基于有限元法的数控弯管成形及回弹研究

基于有限元分析软件ABAQUS,参照轨道车辆用不锈钢管材和数控弯管机,建立了有效的不锈钢管材弯曲成形及回弹有限元仿真模型,研究了弯管在弯曲成形过程中应力分布和管材的弹塑性变形,同时分析了不同弯曲角度下弯管回弹的情况,建立回弹角度与弯曲角度的定量关系。结果表明,在弯管成形过程中,最大mises应力随弯曲角度的增大而增大,但当卸载后在折弯区的残余应力分布与折弯角度成线性关系,此外管材在弯曲后回弹角随着弯曲角度的增大而增大,且呈现出明显的线性关系。     

小弯曲半径弯管的对挤成形

锅炉的弯管大都在弯管机上采用冷弯或热弯成形。管件的弯曲半径越小，其变形程度越大。在管件弯曲变形的同时，还会伴随着截面畸变。由于弯头的极限变形程度和截面畸变的限制，弯头最小弯曲半径必须大于某一极限数值，一般相对弯曲半径大于25。即使采用热弯，并辅以各种防止截面畸变措施，其最小相对弯曲半径一般也不能小于1．5。要想获得更小的弯曲半径的弯头，采用单纯弯曲是不可能实现的。近年来，随着锅炉制造工艺的发展，研究开发了一种小弯曲半径弯头成形新工艺——小弯曲半径弯头对挤成形。一、对挤成形工艺小弯曲半径弯头对挤工艺为…     

矩形截面直角弯管内高压成形过程的数值模拟

内高压成形技术是以轻量化和一体化为特征的一种空心变截面轻体构件的先进制造技术。在汽车工业领域，运用该技术能够生产出质量轻而且具有很高的强度和刚度的零件。矩形截面直角弯管是一类特殊零件，具有典型的直角弯曲特征．常规弯曲工艺无法加工。采用内高压成形技术，可避免常规弯曲方法的不足，实现该类零件的成形。对采用管材内高压成形技术加工矩形截面工件成形过程进行了有限元模拟，对整个管件的成形规律进行了总结分析，对于应用内高压成形技术生产该类零件具有重要指导意义。     

管材激光弯曲的有限元分析

为了研究管材激光弯曲过程中的温度和应力情况,利用有限元软件ANSYS进行分析计算,采用APDL语言编写命令流,生成单元,模拟移动热源载荷.通过分析计算获取温度场,应力应变场的详细信息.分析结果表明管材激光弯曲成形过程中,管材先经历背向激光的弯曲,之后形成面向激光束的弯曲;最后,在加热位置内外表面会发生朝向外侧的凸起变形.     

管材激光成形的数值模拟研究

建立了管材激光弯曲成形的有限元模型,对成形过程进行了数值模拟分析。模拟结果表明对应于加热和冷却阶段,管材的激光弯曲成形分别经历反向弯曲和正向弯曲两个变形阶段。管材加热区与未加热区域之间形成的较大的塑性应变差使得管材整体上产生了朝向激光束的正向弯曲。成形的机理主要表现为增厚机理。未加热区域的管材壁厚基本不变化,不会出现机械弯曲中管材的破裂问题。     

管材弯曲时横截面畸变的试验及有限元分析

在管材弯曲变形试验的基础上,针对管材弯曲过程中的管横截面形状畸变进行有限元分析,模拟所得的变形趋势与试验结果基本吻合。通过分析指出,弯管横截面短轴变化率大于长轴变化率,与弯曲外侧管壁产生较大等效应变有关。另外,由于弯曲变形扩散,使得弯曲终止端的直管段部分产生了一定量的等效应变。     

不同模具组合对0Cr21Ni6Mn9N不锈钢管数控弯曲成形质量的影响

采用有限元法研究了不同模具组合下0Cr21Ni6Mn9N不锈钢管数控弯曲应力应变分布、壁厚变化和截面畸变规律。研究结果表明：在弯曲模、夹块和压块组成的基本模块的基础上,添加防皱块会导致等效应力、切向拉应力和切向拉应变增加,而切向压应力、等效应变和切向压应变减小;添加芯棒会导致切向应力和等效应变减小,而等效应力和切向应变增大;同时添加防皱块和芯棒则会导致等效应力、切向应力和切向应变增大,而等效应变减小。添加防皱块会导致弯管截面畸变率增大,但对壁厚变化率影响不大;添加芯棒能够有效抑制弯管截面畸变,且壁厚减薄率仅为9.0%~9.15%,远小于15%的航空标准。综合考虑0Cr21Ni6Mn9N不锈钢管数控弯曲成形质量和生产成本,可确定出最优的模具组合为弯曲模+压块+夹块+芯棒。     

船用管件弯曲成型的有限元建模与实验验证

基于弯曲成型理论并结合船用管件弯曲成型的实际工况,采用ABAQUS/CAE模块建立了20钢管件的数控弯曲成型有限元模型,对建模过程中的力学模型、几何模型、单元定义、网格划分及其敏感性分析和约束接触设置等步骤进行了详细的说明。通过提取弯曲段横截面的最小壁厚值,与变形前的截面壁厚相比,定义了弯管外侧壁厚的减薄率。同时,通过提取畸变后的管件截面的椭圆长短轴,推导出了截面畸变程度质量指标的计算方法。与实验结果比较,有限元模型的计算结果与实验测量数据之间的相对误差较小,从而验证了有限元模型计算的精确度和可靠性,为管件的弯曲成型加工提供了理论依据,可应用于加工后管件质量的评价。     

电气化铁路特形定位器弯管工装设计

接触网作为电气化铁路供电系统的关键,其稳定性和安全性也越来越受到人们的重视。特形定位器主要用于接触网绝缘关节中心柱处固定接触线位置,保证接触线工作平面平行于轨面,并承受接触线的水平拉力。在特形定位器管生产过程中,容易产生管材弯曲部位附近的直线段截面发生畸变的问题,不仅影响后续装配效率,也制约着定位器管质量的提高。针对此问题,设计出一种防弯管变形工装,成功地解决了管材弯曲过程中管径变形过大的问题。     

钢管弯曲反变形压模

钢管弯曲足管料加工的主要工序之一,一般采用专用弯管机成形,或者用弯管模压制成形,但在圆管弯曲加工中容易出现弯曲截面失圆和起皱等现象。而且圆管弯曲成形后,要达到弯曲截面失圆度小、无压痕也比较困难。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.