二维材料微结构设计与数值模拟软件系统

为了实现二维多元多相异质体材料微观组织结构的"性能导向型"设计、材料微结构的细观力学计算与虚拟失效分析,以平面Voronoi算法为基础, 通过Visual C+ +程序设计并结合OpenGL工具集,开发出用于微结构模块化、可视化设计的材料微观组织结构仿真软件ProDesign.基于该软件构造出二维多晶体与多晶体基复合材料类微结构,采用C语言与Python脚本混合编程的方式,实现微结构在ABAQUS/CAE中的有限元建模,并对模型进行细观力学响应的数值计算与微应力统计分析.最后根据计算结果预测微结构的材料性能,识别"材料结构弱点",评估平面微裂纹的启裂、扩展,推演微结构"虚拟失效行为".     

具有细观结构新材料跨尺度分析的细观元法

建议一种适用于具有细观结构新材料宏细观间跨尺度分析的细观元方法.细观元法在结构的常规有限元内部设置密集细观单元以反映材料细观构造,又通过协调条件将各细观元结点自由度转换为同一常规有限元自由度,再上机计算.此方法可实现材料细观结构到构件宏观响应的直接过渡分析,而计算单元与自由度又等同一般常规有限元,为解决具有细观结构新材料与构件跨尺度分析提供一种新的有力工具.研究了直接从制备时给定的材料组分分布及网状细观结构图形出发计算功能梯度板件宏观响应,给出了不同边界条件功能梯度板件的力学量三维分布形态以及细观结构局部突变引起宏观等应力线图的畸变.     

逐级加荷条件下公路路基沉降变形监测仿真

传统方法未能考虑计算土体固结度与沉降应力,导致公路路基沉降变形监测精准度低、监测效果差,影响公路建设的施工进度.提出逐级条件下公路路基沉降变形监测的方法.首先引入屈服准则构建理想弹塑性本构模型,分析逐级加荷下增量应力的途径,使监测更加稳定;采用自动网格划分法对公路路基进行有限单元网格划分,建立有限元分析模型,再通过上述模型得到公路的有限元参数、计算其固结度与沉降应力,再对沉降应力进行变换得到最终沉降量,实现公路路基沉降变形监测.实验对比结果表明,所提方法在实践中有着优秀的实时性、稳定性和准确性,并且拥有良好的监测效果.     

拉伸载荷下钢芯铝绞线的力学特性仿真分析

为了研究钢芯铝绞线(ACSR)结构参数对其在拉伸载荷下力学特性的影响,基于 ANSYS 参数化设计语言(APDL)建立了 ACSR 参数化有限元模型。以 TACSR/AS-410/70 ACSR 为研究对象,基于数值仿真结果研究了该导线股丝应力分布和分层应力应变随拉伸载荷的变化 规律,通过拉伸实验验证了有限元模型的准确性;并基于上述模型数值模拟了不同节径比和铝 钢比下绞线在拉伸载荷下的力学响应。数值仿真结果表明,随铝钢比增加,ACSR 不同层间最 大等效应力随载荷增加而增加的趋势变小,绞线的最大应力值较低,股丝间应力分布更平均; 而 ACSR 节径比越小,绞制越紧密,其不同层股丝应力也越大。研究结果可为 ACSR 的结构设 计、线夹选型及优化设计等提供重要依据。     

基于内聚力模型的纤维复合材料细观损伤模拟

基于代表性体积单元和内聚力模型，使用内聚力单元和扩展有限元方法分别模拟界面损伤和基体损伤，通过ABAQUS二次开发建立了纤维增强复合材料细观力学模型。以受横向拉伸的碳纤维/树脂代表性体积单元为研究对象，分析对比了不同强度下仅考虑界面损伤时复合材料的力学特性和同时考虑界面、基体损伤时的力学特性。结果表明纤维对基体的增强效果随界面强度提高；扩展有限元方法能在不依赖网格数量的条件下准确描述基体中多条裂纹的萌生及扩展过程，并且捕捉到基体裂纹引起的界面损伤；仅考虑界面损伤时的代表性体积单元平均应力-位移曲线后期呈上升趋势，而同时考虑界面和基体损伤的平均应力-位移曲线后期呈下降趋势。     

CPR1000安全壳结构极限承载能力分析

安全壳的极限承载能力是评估安全壳安全性和可靠性至关重要的指标.在Abaqus中通过分离式建模建立CPR1000堆型安全壳三维有限元模型,在自重及预应力载荷下,施加0~3倍范围内压载荷进行非线性有限元分析.对于破坏准则,提出安全壳的极限承载能力包括功能性失效和结构破坏的2个阶段,并给出相应的破坏准则.计算结果表明,在内压载荷达到1.83倍设计内压时,大量混凝土开裂,钢衬里部分屈服,可认为安全壳达到功能性失效;在内压载荷达到2.16倍设计内压时,预应力筋开始屈服,可认为安全壳达到承载力极限状态.     

金属拉伸试验的测量与控制

如何科学有效的按照标准要求实现应力速率及应变速率控制方式切换,最终得到准确可靠的试验指标值,足目前金属拉伸试验的重要问题;在深入分析金属材料拉伸本构模式基础卜,实现了在试样拉伸过程巾按标准自动切换控制方式并自动判别材料本构模式,自动测定弹性模量E、屈服限σs、条件屈服限σp0.2、延伸牢δ、强度限σb等,在一程实际中取得了良好的应用效果。     

摩擦因数对钢丝绳应力和疲劳寿命的影响分析

以6×36+WS结构钢丝绳为研究对象,在SolidWorks中建立了其三维模型,并导入ABAQUS中,通过定义接触对、设置边界条件,建立了钢丝绳有限元模型。在相同的轴向载荷下,仿真分析了不同摩擦因数对钢丝绳应力分布和疲劳寿命的影响。结果表明,钢丝绳在拉伸状态下,绳股外侧钢丝应力较大,且绳股与绳股接触处钢丝应力最大;随着摩擦因数的增大,钢丝绳应力逐渐增大,疲劳寿命逐渐减小,钢丝绳在应力最大处疲劳寿命最小。     

复合固体推进剂细观力学模型研究

为了建立复合固体推进剂的细观力学模型,首要的问题是建立一个能够真实描述推进剂细观形态结构的颗粒填充模型.文中将推进剂看作是颗粒与基体组成的复合材料,详细地给出了应用分子动力学生成推进剂颗粒填充模型的方法,得到了推进剂颗粒在基体中随机分布的颗粒填充模型.在此基础上,采用细观有限元方法进行了分析,获得了推进剂颗粒与基体内的应力分布情况.研究表明:分子动力学方法可以有效地生成推进剂的细观颗粒填充模型,在此基础上进行的细观力学分析可以有效地考虑固体推进剂细观结构对其力学性能的影响.     

振弦传感器极限拉伸室内试验研究

在大型水利水电工程建设的原位监测工作中,时有锚杆应力计应力超量程问题发生,超过量程后的测试数据的可靠性备受争议。分别对量程为210,310,400 MPa三种振弦式应力计进行了极限拉伸试验,对其超量程极限应力状态下的工作状态进行了研究。结果表明:量程范围内荷载—位移曲线呈线性,一直到锚杆应力计屈服前其测量读数是可靠的,一般荷载超过1.6~2.0倍量程范围的读数存在较大误差。     

Fracture behaviour of single crystal silicon microstructures

The fracture behaviour of single crystal silicon (SCSi) microstructures is analysed based on microme-chanical torsional and tensile experiments. The uniaxial testpieces are characterised by the presence of sharp not-ches at the gauge length extremities. The critical loading conditions are reproduced in a finite element model in order to identify the analogies of the failure conditions in tension and torsion. The stress field in the vicinity of the notch tip (were cracks originate) is analyzed, and fracture mechanics parameters are determined. In the finite element model a crack, reproducing the failure process observed in the experiments, is included. The crack area is incrementally increased and the energy release rate for the critical loading conditions in tension and torsion is calculated. Based on these results a failure criterion is formulated along with a procedure for the mechanical integrity analysis of SCSi microstructures of arbitrary shape and loading conditions.     

用遗传算法确定三次β样条曲线的形状参数

研究了三次β样条曲线插值中形状参数的选取问题。给出了三次β样条曲线的能量模型,提出了一种用遗传算法确定插值三次β样条曲线形状参数的方法。对于给定的插值点,以曲线的形状参数作为决策变量,以插值曲线的能量最小作为目标,利用遗传算法确定最优形状参数。实验结果表明利用该算法得到的插值曲线具有较好的光顺性。     

Automatic tension adjustment for interpolatory splines

The authors deal with anomalous oscillations often exhibited by cubic spline interpolating curves. These oscillations, which are not suggested by the data, can be treated with a shaping parameter called tension, which is introduced by generalizing the cubic spline formation in some fashion. The authors consider the associated problem of estimating the magnitude of the tensions necessary to achieve a desired shape. The analysis is based on a theory they reported earlier, called convexity interval analysis, and it leads to an algorithm that produces suitable tension values for given data automatically, without experimentation or interactive user direction. Three examples are given to illustrate the concepts     

Use of optimal control theory for computing optimal injection policies for enhanced oil recovery

The theory of optimal control of distributed parameter systems has been applied to the problem of determining an optimum injection policy for a chemical flooding enhanced oil recovery process. The optimization criterion is to maximize the difference between gross revenue and cost of chemicals injected. Necessary conditions for optimality are obtained through application of the calculus of variations and the distributed weak minimum principle. A gradient method is used for the computation of optimal injection policies. The performance of the algorithm was examined for the surfactant injection in a one-dimensional flooding problem. Two types of interfacial tension behaviour were considered: a type ‘A’ system in which the interfacial tension is a monotically decreasing function with solute concentration and a type ‘B’ system in which a minimum in the interfacial tension occurs at a nominal surfactant concentration. Different initial values were used in order to establish the convergence of the computational algorithm. For a type ‘A’ system, the shape of the optimum injection strategy was not unique; however, there is a unique optimum for the amount of surfactant needed. For a type ‘B’ system, the shape of the optimum injection was unique as well as the amount injected. The results of this work show that given the properties of an oil reservoir and the properties of a surfactant solution, an optimum injection policy which minimizes a specific economic objective functional can be obtained using distributed parameter control theory.     

输电线脱冰过程中耐张串金具的受力仿真分析

针对脱冰过程中导线张力对输电线连接金具的破坏作用,运用ABAQUS软件分别建立特高压输电线路的导线模型和耐张串连接金具的整体模型.然后基于改变密度法模拟均匀覆冰的六分裂导线和覆冰脱落过程,研究不同步脱冰时各子导线的动态张力和导线束扭转角的变化规律,结果表明未脱冰子导线的动态最大张力大于导线覆冰静态张力,导线动张力与导线...     

Structural shape optimization of shells and folded plates using two-noded finite strips

This paper deals with structural shape optimization of shells and folded plates using two-noded Mindlin-Reissner C(0) finite strips. The whole shape optimization process is carried out by integrating finite strip analysis, cubic spline shape definition, automatic mesh generation, sensitivity analysis and mathematical programming methods in an efficient way. Both thickness and shape variables defining the cross-section of the structure are considered. The objective is to minimize the strain energy with a constraint that the total material volume of the structure remains constant. It is observed that minimization of strain energy leads to optimum structures in which the deflections and stress resultants in the members are considerably reduced. This is illustrated using several examples. The relative contributions of the bending, membrane and shear strain energies are also monitored during the whole optimization process. It is found that most optimal shell and folded plate structures are membrane dominant.     

Reuleaux plasticity: Analytical backward Euler stress integration and consistent tangent

Analytical backward Euler stress integration is presented for a deviatoric yielding criterion based on a modified Reuleaux triangle. The criterion is applied to a cone model which allows control over the shape of the deviatoric section, independent of the internal friction angle on the compression meridian. The return strategy and consistent tangent are fully defined for all three regions of principal stress space in which elastic trial states may lie. Errors associated with the integration scheme are reported. These are shown to be less than 3% for the case examined. Run time analysis reveals a 2.5–5.0 times speed-up (at a material point) over the iterative Newton–Raphson backward Euler stress return scheme. Two finite-element analyses are presented demonstrating the speed benefits of adopting this new formulation in larger boundary value problems. The simple modified Reuleaux surface provides an advance over Mohr–Coulomb and Drucker–Prager yield envelopes in that it incorporates dependencies on both the Lode angle and intermediate principal stress, without incurring the run time penalties of more sophisticated models.     

A first-ply failure analysis of composite laminates

A finite-element computational procedure is developed for the first-ply failure analysis of laminated composite plates. The procedure is based on the first-order shear deformation theory and a tensor polynomial failure criterion that contains the maximum stress, maximum strain, the Hill, Tsai-Wu and Hoffman failure criteria as special cases. By specifying the desired criterion, a first-ply failure analysis of composite laminates subjected to in-plane and/or bending loads can be achieved. A number of problems are presented to evaluate these failure criteria when applied to laminates subjected to in-plane and or bending loads.