基于分形的三维粗糙表面弹塑性接触力学模型与试验验证

基于分形几何理论,利用双变量的Weierstrass-Mandelbrot函数模拟三维分形粗糙表面,建立了三维分形粗糙表面弹塑性接触模型。推导出各等级微凸体发生弹性、弹塑性以及完全塑性变形的存在条件。确定了粗糙表面上各等级微凸体的面积分布密度函数,获得了总接触载荷和真实接触面积之间的关系式。计算结果表明:单个微凸体的临界接触面积与其尺寸相关,随着微凸体等级的增大,微凸体的高度和峰顶曲率半径减小。微凸体的变形顺序为弹性变形、弹塑性变形和完全塑性变形,与经典的赫兹模型保持一致。粗糙表面的力学性能仅与最小等级及后续的6个等级微凸体相关,其余微凸体基本上对整个粗糙表面的力学性能影响很小。最后对粗糙表面的接触力学性能进行了试验测试,验证了该模型的合理性与正确性。     

厚膜永磁阵列微致动器的磁路研究

研究了厚膜永磁阵列微致动器中的磁场分布，并研究了永磁阵列单元几何尺寸对微致动器电磁力的影响。结果表明，厚膜永磁阵列单元高宽比和磁体单元间隔对微致动器电磁力影响较大磁徕单元高宽比为0．7是一个比较合适的尺寸。     

Q235钢单层板对平头刚性弹抗穿甲特性研究

采用撞击实验和理论模型对单层金属板的抗侵彻性能进行了研究,分析了靶体厚度对抗侵彻性能的影响。通过对比撞击实验和理论模型计算结果,验证了理论模型和参数的有效性。结果表明,采用合适的理论模型能够有效地预测靶板在弹体撞击下的弹道极限。此外,分析了靶体在弹体撞击下的塑性变形总耗能,包括靶板局部变形和整体变形的耗能,同时考虑了靶体材料的应变率效应。在平头弹撞击厚靶的工况中,引入了一个修正函数对靶体厚度进行修正。     

真空舱几何结构对离子推力器背溅射沉积影响的计算研究

有效降低溅射沉积影响是离子推力器地面寿命试验需要解决的关键技术问题。本文建立了真空舱壁上溅射物沉积到离子推力器表面的计算模型。结合LIPS-200推力器束流特性和石墨材料内衬,应用该模型分别计算和分析了平面靶圆柱型、平面靶圆锥台型、球面靶圆柱型、凸锥靶圆柱型、凹锥靶圆柱型五种真空舱几何形状与尺寸对离子推力器背溅射沉积的影响关系规律,得到了对具体设计LIPS-200推力器寿命试验真空舱具有指导作用的重要结论。     

HL-2A装置偏滤器靶板上探针阵列和主真空室活动探针的设计加工和诊断

HL-2A装置偏滤器靶板上的平面型朗缪尔探针阵列是用于测量同一极向截面的内外舜口上下四个个性化板上的电子温度、密度、悬浮电位、空间电位、电场舜口流速分布，研究偏滤器中等离子体参数的分布及非对称性。主真空室上磁力传动的马赫／雷诺协强／朗缪尔探针阵列，直接测量边缘等离子体温度，密度，空间电位，电场，环向舜口极向流速，研究边缘参数的涨落舜口相关特性。     

多视角几何三维重建法识别工程结构缺损与变形

裂缝等工程结构表面缺损与弯曲等构件变形是既有工程结构安全性检测鉴定与监测的重要指标,采用数字图像法可有效改善当前人工检查技术的缺点,但在工程实践中显现出定量检测中图像几何变形修正困难、局部损伤难以在整体结构中定位、无法测量钢结构空间变形等问题。结合多视角几何三维重建法的研究与应用可有效解决上述问题。该文对多视角几何三维重建的方法原理与算法实现进行讨论,列举方法实践的经典算法与高效算法;围绕数字图像法检测在工程实践中存在的问题,提出表面投影法解决成像几何变形与损伤定位、逆向工程建模与特征提取识别几何变形损伤;通过结构表面裂缝识别、大型构筑物表面损伤定位、钢结构构件变形识别等3个应用研究,阐述多视角几何三维重建法在结构表面损伤与变形识别中的具体操作方法与比较优势。多视角几何三维重建法具有设备要求低、操作方便快捷、模型色彩丰富、点云精度较高等特点,与数字图像法结合后在工程结构检测监测领域的研究与应用潜力巨大。     

预变形对FeNiC合金马氏体相变形态影响

研究了母相预变形对Fe-23Ni-0.55C合金马氏体相变表面浮凸形貌、组织形态的影响.结果表明:母相预拉伸变形和压缩变形对Fe-23Ni-0.55C合金马氏体影响有所不同.母相预拉伸变形,其马氏体由透镜状变为细针状,表面浮凸角增大;母相预压缩变形,随变形量的增大,不但其马氏体边缘破碎,而且马氏体中脊发生弯曲、甚至断裂.但是母相预变形并未改变其马氏体相变的惯习面和表面浮凸形貌.惯习面仍为{259}f,表面浮凸形貌均为"N"型.     

不同头部形状的PC弹丸撞击LF6铝板实验研究

该文介绍不同头型聚碳酸脂(PC)弹丸撞击LF6铝靶板的动力学响应实验,给出弹靶作用过程中靶体的响应历程,以及过靶后弹体与靶板的变形图像,实验结果表明穿靶机制主要两种:扩孔冲塞型和尖端冲塞后撕裂翻转型。     

基于粗糙表面分形表征新方法的结合面法向接触刚度模型

如何有效预测结合面的接触刚度,是机械结构设计研究的一个重要课题。结合面接触刚度模型主要分为基于统计学特征参数的和基于分形参数的两类。前者依赖于粗糙表面形貌的测量尺度,后者与测量尺度无关。然而,多数研究者在利用分形理论进行建模时,以对应于微凸体接触面积a的尺寸l=a~(1/2)作为微凸体基底尺寸描述微凸体初始轮廓,给出了错误的微凸体变形机制和结合面接触刚度模型。提出了一种基于D,G和最大微凸体高度的粗糙表面轮廓分形表征新方法,探讨了微凸体接触变形机制,建立了与测量尺度无关的粗糙表面接触力学分形模型,揭示了接触刚度的变化规律。研究表明:接触载荷可用表达式F_c=F(E,D,G,h,a_L)描述;当结合面上的接触压力小于其屈服强度时,无论微凸体发生何种变形,结合面均因存在有弹性变形的接触点而具有一定的法向接触刚度。     

利用微电极阵列技术研究合金的腐蚀

随着工业水平的不断发展与提高,合金材料的使用量亦不断增大。然而合金材料的腐蚀问题在工业生产及生态环境中造成了不可估量的损失。为此,国内外学者已经开展了大量关于合金腐蚀机理与防护方面的研究,并取得了一定的进展。微电极阵列技术是一种介于宏观的经典电化学技术和微区扫描探针技术之间的新型电化学测试方法。它既能获取合金大面积电极的整体平均信息,又能探测合金局部微小区域内的电位、电流分布特征,能更加准确地测试合金局部腐蚀过程中非均一的电化学信息。随着国内外学者的不断研究与开发,现已实现微电极阵列的优化。该技术联合其他电化学测试技术和表面科学技术等方法,不断丰富了合金/腐蚀溶液界面的物理、化学及电化学信息。近几年,大量专家学者采用该微电极阵列技术与其他测试技术相结合的方法研究了常用合金在不同环境和腐蚀状态下的局部腐蚀过程及机理,并取得了重要的研究进展。其中,对异材质金属的电偶腐蚀行为及演变规律的研究取得了重大突破。此外,实时耦合的多电极阵列传感器(CMAS)探针的开发应用,对合金局部腐蚀的在线监/检测起到了举足轻重的作用。本文主要综述了微电极阵列技术在研究合金的电偶腐蚀、表面涂层失效、腐蚀环境的影响方面的进展,探讨了微电极阵列技术在表征合金局部电化学不均一性方面的优势与不足,并对其进行了总结和展望。     

弹体头部形状对碳纤维层合板抗冲击性能影响实验研究

为研究弹体头部形状对碳纤维层合板抗冲击性能的影响,利用一级气炮发射卵形头弹、半球形头弹和平头弹,对2 mm厚碳纤维层合板进行了冲击实验。利用公式拟合处理实验数据,揭示弹体头部形状对靶板弹道极限与能量吸收的影响,并且分析靶板冲击损伤形貌及机理特征。研究结果表明:平头弹弹道极限最高,半球形头弹次之,卵形头弹最低。弹体在低速度冲击时,弹体头部形状对靶板能量吸收率的影响更为显著。平头弹冲击时,靶板迎弹面受到均匀分布的环向剪切力,纤维同时被剪切,基体发生大面积剪切破坏。半球形头弹冲击时,靶板迎弹面受到非均匀分布的剪切力和挤压作用,纤维发生剪切断裂和拉伸断裂,基体发生剪切破坏和挤压破碎。卵形头弹冲击时,纤维发生单一的拉伸断裂,而基体则发生挤压破碎。弹体头部形状对靶板损伤的影响主要集中在迎弹面和中部纤维层。     

Oblique penetration of a rigid projectile into a thick elastic–plastic target: theory and experiment

A model of oblique penetration of a rigid projectile into a thick elastic–plastic target has been developed (Roisman et al., Int J Impact Engng 1997; 19: 769–95) which incorporates stress-free boundary conditions at the rear surface of the target. The main objective of the present work is to validate the theoretical model by comparison with new experimental results for normal and oblique penetration of a rigid projectile into a thick plate of Al 6061-T651. Good agreement between theory and experiment is exhibited for the projectile residual velocity and the crater shape.     

环境激励下桥梁结构模态参数识别的改进随机子空间算法

为了剔除稳定图中的虚假模态和避免模态遗漏现象,提高模态参数识别的精确度,提出了一种基于滑动窗口和相似度的桥梁结构模态参数智能化识别算法。基于余弦相似原理提出了频率相似度和振型相似度,并依此构建置信度,以实现对系统真实阶次的自动化确定;引入改进集成经验模式分解算法,以消除响应信号内部的噪声信号,达到消除部分虚假模态的目的;接着引入滑动窗口以实现对响应信号的划分,并通过构建频率相似度、振型相似度以及阻尼比相似度实现多个窗口对应参数结果中同类模态的聚类处理,达到剔除虚假模态和避免模态遗漏的目的。最后将所提算法运用于实际斜拉桥结构的模态参数识别,并将识别结果与现场试验值以及有限元结果进行对比,结果表明,所提算法不仅能有效识别出频率结果还能识别出准确的模态振型图,能够实现桥梁结构模态参数的在线智能化识别。     

Microstructure and electrical conductivity in shape and size controlled molybdenum particle thick film

We study the effects of particle morphology on the microstructure and electrical conductivity of Mo particle thick films. In our study, the shape and size of molybdenum (Mo) particles are modified by mechanical ball-milling and atomic layer deposition (ALD). As the total number of collisions between Mo particles and ball-milling media increases, Mo particles are deformed, and the shape of Mo particles changed from irregular polyhedrons to thin flakes. In the ball-milling process, stress frequency is an important processing parameter governing the deformation and breakage of Mo particles. In addition, ALD-grown TiO₂ layer is found to significantly suppress the growth of Mo particles at high temperature. After 1000 °C annealing, the particle size of the TiO₂ layer-coated film is only half of that of bare Mo particle films. The shape of the particles changes electrical conductivity of the Mo thick films. Large contact area between flake shape particles can increase the carrier mobility of the film and the 5-nm thick TiO₂ layer can provide the inter-particle carrier transport path via a tunneling mechanism. Our results show that the combined use of the ball-milling and the ALD coating leads to Mo thick films with high electric conductivity and large surface area.     

Dynamic response and microstructure evolution of the finite steel target subjected to high velocity impact by copper explosively formed projectile

The dynamic deformation of the finite steel target subjected to high velocity impact of copper explosively formed projectile is investigated by optical, scanning, and transmission electron microscopy. Morphology analysis of fracture surfaces indicates that the copper remainder plated to the crater wall shows extremely plastic deformation, which consists of elongated parabolic dimples, and the mild carbon steel target exhibits excellent brittle features that material fails mainly along the cleavage facets on the rear surface of target under strong impact of explosively formed projectile. In the surface of crater, the whole part of copper remainder and partial material of steel target undergoes completely dynamic recrystallization. The layer thickness of dynamic recrystallization zone, which displays an extreme plastic flow in solid state, is about 21.3 μm in steel target, and the average size of the refined grains significantly decreases to approximately 200 nm. Theoretically calculated results indicate that the temperature increase is associated with shock wave and plastic deformation of steel target and can reach 1352 K, which is 0.75T_m (where T_m is the melting temperature of steel target). The change in microhardness from the crater wall to the matrix of target is consistent with micro‐deformation of grains, and maximum microhardness is observed on the interface between dynamic recrystallization and severe plastic deformation zones of steel target.     

大变形复合材料薄板多体系统动力学建模

本文对大变形复合材料薄板的多体系统动力学建模方法进行研究。基于Kirchhoff假设,法线与中面保持垂直,从格林应变的表达式出发,建立了面内应变和曲率与绝对位置坐标和斜率的关系,在此基础上推导了广义弹性力阵和弹性力阵对广义坐标的导数阵,用绝对节点坐标方法建立了大变形复合材料薄板多体系统的动力学方程,用广义法和和牛顿迭代法求解微分-代数混合方程。对外载荷作用下的复合材料薄板进行数值仿真,通过与ANSYS的仿真结果进行对比,验证了本文建模方法的准确性和快速收敛性。最后,将建模方法应用于复合材料太阳帆板展开机构的数值仿真,分析了不同铺层情况下驱动力和约束力的振动特性。     

Self-Adaptive Grinding for Blind Tip Reconstruction of AFM Diamond Probe

Blind tip reconstruction(BTR) method is one of the favorable methods to estimate the atomic force microscopy(AFM) probe shape. The exact shape of the characterizer is not required for BTR, while the geometry of the sample may affect the reconstruction significantly. A cone-shaped array sample was chosen as a characterizer to be evaluated. The target AFM probe to be reconstructed was a diamond triangular pyramid probe with two feature angles, namely front angle(FA) and back angle(BA). Four conical structures with different semi-angles were dilated by the pyramid probe. Simulation of scanning process demonstrates that it is easy to judge from the images of the isolated rotary structure, cone-shaped, the suitability of the sample to be a tip characterizer for a pyramid probe. The cone-shaped array sample was repeatedly scanned 50 times by the diamond probe using an AFM. The series of scanning images shrank gradually and more information of the probe was exhibited in the images, indicating that the characterizer has been more suitable for BTR. The feature angle FA of the characterizer increasingly reduces during the scanning process. A self-adaptive grinding between the probe and the characterizer contributes to BTR of the diamond pyramid probe.     

Overlaying welding technology and performance of axle tube remanufacturing

Screw failure is one of the main scrap forms for rear axle tube, and thread turning after surfacing is a common means of remanufacturing. This paper takes rear axle tube as the main research topic, which is made of 40Mn and provided by an axle company. Manual electric arc welding, CO2 shielded arc welding and argon shielded arc welding are carried to overlay the damaged thread. The deposited metal consists of two welding material lays.Welding process and overlay properties are characterized by the test and analysis of microstructure, residual stress and hardness of surfacing layers. The results show that
argon shielded arc welding is an effective method to repair the failure thread; its microstructure of fusion area is meticulous and uniform; its residual compressive stress (absolute value) of welding surface is the biggest among the three welding methods; its hardness curve is relatively flat and appropriate for turning.     

飞机驾驶舱后观察窗抗鸟撞试验及数值模拟研究

为了对飞机驾驶舱后观察窗玻璃进行抗鸟撞设计,进行了后观察窗玻璃抗鸟撞试验,试验中测量了观察窗玻璃上两个点的应变时间历程。利用大型商用碰撞分析软件PAM-CRASH建立了全尺寸鸟撞后观察窗玻璃有限元计算模型,对鸟撞后观察窗试验过程进行了数值模拟,比较了应变及位移时间历程曲线的计算结果和试验结果,二者良好的一致性表明计算模型的合理性。在此基础上分析了内外层玻璃厚度及中间空气层厚度对后观察窗结构抗鸟撞动响应的影响规律,为飞机驾驶舱后观察窗玻璃的抗鸟撞设计提供技术指导。