TC4钛合金薄板激光焊接变形的有限元模拟

建立了TC4钛合金薄板激光焊接模型,采用有限元方法分析了板宽对焊接残余应力及失稳变形的影响。结果表明:最高纵向残余拉应力出现在焊缝中心两侧的热影响区;随着板度增大,平均残余压应力和临界失稳力降低;沿着焊接方向的钛合金薄板失稳变形程度随板宽的增加而减小,而垂直于焊接方向的失稳变形程度随板宽的增加而增大;当板宽为120mm时,其失稳变形程度呈马鞍形分布,当板宽为320mm时,马鞍形变形分布特征消失;钛合金薄板失稳变形的z向位移试验值与模拟结果的相对误差为8%,证明模拟结果较准确。     

三维压电介质中不同电边界条件的裂纹分析

在不可导通、可导通和半可导通等三种电边界条件下，系统研究并给出三维无限横观各向同性压电介质中平行于各向同性面的、任意形状的平片裂纹在任意载荷作用下的不连续位移和不连续电势边界积分方程方法。无论平片裂纹的形状如何，结果都表明：对不可导通裂纹，应力强度因子只与机械载荷有关，电位移强度因子只与电载荷有关；而可导通裂纹的应力强度因子和电位移强度因子只与机械载荷有关，电位移强度因子由机械载荷通过压电效应产生。半可导通裂纹所对应的边界积分方程组为非线性方程组，文中给出一种迭代解法。在均布的机械载荷和电载荷作用下。裂纹腔内的电位移为一常数，只与外加载荷有关，而与裂纹形状无关。     

球形封头开孔接管结构屈曲特性研究

针对外压作用下球形封头开孔接管结构,采用有限元非线性屈曲分析方法,探讨不同结构参数对其临界失稳压力Pcr的影响.研究结果表明,当球壳主体参数径厚比一定时,临界失稳压力削弱系数K随开孔率增大而下降,随接管与封头厚度比增大而增大.接管与封头厚度比较小时,计算模型失稳位置位于接管;接管与封头厚度比增至一定值时,计算模型失稳位...     

基于方板对角拉伸试验模型的镀锡板起皱行为数值模拟

基于方板对角拉伸试验(YBT)模型,采用ABAQUS软件对不施加扰动力和不同位置施加扰动力下镀锡板的起皱行为进行了模拟,并进行了试验验证;通过逐级增加夹持宽度,研究了不同起皱高度下方板中心点的应变组合,并绘制镀锡板的起皱高度评定图。结果表明:模拟得到不同位置施加扰动力后方板垂直于拉伸方向的离面位移分布基本相同,扰动力施加位置不会造成起皱行为的显著差异;施加扰动力后,方板中心截面垂直于拉伸方向的离面位移分布模拟结果与试验结果相吻合,说明用扰动力代替实际影响因素的模拟方法是准确的;夹持宽度不同的方板中心点的拉应变与压应变都随起皱高度的增加而增加;在相同起皱高度下,随着夹持宽度的增加,方板中心点的拉应变和压应变均增大。     

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。     

单剪螺栓连接复合材料叠层板螺栓孔周边应力场分布

基于螺栓连接三维实体模型,研究螺栓-孔间隙、挤压面摩擦因数等因素对挤压面上的应力分布的影响。研究发现螺栓连接叠层板每层中在纤维方向上释向应力和周向应力达到最大值,单层板铺层方向是径向应力和周向应力的主要承载方向。螺栓-孔间隙对孔周应力的分布产生较大的影响,径向应力分布具有相似性,间隙越大,径向应力水平越高,最大周向应力反而有所减小,而且间隙的存在使得径向应力的分布发生改变,最大径向应力向外加载荷方向靠近;螺栓-孔接触面的粗糙程度对孔周应力的分布也产生较大的影响。随着摩擦因数的增大,最大径向应力随之减小;最大周向应力随着摩擦因数的增大而减小。     

工艺参数对管材激光弯曲成形影响规律的研究

管材激光弯曲成形是一种柔性金属塑性成形方法。将连续的激光光斑简化为一间歇跳跃的方形匀强面热源,并考虑材料性能参数与温度的相关性,建立了管材激光弯曲成形的热-机耦合有限元工艺仿真模型,对成形过程进行了数值模拟。有限元模拟结果表明:在其他条件不变的情况下,激光弯曲角度随激光功率的增大而增大,两者基本上成线性关系;弯曲角度随扫描速度的升高而减小,随光斑直径的减小而增大,但当光斑直径减小到一定程度后,弯曲角度开始减小;弯曲角度随扫描包角的增大而增大,当扫描包角为180°时,弯曲角度达到最大,弯曲角度随扫描包角的继续增大而减小;扫描次数与弯曲角度间成近似的线性关系,且第一次扫描管材产生的弯曲角度最大。     

四辊轧机滚动轴承偏载与板形影响因素分析

为了分析板带轧机滚动轴承列间偏载和板形的变化规律,利用ANSYS/LS-DYNA有限元软件建立了耦合轧件、工作辊、支撑辊及其轴承座的轧制过程整体变形分析模型,分析了辊径、摩擦系数、变形抗力及张力对轴承载荷分布和板凸度的影响。研究结果表明,轴承偏载程度和板凸度随轧辊半径和张力的增大而减小,随变形抗力的增大而增大;轴承偏载程度随摩擦系数的增大而增大,板凸度随摩擦系数的增大略有减小;轴承偏载程度与板凸度的变化呈显著正相关。研究结果可为板带轧机滚动轴承的使用和板形控制提供有益参考。     

集中载荷作用下双模量圆板弯曲计算

双模量圆板在集中载荷作用下发生弯曲变形时,会形成各向同性的拉伸和压缩区。因此,可把双模量圆板看成两种各向同性材料组成的层合板,采用弹性理论建立了双模量圆板在集中载荷作用下的静力平衡方程,利用此静力平衡方程确定了双模量圆板的中性面位置。在此基础上,建立了集中载荷作用下双模量圆板的弯曲微分方程,求得了圆板的挠度表达式。通过算例讨论分析了双模量对圆板弯曲变形的影响,得到了圆板材料拉压弹性模量相差较大时,其挠度计算不宜采用相同弹性模量经典薄板理论,而应该采用双模量薄板理论的结论。     

板材直流电阻对焊宽度方向温度分布的研究

板材直流电阻对焊过程中，对接端面沿板宽方向的温度分布对焊接接头的质量有很大的影响。采用有限元方法，对板材直流电阻对焊时板宽方向的温度场变化进行了研究。研究表明，对接端面的不良接触造成电流集中，并引起温度分布不均匀；这种现象在焊接初期表现较明显，随加热过程的进行，不均匀程度明显减小。     

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...     

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。     

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.     

Limits of topographic measurement by the scanning tunnelling and atomic force microscopes

Parameters describing the topographic character of a surface (height, surface wavelength, slope and curvature) can be derived from equivalent sinusoidal profiles. The response of a surface-measuring instrument may be modelled in terms of instrument parameters such as stylus radius, and scanning range and resolution. The performance of the instrument may then be mapped as a zone in amplitude-wavelength (AW) space to show the sinusoidal profiles it is capable of measuring. In a first-order analysis the STM and AFM are considered as equivalent to contact-stylus instruments with a notional stylus radius equal to the tip radius plus the gap. Comparisons between different instruments and types of instrument are readily made by mapping in AW space. The error arising from convolution of the sinusoidal profile with that of the finite tip may be quantified and plotted as contours in AW space.     

Fractional order nonsingular terminal sliding mode control for flexible spacecraft attitude tracking

This paper investigates a fractional terminal sliding mode control for flexible spacecraft attitude tracking in the presence of inertia uncertainties and extern...     

奥氏体不锈钢表面双辉等离子渗锆的动力学

利用双辉等离子渗金属技术在0Cr18Ni9Ti奥氏体不锈钢表面制备了一层均匀、致密、呈良好冶金结合的渗锆合金层,并对1 060℃下的渗锆动力学进行了研究。结果表明:随着距锆合金层表面距离的增加,锆元素的含量呈梯度递减,扩散系数逐渐减小,而扩散激活能逐步增大;在1 060℃采用双辉等离子技术渗锆时,渗锆合金层表层的空位密度为2.945×(1012~1013)cm-2,与相同温度下采用常规渗金属工艺相比,提高了1~2个数量级。     

气化炉三维扫描测量与数据处理

以德士古气化炉耐火砖的内壁蚀损检测设备为基础,对采集到的点云数据做了进一步处理.通过对数据的筛选和剔除,实现了数据点的平滑降噪细化和精简.然后利用点云对整、网格划分和分色显示等方法,最终完成了内壁腐蚀情况的三维建模.重点讨论了点云数据的预处理及后处理的方法,并根据内壁耐火砖的腐蚀阈值,提出了一种气化炉内壁腐蚀区域的识别与分割方法.对耐火砖的腐蚀分析、气化炉的生产与维修提供了可靠依据,并在工程应用中获得了一致认可.