腺癌组织和细胞系中miR-511-5p的表达水平。利用miR-511-5p mimics、miR-511-5p inhibitor和/或fem-1同系物C(FEM1C)过表达载体,以及相对应的空白对照载体转染乳腺癌细胞。采用CCK-8法检测细胞增殖水平,Transwell实验检测细胞侵袭能力,流式细胞仪检测细胞凋亡率,Western blotting检测自噬相关蛋白(LC3Ⅱ、Beclin1和p62)和PI3K/AKT通路关键蛋白的表达。TargetScan数据库预测miR-511-5p与FEM1C的结合位点,并通过双荧光素酶报告基因分析进行验证。此外,通过给裸鼠皮下注射mimics NC和miR-511-5p mimics转染的乳腺癌细胞,建立异种移植瘤模型。结果 乳腺癌组织和细胞中miR-511-5p表达均显著下调(P<0.05)。与其他细胞系相比,MDA-MB-231细胞系中miR-511-5p的表达最低。与mimics NC组相比,miR-511-5p mimics组细胞中自噬作用增强,细胞增殖和侵袭能力显著下调,而凋亡水平显著上调(P均<0.05)。与miR-511-5p mimics组相比,miR-511-5p mimics+自噬抑制剂3-甲基腺嘌呤(3-MA)组中自噬作用减弱,细胞增殖和侵袭能力显著上调,而凋亡水平显著下调(P均<0.05)。FEM1C作为miR-511-5p的靶基因,且两者的表达呈负相关。在功能上,miR-511-5p通过靶向FEM1C显著抑制了p-PI3K/PI3K和p-AKT/AKT的比率,增加了自噬水平(P<0.05);而过表达FEM1C显著促进了细胞的增殖和侵袭能力,抑制了细胞凋亡(P<0.05),逆转了miR-511-5p mimics对MDA-MB-231细胞的影响。裸鼠体内成瘤实验结果显示,miR-511-5p过表达可抑制肿瘤生长。结论 miR-511-5p通过下调FEM1C的表达来诱导自噬和阻断PI3K/AKT信号通路,进而抑制细胞增殖和侵袭并促进凋亡,为乳腺癌的治疗提供了新的靶点。

基于CS-FEM的某制导炮弹弹体动力特性分析

常规有限元法采用六面体单元进行动力特性分析时,由于数值模型刚度过大导致计算误差较大且无法克服网格畸变。因此,文中在常规有限元法的基础上引入梯度光滑技术,采用基于单元的光滑有限元法(CS-FEM)对某制导炮弹弹体进行动力特性分析,该方法能有效降低系统数值模型刚度且无需进行坐标变换和形函数求导,从而避免网格畸变带来的精度降低及求解困难等问题。计算结果表明:相同网格数目情况下,CS-FEM能够有效提高弹体固有频率及振型的求解精度,同时具有较高的收敛速度,在制导炮弹弹体动力特性分析方面具有较好的应用前景。

Stability and reinforcement analysis of rock slope based on elasto-plastic finite element method

The rigid body limit equilibrium method(RBLEM) and finite element method(FEM) are two widely used approaches for rock slope's stability analysis currently. RBLEM introduced plethoric assumptions; while traditional FEM relied on artificial factors when determining factor of safety(FOS) and sliding surfaces. Based on the definition of structure instability that an elasto-plastic structure is not stable if it is unable to satisfy simultaneously equilibrium condition, kinematical admissibility and constitutive equations under given external loads, deformation reinforcement theory(DRT) is developed. With this theory, plastic complementary energy(PCE) can be used to evaluate the overall stability of rock slope, and the unbalanced force beyond the yield surface could be the identification of local failure. Compared with traditional slope stability analysis approaches, the PCE norm curve to strength reduced factor is introduced and the unbalanced force is applied to the determination of key sliding surfaces and required reinforcement. Typical and important issues in rock slope stability are tested in TFINE(a three-dimensional nonlinear finite element program), which is further applied to several representatives of high rock slope's stability evaluation and reinforcement engineering practice in southwest of China.

TIME DISCONTINUOUS GALERKIN FINITE ELEMENT METHOD FOR DYNAMIC ANALYSES IN SATURATED PORO-ELASTO-PLASTIC MEDIUM

A time-discontinuous Galerkin finite element method for dynamic analyses in saturated poro-elasto-plastic medium is proposed.As compared with the existing discontinuous Galerkin finite element methods,the distinct feature of the proposed method is that the continuity of the displacement vector at each discrete time instant is automatically ensured,whereas the discontinuity of the velocity vector at the discrete time levels still remains.The computational cost is then obviously reduced, particularly,for material non-linear problems.Both the implicit and explicit algorithms to solve the derived formulations for material non-linear problems are developed.Numerical results show a good performance of the present method in eliminating spurious numerical oscillations and providing with much more accurate solutions over the traditional Galerkin finite element method using the Newmark algorithm in the time domain.

DESIGN OPTIMIZATION FOR TRUSS STRUCTURES UNDER ELASTO-PLASTIC LOADING CONDITION

In this paper, a method for the design optimization of elasto-plastic truss structures is proposed based on parametric variational principles （PVPs）. The optimization aims to find the minimum weight/volume solution under the constraints of allowable node displacements. The design optimization is a formulation of mathematical programming with equilibrium constraints （MPECs）. To overcome the numerical difficulties of the complementary constraints in optimization, an iteration process, comprising a quadratic programming （QP） and an updating process, is employed as the optimization method. Furthermore, the elasto-plastic buckling of truss mem- bers is considered as a constraint in design optimization. A combinational optimization strategy is proposed for the displacement constraints and the buckling constraint, which comprises the method mentioned above and an optimal criterion. Three numerical examples are presented to show the validity of the methods proposed.

Dynamic Buckling of Elasto-Plastic Cylindrical Shells Under Axial Fluid-Solid Impact Load

The dynamic buckling of elasto-plastic cylindrical shells under axial fluid-solid impact is investigated theoretically. A simplified liquid- gas- structure model is given to approximately imitate the problem. The basic equation of the structure is derived from a minimum principle in dynamics of elasto-plastic continua at finite deformation, and the flow theory of plasticity is employed. The liquid is incompressible and the gas is compressed adiabatically. A number of numerical results are presented and the characteristics of the buckling behavior under fluid-solid impact are illustrated.

基于FEM的超高压液压顶升装置力学特性分析

液压顶升装置各部件在超高压下的力学特性是影响其性能的主要因素,也是超高压技术的难题。采用有限元方法研究超高压液压顶升装置各部件的材料、内径、厚度等不同时,其液压系统刚度、模态、固有频率、位移、应力的变化规律。有限元计算结果与压力试验结果较为接近,验证了有限元模型及边界条件的有效性。结果表明:液压弹簧刚度随液压缸内径增大而增加、随振幅增加而下降,其影响随内径增加而减少;系统前3阶固有频率随地面强度增大而增加;Bonded工况极限应力值最小,Frictionless工况极限应力最大,极限应力随地面强度增加而减少;C20地面时,最大位移随摩擦因数增加而增加,最大应力随地面强度增加而增加;C30地面时,最大位移随摩擦因数增大先增后减,其位移、应力临界摩擦值分别为0.43、0.59;结构钢地面时,极限位移显著减少。液压缸同长度不同位置极限位移差值随地面强度而增加;液压缸底端应力值随地面强度增加而增加;液压缸外表面一孔侧位移均小于二孔侧,且极限位移更靠近顶端,并交替出现极值。分析了超高压液压装置的应力-应变过程,为其结构设计、密封设计及使用提供了参考。

NONLINEAR AND ELASTO-PLASTICITY CONSOLIDATION MODELS OF UNSATURATED SOIL AND APPLICATIONS

The non-linear constitutive model suggested by the authors and the Alonso's elasto-plasticity model of unsaturated soil modified by the authors are introduced into the consolidation theory of unsaturated soil proposed by CHEN Zheng-han, and the non-linear and the elasto-plasticity consolidation models of unsaturated soil are obtained. Programs related to the two consolidation models are designed, and a 2-D consolidation problem of unsaturated sail is solved using the programs, the consolidation process and the development of plastic;one under multi-grade bad are studied. The above research develops the consolidation theory of unsaturated soil to a new level.

EFFECTIVE NUMERICAL METHODS FOR ELASTO-PLASTIC CONTACT PROBLEMS WITH FRICTION

Several effective numerical methods for solving the elasto-plastic contact problems with friction are pres- ented.First,a direct substitution method is employed to impose the contact constraint conditions on condensed finite ele- ment equations,thus resulting in a reduction by half in the dimension of final governing equations.Second,an algorithm composed of contact condition probes and elasto-plastic iterations is utilized to solve the governing equation,which distinguishes two kinds of nonlinearities,and makes the solution unique.In addition,Positive-Negative Sequence Modifica- tion Method is used to condense the finite element equations of each substructure and an analytical integration is intro- duced to determine the elasto-plastic status after each time step or each iteration,hence the computational efficiency is en- hanced to a great extent.Finally,several test and practical examples are pressented showing the validity and versatility of these methods and algorithms.

Measurement of length-scale and solution of cantilever beam in couple stress elasto-plasticity

Owing to the absence of proper analytical solution of cantilever beams for couple stress/strain gradient elasto-plastic theory, experimental studies of the cantilever beam in the micro-scale are not suitable for the determination of material length-scale. Based on the couple stress elasto-plasticity, an analytical solution of thin cantilever beams is firstly presented, and the solution can be regarded as an extension of the elastic and rigid-plastic solutions of pure bending beam. A comparison with numerical results shows that the current analytical solution is reliable for the case of σ0 〈〈 H 〈〈 E, where σ0 is the initial yield strength, H is the hardening modulus and E is the elastic modulus. Fortunately, the above mentioned condition can be satisfied for many metal materials, and thus the solution can be used to determine the material length-scale of micro-structures in conjunction with the experiment of cantilever beams in the micro-scale.