Dynamic Stability of a Fluid-Coveying Cantilevered Pipe on an Additional Combined Support

Based on an analytical study, a numerical analysis is made of the dynamic stability of a cantilevered steel pipe conveying a fluid. The pipe is modeled by a beam restrained at the left end and supported by a special device (a rotational elastic restraint plus a Q-apparatus) at the right end. The numerical analysis reveals that the critical velocity of the fluid depends on the governing parameters of the problem such as the ratio of the fluid mass to the pipe mass per unit length and the rotational elastic constant at the right end     

干燥和水饱和花岗岩的动态断裂特性

利用霍布金森压杆实验研究了干燥和水饱和花岗岩试件的动态应力应变关系。实验得到了干燥和水饱和花岗岩试件的平均动态拉断强度，表明水饱和花岗岩试件和干燥花岗岩试件的抗拉强度与加载速率具有不同的关系。对实验中实测试件层裂片的厚度进行了计算分析，对岩石类介质的动态断裂准则提出了初步见解。     

一类平面自治非线性时滞控制系统的多稳态和混沌

众所周知，平面自治系统即使具有光滑非线性存在，系统也不会出现复杂的动力学行为。本文研究这样的系统存在时滞时，时滞量对系统的动力学行为的影响。通过对一个平面自治非线性系统引入时滞反馈，得到数学模型。利用泛函分析和平均法建立系统平衡态随时滞量变化的失稳机理，研究表明：时滞量平面自治系统动力学行为的影响是本质的．时滞量不但可以使系统出现Hopf分岔，产生周期振动。而且还可以使系统出现多稳态的周期运动或周期吸引子，这些共存的吸引子相碰是导致系统复杂的动力学行为，包括概周期和混沌运动。     

含孔软铁磁材料Mindlin板中弹性波散射问题

基于考虑磁弹相互作用的Mindlin板弯曲波动方程，采用波函数展开法，分析研究 了含孔软铁磁材料Mindlin板中弹性波散射与动应力集中问题，给出了问题的分析 解和数值算例. 通过分析发现：磁感应强度对动弯矩集中系数和动剪力集中系数有 增加的作用，特别是在低频的情况下.     

轴向瞬间阶梯载荷下圆柱壳动力屈曲的双特征参数分析

对于轴向瞬间阶梯载荷下圆柱壳的弹性非轴对称动力屈曲问题，将临界应力和屈曲惯性项指数参数作为双特征参数求解。由能量转换和守恒准则，导出压缩波阵面上的屈曲变形附加约束条件。失稳控制方程、边界条件和波阵面上的连续条件，连同此附加约束条件构成求解两个特征参数和动力失稳模态的完备定解条件。由伽辽金法得出求解双特征参数问题的数值方法。     

Dynamic shearing resistance of molten metal films under high pressures and extremely high shearing rates

In the present study plate-impact pressureshear experiments have been conducted to study the dynamic shearing resistance of molten metal films at shearing rates of approximately 10⁷ s⁻¹. These molten films are generated by pressure-shear impact of relatively low melt-point metals such as 7075-T6 Al alloy with high hardness and high flow-strength tool-steel plates. By employing high impact speeds and relatively smooth impacting surfaces, normal interfacial pressures ranging from 1–3 GPa and slip speeds of over 100 m/s are generated during the pressure-shear loading. The resulting friction stress (∼100 to 400 MPa) combined with the high slip speeds generate conditions conductive to interfacial temperatures approaching the fully melt temperature regime of the lower melt-point metal (7075-T6 aluminum alloy) comprising the tribo-pair. During pressure-shear loading, laser interferometry is employed to measure normal and transverse motion at the rear surface of the target plate. The normal component of the particle velocity provides the interfacial normal traction while the transverse component provides the shearing resistance of the interface as it passes through melt. In order to extract the critical interfacial parameters, such as the interfacial slip-speed and interfacial temperatures, a Lagrangian finiteelement code is developed. The computational procedure accounts for dynamic effects, heat conduction, contact with friction, and full thermo-mechanical coupling. At temperatures below melt the flyer and target materials are described as an isotropic thermally softening elastic-viscoplastic solid. For material elements with temperatures in excess of the melt point, a purely Newtonian fluid constitutive model is employed. The results of this hybrid experimental-computational study provide insights into the dynamic shearing resistance of molten metal films at high pressures and extremely high shearing rates.     

简支梁振台的理论解及位移测试

利用由机械振动理论推导出的等截面简支梁的理论解,推导出了带集中质量的简支梁振动台的理论解,并通过分析动态条件下简支梁的位移与应变之间的关系,证明了:在动态条件下梁的位移与应变之间存在很好的正比关系。利用梁的位移与应变之间正比关系,如果在梁上适当位置粘贴应变片,通过测试应变就能准确地测得梁的动态位移。本文通过实例证明了该方法确实可行,理论解与实测结果非常吻合。这为简支梁的动态测试提供了有效而简便的方法。     

主动移频式动力吸振器及其动力特性的研究

动力吸振器是振动控制中比较有效的减振装置,只要吸振器(子系统)的振动固有频率与振动物体(主系统)的振动频率相同,即可有效地消除主系统的振动。但传统动力吸振器的控制频率带宽较窄,限制了其稳定性和减振效果的提高。本文通过独特的机械设计,研制了一种可以通过调节自身的几何参数,使得其固有频率随几何参数线性变化的主动移频的新型动力吸振器,并初步设定了相应的控制方法。文中还对其动力学特性进行了理论分析和实验测试,分析了它的机理,评估了它的实际减振效果。研究结果表明该吸振器可以大范围调节自身固有频率,有效拓宽吸振频带,具有良好的减振性能和稳定性。     

基于光学和扫描显微平台的微尺度实验力学检测技术和装置研究

本文基于光学和扫描显微平台,介绍了本研究组在微尺度实验力学检测技术和设备方面的最新研究成果。在检测技术方面涉及显微散斑干涉技术、微标记阵列检测技术、晶粒变形分析技术、光学探针动静态变形分析技术;在检测系统和装置方面介绍了新近开发的双视场薄膜检测系统、散斑微干涉系统、微标记检测平台、AFM和SEM单轴拉伸装置、三维微定位与加载系统、微力传感器及其标定装置、微动平台驱动装置等。探讨了微尺度实验力学检测中的问题和新的检测技术,给出了一些典型的应用和相关装置。