多孔极化PZT95/5铁电陶瓷单轴压缩力学响应与放电特性

采用添加造孔剂的方法制备了四种不同孔隙率PZT95/5铁电陶瓷,对其进行电场极化,随后开展了准静态单轴压缩实验,讨论了畴变、相变以及孔隙率对极化PZT95/5铁电陶瓷的力学响应与放电特性的影响.研究结果表明:(1)多孔极化PZT95/5铁电陶瓷非线性力学响应行为主要归因于畴变和相变的共同作用,与内部孔洞变形和坍塌基本无关;(2)在准静态单轴压缩下极化PZT95/5铁电陶瓷的去极化机制是畴变和相变的共同作用;(3)孔隙率对极化PZT95/5铁电陶瓷的弹性模量、压缩强度有明显的影响,而对断裂应变的影响较小;(4)极化PZT95/5铁电陶瓷畴变和相变开始的临界应力都随着孔隙率的增大而线性衰减,但相变开始的临界体积应变却不依赖孔隙率;(5)极化PZT95/5铁电陶瓷电荷饱和释放量随着孔隙率呈线性减小,但孔隙率对电荷释放速率基本没有影响.     

侧向稀疏对PZT—95／5陶瓷冲击去极化影响的研究

采用平面冲击波加载，对样品在不同封装介绍（不同侧向稀疏程度的情况下）和几何尺寸条件下进行冲击去极化实验，结果表明侧向稀疏导致电荷释放以近乎线性关系减小；根据实验条件拟合出物理计算模型，利用流体弹塑性模型，采用有限元计算方法对样品中的冲击压力进行三维计算，计算结果能很好地解释实验现象。     

PZT—95／5陶瓷微粉的一种简单制备方法

用常规的陶瓷生产工艺合成陶瓷微偻缺点是粒径仿大，分布不均匀，而且难以避免杂质的混入，对烧结制品的稳定性易产生不良影响，用一种简单的溶胶-凝胶（Sol-Gel)工艺制作出的PZT-95/5陶瓷微粉通过扫描电镜分析，粒径小于200mm且分布均匀，通过对溶胶-凝胶过程的分析，认为只要在原材料中有一种金属醇盐，就可以形成多组分共存的溶胶-凝胶。     

PZT—95／5陶瓷流体静压相变实验研究

采用常规的氧化物陶瓷生产工艺与多孔技术相结合的方法，制作出不同宏观密度的PZT－95／5陶瓷样品，进行流体静压相变实验。研究表明，陶瓷材料的铁电－反铁电相变与陶瓷中气孔的存在有密切的关系，运用气孔塌陷假设可以对此现象进行定性解释，研究结果和Sandia实验室给出的结果相符合。     

基于ANSYS/LS-DYNA的钢板混凝土墙冲击实验的有限元分析

运用经典的显式非线性动力分析软件ANSYS/LS-DYNA,分析了1/7.5缩尺飞机模型撞击钢板混凝土墙的冲击实验。选用两种不同的混凝土材料本构模型(Winfrith模型、CSCM模型)模拟混凝土的非线性破坏过程,将钢板混凝土墙的破坏模式以及飞机模型的残余速度等与实验结果进行了对比。结果表明,有限元分析结果与实验吻合较好,且Winfrith材料模型能够更好地模拟混凝土的大应变、高应变率的非线性性能,验证了钢板混凝土墙和飞机材料本构模型的选取以及整个分析方法的适用性和有效性。     

编织Kevlar/Epoxy复合材料层合板在冲击荷载下的动态响应

通过编织Kevlar/Epoxy复合材料层合板的平头弹冲击实验,分析了结构在不同冲量下的变形失效模式以及结构的抗冲击性能。实验表明复合板的变形失效模式主要表现为:(1)弹性变形;(2)复合板表面嵌入失效及整体塑性大变形;(3)背面纤维拉伸断裂及分层失效。基于实验研究,运用LS-DYNA 971有限元程序对铺层数不同的复合板在冲击载荷作用下的动态响应过程进行了数值模拟,模拟结果与实验吻合较好,子弹作用区域边缘处首先发生近似圆形的嵌入失效,而在板背面发生近似正方形的破坏区域;计算中重点分析了铺层数对结构动力响应的影响,在一定冲量范围内,通过对铺层数的优化,能够有效地减小后面板挠度,提高结构的能量吸收效率,增强结构的抗冲击性能。     

V-5Cr-5Ti的常温动态压缩力学性能

采用分离式霍普金森压杆(SHPB)装置,在常温下对V-5Cr-5Ti合金分别进行了应变率效应试验、 限制应变试验和应变累积的动态压缩试验;分析了应变率、应变累积对V-5Cr-5Ti合金动态压缩性能的影响; 并对压缩试验后的试件进行了金相分析。结果表明,V-5Cr-5Ti合金具有明显的应变率和应变历史效应,而 应变历史对材料的动态压缩性能的影响更明显。在高应变率下,应变低于0.20时,出现孪晶组织;而应变高 于0.20时,孪晶组织急剧减少甚至消失。     

平纹编织C/SiC复合材料低速冲击数值模拟

首先,基于空气炮装置进行了2D-C/SiC薄板在冲击速度为79~219 m/s范围内的低速冲击实验,对碎片云团发展过程进行高速摄影记录;其次,基于Autodyn软件正交各向异性复合材料模型,推导2D-C/SiC材料相关参数;选取SPH求解器建立二维计算模型,对实验工况进行数值模拟,并基于碎片云结构、B扫描检测结果和碎片云轴向发展速度验证了该模型可以很好地描述C/SiC材料在冲击载荷作用下的脆性特征和软化行为。最后,基于数值模拟结果推导得出了钢弹丸冲击C/SiC材料的极限侵彻深度预测公式。     

本构模型对复合材料中X射线热击波数值模拟结果的影响

以碳酚醛靶中的一维应变热击波为例,讨论本构模型对热击波数值模拟结果的影响.数值模拟采用3种本构模型,即各向同性理想弹塑性本构模型、各向异性理想弹塑性本构模型及各向异性动态弹塑性本构模型.结果表明:与各向同性理想弹塑性、各向异性理想弹塑性本构模型相比,利用各向异性动态弹塑性本构模型获得的热击波应力峰值较小、应力峰值衰减较...     

陶瓷/金属复合装甲冲击响应的三维SPH法分析

采用自编三维SPH程序对弹体侵彻陶瓷/金属复合装甲问题进行了数值模拟.为了描述金属和陶瓷材料非线性变形及损伤特性,在程序中嵌入Johnson-Cook和Johnson-Holmquist Ⅱ本构模型及Mie-Gruneisen状态方程.SPH计算得到的典型位移随时间变化曲线与实验结果吻合较好.通过数值模拟合理再现了弹体...     

高应变率下多孔未极化PZT95/5铁电陶瓷的非线性力学行为

采用添加造孔剂的方法制备了4种不同孔隙率的未极化PZT95/5铁电陶瓷。采用基于超高速相机与数字图像相关性方法的试样全场应变测量技术以及分离式霍普金森压杆（SHPB）技术,对多孔未极化PZT95/5铁电陶瓷进行高应变率单轴压缩实验研究。全场应变测量结果显示:轴向应变仅在试样中部分布较均匀,将该区域的平均应变作为应力-应变关系中的试样应变测量值较为合理,而由SHPB原理计算的试样应变值明显偏大,需要摒弃或修正传统的SHPB数据处理方法。通过波形整形技术实现了恒应变率加载,弱化了径向惯性效应的影响,揭示出多孔未极化PZT95/5铁电陶瓷的压缩强度具有显著的应变率效应。通过分析试样轴向应变和径向应变随着加载应力的变化,阐明多孔未极化PZT95/5铁电陶瓷的非线性变形行为的物理机制是畴变和相变共同作用,并发现畴变临界应力和相变临界应力都随着应变率升高而增大。保持加载应变率不变,讨论了孔隙率对多孔未极化PZT95/5铁电陶瓷动态力学行为的影响,发现随着孔隙率的升高,动态压缩强度呈非线性衰减,而畴变临界应力和相变临界应力则基本呈线性衰减。     

INVESTIGATION ON STABILITY OF PZT/EPOXY PIEZOCOMPOSITE WITH PRESSURE AND TEMPERATURE

With the universal test machine and temperature test chamber, the effect of pressure and temperature on the behavior of 1-3 and 1-3-2 piezocomposites prepared with PZT/epoxy in our lab has been investigated through electrical impedance and dielectric analysis. The permittivity, resonant frequency and dielectric loss of the composites have been measured under vertical stress and temperature, and the variety of the material properties under pressure and temperature could also be obtained. The pressure and temperature stability of the composites have been assessed through experiments. The data of these two types of composites indicated that the stability of 1-342 composite with pressure was better than that of 1-3 composite, and two composites have almost the same dielectric stability with temperature. However, 1-3-2 composite showed slower frequency variation than 1-3 composite.     

PZT压电陶瓷高温变形与失效的实验研究

随着工业设备集成化进程的加快,PZT压电陶瓷获得越来越广泛的应用,其工作环境也越来越复杂.例如,新一代节能环保型发动机中起致动作用的压电陶瓷叠层驱动器,工作时要承受力-热-电载荷的共同作用.因此,研究PZT压电陶瓷在高温下的变形与失效行为,对工业设计具有重要的指导意义.为此,本文利用自行搭建的压电陶瓷高温下电滞回线、蝶形回线和应力退极化曲线的测试装置,研究了PZT压电陶瓷在不同温度下的电致变形和应力退极化行为,得到了材料在不同温度下的电滞回线、蝶形回线、应力电位移曲线和应力应变曲线.实验结果表明,随着温度的升高,由电滞回线测得的剩余极化逐渐减小,蝶形回线逐渐变扁;由应力退极化产生的剩余极化和剩余应变也逐渐减小.极化量的改变是由材料的热释电效应(自发极化随温度的升高而减小)造成的,而应变量的变化是由晶胞畸变随着温度升高而减小所致.     

Notes on the X-ray Theory

My aim is to better compare thermoelasticity theory with a continuum theory of X-ray observations of crystals, to be described, to make it easier to adapt ideas and techniques from one to the other. To this end, I will present some different ways of formulating the X-ray theory. Also, I will adapt symmetry considerations from the former, partly to analyze problems of a kind not considered in thermoelasticity theory. This revised version was published online in August 2006 with corrections to the Cover Date.     

A95陶瓷材料的动态压缩测试研究

为了得到陶瓷材料有效的实验结果,必须采用多种改进措施(PulseShaper、高强度和高刚度垫块、直接测试试样应变以及使用较大长径比的试样)来满足SHPB装置所要求的基本假设条件。研究以A95陶瓷的测试为例,通过数值模拟分析证明:针对陶瓷材料改进的SHPB装置,可以得到陶瓷材料的有效压缩应力 应变曲线和压缩破坏强度。但是在分析材料的压缩破坏强度时,必须排除劈开破坏的干扰。数值模拟研究发现,压缩测试中出现的劈开破坏是由卸载过程中出现的局部横向(沿直径)拉伸造成的拉伸破坏。在修正了弥散对压缩破坏强度的影响后,研究得到了A95陶瓷的压缩破坏强度为3.5GPa。A95陶瓷的高应变率压缩应力 应变曲线显示了良好的线弹性,并且曲线的斜率与杨氏模量相同。     

A method for the study of turbulent mixing using fluorescence spectroscopy

The mixing of two feed streams in a reactor, one with a fluorescent tracer, the other without, results in a fluctuating concentration field, due to the turbulent flow. Fluorescence spectroscopy allows the characterization of the fluctuations at small scale and high frequencies. Measurements have been made with a spatial resolution of about 30 μm and up to a frequency of 5,000 Hz. Methods have been developed to determine the variance (intensity of segregation) and the power spectra. The spectra can be used to calculate the integral scale of the fluctuations, and in some cases the microscale and dissipation rate. Two optical setups are presented, one based on a nonfocused and the other on a focused laser beam. It is shown that only the focused system has sufficiently high laser flux density and sufficiently small measurement volume to give useful results at the desired characteristic size and frequency. As a demonstration of the method, the turbulent mixing in a continuous stirred tank reactor has been studied. Experiments were carried out in a 225 cm³ baffled reactor, stirred by a six-bladed Rushton disk turbine. The effects of stirring speed and position on the mixing were investigated.     

X-ray diffraction study of the fatigue behavior of a shot-peened aluminum-lithium alloy

The effect of different shot-peening treatments on the cyclic fluctuating bending fatigue behavior of a new aluminum-lithium alloy (the 2091) has been investigated. The residual-stresses in-depth profiles have been defined just after the shot peening using mainly the X-ray diffraction method. To reach a given depth inside the material, the surface layer was removed by electro-polishing. The acquired data had to be then corrected in order to account for the redistribution of the stresses during the polishing. Furthermore, this alloy contains up to 15-percent intermetallic precipitates. Moreover, the X-rays penetrate deeply inside the material (23 m). For these reasons, a special procedure, based on a self-consistent micromechanical scheme, has been developed to correct the acquired data. The stress profiles obtained by this procedure are compared to those obtained by other mechanical experimental methods and those calculated by a theoretical shot-peening method. Shot peening improves the life of the material but the surface residual stresses are partially released during the first cycles of fatigue and are then quickly stabilized.Paper was presented at the 1994 SEM International Conference on Residual Stresses (ICRS4) held in Baltimore, MD on June 8–10.