冲击载荷下线性硬化材料中球面应力波场的理论计算方法研究

基于线性硬化塑性本构模型,建立了冲击载荷作用下弹塑性球面应力波场的理论求解方法.首先,分析了冲击载荷卸载速率对球面应力波传播的影响,得到了3种不同类型的应力波传播图像.在此基础上,建立了弹性阶段、塑性加载阶段以及卸载阶段球面波动方程的理论求解方法,给出了质点位移、质点速度、应力和应变等物理量的计算方案.与已有理论方法相比,该方法考虑了不同载荷卸载速率条件下应力波的不同传播情况,并且给出了卸载阶段应力波参量计算方法,具有更广的适用范围.利用上述方法计算了恒定冲击载荷和不同指数衰减冲击载荷作用下弹塑性球面应力波场参量,在弹性阶段和塑性加载阶段,理论计算得到的物理量与已有理论方法和数值模拟结果基本吻合,在卸载阶段,已有理论方法不再适用,而本文理论计算得到的物理量与数值模拟结果基本吻合,验证了该理论方法的正确性.     

冲击加载下20钢中弹性前驱波衰减与应力松弛行为实验研究

 通过改变样品厚度，对平面冲击加载下20钢的弹性前驱波的波幅衰减和应力松弛进行了实验研究。采用激光速度干涉测速仪（VISAR）实测了样品后自由面速度历史，采样频率达到1 ns，保证了实验结果的准确性。实验结果显示：Hugoniot弹性极限随着传播距离呈指数衰减，在所研究的样品厚度范围内，Hugoniot弹性极限减小了44%；应力松弛行为和弹性前驱波的上升沿时间也依赖于传播距离；冲击加载的强度对材料动态屈服行为的影响很小。     

两侧有固体层负载时板中Lamb波的传播

本文研究了薄板二面有固体导负载时板中Ｌａｍｂ波的传播，从弹性波理论出发并结合应的边界条件，导出板中Ｌａｍｂ波的色散方程，数值计算表示，不管作为自由状态时板中Ｌａｍｂ波相速（板厚取定时）是大于或小于外层固体的声表面波波速，板中对称及反对称模式的Ｌａｍｂ波相速都随着外层固体层厚度增加而变化并且渐近于外层固体的声表面波波速，数值计算又表明，对很薄的板，板中对称及反对称模式的相速均随负载板的厚度呈线性变化     

激光在铝靶中形成应力波的传播

采用两种尺寸全电极式的x切割石英压力计,测量了自由入射面加K_8玻璃窗口两种状态下不同厚度(0.5～4.0mm)铝靶背面的应力应变过程。入射激光波长1.06μm、脉宽20 ns、平均功率密度10~7～10~8W/cm~2、会聚光斑直径8mm。结果表明:激光脉宽不变时,能量密度I愈大,应力波峰压σ_(max)愈高,σ_(max)∝I~2;当I=3～7J/cm~2时,应力波峰值压力与传播距离x的定标关系为:σ_(max)∝x~(-(1.02～1.29));测得应力波形状与解析计算相吻合,证实了在上述光强范围内激光在铝靶中产生应力波的热弹性机制。     

冲击载荷下分层梯度泡沫材料中的应力波传播特性

以一维应力波传播理论为基础,建立了3层金属泡沫材料受到刚性块撞击时的理论模型,研究了刚性块撞击3层泡沫圆杆时的动力响应过程,从理论上给出了刚性块在撞击过程中的速度衰减规律数值解。利用ANSYS/LS-DYNA分析了受刚性块撞击时塑性应力波在3层泡沫材料中的传播过程,比较了刚性块以及层间界面处节点速度的变化规律。通过对比有限元结果与理论结果发现:理论模型能够较好地预测冲击载荷下分层泡沫材料各界面的速度衰减规律;3层梯度泡沫材料比相同质量的单层均质泡沫材料具有更加高效的吸能和缓冲能力。由于理论假设忽略了反射波以及泡沫材料应变硬化效应的影响,理论解与有限元模拟结果之间存在一定的误差。     

用元胞法研究层合材料中的应力波

 介绍了元胞法,利用该方法模拟了材料弹性动态响应问题,并与传播矩阵方法的结果进行了比较。该方法易于程序实现,能很好地处理材料的层界面,协调计算精度与计算量之间的矛盾,比传统的差分法和有限元法减少了计算量。     

各向异性超常材料中倒退波的传播研究

研究了完全各向异性超常材料中的倒退波传播现象,得到了在材料本征轴和传输轴成任意角度情形下倒退波形成的条件,分析了超常材料的介电张量和磁导率张量、电磁波的偏振方式对倒退波形成和传播的影响. 在此基础上,进一步分析了几种不同色散曲线关系的各向异性超常材料中倒退波的产生情况,获得了电磁波波矢和坡印亭矢量(能流)夹角的具体表达式和倒退波传播的一般性结论. 此外,还研究了近零介电常数超常材料中倒退波的传播特性,发现在此类超常材料中倒退波只能是完美倒退波. 关键词： 超常材料 负折射 倒退波 各向异性     

多层介质对应力波传播特性影响分析

 通过在气炮上进行多层介质的低速冲击实验及相应的数值计算，分析了不同组成的多层介质对应力波传播特性的影响。结果表明：多层介质中的泡沫材料不仅能够改变应力波的幅值与作用时间，而且具有显著的吸能效果，引起应力波在传播过程中在各层介质中能量与动量分配的改变。通过对泡沫铝和泡沫混凝土两种软材料在多层介质中作用的比较表明，在低速冲击的实验条件下，含泡沫混凝土的多层介质具有较好的削波作用，含泡沫铝的多层介质具有较好的吸能性能。     

谱元法数值模拟约束结构内炸药中应力波的传播

针对高速侵彻类战斗部在侵彻过程中的装药安定性以及在意外事故中的安全性问题,对约束结构内炸药在冲击加载下的应力波传播规律进行了模拟研究。计算了不同侵彻速度下弹体的冲击响应函数,并将具有高精度和低耗散特点的谱元法应用于约束结构内凝聚炸药中的应力波传播模拟;考虑炸药-金属界面的动摩擦特性,计算了冲击加载下由动摩擦引起的装药-壳体界面温升,以及装药内部的塑性功积累。成功地将谱元法应用于凝聚炸药中应力波传播过程的模拟,模拟结果对更准确地评估热点生成机制,以及进行装药安定性分析具有参考意义。     

Ultrasonic beam focusing characteristics of shear-vertical waves for contact-type linear phased array in solid

We investigate the beam focusing technology of shear-vertical(SV) waves for a contact-type linear phased array to overcome the shortcomings of conventional wedge transducer arrays. The numerical simulation reveals the transient excitation and propagation characteristics of SV waves. It is found that the element size plays an important role in determining the transient radiation directivity of SV waves. The transient beam focusing characteristics of SV waves for various array parameters are deeply studied. It is particularly interesting to see that smaller element width will provide the focused beam of SV waves with higher quality, while larger element width may result in erratic fluctuation of focusing energy around the focal point. There exists a specific range of inter-element spacing for optimum focusing performance. Moreover, good beam focusing performance of SV waves can be achieved only at high steering angles.     

Stress waves propagation in solids under high-speed liquid impact

The high-speed liquid/solid impact phenomenon is often seen in many technicalfields such as, water jet cutting technology[1], rain erosion of aviation vehicles[2] and ro-tor blades erosion in large steam turbines[3]. Recently, China Aerodynamics ResearchCenter reported experimental results of rain erosion of hypervelocity projectile[4]; Xi’anJiaotong University reported numerical simulation of high-speed liquid drop impact on asolid surface[5]. In analyzing the mechanism of material’s dama…     

材料强度对电磁驱动固体套筒内爆过程的影响

电磁驱动柱形固体套筒内爆加载技术是高能量密度物理实验研究的重要加载方式。由于固体金属具有一定的结合强度, 需外加载荷达到特定阈值才会发生塑性流动, 且在内爆过程中塑性做功会耗散部分电磁力做功而变成金属材料的内能, 进而对固体套筒的内爆过程产生影响。通过弹塑性力学平面轴对称问题的解, 给出了套筒发生塑性流动时外加电流（即屈服电流）与套筒参数的关系。利用考虑材料强度的零维不可压缩模型对铝套筒的内爆过程进行模拟, 并分别与简单零维模型和实验数据进行对比, 结果发现当电流峰值远大于（20倍于）屈服电流时, 金属材料强度的影响甚微;而当峰值电流只数倍于屈服电流时, 金属材料强度的影响便不能忽略。     

Effects of initial compression stress on wave propagation in carbon nanotubes

An analytical method to investigate wave propagation in single- and double- walled carbon nanotubes under initial compression stress is presented. The nanotube structures are treated within the multilayer thin shell approximation with the elastic properties taken to be those of the graphene sheet. The governing equations are derived based on Flügge equations of motion. Frequency equations of wave propagation in single and double wall carbon nanotubes are described through the effects of initial compression stress and van der Waals force. To show the effects of Initial compression stress on the wave propagation in nanotubes, the symmetrical mode can be analyzed based on the present elastic continuum model. It is shown that the wave speed are sensitive to the compression stress especially for the lower frequencies.     

深远海线性内波条件下声场时间相关性的空间分布

深海声场特定的干涉结构导致其时间相关性的空间起伏,研究这种空间特性可以为水声信号的探测与处理提供重要参考。利用抛物方程声场仿真模型,联合Monte-Carlo数值方法计算分析了深远海线性内波条件下声场时间相关性的空间分布特性。与现有的研究相比,给出了时间相关性的距离和深度起伏特征。结果表明,当接收达到一定距离,声场时间相关性的空间分布具有与声场干涉条纹类似的结构,声场干涉越强,时间相关性越好。此外,声源频率和声速标准差的变化会引起时间相关性空间分布规律的改变,且会聚区传播模式下的改变强于深海声道传播模式。     

The effect of initial stress on the propagation behavior of SH waves in piezoelectric coupled plates

This study analytically investigates the propagation of shear waves (SH waves) in a coupled plate consisting of a piezoelectric layer and an elastic layer with initial stress. The piezoelectric material is polarized in z-axis direction and perfectly bonded to an elastic layer. The mechanical displacement and electrical potential function are derived for the piezoelectric coupled plates by solving the electromechanical field equations. The effects of the thickness ratio and the initial stress on the dispersion relations and the phase and group velocities are obtained for electrically open and mechanically free situations. The numerical examples are provided to illustrate graphically the variations of the phase and group velocities versus the wave number for the different layers comparatively. It is seen that the phase velocity of SH waves decreases with the increase of the magnitude of the initial compression stress, while it increases with the increase of the magnitude of the initial tensile stress. The initial stress has a great effect on the propagation of SH waves with the decrease of the thickness ratio. This research is theoretically useful for the design of surface acoustic wave (SAW) devices with high performance.     

用线阵CCD标定光纤端部位置

为了标定光纤端部在平面上的位置，采用线阵ＣＣＤ 对光纤的出射光进行扫描，对于接收到的数据采用重心法进行处理，并通过改变实验条件以达到较为理想的结果。     

Study of charged and neutral minimal supersymmetric standard model Higgs boson decays and measurement of tan <Emphasis Type="Italic">β</Emphasis> at the compact linear collider

The minimal supersymmetric extension of the standard model (MSSM) predicts the existence of new charged and neutral Higgs bosons. The pair creation of these new particles at the multi-TeV e ⁺ e ⁻ compact linear collider (CLIC), followed by decays into standard model particles, were simulated along with the corresponding background. High-energy beam-beam effects such as ISR, beamstrahlung and hadronic background were included. We have investigated the possibility of using the ratio between the number of events found in various decay channels to determine the MSSM parameter tan β and we have derived the corresponding statistical error from the uncertainties on the measured cross-sections and Higgs boson masses.      

Charged and neutral minimal supersymmetric standard model Higgs boson decays and measurement of tan <Emphasis Type="Italic">β</Emphasis> at the compact linear collider

The minimal supersymmetric extension of the standard model (MSSM) predicts the existence of new charged and neutral Higgs bosons. The pair creation of these new particles at the multi-TeV e ⁺ e ⁻ compact linear collider (CLIC), followed by decays into standard model particles, were simulated along with the corresponding background. High-energy beam-beam effects such as ISR, beamstrahlung and hadronic background were included. We have investigated the possibility of using the ratio between the number of events found in various decay channels to determine the MSSM parameter tan β and we have derived the corresponding statistical error from the uncertainties on the measured cross-sections and Higgs boson masses.