Proposal and use of a void model for inclusion cracking for simulating inner fracture defects in drawing of ferrite–pearlite steels

A void model for inclusion cracking is proposed and used for simulating inner fracture defects in the drawing of ferrite–pearlite steels. First, a void model for inclusion cracking is proposed based on the void model for inclusion-matrix separation previously proposed by the author. Next the simulation and experiment of the multipass drawing are performed using four types of ferrite–pearlite steels. The inner diameter of the die at which the material fractures, the material density distribution in the radial direction after drawing through the die preceding that at which the material fractures, and the material shape in the longitudinal section after drawing through the die at which the material fractures calculated from the simulation, are compared with those obtained experimentally. Finally, the validity of the proposed void model is confirmed by comparing the simulation and experimental results.     

A study of material flow systems (input/output) in high-bay warehouses

A method of planning and designing product sorting systems in warehousing is described. The theoretical background of the analytical models and simulation modelling is given. A calculation of the capacity of elements for joining and dividing for different priorities of material flow is described. New parameters are introduced in the formula for calculating the average number of unit loads in a system for joining, in the direction of the slave flow and for a simple analytical model for joining material flows with two different priorities with an exponential distribution of inter-arrival time. Simulation results are obtained using the GPSS/FON simulation language. Some characteristic results, used in the process of planning and design of two new distribution centres in Belgrade, are shown.     

The importance of parameter-dependent coefficient of restitution in discrete element method simulations

The coefficient of restitution (COR) is an important constant that represents the energy dissipation during contact between two objects. Simulation using the conventional discrete element method (DEM) involves a constant COR. This study presents a DEM simulation method that uses a parameter-dependent COR. The parameter-dependent COR was obtained from a collision incident between spherical particles and a plate surface using a drop-test apparatus. Glass and polypropylene beads of 3–6-mm diameter were used while acrylic and steel were used as the plate surfaces. The particle trajectories were captured by a high-speed camera and analyzed by an image analyzer. The COR was then correlated to a parameter-dependent COR function that depends on the material, impact velocity, and temperature. Free-fall DEM simulations using a constant COR and parameter-dependent COR were compared. The parameter-dependent COR approach obtained better agreement with experimental results than the constant-COR approach. The proposed concept could be applied for other material combinations with a wide range of operating conditions to obtain a database of parameter-dependent COR values for the simulation of solid handling applications.     

基于Johnson-cook本构模型的EPE包装跌落冲击模拟

目的将聚乙烯泡沫塑料在动态压缩试验下得到的力学性能引入有限元中,创建材料模型,并应用于跌落冲击仿真分析,以提高仿真的精确度。方法通过聚乙烯泡沫塑料在不同速率下的压缩试验,得到真实的应力-应变曲线,并基于Johnson-cook本构模型在有限元中建立EPE的材料模型。最后用AnsysWorkbench中的LS-DYNA模块对聚乙烯泡沫缓冲包装的跌落过程进行仿真分析,用LS-PREPOST软件进行后处理。在此基础上,对比分析仿真结果和实验结果。结果仿真结果的误差分别为0.85%,1.6%,2.97%,与实验结果基本一致。结论基于Johnson-cook本构模型构建的聚乙烯泡沫塑料有限元材料模型能有效提高低速冲击的仿真精度,为非线性材料和应变率敏感材料的有限元动态冲击分析提供了参考。     

基于弯曲实验的DP980力学性能研究

目的 针对仅通过单向拉伸实验无法准确表征金属板材在弯曲成形过程中的力学性能变化的问题,研究通过弯曲实验获取材料力学性能参数.方法 对高强钢DP980展开力学性能测试研究,主要通过弯曲实验对材料弯曲变形过程中形成的弯矩曲率进行测试,将得到的弯矩曲率转化为应力-应变.分别将弯曲和拉伸得到的应力-应变数据导入到三点弯和辊弯成形有限元仿真中,预测板材的成形角度.结果 DP980弯曲变形时的屈服强度要大于轴向拉伸时的屈服强度;分别利用弯曲和拉伸实验测得的应力-应变数据进行仿真,与三点弯实验结果对比发现,采用弯曲实验得到的应力-应变数据对回弹量的预测偏大,而利用拉伸实验得到的应力-应变数据进行仿真,仿真得到的回弹量则偏小,弯曲实验下变形过程中的应变变化数据更加符合真实过程,与辊弯实验对比发现,利用弯曲实验数据进行仿真可以更准确地预测V形板的最终成形角度.结论 相较于单向拉伸实验,通过弯曲实验获取的材料力学性能参数可以更准确地描述材料在三点弯、辊弯成形过程中的力学性能变化.     

An expression for contact area between particles in a powder compact in terms of the porosity

An equation for contact area between powder particles in a powder compact, in terms of the porosity, has been derived using a geometry representing spherical voids of different sizes distributed in a material matrix. This equation is verified using experimental data as well as results obtained from computer simulation of powder compaction using a finite element method.     

生物基育苗秧钵包装容器的力学性能测试与分析

目的对一种由稻壳粉为主要材料制备的生物基育苗秧钵包装容器的力学性能进行测试。方法通过静态拉伸试验测得其弹性模量及泊松比,然后通过对秧钵整体的压缩实验,测得秧钵杯体不同位置处的极限载荷。在此基础上,利用有限元软件对该秧钵进行模拟计算。结果通过模拟计算发现,该秧钵在受压时整体的应力分布可以分为4层,其中上层杯口处的应力最大,最容易破坏,而秧钵中间部分的应力则较小。结论该模拟结果与实验结果基本吻合。     

橡胶隔振器大变形有限元分析

以橡胶隔振器为研究对象,基于超弹性本构模型,对拉伸、压缩、剪切状态下分别进行有限元计算,探讨橡胶等不可压缩材料大变形有限元建模技术;重点研究橡胶结构不同受载方式下变形模式及有限元分析所需要的材料试验数据。经与试验结果对比分析,得到隔振器三种状态下,填充超弹本构模型最优的材料数据类型,为橡胶结构件的数值模拟提供有益参考。     

Nonlinear Dynamic Behavior of Granular Materials in Base Excited Silos

Nonlinear behavior of granular materials stored in steel silos subjected to dynamic base excitation due to earthquake is presented in the current article. Three-dimensional finite element (FE) modeling of the granular material silo is carried out under three-directional earthquake ground acceleration time histories. Granular material is modeled by adopting a continuum approach. The nonlinearity of the granular materials is represented by a hypoplastic material law in the FE approximation. The interface between the granular material and the silo wall is modeled by using surface-to-surface based contact formulation. The horizontal and vertical displacements of the granular material under earthquake ground acceleration at various depths of the silo are studied. Moreover, the stresses induced in the steel silo are also investigated. The static FE simulation and the analytical solution obtained by using Janssen's theory are observed to be in close agreement. Also, the dynamic FE simulations compare with the calculated results using Eurocode 8 part 4 with reasonable accuracy. The stresses in the steel silo wall are higher for loose packing of the granular material as compared to that for the dense packing.     

Determination of Material Parameters of Welded Tube via Digital Image Correlation and Reverse Engineering Technology

Material characteristics play an important role in tube hydroforming (THF). A method, based on digital image correlation (DIC) and reverse engineering (RE) technology, is proposed to determine the material parameters of a welded tube in hydroforming with a single tubular blank. The material parameters of the weld and parent metal are determined by applying membrane theory and the force equilibrium equations, as well as the deformation data which are obtained by DIC and RE technology in the THF process. Finite element simulations of welded THF are performed with these material parameters and the maximum bulge radii and axial profiles of the weld and parent the metal obtained from the simulations are compared with those obtained from the hydroforming experiments to verify the reliability of the proposed method. The results show that the material parameters of the weld are lower than those of the parent metal. With the material parameters adopted in FE simulation there is a good agreement between the simulation and the experiment as for the maximum bulge radii and axial profiles of the weld and parent metal. This verifies that the proposed method is acceptable for determining material parameters of a welded tube.     

Correlation of tensile and flexural responses of strain softening and strain hardening cement composites

Closed form equations for generating moment–curvature response of a rectangular beam of fiber reinforced concrete are presented. These equations can be used in conjunction with crack localization rules to predict flexural response of a beam under four point bending test. Parametric studies simulated the behavior of two classes of fiber reinforced concrete: strain softening and strain hardening materials. The simulation revealed that the direct use of uniaxial tension and compression responses under-predicted the flexural response for strain softening material while a good prediction for strain hardening material was obtained. The importance of strain softening range on the flexural response is discussed using non-dimensional post-peak parameters. Results imply that the brittleness and size effect are more pronounced in the flexural response of brittle materials, while more accurate predictions are obtained with ductile materials. It is also demonstrated that correlations of tensile and flexural results can be established using normalized uniaxial tension and compression models with a single scaling factor.     

一种钢板材料动态拉伸本构方程确定以及试件尺度效应研究

采用数值模拟方法,优化设计了Hopkinson拉伸实验中,QP980CR钢的片状试件尺度。对所设计的试件,在MTS(810材料试验机)上进行了准静态拉伸试验,在Hopkinson拉杆装置上进行了不同应变率及不同温度的动态拉伸试验。由准静态及动态拉伸试验结果,确定了试件材料的J-C型动态拉伸本构方程。基于确定的试件动态拉伸本构方程,采用数值模拟方法,研究了Hopkinson拉伸试验中,试件的形状和尺度对测试结果的影响。     

缠绕肋缠绕过程试验及力学行为分析

首先通过单向拉伸试验测试和理论计算两种方法得到4层(45?/?45?/45?/?45?)铺设碳纤维复合材料的弹性模量,作为文中数值计算及弯矩分析的材料参数。通过4层(45?/?45?/45?/?45?)铺设碳纤维复合材料肋进行整体缠绕过程试验,得到肋整体缠绕过程肋表层应变和缠绕弯矩。利用ABAQUS分别建立了复合材料肋整体缠绕精细有限元模型,实现了缠绕一周过程强几何非线性数值模拟分析,得到各层应力、应变特征和缠绕弯矩,并与试验结果比较分析。进而给出缠绕弯矩解析表达式,并对材料铺设与厚度进行分析,得到缠绕过程最优材料铺设机理与最大厚度分析方法。该文对缠绕肋设计和深入研究具有重要参考价值。     

Numerical Analysis of Bird Impact on Glass-Reinforced Leading Edge of an Aircraft Wing

The paper describes the methodology of modeling and simulation of bird impact mechanism of GLARE laminate structures. The bird is modeled using Lagrangian concept. Explicit finite element techniques have been developed to simulate the impact mechanics. The study involves deeper understanding of impact dynamics and contact mechanics. The bird impact analysis has been carried out on typical configuration of GLARE 3/2, 4/3, 5/4, 6/5, 7/6 and 8/7. The results of stress propagation and material deformation at high strain rate have been obtained. Results from the numerical analysis are compared with experimental results, and the material is found to be capable of absorbing the impact energy. The results also show that the bird material model chosen to simulate for carrying out impact mechanics analysis is found to be capable of capturing most of the complex behavior exhibited by functional structural material GLARE.     

航空接头锻件等温锻压成形工艺

为了提高航空锻件的综合性能,通过等温锻压工艺研究了航空接头锻件的成形过程,采用Deform3D有限元软件对高筋薄壁铝合金航空接头锻件的锻压成形工艺进行了仿真研究,在实验室油压机上开展了缩比(1∶5)锻件的成形工艺实验.研究结果表明:在坯料与模具温度均为450℃、成形速度为0.1 mm/s的等温模锻工艺下,材料变形抗力比常规热模锻降低70%,材料在模腔中的流动性提高,锻件充填完好,锻件变形均匀,应力集中降低;等温锻造工艺可使锻件获得流线顺畅、晶粒细小、力学性能优良的纤维组织,避免了热模锻易出现的涡流、折叠、穿流、充填不满等锻造缺陷;仿真与实验结果吻合,为航空接头锻件锻压成形工艺的制订提供了依据.     

蓄冷球凝固的FLUENT数值模拟研究

利用计算流体力学软件FLUENT凝固/熔化模型对一种相变材料蓄冷球的凝固过程进行数值模拟研究,得到了在第一类边界条件下蓄冷球凝固过程的温度场分布、相界面移动规律,并分析了凝固时间与壁面温度和球径的关系。所得到的结论对相变问题的数值模拟以及相变蓄能装置的设计具有重要的参考价值。     

高纯电子级溴化氢合成研究之一 ——反应动力学特性及其机理

为解决高纯电子级溴化氢源头制备的工程技术难点,对溴化氢合成过程的各基元反应进行了深度剖析,采用随机算法进行了动力学模型构建与模拟。通过公式推导,并结合实验结果,得到了宏观总动力学方程。根据溴化氢合成动力学特性,总结了溴化氢燃烧链式反应的机理。同时,考察了不同温度、投料比对溴化氢合成的影响。得到的一系列结论可以为干法无硫溴化氢原料合成的产业化提供科学支撑。     

Cyclic hysteresis of AZ31B extrusion under load‐control tests using embedded sensor technology

The fatigue behaviour of AZ31B extrusion magnesium alloy under load‐control cyclic test conditions is estimated using a combination of simulation and experimental results. The strain measurement of this asymmetric material is found experimentally using a Fibre Bragg Grating (FBG) sensor during rotating bending tests. Then, to analyse applied stresses in the sample – particularly in the plastic deformation range – the Variable Material Property (VMP) method is employed. Using this simulation method, the hysteresis loops of two critical top and bottom elements of the sample's cross section under different bending moments are obtained. Finally, the strain of the sample during rotating bending, as measured by the embedded FBG sensor, is related to the stresses obtained from the modeling using a mapping function. The hystereses obtained from this combination of the modeling and experimental results are compared with the results of a companion strain‐control pull–push test in which the input strain history was that of measured by the FBG sensor. Observations verify that the stresses of the combined VMP‐FBG hysteresis loops have good compatibility with the stress responses obtained through the experiment. The hybrid model introduced in this work can be employed to capture cyclic hysteresis, and hence estimate the fatigue life, under load‐controlled rotating bending tests.     

采用非连续变形分析对空气冲击湿砂造型过程的数值模拟

空气冲击湿砂造型过程有着本身的特点：快速冲击，离散的材料体系，材料非线性和几何大变形并存，是一个非常复杂的力学过程。本文首次使用非连续变形分析(DDA)的方法建立了粘弹性本构非连续块体模型模拟松散型砂体系，对松散型砂在空气冲击作用下的密实过程进行了数值模拟。通过与相应的实验数据以及有限元方法的计算结果进行比较，本文得出以下结论：非连续变形分析方法可以较好地解决湿砂造型空气冲击紧实过程的数值模拟问题，其应力时间曲线与实测曲线趋势基本相同，相对于有限元方法的计算结果来说，DDA的计算应力值与实测应力值的偏差比较小；使用非连续变形分析进行松散型砂应力场的数值模拟比有限元方法更接近真实情况。     

双稳态复合材料层合结构的黏弹性模型

为探明双稳态复合材料层合结构在复杂环境条件下的应用,对双稳态复合材料层合结构的黏弹性行为进行了研究。首先,将纤维简化为弹性材料,考虑基底材料的黏弹性行为。然后,根据纤维和基底的材料属性,通过理论分析得到了双稳态复合材料层合结构的黏弹性材料属性;根据经典层合板理论、最小应变能原理和Maxwell黏弹性模型建立了双稳态复合材料层合结构的黏弹性模型,通过理论分析得到其第二稳态主曲率与扭曲率随加载时间和温度的变化关系。同时,利用有限元软件ABAQUS及其子程序UMAT建立了相应的有限元模型,研究了加载时间和温度对层合结构第二稳态性能的影响。理论与模拟结果均表明:层合结构第二稳态主曲率随加载时间的延长和温度的升高而增大;扭曲率随加载时间的延长而减小,一般情况下随温度的升高而增大,但在加载时间较长且温度较高时,可能会出现扭曲率随温度升高而减小的情况。理论计算结果与有限元模拟结果的比较显示两者吻合较好,可以通过有限元模拟对双稳态复合材料层合结构的黏弹性行为进行研究。