钢丝绳捻制成形接触问题的有限元分析

基于虚功原理建立了钢丝绳捻制成形过程中考虑接触摩擦时的刚度方程,将小球分裂算法用于接触搜索,Augmented Lagrange法用于计算接触力．以钢丝绳一次捻制成形过程为例,分析了摩擦系数和自扭转系数对接触应力和加工应力域变的影响．研究结果表明。摩擦系数对剪应力的影响比对等效应力和等效塑性应变的影响大;考虑摩擦时钢线表面的轴向残余应力计算结果比无摩擦条件下的计算结果更接近实验结果．     

轴向加载下不同捻向多股钢丝绳的力学行为研究

多股钢丝绳在工程结构中广泛应用，其中多数钢丝经过两次捻绕成为二次螺旋钢丝。基于Love弹性曲杆理论和变形前后钢丝绳结构状态分析，建立了轴向加载下考虑二次螺旋钢丝局部变形行为的多股钢丝绳弹性理论模型，并通过有限元模拟研究了钢丝绳的弹塑性力学响应。将弹性理论模型结果与有限元模拟结果、Costello模型进行了对比验证，进一步分析了不同捻向钢丝绳(顺捻、交互捻)整绳和局部钢丝的力学行为。研究发现二次螺旋钢丝的局部响应不同于单股绳一次螺旋钢丝，钢丝的弯曲和扭转变形沿钢丝绳截面周期性变化。整绳受拉伸载荷时，沿钢丝轴线的拉伸变形占主要部分，交互捻钢丝的弯曲和扭转变形均小于顺捻钢丝，且扭转变形的方向与顺捻钢丝相反。在通常弹性使用范围内，交互捻钢丝绳沿钢丝截面的最大拉伸和扭转应力均小于顺捻钢丝绳，且产生的反作用扭矩更小，因此优于顺捻钢丝绳。     

金属板料拉延二次成形的有限元法模拟

建立了二次拉延成形加工的有限元分析计算模型;采用一次成形-回弹计算-二次成形的连续计算过程模拟了实际加工过程;有限元计算采用动力显式计算程序MSC/DYTRAN;用主从面（master surface-slave surface)模型定义板料和模具的接触,摩擦力用库仑定律计算;利用动力松弛法对成形过程中的回弹进行了计算。模拟结果和实际零件比较,证明模型合理,自满稳定,结果可靠,具有良好的应用价值。     

板材多点成形过程的有限元分析

多点成形过程采用静力隐式格式进行数值模拟是比较合适的。本文建立了用于多点成形过程分析的静力隐式弹塑性大变形有限元方法 ,给出了对稳定迭代收敛过程效果较好的板壳有限单元模型、处理多点不连续接触边界的接触单元方法以及增量变形过程中应力及塑性应变计算的多步回映计算方法。基于这些方法编制了计算软件 ,应用该软件进行了矩形板的液压胀形过程及球形模具拉伸成形过程的有限元分析 ,数值计算结果与典型的实验结果及计算结果吻合很好。最后给出了球形、圆柱形目标形状的实际多点成形过程的数值模拟结果。     

中频感应局部加热弯管回弹的研究

对中频感应局部加热弯管在不同钢管材料及规格，不同弯曲半径及弯曲角度等工艺参数时的加载和卸载的力能参数，应力应变进行了分析和实验研究，提出了中频感应局部加热弯制大直径钢管的回弹理论，计算结果与有限元模拟结果以及实际弯制的２０，１０ＣｒＭｏ９１０和１２Ｃｒ１ＭｏＶ等钢管弯头实测的回弹量吻合良好。     

宽板塑性弯曲成形过程中的板厚变化规律

根据宽板弯曲过程中的变形与应力分布特征，提出了一种计算弯曲过程中板料厚度随弯曲程度变化的新的近似解答方法．该方法基于塑性增量理论，应用塑性成形过程的体积不变假设和弯曲过程的平面假设．作为算例，得到了理想刚塑性材料的板料厚度、变薄系数以及应变中性层内移系数随板料弯曲内表面曲率半径变化的规律，并与实验数据进行了比较，两吻合良好．     

板带钢热连轧及微观组织演变非线性三维仿真

 普碳钢热连轧成形过程是一个高度非线性的问题，存在几何非 线性，材料非线性和接触非线性. 本文针对上海宝钢2050热连轧生产 线进行研究，通过实验确定SS400钢的真应力-应变曲线，确定该钢种 的变形抗力与温度、应变、应变率的关系，对有限元软件ABAQUS进行 二次开发，将率相关的各向同性强化变形抗力模型写入用户材料子程 序，对轧制过程中的温度场，应力-应变场进行完全热力耦合的分析. 同时，对轧制过程中工件微观组织(晶粒度)的演变过程进行数值模拟， 从而为保证成形件的质量、制定合理的成形工艺等提供可靠依据，同 时为最终实现产品性能的在线数值预报奠定基础.     

塑性成型弹塑性有限元模拟的静水压力间接计算法

在单元内偏应力导数精度分析的基础上，了偏应力导数佳点逐层积分建立了修正的静水压力间接算法，将该方法应用于金属成型过程的弹塑性有限元模拟中，较好了解决了大步长时应力计算精度低的问题，提高了计算效率，算例表明，在变形总量和应变步长都较大的情况下。用庐方法计算得到的应力和变形载荷仍具有较好的精度。     

重型车驾驶室结构特性仿真分析与研究

针对某重型车驾驶室结构特性分析与优化的问题进行研究,采用CATIA软件对驾驶室进行几何建模,利用HYPERMESH软件建立有限元模型,并进行自由模态仿真分析;利用试验模态和计算模态分析对比的方法,验证了有限元模型的有效性;结合此款驾驶室的承载特点,利用MSC.Patran/Nastran对驾驶室的弯曲和扭转工况进行刚度和强度仿真计算,利用Fatigue对扭转工况下驾驶室的疲劳强度进行仿真计算,给出了驾驶室的易疲劳破坏位置。研究结果表明:驾驶室固有频率为37.826Hz,避开了激振频率,避免了共振现象;在扭转、弯曲两种工况下,驾驶室产生的最大应力分别为108MPa、38.8MPa,均小于材料许用应力,弯曲、扭转刚度满足要求,驾驶室抵抗变形的能力较好,结构设计合理。     

用于板料成形反向模拟的特殊应力更新算法

提出了一种改进的反向模拟法,以最终构型为研究对象,采用Euler坐标系,基于虚功原理获得有限元列式. 改进的反向模拟法采用了一种基于塑性流动理论的本构方程,可以充分考虑应变历史对塑性变形的影响. 为了避免流动理论应力更新算法过程中关于未知量\Delta\lambda 的非线性方程的求解,引入等效应力思想,无需Newton-Raphson迭代直接计算未知量\Delta \lambda . 盒形件的拉深实例中,传统的基于塑性形变本构方程的反向模拟法和改进的基于塑性流动本构方程的反向模拟法计算结果,分别与基于增量有限元法的正向数值模拟求解器LS-DYNA计算结果进行对比. 通过获得的坯料轮廓、成形极限图、等效应变分布、计算效率等的比较,验证了所提出的基于塑性流动理论本构模型的应力更新算法的有效性.      

Response of a wire rope strand to axial and torsional loads: Asymptotic modeling of the effect of interwire contact deformations

The refined discrete mathematical model of a simple helical wire rope strand is developed. The effect of the transverse contraction of the wire strand through Poisson’s ratio and also through local contact deformations (wire flattening) has been studied in detail. In order to express the interwire contact deformation in terms of the parameters describing the strand deformation, we formulate a two-dimensional model interwire contact problem. The interwire contact interaction is treated as a frictionless unilateral plain strain problem. The nonlinear model interwire contact problem has been solved by the method of matched asymptotic expansions. The constitutive equations for a helical wire rope strand, which take into account both the Poisson’s ratio effect and the effect of contact deformation, are obtained in a closed form.     

The effect of cell irregularity on the high strain compression of 2D Voronoi honeycombs

The in-plane compression of low-density irregular Voronoi honeycombs with periodic boundary conditions has been simulated to engineering strains of 0.6 using finite element analysis. Different degrees of geometric irregularity in the honeycomb cells, as quantified using a regularity parameter, have been employed. The stress–strain predictions reveal that, for a fixed relative density, a more irregular honeycomb has a higher tangential modulus at low strain but supports a lower compressive stress at higher strain (above approximately 0.04) when compared with a more regular honeycomb. A combined ‘springs in parallel’ and ‘springs in series’ model has also been compared quantitatively with the simulation stress–strain results, the relative importance of the ‘springs in series’ mechanism having been found to increase with the irregularity of the honeycomb and, in many cases, with the applied compressive strain. In addition, the dependency of the Poisson’s ratio, the maximum bending strain in the cell walls, and the mean junction rotation upon the applied compressive strain have also been determined for a range of honeycomb irregularities.     

冲击载荷作用下柱壳链中的弹性波传播简化模型及其解析解

柱壳链能引起波形的弥散,具备操控波形的潜力。建立了柱壳链结构的等效连续介质模型和细观有限元模型,研究了质量块冲击作用下柱壳链中的弹性应力波传播过程及其几何弥散特性。基于考虑横向惯性修正的Rayleigh-Love波动方程,建立了柱壳链在质量块冲击下的控制方程,采用Laplace变换及其逆变换获得了位移场、速度场和应变场的解析解,所得结果与细观有限元模拟结果较好吻合。结果表明,在冲击过程中应变和速度峰值均逐渐减小,应变峰值、振荡幅度和波形前沿宽度与泊松比和惯性半径相关,泊松比和惯性半径越大,应变峰值越小,应变分布振荡越剧烈,波形前沿宽度越宽。     

The mechanical behavior of a wire rope with an independent wire rope core

A new model for simulating the mechanical response of a wire rope with an independent wire rope core is presented. The rope is subjected to both an axial load and an axial torque. In contrast with previous models that consider the effective response of wound strands, the present model fully considers the double-helix configuration of individual wires within the wound strand. This enables to directly relate the wire level stress to the overall load applied at the rope level. The model assumes a fiber response of individual wires. Two alternative kinematics of the wires are considered, and are used to predict the elastic response of the rope. The postulated kinematics are theoretically validated and the predicted rope response is in agreement with new experimental data. The new model enables the extraction of the stress at the wire level that can be used in turn to estimate global features of the rope such as force interaction between wires, rope stiffness, strength, and fatigue life.     

拱脚结构的模型实验与有限元分析

本文应用环氧树脂材料浇铸成某大跨度桥梁预应力拱脚模型,采用精密铸造成型方法做出模型中的四条索道孔。用自行研制的传感器施加四条模拟钢索的索力,通过专门设计的加载装置,使用精确的滑轮导向,在5个截面上分别施加剪力Q、弯矩M和轴力N,并考虑自重载荷,进行了电测模型实验。应用ANSYS软件对拱脚实际结构进行了有限元分析,根据模型实验时索与索道孔壁的接触情况建立了力的边界条件,使有限元计算与真实情况接近,计算误差大为减小。同时将实验与有限元分析结果进行了比较,变化规律一致,数值较为接近。对拱脚的优化设计提供了重要的参考依据。     

Micro-mechanical modelling of strain induced porosity under generally compressive stress states

This paper is concerned with the nucleation and growth of voids in a titanium alloy undergoing high temperature deformations under generally compressive stress states typical of forging processes. A micro-mechanical model for void nucleation has been developed based on a debonding process between primary alpha particles and the beta matrix. The finite element model developed has been used to examine in detail the stress state sensitivity of void nucleation within the particle-matrix system. The results obtained are compared with other phenomenological approaches showing good agreement for most stress states, but giving different results for a range of compressive stress states. A continuum-level representation of the micro-mechanical results has been obtained and implemented into a finite element model. Cylindrical specimen compression tests have been carried out over the strain rate range 0.005-5.0s⁻¹ and temperature range 925–975°C under conditions of high specimen-die friction.Regions of stress triaxiality that are tensile in nature were therefore generated, and the specimens tested to an overall strain of 0.5 were sectioned, polished and etched. The resulting distributions of voids were quantified, and compared with those predicted using the finite element model discussed above. Good quantitative agreement was obtained both in terms of the magnitude of the area fractions of voids and their distributions. The model also captures reasonably well the strain rate and temperature dependence of the voiding. However, the model assumptions of uniform distributions of alpha particles which are all perfectly spherical and with identical interfacial bond strengths are overly simple, and need to be improved.     

Crystal plasticity finite element modeling of mechanically induced martensitic transformation (MIMT) in metastable austenite

A new crystal plasticity model incorporating the mechanically induced martensitic transformation in metastable austenitic steel has been formulated and implemented into the finite element analysis. The kinetics of martensite transformation is modeled by taking into consideration of a nucleation-controlled phenomenon, where each potential martensitic variant based on Kurdjumov–Sachs (KS) relationship has different nucleation probability as a function of the interaction energy between externally applied stress and lattice deformation. Therefore, the transformed volume fractions are determined following selective variants given by the crystallographic orientation of austenitic matrix and applied stress in the frame of the crystal plasticity finite element. The developed finite element program is capable of considering the effect of volume change by the Bain deformation and the lattice-invariant shear during the martensitic transformation by effectively modifying the evolution of plastic deformation gradient of the conventional rate-dependent crystal plasticity finite element. The validation of the proposed model has been carried out by comparing with the experimentally measured data under simple loading conditions. Good agreements with the measurements for the stress–strain responses, transformed martensitic volume fractions and the influence of strain rate on the deformation behavior will enable the model to be promising for the future applications to the real forming process of the TRIP aided steel.     

不同爆炸冲击震动输入对整体隔震系统隔震效果的影响

采用已获得国家实用新型专利技术的鼓形钢丝绳隔震器对2层钢框架结构进行整体隔震,在隔震系统一定的情况下,对其输入形式统一的爆炸冲击信号,利用有限元数值模拟其隔震效果。通过改变输入加速度信号的主脉宽和幅值,研究了爆炸冲击信号的主脉宽和幅值对整体隔震结构的隔震率的影响,从而加深对整体隔震系统的认识,有利于促进整体隔震技术的研究,对工程实践具有指导意义。 更多还原     

输电塔线体系断线动力响应及杆塔破坏模拟研究

利用ABAQUS软件建立500kV典型输电线路段塔线耦合体系的精细有限元模型,数值模拟覆冰塔线耦合体系断线后的动态响应和杆塔破坏过程。对杆塔引入等效塑性应变破坏准则,当单元的最大等效塑性应变达到许用值时,删除单元以模拟杆塔的破坏。数值模拟结果与按我国电力设计规程以及IEC设计规程的计算结果比较表明:地线断线时用塔线模型和规程计算得到的杆塔应力的差别较导线断线时大,地线和导线断线时杆塔的最大应力均大于两种规程的计算值;杆塔上与地线连接的角担是断线时的薄弱区域。现行电力设计规程中采用静力分析方法对断线产生的冲击动力作用的估计不足。