环件闭式轧制力和力矩上限计算

本文用连续速度场的上限法导出了环件闭式轧制力和力矩计算式，并与环件轧制实验结果作了比较。     

环件闭式轧制力和力矩上限计算

本文用连续速度场的上限法导出了环件闭式轧制力和力矩计算式，并与环件轧制实验结果作了比较。     

铝板轧制过程中的理论与实验研究

本文采用三维弹塑性有限元法对铝板轧制过程进行了计算机模拟,文中同时考虑材料、几何双重非线性,利用 Update-Lagrangian 叠加原理,对铝板轧制从非稳态到稳态进行了模拟计算.首次应用密栅云纹法研究了铝板横向变形.理论计算结果同实测结果有较好的吻合.文中还给出了一些实验难于处理的金属流动信息和应力分布信息.     

基于灰色关联分析的神经网络轧制力预报模型的研究

为了进一步提高采用神经网络对热轧机轧制力的预报精度及建模速度,在分析研究目前已有的各种轧制力预报模型的基础上提出:在采用神经网络进行轧制力预报时,必须首先根据对象合理确定神经网络的输入变量.本文采用灰色关联分析法,利用生产现场实际数据,对影响轧制力设定值计算的多种因素与轧制力进行了相关性分析,最终简化了神经网络的结构,提高了模型的在线应用能力.     

铝材轧制过程中润滑添加剂吸附特性研究

依据铝材轧制过程中润滑油添加剂浓度对摩擦因数的影响，同时以Ｔｅｍｋｉｎ吸附理论为基础，设定添加剂分子在摩擦表面的覆盖率与摩擦因数的联系，提出了铝材轧制过程中润滑添加剂吸附有的求解方法，还定义了铝材轧制时润滑添加剂饱和吸附最低浓度的概念，通过二辊轧机测定了在不同添加剂浓度时纯铝材轧制过程中的摩擦因数，并且计算了相应的润滑添加剂的吸附自由能及其饱和吸附最低浓度，表明理论分析结果与实测结果具有良好的一致     

四辊组合孔型冷轧方钢时轧制压力计算

采用主应力估值法,推导在四辊组合孔型中由圆坯轧制方钢时有关力参数计算式.实验表明,轧制压力的计算与实测的结果基本吻合.这为今后有关设计和生产,提供了简易可靠的力参数数学模型.     

四辊组合孔型冷轧方钢时轧制压力计算

采用主应力估值法,推导在四辊组合孔型中由圆坯轧制方钢时有关力参数计算式.实验表明,轧制压力的计算与实测的结果基本吻合.这为今后有关设计和生产,提供了简易可靠的力参数数学模型.     

三维轧制变形场的配置法解

本文用变分法-配置法研究了轧制时的变形问题。计算结果与实验结果吻合较好,说明配置法是一种较好的方法,应继续研究并推广使用。     

计算机软硬件配置对有限元计算速度和精度的影响

针对有限元模拟,如发展板材轧制快速有限元计算对计算精度和计算速度的不断提高,研究了快速发展的计算机软硬件条件对计算速度和计算精度的影响.自行开发了板材轧制刚塑性有限元程序,选用了1台工作站和4台不同硬件配置PC机,装有三种常用操作系统windows,Linux,IRIX,分析了计算机软硬件对板材轧制有限元计算精度如轧制力和前滑,和对计算时间和迭代次数的影响.提出了有限元计算的合理计算机配置,为有限元模拟计算机配置的选择提供参考,并为板材轧制高精度的快速在线计算提供计算机软硬件平台.     

无网格RKPM法模拟平板轧制过程

将无网格再生核质点法(RKPM)用于刚塑性可压缩材料轧制过程的模拟,采用罚函数满足本质边界条件,选用矩形影响域的张量积核函数,利用有限元网格作为积分单元,对求解域内和边界上采用不同的高斯积分方案。并将计算结果与刚塑性有限元计算结果和文献中的实验数据相比较,说明RKPM方法用于刚塑性可压缩材料轧制过程的可行性和正确性。     

基于LBM的铝微滴斜柱沉积水平偏移研究

金属微滴沉积制造技术采用逐点堆砌方式成型, 为斜柱沉积提供无支撑制造方式, 具有高度灵活性. 本文针对铝液滴斜柱连续沉积过程, 建立格子玻尔兹曼模型进行数值模拟, 研究液滴在凝固表面上的水平偏移运动. 根据表面能充放过程, 沉积运动被划分为下落、快速扩张、慢速扩张、回弹4个阶段, 其受力状态由表面能、重力势能、动能和黏性耗散趋势得到. 液滴内部流动在扩张阶段中表现为滑动状态, 而在回弹阶段中表现为滚动状态. 液滴偏移运动的加速阶段主要发生在扩张阶段, 而偏移距离则在回弹阶段中产生. 扩张阶段的受力状态表明偏移运动的主要推动力为重力和毛细力. 随着液滴轴线距离的增大, 扩张阶段中的加速段时间缩短、速度峰值提高, 使水平偏移距离呈先增大后减小的趋势, 这种阶段化特征源于加速段时长和速度极大值的竞争关系. 不同沉积高度和固液浸润度下, 偏移距离均保持相同的演化趋势. 在相同的轴线距离下, 偏移距离随固液浸润度的增大而减小, 随沉积高度的增大而减小. 通过拟合水平偏移距离演化规律、优化扫描步距, 能够实现斜柱的均匀沉积, 并使倾角与理论结果一致.      

Modelling and simulation of process-integrated powder coating by radial axial rolling of rings

In this paper, we present finite element (FE) process simulations of a new production method used to coat ring-shaped work pieces with functional layers. Similarly to the conventionally applied hot isostatic pressing (HIP), this new coating method is based on powder metallurgy. It is expected to overcome some important drawbacks by integrating the consolidation of the powdery layer material into the hot rolling of the substrate ring. This makes HIP dispensable. Nevertheless several difficulties arise through the process integration. E.g., the presence of the compactable layer requires a different handling of the rolling stage compared with classical ring rolling. FE simulations shall support the design of this new process in order to investigate critical process parameters. For this purpose, new finite element modules have to be developed. A crucial point is the adequate modelling of the layer material. In this regard, we present a rate-dependent finite strain material model that describes the consolidation of the layer material in a thermodynamically consistent way. Moreover, FE process simulations of the new production method are presented and compared with experimental results.     

Heat transfer associated to a hot surface quenched by a jet of oil-in-water emulsion

In hot rolling, the mechanical properties of steel alloys are conditioned by the rolling process but a great part is ensured by the cooling of the hot strip mill. Well controlling this cooling rate and its homogeneity is thus of primary importance for obtaining steels with desired mechanical properties. As the water used in the cooling stage of the rolling process can be polluted by oil (in hot mill strip, some oil is used to lubricate the rolls and a part of it can pollute the water), it is important to know how much varies the cooling rates when water is polluted. In this study, transient cooling has been investigated during quenching of a hot metal disk with various subcooled oil-in-water emulsion jets. The aim of this work is to compare the cooling efficiency of oil-in-water emulsion jet with a pure water jet. Experimental investigations of axisymmetric jet impingements on a preheated hot metal disk (500-600 °C) have been performed with various oil-in-water emulsions. The transient cooling heat fluxes on the quenched side are estimated by coupling the measurement of the temperature field of the other side (rear face) with a semi-analytical inverse heat conduction model.     

连铸板坯热轧中角部裂纹变化的研究

采用有限元方法对轧件角部横向和纵向裂纹在多道次立-平轧制过程中变形行为进行了模拟,分析了裂纹的闭合与扩展行为．结果表明:采用平立辊,裂纹很好闭合,但变形程度大,可能延伸和往轧件顶面移动,对角部横向裂纹,裂纹尖端节点往外扩散,对三角形横向和纵向裂纹,裂纹可能发生折叠;采用孔型立辊,立轧后,轧件裂纹很好地闭合,平轧后,横向和侧面纵向裂纹可能被拉开,顶面纵向裂纹闭合较好,只有三角形横向裂纹可能发生折叠．     

滚压强化的残余应力的数值仿真及工艺分析

表面滚压强化,由于在表层引起加工硬化和残余压应力,可以十分有效地提高构件、零件疲劳强度,而滚压强化的有限元数值仿真,将成为分析优化滚压强化工艺的重要手段.本文建立了连续多、圈滚压工艺的有限元数值仿真模型,获得了比较合理的滚压变形与残余应力结果.在此基础上对滚压工艺做了进一步分析.结果表明,滚压变形的进给量太大.滚压的转速太快都容易造成工件表层残余应力分布的不均匀甚至形成残余拉应力;在滚压与未滚压的过度区域,从表面到心部的近1mm范围内,均未出现人们通常所担心的残余拉应力.这将在工程生产实践中,为滚压工艺制订提供重要的依据.     

Analysis of cyclic crack growth in high strength roller bearings

The lives of ball and roller bearings and raceways depend on the number of rolling contacts consumed by 3 stages of the failure process: (i) the preinitiation; (ii) crack initiation, and (iii) crack growth stages. This paper employs fracture mechanics analyses to estimate the portion of the bearing life residing in the crack growth stage. Rough estimates of: (a) the Mode II, ΔK_II driving force for small cracks below the rim surface subjected to repeated 2-dimensional, pure rolling contacts, (b) the corresponding crack growth rates, and (c) the number of contacts to failure, are obtained as a function of the peak contact pressure, initial flaw size and other variables. Factors influential to the growth stage are identified. Finally, the comparisons with measured total lives provide insights into the validity of the analysis and the importance of growth relative to the preinitiation and crack initiation stages.     

Modeling wheel-induced rutting in soils: Rolling

Theoretical models for predicting penetration of non-driving (towed) rigid cylindrical wheels rolling on frictional/cohesive soils are presented. The models allow for investigating the influence of soil parameters and wheel geometry on the relationship between the inclined rolling force and wheel sinkage in the presence of permanently formed ruts. The rolling process is simulated numerically in three dimensions using the finite element code ABAQUS. The numerical simulations reveal that the advanced three-dimensional process of rutting can be regarded as steady, and an approximate analytic model for predicting sinkage under steady-state conditions, which accounts for three-dimensional effects, is also developed. The differences between wheel rolling and wheel indentation (considered in a separate paper) are discussed. Numerical and analytic results are compared with test results available in the literature and obtained from preliminary small-scale experiments, and general agreement is demonstrated.     

Mathematical model for cold rolling based on energy method

There is an increasing requirement for improved accuracy of the rolling models which are widely used in rolling plant in order to produce high-quality products, because this accuracy is important for rolling schedule setup and automatic control. A three-dimensional mathematical model for cold rolling using tangential velocity field and energy method is firstly proposed to investigate the deformation of the strip at the roll gap based on elastic and plastic mechanics. The field and geometrical approximation yield criterion are used to integrate the internal plastic deformation power. The friction power is analyzed using the co-line vector inner product method. Finally, the analytical expressions of roll separating force and roll torque are obtained quickly considering the effect of roll flattening on the roll separating force. The predicted roll separating forces are consistent with other researchers’ models, especially for on-line measured roll separating forces in a tandem cold rolling plant. The accurate predicted results provide valuable guidelines for optimization of rolling process.     

Qualitative analysis of a rolling hoop with mass unbalance

The dynamical behavior of a rolling hoop with an unbalanced point mass under the influence of gravity is discussed. The whole process from rolling to hopping of the hoop is analyzed qualitatively. The conditions of slipping, hopping and touching down of the hoop are obtained. It is shown that the hoop cannot maintain a pure rolling before hopping up, and the slippage is unavoidable. The hoop has neither vertical velocity nor vertical acceleration at the moment when the normal constraint force vanishes. The hopping motion of the hoop can occur only when the derivative of the vertical acceleration with respect to time is positive. It requires that the angular velocity of the hoop should be larger than a critical value, and the mass point should be located in the fourth quadrant of the hoop circle at the moment of hopping. The whole process of the pure rolling, rolling with slipping, hopping and falling motions of the hoop is shown in the phase plane, and the physical explanation of the hopping motion is given.     

接触应力对FCB车轮钢组织演变与性能的影响

利用双盘滚动摩擦磨损试验机进行了贝氏体车轮钢的滚动磨损试验,采用扫描电子显微镜(SEM)、电子背散射衍射(EBSD)分析不同接触应力条件下贝氏体车轮钢次表层微观组织演变. 结果表明:在滚动磨损条件下,磨损机制由黏着磨损转变为疲劳磨损,增大接触应力对黏着磨损阶段的磨损量影响不大,但会显著增加疲劳磨损阶段的磨损量;贝氏体车轮钢在塑性变形的过程中,贝氏体铁素板条中位错逐渐增值、先累积形成小角度晶界,而后形成大角度晶界,使贝氏体铁素体发生细化;接触应力的大小影响表层组织的演变,当接触应力增至1 150 MPa时,晶粒细化为超细等轴晶,继续增加接触应力,组织变化并不明显. 接触应力大小会影响贝氏体车轮钢的表面硬度. 接触应力增加使贝氏体车轮钢的表面硬度增高,硬化层深度增大.