Nonlinear stationary torsional waves in an elastic rod

A mathematical model that generalizes the equation for torsional vibrations of a Coulomb rod by accounting for finite deformations is proposed. The presence of geometric nonlinearity is shown to introduce dispersion so that nonlinear stationary waves may exist even in a linear environment without dispersion.     

Intensive longitudinal and torsional waves in a bar

The paper considers the problems of longitudinal waves propagating in a twisted bar and of the formation of nonlinear steady-state longitudinal and torsional waves.     

Effect of an interior viscous fluid on the propagation of torsional waves in an elastic pipe

The paper theoretically deals with the effects of the interior viscous fluid on the speed and attenuation of torsional waves propagating in an elastic pipe. Expressions for the phase speed and attenuation are obtained as functions of the viscosity and mass density of the adjacent fluid by exact and asymptotic analyses. Exact solutions with transcendental equations lead to an implicit relationship between the quantities of interest. In order to relate explicitly the parameters with physical meaning, asymptotic solutions are derived by the perturbation method. The approximate solutions are in good agreement with the exact solutions for a wide range of parameter values. The results provide quantitative information of the reduction of phase speed and the increase of attenuation affected by the fluid viscosity.     

Axial stress waves in an elastic–perfectly-plastic bar

A bar, made from an elastic–perfectly plastic material, fixed at one end, suddenly has an axial load applied at the other end. After its sudden application, the load is held constant. If the load is less than half the yield load for the bar, and in the absence of damping, the load causes a stress wave to pass up and down the bar, all behaviour being elastic. At any point within the bar length, the stress varies, in a stepwise fashion, between zero, and twice the stress corresponding to the applied load. This is the classical elastic solution. However, if the load is greater than half the yield load, when the stress wave first hits the fixed end, yielding will occur, and a simple model is proposed in this paper to allow for yielding. The model incorporates two zones separated by the stress wave, as in the elastic solution, together with a third zone, concentrated, and adjacent to the fixed support, in which all plastic straining takes place. The paper describes and verifies the model, and presents the predictions that it gives for various levels of load.     

Transient torsional vibrations of a rigid mass connected to an elastic half-space by an elastic circular rod

Applying Laplace transformations with respect to time and numerical inverse Laplace transformations, the transient torsional vibrations of a rigid mass connected to an elastic half-space by an elastic rod are analyzed under two specific incident pulse loads. The time histories of the rigid mass rotation are presented. Application of the numerical inverse Laplace transformations enables us to obtain the time histories of the rigid mass rotation accurately and fairly quickly by utilizing a digital computer. This method is applicable to the transient problem of a rigid mass connected to a half-space by an elastic medium or a finite elastic medium on a half-space, e.g. machines such as a press or a pile driver footed on a foundation, if the shape of the incident pulse is not very complicated and the maximum time T_max is not too long. When the slenderness ratio of the rod is small, the damping effect of the half-space on the rigid mass rotation due to waves radiating to infinity is small, regardless if the shear modulus ratio of the half-space and the rod is large or not. The amplitude of the rigid mass roation increases and its period lengthens as the shear modulus ratio increases.     

某发射装置串联式扭杆平衡机的设计

根据平衡机需要在满载和空载两种工况下工作,设计空间限制大等特点,提出了扭杆平衡机由四连杆机构与串联式扭杆连接而成,左右两侧完全对称布置的设计方案.给出了双向串联式扭杆平衡机设计主要参数的计算方法及其加工工艺.引入扭杆单位长度刚度系数,使设计具有一定的新颖性.经预扭试验测定,其扭转角和相应的扭矩均达到了设计要求.     

Sensitivity and resonant frequency of an AFM with sidewall and top-surface probes for both flexural and torsional modes

The resonant frequencies and flexural sensitivities of an atomic force microscope (AFM) with assembled cantilever probe (ACP) are studied. This ACP comprises a horizontal cantilever, a vertical extension and two tips located at the free ends of the cantilever and the extension, which makes the AFM capable of simultaneous topography at top surface and sidewalls of microstructures especially microgears, which consequently leads to a time-saving swift scanning process. In this work, the effects of the sample surface contact stiffness and the geometrical parameters such as the ratio of the vertical extension length to the horizontal cantilever length and the distance of the vertical extension from clamped end of the horizontal cantilever on both flexural and torsional resonant frequencies and sensitivities are assessed. These geometrical effects are illustrated in some figures. The results show that the low-order vibration modes are more sensitive for low values of the contact stiffness, but the situation is reversed for high values.     

Velocities of energy and wave pulse transfer by flexural waves propagating in a beam lying on a nonlinear elastic base

Flexural oscillations of a Bernoulli-Euler beam lying on a nonlinear elastic base are considered. Equations of energy and wave pulse transfer in the system are given.     

调整弹性零件抗扭刚度的研究

介绍了改变弹性零件直径,调整抗扭刚度的方法,给出弹性零件直径与抗扭刚度的关系,并提出了直径及加工公差的计算方法。     

Sensing characteristics of contact-type transducer for flexural waves

For the purpose of understanding and improving the stress wave factor technique and the travelling wave control method, the sensing characteristics of contact-type transducers for flexural waves are investigated in this paper. Two kinds of frequency response functions (FRF) are presented to characterize the transducer sensing results: one is for any harmonic plane wave, and the other for any point source disturbance. The two FRF are both expressed in the form of explicit physical interpretations which distinguish the influences from the transducer itself and from the tested structure. Based on this, three characteristic lines about the FRF are presented: one is a scattering line which means the FRF is dominated by the nature of wave scattering or wave reflection, the other two are transducer’s mass and spring lines which imply the transducers properties dominate the FRF. Using these three lines, the difference between general ultrasonic transducers and general vibration transducers can be clearly identified. Finally using the fast Fourier transform (FFT) technique, some typical time domain numerical results of the transducer output are also presented to show some important sensing characteristics.     

Displacement fields in waves generated by flexural oscillations of plates

A technique has been suggested for calculating acoustic displacement fields in waves generated by flexural oscillations in plates of finite dimensions in gaseous media at different frequencies, plate dimensions, and elastic parameters in both pulsed and cw modes. Acoustic fields in flexural resonant transducers with emitters shaped as round plates have been studied both theoretically and experimentally.     

On dispersion of elastic waves in rings

The governing equations for the vibrations of curved rings is derived with the effects of centerline extensibility and a type of Winkler-Bach effect, associated with the shift in neutral axis due to ring curvature included. The propagation of harmonic waves is considered and the governing dispersion relations derived and illustrated.     

Characteristics of elastic waves generated by fatigue crack penetration and growth in an aluminum plate

The characteristics of elastic waves emanated from crack initiation in 6061 aluminum alloy subjected to fatigue loading are investigated through experiments. The objective of the study is to determine the differences in the properties of the signals generated from fatigue test and also to examine if the sources of the waves could be identified from the temporal and spectral characteristics of the acoustic emission (AE) waveforms. The signals are recorded using nonresonant, flat, broadband transducers attached to the surface of the alloy specimens. The time dependence and power spectra of the signals recorded during the tests were examined and classified according to their special features. Six distinct types of signals were observed. The waveforms and their power spectra were found to be dependent on the crack propagation stage and the type of fracture associated with the signals. The potential application of the approach in health monitoring of structural components using a network of surface mounted broadband sensors is discussed.     

Destabilizing effect of additional restraint on elastic bar structures

This paper revises the well-known theorem; “The addition of restraint to a structure cannot decrease its elastic critical load”. It is pointed out by theoretical arguments and simple examples that this theorem is valid only if the displacement components in the buckling direction are additionally restrained. But additional restraints on pre-buckling displacements, which are orthogonal to the direction of buckling, can decrease the elastic critical load factor of the structure. In the case of additional restraints on prebuckling displacements, by the Dunkerley theorem, a bracketing formula is presented which gives lower and upper bounds to the minimum positive critical load factor of the modified structure with the help of minimum positive critical load factors of different loading patterns on the original structure.     

橡胶套筒弹性联轴器扭振动态特性计算

以橡胶套筒弹性联轴器为研究对象,通过建立通用的力学模型,理论计算得出弹性联轴器扭振的动态特性以及内部应力。通过采用有限元软件,选择合适的参数,成功模拟弹性联轴器中橡胶件的力学性能,利用计算机模拟,得出联轴器的转角、角速度曲线,验证了理论计算的正确性。     

Factors affecting attenuation of torsional waves in pipes loaded on contact viscoelastic media

Results of theoretical and experimental studies of the attenuation of torsional waves in pipes depending on the conditions of loading on viscoelastic media, pipe dimensions, and excitation frequency are presented. The results can be used for justification of pipe testing parameters such as insonification range and sensitivity when developing guided-wave techniques for pipelines of different sizes under various service conditions.     

弹性压杆稳定计算的方块脉冲函数法

弹性压杆特别是变截面压杆，要推导出其稳定方程和计算临界载荷是十分繁琐甚至是不可能的。这里利用方块脉冲函数(BPF)的良好运算性质直接求解弹性压杆稳定的能量泛函极值，将计算临界载荷转化为求矩阵的特征值问题，从而得到了计算弹性压杆失稳临界载荷的一种新的数值方法。该方法对于等截面压杆和变截面压杆均适用，具有计算简洁、便于计算机处理等优点，有很好的工程应用价值。     

Reflection characteristics of longitudinal waves in a semi-infinite cylindrical rod connected to an elastic infinite plate

The reflection characteristics of longitudinal strain waves in a semi-infinite cylindrical rod connected to an elastic infinite plate are investigated theoretically and experimentally. In the analysis, both the Mindlin plate theory which includes the effects of plate rotary inertia and shear deformation and the classical plate theory are employed. Taking account of the experimental results of the incident strain pulses produced by the impact of spherical balls, the shapes of the incident pulses for the numerical calculations are assumed to be square of a half sinusoid. Applying Laplace transformations with respect to time and numerical inverse Laplace transformations, the time histories of the longitudinal strain at the arbitrary points of the rod are presented. The differences between the reflected waves obtained from the Mindlin plate theory and those from the classical plate theory are large when the plate thickness is large and/or the plate is soft compared with the rod. Thus, the effects of plate rotary inertia and shear deformation are large in the case of thick and/or soft plate. Experimental results are closer to the numerical results obtained from the Mindlin plate theory than those obtained from the classical plate theory.     

初始挠度及中间弹性支撑对压杆稳定的影响分析

实际工程结构中的细长杆受压时,当存在初始挠度及中间弹性支撑时,不能用经典的欧拉公式计算杆件的屈曲临界载荷.利用有限元软件ANSYS对实际工程结构进行非线性屈曲分析,能够考虑到杆件的初姑挠度以及中间弹性支撑对临界失稳载荷的影响.计算结果表明:机车径向转向架耦合杆初妊挠度为10 mm时,对应的临界失稳载荷相对欧拉公式计算结...     

表面弹性波OPCM传感器的标定

标定了一种被称为正交异性压电复合材料(OPCM)的声发射(AE)传感器.利用断铅信号作为声源,SR-15型AE传感器作为标准传感器,以比较法研究了OPCM的脉冲响应.在玻璃纤维板上重点研究了OPCM的正交异性特性--陶瓷项数量的影响及响应规律的描述.实验结果表明,该传感器适于探测表面弹性波,陶瓷项数达到30,正交异性显著,能够很好地减小噪声、边界回弹波等信号对诊断信号的干扰,有助于板类结构健康监测.