扭压复合加载新工艺

扭压复合加载成形新工艺是在成形中沿坯料高度方向施加扭矩,将工件与工具间摩擦的有害作用转变为有益的作用,从而减少变形力,提高工件的组织性能。本文着重阐述了其理论基础、特点及工艺因素带来的影响。     

基于AutoForm的天地盖成型起皱仿真研究

为了解天地盖工件的成形起皱机理,以995铝合金为研究对象,通过有限元分析方法,利用Auto Form软件定量模拟坯料在不同形状、压边力、冲压速度、摩擦因数、圆角半径和凸模工艺面宽度下的成形起皱。结果表明：与长方形和圆角形坯料相比,采用切角的八边形坯料可以减轻工件的成形起皱;冲压速度对工件的成形起皱影响较小,几乎可以忽略不计,而压边力、摩擦因数和圆角半径的影响则相对较大,选用较大压边力、摩擦因数和圆角半径可以减轻工件的成形起皱;凸模工艺面宽度越小,工件成形起皱越小。该研究结果为实际生产提供了理论依据。     

搅拌摩擦焊接过程数值仿真的完全热力耦合模型

提出了搅拌摩擦焊接过程的完全热力耦合模型,以模拟AL6061-T6铝合金焊接构件在焊接过程中的温度场和材料变形情况,试验结果证明了该模型的有效性。计算结果显示,在焊接过程中,材料的最高温度低于熔点。在工件底面搅拌头后方存在一个低塑性应变区域,这是由搅拌摩擦焊接材料的特有流动形式所决定的。在工件上表面塑性应变的分布与试验中观测到焊接构件表面的环状纹理相似。     

AZ31镁合金在不同温度场挤压中的数值模拟

在试验基础上，采用有限元方法对AZ31镁合金在不同温度场中的挤压成形过程进行了数值模拟，详细分析了各种工艺参数对挤压中变形载荷、应变分布和温度场分布等的影响。结果表明：不同挤压条件下的挤压力模拟值与实测值相对误差小于10％，模拟结果与实际值比较接近；即使坯料和模具不加热，坯料挤出时的温度都达到了340℃以上；在坯料为常温、模具为300℃时的情况下，挤压力开始时较大，接近于常温变形时的挤压力，但随后挤压力下降；随摩擦因数增大挤压力有明显增加。坯料为常温时，随模具温度增加，挤压力开始变化不大，但当超过100℃后有明显下降。     

大型钢锭内部空洞性缺陷锻合过程的实验研究

本文采用均匀压缩热钢模拟实验,研究了内部空洞在锻合过程中受应力应变的影响,提出空洞沿最大压应变方向闭合,并经由变形→压合→扩散焊合三个阶段得以消除的机制。对坯料内部三维变形条件下对称面上应变分布的实验测量与计算结果,发现在平砧拔长条件下,应变峰值随砧宽比变化而移动的规律,以及在连续锻造过程中,两砧交界处的坯料中心存在小变形区的现象。     

基于FEM的电磁缩径耦合场数值模拟

对管件电磁缩径的磁场力和动态变形进行了耦合场FEM数值模拟。应用ANSYS计算作用在管件上的瞬态磁场力,然后以该力为边界条件模拟工件高速变形,实现管件变形与磁场力之间的耦合。研究结果表明,作用于工件的磁场力及其径向变形分布不均匀;工件变形可以间接说明磁感应强度和磁场力的分布;工件变形较大时,全耦合模拟结果较半耦合模拟更合理,而变形较小时,二者模拟结果相近。管件变形的模拟值与测量结果吻合较好。     

摩擦因数与模角对扭转挤压模具影响的研究

为了优化扭转挤压模具,基于刚塑性有限元理论,应用Deform-3D软件对T2纯铜坯料在扭转挤压下的成形过程进行数值模拟,对比分析了不同摩擦因数与模角情况下,载荷的挤压行程曲线、坯料的等效应变和模具的磨损。结果表明,增大摩擦因数与模角均可增大坯料的变形量,且增大模角效果更明显。     

制坯辊锻在铁路车辆组合式制动梁中间支柱生产中的应用

1．辊锻技术概述 辊锻是将轧制变形引入锻造生产的一种成形工艺。在辊锻变形过程中，坯料在高度方向经辊锻模压缩后，除一小部分金属横向流动外，大部分金属沿坯料的长度方向流动，其实质是坯料在压力作用下的延伸变形过程，适用于减小坯料截面。因此，辊锻既可以作为模锻前的制坯工序为长轴类锻件提供锻造用毛坏（称为制坯辊锻），亦可在辊锻机上实现主要的锻件成形过程或直接辊制出锻件（称为成形辊锻）。     

单晶铜原子力显微镜加工过程亚表面变形层的分子动力学仿真

建立了原子力显微镜针尖切削单晶铜的三维分子动力学模型,采用嵌入原子势模拟工件原子之间的作用,采用Morse势模拟工件原子和刀具原子之间的作用.研究了工件材料的不同晶向和刀具切削方向、切削速度对工件亚表面变形层深度的影响.引入了原子势能变形判据,通过分析不同变形区域内原子的势能变化判断工件变形程度.观察了不同切削状态下亚表面原子势能的变化,发现工件材料晶向和切削方向对亚表面变形层深度有着显著影响.在切削速度为20～250 m/s范围内,切削速度对亚表面变形层深度没有影响.     

金属塑性成形技术基础讲座：第五讲 板料成形方法（下）

2.弯曲与卷边 弯曲是用模具把金属坯料弯折成所需形状的过程。可以在各类机械或液压压力机上进行,弯曲过程简图见图7。金属坯料在凸模压力作用下,发生整体弯曲变形。工件弯折部分的内侧被压缩,外侧被拉伸。其变形程度的大小与弯曲半径r有关。r越小,变形程度越大,金属的加工硬化作用越强,但r太小,就有可能在工件弯曲部分的外侧发生     

脉冲激振枪

Impulse exciting gun is a new type of impulse exciter developed by authors. When it works, the shock head in the gun impacts the object to be measured at a certain speed, so that an impulse. Force is exerted on the object in fraction of a second. At the same time, the force transaucer with the shock head converts the impulse force into electrical signal for output. Thus the impulse excition for the objects to be measured as well as dynamic measurement have been completed just once. Impulss exciting gun involves three main parts called adjusting mechanism, localizing mechanism and returning mechanism. Adjusting mechanism can easily change rigidity of impulse head and the initial velocity of impact, in order to control contact continuance (force impulse breadth) and maximal presure Fm.. (force impulse peak value) between the 'shock head and the object. The function of localizing mechanism is to control exerted force point and its direction more accuratly. And setting up a returning mechanism is to avoid touching again between the shock head and the object after they collide with each other. Outward appearance of the gun is in figure 1. As for main technique indexes of impulse exciting gun see table 1 and figue 4-3.Impulse exciting gun is not only of simple structure, but also reliable and convenient to use. Furthermore, force impulse breadth and its peak value and exerted force point and its direction may be accuratly controlled when used. Those special advantages of the gun over impulse exciters now available make it come into vise in some scientific research departments and colleges.     

冲模振动噪声分析

分析高速旋转压片机的冲模在主压时工作状况,以及所受的周期性作用力。高速旋转压片机的噪声主要由于冲模的振动产生的。把主压时片芯和下冲模当作一根做轴向振动的复合棒,这根复合棒受到周期性作用力作用,发生周期性振动,产生周期性噪声。结合下冲模和片芯的性质,利用复合棒振动的边界条件,写出复合棒的各段近似振动方程,由振动方程写出冲模的辐射噪声声场的声压方程,通过试验值与仿真值比较来验证该模型的合理性和可行性。     

Facile characterization of ripple domains on exfoliated graphene

Ripples in graphene monolayers deposited on SiO(2)∕Si wafer substrates were recently shown to give rise to friction anisotropy. High friction appears when the AFM tip slides in a direction perpendicular to the ripple crests and low friction when parallel. The direction of the ripple crest is, however, hard to determine as it is not visible in topographic images and requires elaborate measurements of friction as a function of angle. Here we report a simple method to characterize ripple crests by measuring the cantilever torsion signal while scanning in the non-conventional longitudinal direction (i.e., along the cantilever axis, as opposed to the usual friction measurement). The longitudinal torsion signal provides a much clearer ripple domain contrast than the conventional friction signal, while both signals show respective rotation angle dependences that can be explained using the torsion component of the normal reaction force exerted by the graphene ripples. We can also determine the ripple direction by comparing the contrast in torsion images obtained in longitudinal and lateral scans without sample rotation or complicated normalization.     

永磁同步电机转子起始位置检测新方法

针对目前永磁同步电机(PMSM)起始位置检测方法存在依赖精确的电流检测电路或需要复杂的建模和计算等问题,提出了一种永磁同步电机起始位置的新型检测方法.该方法在电机加电启动时按一定顺序给电机施加24个特殊空间矢量,使电机转子在较短时间内产生微小抖动,通过判断抖动的方向来推算此时电机的转子位置,该方法具有简单易实现的优点....     

超声振动和切削液联合作用下的刀刃非物理锐化

超声辅助切削和切削液的联合使用能减小切削力和降低表面粗糙度,试图说明其机理,目的是为开发精密和超精加工技术打下基础。超声辅助切削和切削液的联合使用,从性质上改变了刀刃施加给工件表面的作用力,包括摩擦力和压力：在无切削液情况下,刀刃切入时,前刀面和后刀面施加给被切削面的摩擦力方向是指向刀刃;在有切削液情况下,刀刃切入时,前刀面和后刀面施加给被切削面的摩擦力方向是背向刀刃。背向刀刃的摩擦力,相对于指向刀刃的摩擦力而言,会导致剪切角增大,等效于更锋利的刀刃所产生的剪切角;切削液的存在使得刀刃施加给工件的力更加集中,等效于圆角半径更小的刀刃所能达到的效果;切削液在刀尖部位的压力分布不利于工件表面产生微裂纹。也就是说,超声辅助切削和切削液的联合使用起到了更锋利即更小圆角半径刀刃所起的效果,称之为非物理锐化。     

Atomic-scale finite-element model of tension in nanoscale thin film

In this paper, a 2D atomic-scale finite-element model of tension in nanoscale thin film is developed in which Morse’s potential energy function is used to model the interactive forces between atoms. The model is fed into the finite-element package LS-DYNA and both a single integration point and an explicit solution method are used for solving the tension process rapidly to investigate the size effect of different film thicknesses and the effect of different atomic vacancy ratios on nanoscale thin film under tension. The results show that since the applied displacement is exerted at both ends for different thickness of a perfect crystal, a neutral line is formed at the middle of the material. The material slides along the easiest slip direction to cause a “necking” feature on both sides. The stress initially increases with the gradual increase of strain and thicker film shows a larger tensile stress. After the film experiences the peak stress, the stress then decreases with the gradual increase of strain. While the applied displacement is applied at both ends for different vacancies, a neutral line is formed at the middle of material, but this is not apparent due to the random scattered vacancies. The material slides along the easiest slip direction from left to right, and the stress concentration areas near the constrained ends form “necking” features. Stresses are not zero at zero strain. Tension tests for different vacancy ratios show different maximum stresses. Film with a larger vacancy ratio shows a lower stress at the same strain. As the vacancy ratio of the film under tension increases, the strength and elastic modulus reduces.     

导弹无依托发射场坪承载能力分析

为评估无依托发射场坪的强度稳定性,需要对导弹发射车的对地荷载做详尽分析,找出最大应力工况。文中分析了导弹发射过程中的各种工况,并进行了力学计算,通过对比,判断出发射车对地最大载荷状态,以此作为场坪强度评估的理论依据。同时,通过构建支腿对地载荷检测系统,实测了支腿对地压力,通过对比分析,验证了计算方法的合理性。研究结果可以为导弹采用无依托发射时的场坪选取和强度判断提供参考。     

Cytoskeletal response of microvessel endothelial cells to an applied stress force at the submicrometer scale studied by atomic force microscopy

Cytoskeleton fibers form an intricate three-dimensional network to provide structure and function to microvessel endothelial cells. During accommodation to blood flowing, stress fiber bundles become more prominent and align with the direction of blood flow. This network either mechanically resists the applied shear stress (lateral force) or, if deformed, is dynamically remodeled back to a preferred architecture. However, the detailed response of these stress fiber bundles to applied lateral force at submicrometer scales are as yet poorly understood. In our in vitro study, the tip, topography probe in lateral force microscopy of atomic force microscopy, acted as a tool for exerting quantitative vertical and lateral force on the filaments of the cytoskeleton. Moreover, the authors developed a formula to calculate the value of lateral force exerted on every point of the filaments. The results show that cytoskeleton fibers of healthy tight junctions in rat cerebral microvessel endothelial cells formed a cross-type network, and were reinforced and elongated in the direction of scanning under lateral force of 15-42 nN. Under peroxidation (H(2)O(2) of 300 micromol/L), the cytoskeleton remodeled at intercellular junctions, and changed over the meshwork structures into a dense bundle, that redistributed the stress. Once mechanical forces were exerted on an area, the cells shrank and lost morphologic tight junctions. It would be useful in our understanding of certain pathological processes, such as cerebral ischemia/reperfusion injury, which maybe caused by biomechanical forces and which are overlooked in current disease models.     

天文望远镜底座注塑成型模拟

针对注塑成型过程中,影响注塑质量因素多的问题,运用CAE技术,对某型号天文望远镜底座进行注塑成型模拟,预测可能出现的缺陷,得出一组经过CAE分析优化的数据应用于实际生产,缩短模具的试模时间,获得合格的产品.     

颚式破碎机的挤压过程分析

破碎机破碎腔内的物料可分为被挤压破碎和向下流动两个过程。由于动颚运动的复杂性,物料的破碎过程并不是简单的静态挤压破碎。文章从多体动力学角度出发,建立物料破碎模型的基础上,明确了物料在复摆颚式破碎机破碎腔内破碎过程中受到挤压的过程,并给出了确定方法,为进一步分析挤压过程中物料受到的挤压量、物料与颚板的相对运动提供了必要的基础。