An analysis of the nosing process of metal tubes

In this paper, the finite element method is used to investigate the cold nosing process of partially laterally constrained metal tubes with a conical die from a tube billet. A series of simulations on the tube nosing using the FEM program ANSYS/LS-DYNA was carried out. The influences of the process parameters such as tube length, tube thickness, die fillet radius, die angle, friction factor, strength coefficient and strain hardening exponent of the billet material on the critical nosing ratio of the tube are analysed. Experiments were carried out with stainless steel SUS304 tube billets at room temperature, and the results of experiments were compared with the FEM calculations.     

On the quasi-static piercing of square metal tubes

This paper investigates the energy absorption properties of square tubes pierced by pointed punches under quasi-static conditions. In a series of tests, square section pyramidal punches and conically headed cylindrical punches were pierced slowly into square steel tubes having 40×40 mm² outside dimensions. Wall thicknesses of 1.6 and 2.5 mm were tested, and the length of tubes was varied. Some typical loads were plotted against deflection, and a number of interesting conclusions were drawn from the tests. Based on the test results and observations, preliminary theoretical considerations are presented. The theoretical results agree fairly with the experiments.     

Mechanics of static and dynamic inversion processes

The paper presents an experimental and theoretical analysis of tube inversion process under quasi-static and dynamic loading conditions. The aim of the work is to propose a method of predicting the dynamic inversion load based on the quasi-static data. The method employs the principle of conservation of energy of the body in collision which is totally dissipated through plastic deformation of the tube under an inversion process. A dynamic inversion test was performed by means of drop hammer against the tube—die assembly. The hammer was coupled to an accelerometer to permit dynamic load readings. The results demonstrated that for a given impact velocity, the axial shortening as well as the dynamic inversion load compare very well to those predicted from the theoretical quasi-static results. The quasi-static and dynamic experiments were carried out on copper and brass tubes. Different inversion die radii were also used. In addition other relevant parameters will be discussed.     

Numerical investigations on a new type of energy-absorbing structure based on free inversion of tubes

A new type of structure, called retractable tube, is introduced in the present work to overcome the drawbacks of two traditional types of invertubes. The inversion processes of the proposed tubes under axial compression are simulated by using the non-linear finite element code LS-DYNA and the features of the force-displacement curves and the deformation modes of the proposed tubes are analyzed. A comparative study is conducted to compare the energy absorption characteristics of the new proposed tubes with the plain circular tubes based on the performance indices used most commonly for energy-absorbing devices. The results show that the whole efficiencies of the new proposed tubes are significantly higher than those of the corresponding plain circular tubes. In addition, a parametric study is carried out to investigate the effects of geometric parameters on the behavior of retractable tubes.     

On the axial splitting and curling of circular metal tubes

The present paper investigates the axial splitting and curling behaviour of circular metal tubes. Mild steel and aluminum circular tubes were pressed axially onto a series of conical dies each with different semi-angle. By pre-cutting eight 5 mm slits which were distributed evenly at the lower end of each tube, the tube split axially and the strips curled outward. Experiments showed that this mechanism results in a long stroke and a steady load. An approximate analysis is presented which successfully predicts the number of propagated cracks, the curling radius and the force applied. This analysis takes into account ductile tearing of the cracks, plastic bending/stretching and friction. Effects of tube dimensions, semi-angle of the die and friction are discussed in detail.     

Inelastic wrinkling and collapse of tubes under combined bending and internal pressure

The problem of inelastic bending and collapse of tubes in the presence of internal pressure is investigated using experiments and analyses. The experiments involve 1.5-inch diameter, D/t=52 stainless steel tubes bent to failure at fixed values of pressure. The moment-curvature response is governed by the inelastic characteristics of the material. Bending induces some ovalization to the tube cross section while, simultaneously, the internal pressure causes the circumference to grow. Following some inelastic deformation, small amplitude axial wrinkles appear on the compressed side of the tube, and their amplitude grows stably as bending progresses. Eventually, wrinkling localizes, causing catastrophic failure usually in the form of an outward bulge. Internal pressure stabilizes the structure, it increases the wavelength of the wrinkles and can increase significantly the curvature at collapse. The onset of wrinkling is established by a custom bifurcation buckling formulation. The evolution of wrinkling and its eventual localization are simulated successfully using a FE shell model. The material is represented as an anisotropic elastic-plastic solid using the flow theory, while the models are assigned initial geometric imperfections with the wavelength of the wrinkling bifurcation mode. It is demonstrated that successful prediction of collapse requires very accurate representation of the material inelastic properties including yield anisotropies, and that as expected, the collapse curvature is sensitive to the imperfection amplitude and wavelength imposed.     

On amplification of stress waves in cylindrical tubes under internal dynamic pressures

This paper presents a set of closed form solutions for the elastodynamic structural response of thin cylindrical tubes to internal moving pressures with specific profiles. The solution set includes newly derived expressions for transverse shear and axial strains plus modified expressions for the reflected structural waves. These expressions are used to study the amplification of flexural and shear stress waves caused by internal gaseous detonation and shock loading. It is shown how the three different critical speeds at which the resonance of the structural waves occur can be computed. The development of stress waves in a thin aluminum tube is studied over a wide range of speeds and the magnitudes of dynamic amplification factors are determined. In particular, the occurrence of transverse shear resonance at the second critical speed is studied. The peak value of the shear stress at this speed is found to be significantly higher than the finite element results reported by other researchers. Finally, an adjusted form of the general solution is used to investigate the response of a thin tube to internal shock loading. The predicted vibrational spectrums were in very good agreement with the experimental results reported in the literature.     

A numerical study on the impact response and energy absorption of tapered thin-walled tubes

Tapered tubes have been considered desirable impact energy absorbers due to their relatively stable mean load–deflection response under dynamic loading. Relatively few studies have been reported on the energy absorption performance of tapered tubes compared with straight tubes. This paper compares the energy absorption response of straight and tapered thin-walled rectangular tubes under both quasi-static and dynamic axial impact loading, for variations in wall thickness, taper angle, impact mass and impact velocity. It is found that the dynamic response of tapered tubes is more sensitive to impact velocity and wall thickness than taper angle for lower impact velocities. Inertia effects influenced the dynamic response for both straight and tapered tubes, yet were less significant for the latter. Overall, the results indicate that the energy absorption response of tapered tubes can be controlled via their wall thickness and taper angle, and this highlights their potential for use as energy absorbers. Analysis has been undertaken using a finite element model, validated using existing theory.     

Nonlinear dynamic analysis of coupled gear-rotor-bearing system with the effect of internal and external excitations

Extensive studies on nonlinear dynamics of gear systems with internal excitation or external excitation respectively have been carried out. However, the nonlinear characteristics of gear systems under combined internal and external excitations are scarcely investigated. An eight-degree-of-freedom(8-DOF) nonlinear spur gear-rotor-bearing model, which contains backlash, transmission error, eccentricity, gravity and input/output torque, is established, and the coupled lateral-torsional vibration characteristics are studied. Based on the equations of motion, the coupled spur gear-rotor-bearing system(SGRBS) is investigated using the Runge-Kutta numerical method, and the effects of rotational speed, error fluctuation and load fluctuation on the dynamic responses are explored. The results show that a diverse range of nonlinear dynamic characteristics such as periodic motion, quasi-periodic motion, chaotic behaviors and impacts exhibited in the system are strongly attributed to the interaction between internal and external excitations. Significantly, the changing rotational speed could effectively control the vibration of the system. Vibration level increases with the increasing error fluctuation. Whereas the load fluctuation has an influence on the nonlinear dynamic characteristics and the increasing excitation force amplitude makes the vibration amplitude increase, the chaotic motion may be restricted. The proposed model and numerical results can be used for diagnosis of faults and vibration control of practical SGRBS.     

差分吸收NO_2激光雷达波长漂移和能量波动对浓度反演的影响

为评估差分吸收二氧化氮激光雷达中激光器的稳定性对反演浓度的影响,以NO_2的吸收谱和激光雷达方程为基础,分析了波长漂移和能量波动对距离分辨差分吸收激光雷达浓度反演带来的相对误差。采用两台Nd:YAG激光器的354.7nm波长分别泵浦两台染料激光器的方式,产生差分吸收探测所需的两个波长λon(448.10nm)和λoff(446.80nm),搭建探测大气NO_2实验系统,并就波长漂移和能量波动对NO_2浓度反演影响进行了实验验证。实验结果表明:在没有稳频条件下,当λon和λoff波长漂移≤0.005nm时,引起的浓度相对误差为≤3%;能量波动对反演浓度没有影响,但能量降低减小探测距离,当能量下降≤5%时,探测距离≤100m,实验结果与理论计算基本一致。最后,开展了大气NO_2浓度实验观测,获得实验期间水平及垂直高度0.5~3km内NO_2浓度的分布廓线,系统稳定可靠。本方法为实用化NO_2差分吸收激光雷达的设计及应用提供了理论依据及技术支持。     

The effects of total internal reflection on the spread function along the axis in confocal microscopy

A broadening and splitting of the axial spread function is observed when high-numerical-aperture (NA) oil-immersion objectives are used on a confocal microscope to examine dielectric interfaces when the refractive index below the boundary is lower than the NA of the objective. The phenomena is due to total internal reflection probably as a consequence of the Goos-Hänchen shift. If total internal reflection occurs when undertaking confocal microscopy, this shift creates obvious problems when the optical sectioning capabilities must be optimal in reflectance mode and more subtle difficulties can arise when examining fluorescent emission. Alternatively, deliberately inducing total internal reflection can be used to estimate the refractive index in component parts within foams, emulsions and aerated specimens where such measurements can be relatively difficult to make by other means. Furthermore, the examination of total internal reflection with a confocal microscope permits the phenomena of total internal reflection itself to be probed with very high illumination intensities without disturbing the boundary conditions with an external probe. Finally, other changes in the apparent position of the focus were noted to occur when high-NA oil-immersion objectives are used to examine specimens such as metal mirrors.     

闭孔泡沫铝力学特性及其在汽车碰撞吸能中的应用研究进展

汽车低能耗、安全和轻量化已经成为汽车领域研究的热点问题,闭孔泡沫铝作为一种轻质吸能金属材料,在低密度下具有良好的比刚度和比强度,同时具有良好的抗冲击性和能量吸收性,已逐渐引起汽车产业界地重视。简述泡沫铝单轴压缩试验中弹性模量、抗压强度、屈服强度、平台应力、致密化应变等参数的定义和试验标准;综述闭孔泡沫铝的本构方程的研究现状,重点讨论屈服面模型;总结泡沫铝的微观结构有限元建模方法,比较商业软件中集成的宏观材料模型。归纳吸能材料的特点,分析闭孔泡沫铝的吸能能力和抗冲击能力;综述应变率和冲击速度对泡沫铝吸能特性有无影响的研究进展,并对可能存在的影响进行解释。总结闭孔泡沫铝在汽车轻量化和碰撞安全性领域的应用,具体分析典型的案例。指出当前闭孔泡沫铝的力学特性及其在汽车结构中应用存在的问题与难点,总结并提出本研究领域可以借鉴的研究方向。     

微纳尺度材料内耗测量系统的设计与实现

提出了一种非接触式的内耗测量方法。通过对碳纤维材料试样进行交变静电激发,在显微系统下记录强迫振动过程的高帧率图像,完成了微纳尺度材料内耗测量系统的设计。实验结果表明该系统能实现低频和高频内耗的非接触式测量,测量频率范围大,系统扩展性强。     

Elimination of the effects of stray light in measurements by total internal reflection aqueous fluorescence (TIRAF)

Total internal reflection aqueous fluorescence has been shown to be capable of achieving spatial resolution in surface contours of about 1 nm. When used with highly structured objects, errors in measurements can arise from light scattered either by the object or within the body of the microscope. We describe how these errors can be eliminated when studying surface contours of human platelets.     

等透射率冲击部件动态反演综合中的误差分析

针对弹性杆形部件中的作用力和速度传播特征矩阵的构造过程，即多项式根的替换操作，采用减小运算中舍入误差的树型分析法，分析了等透射率冲击部件动态反演综合中误差的来源，重点研究了传递矩阵中多项式系数的两种求解方法；结合多项式零点条件的意义，探讨了多项式的良态和病态零点对反演解的影响，从而进一步研究了离散单元数N和部件设计精度之间的关系。     

Detection of faults in the bonding between commercial polyethylene anticorrosive coatings and metal tubes

A method of diagnostic nondestructive testing is proposed for workshop, depot, and route conditions to detect discontinuities in adhesion of commercial polyethylene anticorrosive coatings on metal tubes.     

神经网络逆软测量方法的拓展及在生物浸出过程中的应用

在前期工作中,提出了基于内含传感器的逆软测量方法,其中逆软仪表的构造仅仅是基于直接可测的状态来实现的。对该方法进行了拓展,首先将用于构造逆软仪表的直接可测量由直接可测的状态拓展为函数变量,然后对逆软仪表的建模算法进行了改进。这种拓展和改进不仅增加了逆软仪表构造成功的可能性,而且可以降低构造逆软仪表所需的直接可测量的导数的阶数,便于工程实现和应用。另外,采用神经网络来逼近理论上存在的逆软仪表,并得到了神经网络逆软仪表,从而解决了解析逆软仪表难以实现的工程应用瓶颈。最后将神经网络逆软仪表应用于生物浸出过程,实现了其不直接可测状态的在线软测量。仿真结果表明神经网络逆软仪表的软测量值与真实值非常接近,从而验证了该方法的有效性。     

轴向预压缩双晶片动力学模型与特性分析

基于欧拉梁的假设,将双晶片简化为3层压电层合梁,由Hamilton原理建立系统的动力学模型,得到描述轴向预压缩压电双晶片的偏微分方程及特定边界条件,通过求解上述微分方程的边值问题得到双晶片在不同轴向力下的输出特性的解析表达式。利用有限元软件对双晶片进行仿真,验证了理论分析的正确性,增加理论分析结果的可信度。最后通过实验的方法研究双晶片的静、动力学特性,证明了施加轴向力可以降低双晶片的弯曲刚度和固有频率,显著增加其机电耦合效率,提高力和位移输出能力。轴向力虽然会影响双晶片启动时的位移峰值,但是对响应时间和带宽影响较小,大轴向力下双晶片仍具有带宽高与响应快的优势。     

轴向预压缩双晶片动力学模型与特性分析

基于夹层结构是非常理想的抗爆炸冲击、弹道侵彻的轻质结构材料,制备了双层K-cor夹层结构试样。首先,采用一级轻气炮系统实验研究了双层K-cor夹层结构的高速冲击响应;其次,建立了双层K-cor夹层结构的有限元模型模拟了高速冲击过程,并利用该模型分析了高速冲击过程中的能量吸收和破坏模式;最后,讨论了结构的变化对于高速冲击性能的影响。结果表明：双层K-cor夹层结构相比单层结构的弹道极限速度提升了8.3%,模拟结果与实验值吻合较好;双层结构的优势在于更多界面在冲击作用下导致的吸能机制增加;提高Z-pin植入密度能够切实有效地提升K-cor的高速冲击性能。     

内外驱动兼备的球形机器人结构设计

球形机器人是机器人运动方式的突破,其最大的特点是运动方式特殊,球形的外壳将使机器人能在失稳后获得最大的稳定性,球形机器人能用最少的自由度以欠驱动的方式实现全方位运动.针对目前球形机器人能源供给问题,提出一种内外驱动兼备的充气球式球形机器人,以外部自然风力为主要驱动力、内部电机驱动为辅助动力,兼具外部风能驱动和内部电机驱动的优点,较好地解决能源供给和自主运动的问题.通过对运动原理和设计方案的分析研究,完成球形机器人的结构模型及主要零部件设计.