AZ31镁合金型材温热弯曲实验研究

采用自制弯曲装置进行了AZ31镁合金型材弯曲成形实验,研究了型材成形温度和型材弯曲角度对镁合金型材弯曲性能的影响.结果表明:采用温热弯曲工艺可以成形出AZ31镁合金型材弯曲件;弯曲后的型材外缘筋部厚度值减小,其余筋部厚度值均增大;在相同的弯曲角度和模具预热温度条件下,随着坯料温度的升高型材回弹角度减小.AZ31镁合金型...     

锂电池极片辊压工艺变形分析

目的 减小锂离子电池正负极片厚度的不一致性。方法 以锂离子电池正负极片辊压工艺为研究对象,通过理论分析的方法,针对不同压力、不同截面的压辊在工艺变形过程中的挠曲变形和弹性变形进行探讨,并分析不同变形对极片厚度不一致性的影响。同时,对在企业中广泛应用的热压工艺进行分析。结果 正负极片在不同压力下均会发生挠曲变形和弹性变形,前者增加了厚度不一致性,随着压力的增加,挠曲变形程度增大;在辊压工艺中,尽量将极片中心线和压辊中心线对齐,两者有偏移会增加挠曲变形,从而增加极片厚度的不一致性,两者偏移距离越大,挠曲变形也随着增加;此外,压辊直径、压辊弹性模量,以及极片宽度等因素也会影响挠曲变形。结论 辊压工艺中,可以从压辊角度进一步提高极片厚度的均匀性。     

型材截面几何特征对绕弯成形翘曲的影响

为提高铝合金型材绕弯成形后弯曲件的尺寸精度,运用仿真分析的方法研究了在绕弯成形过程中截面几何特征对竖直壁型材成形翘曲的影响.改变具有竖直壁结构型材的截面几何特征,得到不同型材的成形结果并进行对比分析.结果表明:增加竖直壁型材外侧横向特征的对称性有助于减小成形翘曲变形;增加内侧特征能够显著减小翘曲.该研究结果可以指导型材截面设计,减少成形的难度.     

铝合金型材拉弯成形回弹的有限元模拟

对回弹进行有效预测与控制是提高型材弯曲件精度的关键.为了分析轴向作用力对拉弯制件回弹的影响,采用动力显式有限元仿真软件Pam-Stamp2000对中空矩形截面铝型材AA6082(T5)转臂式拉弯成形过程进行了数值模拟,并与实验结果进行了对比.结果表明:增加预拉可以减小制件的回弹,但预拉达到一定水平后,继续加大预拉力对减小回弹将基本不起作用;当预拉不充分时,增加补拉同样有利于减小制件的回弹,但过大的补拉力对于减小回弹几乎没有任何帮助.可见,型材拉弯成形制件的回弹不仅与加载顺序及加载程度密切相关,同时也受到材料应变硬化特性的制约.     

粘接界面泡沫铝夹芯板的三点弯曲失效数值模拟

对粘接界面泡沫铝夹芯板三点弯曲载荷下的变形特性进行了实验和数值模拟方面的研究。基于有限元软件ABAQUS建立了泡沫铝夹芯板的三维有限元模型,应用内聚力模型对三点弯曲过程中典型的破坏模式——面板与芯层的界面脱粘给予了合理的模拟,模拟所得的结果与实验结果比较吻合。并在此基础上分析了面板和芯层厚度对夹芯板承载能力和吸收能量能力的影响。结果表明,增加芯层的厚度能够更大程度上提高泡沫铝夹芯板的承载能力和吸收能量的能力。     

一种用微弯曲实验测定内禀材料长度的新方法

提出了一种用微弯曲实验测定材料的与应变梯度塑性相联系的内禀长度的新方法.由一组不同的加载时曲率半径Ri和对应的卸载后曲率半径RFi的比值与Ri的关系,求出屈服强度与杨氏模量的比和硬化系数与杨氏模量的比;再应用这两个比值求出不同样品厚度的无量纲弯曲力矩与表面应变的实验关系曲线,对曲线拟合求出材料的内禀长度.将这种方法用于测定铝的内禀材料长度,研究其弯曲强度的尺寸效应,所得结果与前人用微弯曲和微拉伸两种实验方法得到的结果符合得很好.     

较浅压入下针尖曲率半径对纳米压入硬度影响的比较研究

基于3种不同曲率半径压头针尖对熔融石英进行纳米压入,用原子力显微镜（AFM）直接法测得压头针尖的面积函数及针尖曲率半径。研究表明,在极浅压入条件下,压头曲率半径的变化会导致硬度值的测量误差,曲率半径越小的压头针尖随接触深度的变化会更快得到真实值;相同的压入深度,曲率半径小的压头针尖测得的压入硬度值比曲率半径大的测得的压入硬度值更接近其真实值。     

较浅压入下针尖曲率半径对纳米压入硬度影响研究

基于3种不同曲率半径压头针尖对熔融石英进行纳米压入,用原子力显微镜(AFM)直接法测得压头针尖的面积函数及针尖曲率半径。研究表明,在极浅压入条件下,压头曲率半径的变化会导致硬度值的测量误差,曲率半径越小的压头针尖随接触深度的变化会更快得到真实值;相同的压入深度,曲率半径小的压头针尖测得的压入硬度值比曲率半径大的测得的压入硬度值更接近其真实值。     

铝合金-聚合物复合层板弯曲回弹理论分析

针对铝合金-聚合物复合层板弯曲回弹问题,分析了复合层板弯曲过程表面层铝板及中心层聚合物的变形特征,建立了复合层板平面应变纯弯曲回弹理论分析模型.采用建立的模型预测了复合层板纯弯曲过程回弹角变化,并与实验结果进行了对比,分析了聚合物层厚度及铝合金板材力学性能对回弹的影响规律.结果表明:随着中心聚合物层厚度的增加,复合层板回弹角降低;随着表面层铝板强度的降低,复合层板回弹角减小.理论预测结果与实验结果一致,说明了本文推导的理论模型的可靠性.     

复杂截面型材力控制拉弯成形数值模拟分析

复杂截面挤压型材的高精度拉弯成形是制造框架式车身的关键技术.本文基于动态显式有限元软件PAM-STAMP,针对一种典型的框架武车身用复杂截面挤压型材,对其力控制方式的直进台面式拉弯成形进行了数值模拟研究,对比分析了两种截面形状的型材截面畸变和回弹随补拉力增大的变形规律,并得到了摩擦系数对成形精度的影响.数值模拟结果表明,增加型材截面的变形刚度,可以显著地减小截面畸变和回弹;增加补拉力,增大了截面畸变但减小了回弹;增大摩擦系数,截面畸变量减小而回弹增加.     

工艺参数对剪切旋压旋压力和壁厚差的影响

在锥形件剪切(变薄)旋压过程中,旋压力分析对于确定工艺参数及设备选型都具有重要意义,而壁厚差是衡量旋压件成形质量的关键指标之一.基于ABAQUS/Explicit平台建立了锥形件剪切旋压的三维有限元模型,进而获得了偏离率、旋轮圆角半径、旋轮进给量、芯模转速及旋轮直径对LY12M锥形件剪切旋压旋压力和壁厚差的影响规律.研究表明:旋压力随偏离率增加而减小,随旋轮圆角半径、旋轮进给量、芯模转速的增加均呈上升变化趋势;偏离正弦律的程度越大,壁厚差越大;旋轮圆角半径为毛坯厚度的1～2倍,壁厚差较小;较大的旋轮进给量和芯模转速有利于减小壁厚差.旋轮直径对旋压力和壁厚差的影响不显著.     

曲率半径对双层药型罩EFP战斗部成形及侵彻的影响?

利用ANSYS/LS-DYNA仿真软件研究了药型罩曲率半径对双层药型罩EFP战斗部成形及侵彻特性的影响规律。数值计算结果表明,当药型罩曲率半径的相对值在0.67~0.93时,弧锥结合型双层药型罩EFP战斗部可成形具有良好外形的侵彻体;此时,成形侵彻体的最大侵彻深度约为1倍装药口径。试验结果表明,双层药型罩EFP战斗部成形侵彻体能够有效击穿2层2 cm厚45#钢靶,成形侵彻体对钢靶侵彻的开口形状近似呈现圆形,是具有相同装药结构EFP战斗部成形侵彻体侵彻深度的2倍左右。研究结果可以为双层药型罩EFP战斗部结构优化设计提供参考。     

大尺寸2024-T351铝合金喷丸成形曲率变化规律研究

目的 以喷丸成形工艺下的2024-T351铝合金平板件和单筋件为研究对象,分析弦向及展向曲率半径试验值与拟合值的变形规律。方法 针对试件厚度、喷丸压力、喷丸速度、预弯量4个参数进行喷丸成形操作的正交试验,通过测量成形后曲率的变化规律,分析不同参数组合对平板件和单筋件成形变化规律的影响。结果 在不考虑材料性能波动的情况下,随着平板件厚度和喷丸速度的增大,平板试件的弦向曲率半径和展向曲率半径均呈递增趋势;而随着喷丸压力的增大,平板试件的弦向曲率半径和展向曲率半径则呈现递减趋势,即当平板件厚度和喷丸速度增大时,喷丸成形对平板试件弯曲的影响程度有所增大,曲率半径减小;反之,喷丸成形对平板试验件弯曲的影响程度减小,曲率半径增大。结论 在忽略初始状态并将其假设为自由状态或给定预弯量状态的条件下,随着喷丸速度的增大,单筋试件的曲率半径递增,试验值与拟合值的变化趋势基本相符,二者最大偏差为11.2%。     

坯料随机局部弯曲对滚弯成形结果影响的蒙特卡洛分析

采用蒙特卡洛有限元模拟方法研究了坯料局部的随机弯曲对滚弯成形结果的影响。为了提高滚弯模拟的效率,提出了基于欧拉网格和经典梁单元的滚弯模拟方案,并与传统有限元模型和理论解对比验证了该方案的正确性。在此基础上模拟了具有零均值正态分布的局部曲率的超长坯料的滚弯过程,并统计产品曲率半径的分布规律。结果表明:输出曲率半径分布近似满足正态分布,且随着坯料曲率标准差的增大,均值减小,方差增大,宏观上表现为产品半径减小。产品的目标半径越大,代表性单元长度越长,受初始弯曲的影响就越大;对于给定的目标形状,辊轮位置参数对实际输出半径的分布没有影响。     

塑性弯曲变形对金属组织性能影响的研究

本文在分析强烈塑性变形(severe plastic deformation)对金属材料组织性能影响的基础上,进一步研究金属材料经过反复塑性弯曲变形后,其内部组织性能的变化规律.以H85黄铜板材为对象,采用MARC有限元等方法计算不同弯曲半径与板厚之比(r/h,简称:径厚比)对金属材料内部累积应变的影响,同时通过金相组织分析和显微硬度测定,进一步确定其内部晶粒尺寸的变化规律.研究表明,金属板材经过反复塑性弯曲变形后,其内部累积应变量大小沿厚度分布随离中性层距离增加而增大、晶粒尺寸则随之变小、金属的显微硬度随之增加.而且随着径厚比(r/h)减小,其累积应变量效应越显著.     

铝合金矩形截面管充液成形工艺研究

目的研究低延伸率和低厚向异性指数的铝合金管,在充液成形过程中的材料变形行为。方法采用低压预成形的方法来改善管坯材料的流动,并与传统不带内压的预成形结果进行了对比。结合有限元分析手段研究了铝管弯曲过程管坯尺寸、弯曲半径的选择对零件壁厚分布的重要性。结果有限分析方法结合试验研究表明,低压预成形可以有效抑制铝合金弯曲轴线管件的开裂。结论初始管材截面外壁周长应等于或略小于模具截面内壁周长;弯曲半径的选取要兼顾弯曲工艺难度和管坯贴模度;低压预成形能够大大改善矩形截面过渡圆角区的材料流动,避免破裂、死皱等典型缺陷的发生。     

Passivation layer effect on surface integrity induced by Cu-CMP

To achieve efficient Cu-Chemical-Mechanical Polishing planarization at miniaturized device dimensions, there is a need for a better understanding of the surface integrity induced by the process. Surface quality and stresses are the two selected indices in this article to evaluate the Cu-CMP process induced surface integrity. The thickness of the passivation layer and the penetration depth of abrasives are considered as the main effects for the generations of surface qualities and residual stress. Experimental validation on copper films on silicon wafer was performed by CMP with different pads and slurries to generate varied residual stresses and surface qualities. Depth of scratches and surface roughness were measured by the atomic force microscope. The stress measurements of the thin films were performed by a Grazing Incident X-ray diffraction instrument with its principles based upon modified sin²Ψ method. Accordingly, the surface roughness and stress were related to the thickness of the passivation layer and the CMP process conditions. When the penetration depth is larger than the passivation layer thickness, the roughness values are mainly decided by the selection of pads and the resultant penetration depth. In addition, the residual stress profiles are dependent on the CMP process conditions which include the slurries and pad parameters. The stress profile obtained for the slurry SDK with soft pad Politex composed smallest maximum tensile stress below the surface and a steady transition of stress profile compared to the stress profile obtained at the initial condition. At the condition for the same slurry SDK, but with a hard pad of IC1000, the CMP process induced larger maximum stress and sharper profile transition.     

Multiscale Analysis of the Effect of Debris on Fretting Wear Process Using a Semi-Concurrent Method

Fretting wear is a phenomenon, in which wear happens between two oscillatory moving contact surfaces in microscale amplitude. In this paper, the effect of debris between pad and specimen is analyzed by using a semi-concurrent multiscale method. Firstly, the macroscale fretting wear model is performed. Secondly, the part with the wear profile is imported from the macroscale model to a microscale model after running in stage. Thirdly, an effective pad’s radius is extracted by analyzing the contact pressure in order to take into account the effect of the debris. Finally, the effective radius is up-scaled from the microscale model to the macroscale model, which is used after running in stage. In this way, the effect of debris is considered by changing the radius of the pad in the macroscale model. Due to the smaller number of elements in the microscale model compared with the macroscale model containing the debris layer, the semi-concurrent method proposed in this paper is more computationally efficient. Moreover, the results of this semi-concurrent method show a better agreement with experimental data, compared to the results of the model ignoring the effect of debris.     

Fracture in bending – The straining limits of monolithic sheets and machined tailor-made blanks

This paper studies fracture in the bending of monolithic sheets and machined tailor-made blanks made of high strength aluminum alloys commonly used in the aircraft industry as well as the effects of sheet thickness and thickness difference on their forming limits. Tailor-Made Blanks (TMBs) are sheet metal assemblies that are composed of sheets with different thicknesses and/or materials. Machining is among the techniques that can be used for creation of the needed thickness variations and is the one that is studied in this paper, because it isolates the effects of thickness difference from those of the welding/joining process. The selected materials are 2024-T3 and 7075-T6 representing 2000 and 7000 series aluminum alloys. Two sets of experiments are carried out to identify the effects of sheet thickness and thickness difference on the forming behavior of the selected alloys. The first set of the experiments is tensile testing. The tensile properties of sheets with different thickness and thickness ratios including the plasticity parameters are determined in the first set of experiments. The second set of the experiments is air bending. The minimum bending radii of materials with different thicknesses and thickness ratios are determined in the second set of experiments. Then, the forming limits are determined using a theoretical approach and the experimentally-determined forming limits are compared with the theoretically-determined ones. The results of the tensile testing and air bending are studied both separately and in comparison with each other to identify the trends and to understand the mechanisms governing the observed trends. It is shown that the minimum bending ratio increases as the sheet thickness increases and that the minimum bending radius slightly (10–12%) increases as the thickness ratio increases from 1 to 2.