Studies of a Magnetocumulative Source of Electromagnetic Pulses with a Double Inductive Energy Storage

An energy source based on a helical magnetocumulative generator with simultaneous initiation of an explosive charge on the axis was developed. The generator operates on a double inductive energy storage with current circuit breakers in each storage. The main analytical dependences of the pulse amplitude and shape on the parameters of the double inductive energy storage were obtained. In an experiment with such an energy source, a voltage pulse of 770 – 800 kV was obtained on a breaker made of electrically exploding wires. The voltage at possible load points was 1300 – 1350 kV. The duration of the voltage pulse edge from 0.1U _max to 0.9U _max did not exceed 0.5 sec.     

Energy transfer from an inductive storage to an inductive load by means of an explosive current disconnect

A study is made of switching of current from an inductive storage by electrical explosion of a wire shunting an inductance in conformity with a model based on surface vaporization waves. It is established that the nature of the process is determined by certain generalized dimensionless parameters of the system. The modes of most efficient transfer of energy to the load are determined.     

载流圆形薄板的磁弹性应力与变形分析

本文在建立非定常电磁场和机械载荷作用下载流圆形薄板非线性变形状态下的磁弹性二维关系方程和运动方程的基础上，对其在非静态电磁场和机械载荷联合作用下的位移及应力进行了分析，获得了耦合场中一些参量的变化规律，通过具体算例，得出了载流圆形薄板在机械场和电磁场作用下的位移及应力与通电电流强度之间的关系，并解决了圆板中心处的奇异性问题，给出了在轴对称条件下的数值解，计算结果表明，改变通电电流及电磁感应强度的大小，可以改变载流薄板的应力和变形状态，达到控制薄板的受力和变形的目的。     

不确定性移动载荷激励下弹性简支梁的动态响应边界分析及应用

不确定性移动载荷激励下的弹性梁振动是土木、机械和航空航天等工程领域普遍存在的一类重要问题。在许多实际工程中,不确定移动载荷的样本测试数据有限或测试成本较高,本文引入区间过程模型对此类动态不确定性参数进行描述,提出了一种求解不确定移动载荷激励下弹性梁振动响应边界的非随机振动分析方法。首先,介绍了确定性移动载荷激励下弹性梁的振动微分方程及其解析求解方法;其次,引入区间过程模型,以上下边界函数的形式对不确定性移动载荷进行度量,进而基于模态叠加法发展出弹性梁振动响应边界求解的非随机振动分析方法;最后,将上述非随机振动分析方法应用于车桥耦合振动问题。     

Stress-strain state of an ice sheet subjected to a moving load under shallow-water conditions

The following two classes of problems of determining the stress-strain state of an ice sheet under a moving load are considered: determination of the resonant velocity for a load moving over a continuous ice field and calculation of the deflections of an ice field with a bounded ice-free zone subjected to a moving load. The problems are solved in a dynamic formulation. The algorithm of solution is based on the finite-clement method and finite-difference methods. Examples of calculations are given. Komsomol'sk-on-Amur State Technical University, Komsomol'sk-on-Amur 681013. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol 41, No. 4, pp. 206–210, July–August, 2000.     

爆炸载荷特征参数对无限长圆柱壳弹性动态响应的影响

采用含有三角脉冲载荷和准静压载荷的爆炸载荷加载,利用单自由度模型对无限长圆柱壳体（即等效平面应变圆环）的弹性动态响应进行了力学分析,获得了径向位移响应解析解及准静压阶段弹性响应振幅的解析解。基于所得解析解,通过控制变量法分析了载荷压力及载荷分界点时刻（即三角脉冲载荷与准静压载荷作用的分界点时刻）对径向位移最大值、准静压阶段弹性响应振幅的影响规律,更加深入地研究了爆炸载荷对结构响应的影响。本文主要从准静压幅值与三角脉冲峰值的比值以及载荷分界点时刻两个主要特征参数入手,结合结构的呼吸振动频率来研究爆炸载荷对无限长圆柱壳弹性动态响应的影响。在研究中发现存在临界时刻:当载荷分界点时刻早于临界时刻时,径向位移最大值出现在准静压阶段;当载荷分界点时刻晚于临界时刻时,获得了便于直观判断径向位移达到最大值时所处载荷阶段的分区图。基于前述解析解的分析,还获得了不同影响因素导致的振幅变化的单调性分区图,便于判别载荷压力的变化所致的准静压阶段振幅的增减趋势。通过研究获得的爆炸压力载荷对结构响应的影响规律,可为爆炸容器设计以及结构防护基础研究提供参考。     

载流圆锥薄壳的磁弹性应力与变形分析

在建立旋转壳体的非线性磁弹性运动方程的基础上,研究了电磁场和机械载荷联合作用下载流圆锥薄壳的磁弹性效应．通过算例,得到了载流圆锥薄壳的位移及应力与通电电流强度之间的关系．解决了圆锥薄壳顶点处的奇异性问题,给出了轴对称条件下的数值解．计算结果表明：改变通电电流强度,可以改变载流圆锥薄壳的应力与变形状态,达到控制圆锥薄壳的受力与变形的目的．     

Shear waves in an elastic-plastic material due to a supersonic surface step load

A step shear load moves steadily on the surface of an elastic-plastic half space at a speed exceeding the elastic shear wave speed of the material. The orientation of the shear traction is such that the deformation is two-dimensional antiplane strain. Two different representations of the rate independent elastic-plastic material response are considered. The first material model is based on the associated flow rule and the Mises yield condition with isotropic hardening, whereas the second model is based on a particular flow theory of plasticity which represents incremental behavior at a corner of the instantaneous yield surface. Both models predict the same response under the same proportional loading. The stress history experienced by a typical material particle during passage of the load step is determined, and the variation of final strain with the magnitude of the load step is calculated. One conclusion resulting from comparison of results for the two material models for this problem is that the influence of yield surface vertex formation is not significant.     

Non-linear principal resonance of an orthotropic and magnetoelastic rectangular plate

Based on the von Karman plate theory of large deflection, we have derived a non-linear partial differential equation for the vibration of a thin orthotropic plate under the combined action of a transverse magnetic field and a transverse harmonic mechanical load. The influence of the magnetic field is due to the magnetic Lorentz force induced by the eddy current. By employing the Bubnov-Galerkin method, the non-linear partial differential equation is transformed into a third-order non-linear ordinary differential equation. The amplitude-frequency equations are further derived by means of the multiple-scale method. As numerical examples for an orthotropic plate made of silver, the influence of the magnetic field, orthotropic material property, plate thickness, and the mechanical load on the principal resonance behavior is investigated. The higher-order effect and stability of the solution are also discussed.     

Nonlinear interface shear fracture of end notched flexure specimens

The nonlinear analytical solutions of an end notched flexure adhesive joint or fracture test specimen with identical or dissimilar adherends are investigated. In the current study, a cohesive zone model (with arbitrary nonlinear cohesive laws) based analytical solution is obtained for the interface shear fracture of an end notched flexure (ENF) specimen with sufficiently long bond length. It is found that the scatter and inconsistency in calculating Mode II toughness may be significantly reduced by this model. The present work indicates that the Mode II toughness G_IIc under pure shear cracking condition is indeed very weakly dependent on the initial crack length. And this conclusion is well supported by the experimental results found in the literature. The parametric studies show that the interface shear strength is the most dominant parameter on the critical load. It is also interesting to note that with very short initial crack length and identical interface shear strength, higher Mode II toughness indeed cannot increase the critical load. Unlike the high insensitivity of critical load to the detailed shape of the cohesive law for Mode I peel fracture, the shape of the cohesive law becomes relatively important for the critical load of joints under pure Mode II fracture conditions, especially for joints with short initial crack length. The current study may help researchers deepen the understanding of interface shear fracture and clarify some previous concepts on this fracture mode.     

雨载作用下浮顶结构有限元分析的载荷修正法

浮顶结构的受力与变形之间存在着非线性的耦合关系,这给计算分析带来了很大的麻烦。为了解决这一问题,本文提出了单盘式浮顶结构在雨水载荷作用下有限元分析的载荷修正计算方法。通过对浮顶结构力学模型的分析,建立了浮顶结构载荷与单盘挠度之间的关系式,并基于这一关系式给出了浮顶结构有限元分析的载荷修正法和相应计算方案。载荷修正法的基本思想是,首先利用有限元方法对浮顶结构进行几何大变形非线性分析,然后通过迭代修正来调整载荷大小,使得计算得到的载荷与挠度满足给定关系式,最终获得浮顶结构的变形与受力情况。最后,将计算结果与试验结果进行了比较,验证了本文提出的计算方法的有效性和可靠性,为浮顶结构的进一步有限元分析打下基础。     

Energy method solution for the postbuckling response of an axially loaded bilaterally constrained beam

Bistable and multistable structures have shown great usefulness in many applications such as MEMS actuation and energy harvesting. Bistability of structures can be achieved through buckling. Confining a buckled beam between two lateral constraints allows it to buckle into higher modes as the axial load increases. This paper presents a theoretical study of the postbuckling response of a bilaterally constrained elastica subjected to gradually increased axial load. Equilibrium states are determined using an energy method. Under small deformation assumptions, the total potential energy is minimized under the defined constraints. The presented model allows for an accurate representation of the flatting behavior and the increase in the length of contact areas with the lateral constraints before the sudden snapping between equilibrium states. Mode transitions are manifested by jumps in the response curves. Previously developed models based on geometry and symmetries overestimate the required forces for higher equilibrium modes and do not match experimental observations. Results are validated with experimental force–displacement measurements under both force- and displacement-control. The kinetic energy released during buckling mode transitions is determined by a dynamic analysis.     

Effects of surface impedance on current density in a piezoelectric resonator for impedance distribution sensing

We study the relationship between the surface mechanical load represented by distributed acoustic impedance and the current density distribution in a shear mode piezoelectric plate acoustic wave resonator. A theoretical analysis based on the theory of piezoelectricity and trigonometric series is performed. In the specific and basic case when the surface load is due to a local mass layer, numerical results show that the current density concentrates under the mass layer and is sensitive to the physical as well as geometric parameters of the mass layer such as its location and size. This provides the theoretical foundation for predicting the surface impedance pattern from the current density distribution, which is fundamental to the relevant acoustic wave sensors.     

Evaluation of the fatigue life of a tractor’s transmission spiral bevel gear

Conventional tractor transmission spiral bevel gears are designed and evaluated based on the engine rated load, which is significantly higher than the load conditions in the field. In this study, the fatigue life of a spiral bevel gear is evaluated to obtain data for design optimization. The equivalent load was calculated using the field load data, and the integrated equivalent load was calculated based on the annual usage of major field operations in Korea. The fatigue life of three spiral bevel gear samples was evaluated using the accelerated life test (ALT) under an engine rated load condition of 120%. It was also evaluated under engine rated, plow equivalent, and integrated equivalent load. Fatigue life was estimated using the ALT results and the fatigue damage exponent based on the ALT equation. We observed that the fatigue life of the spiral bevel gear under the plow equivalent and integrated equivalent loads is higher than that under the rated load by 214 and 9,400 times, respectively. The results of this study can provide useful information for the design optimization of tractor transmission spiral bevel gears considering the field equivalent load.     

Saturation of a plate with an environmental impurity under mechanical loading conditions

We analyze a model of saturation of a thin plate with an alloying element under uniform loading with a distributed constant load. The appearance of internal stresses accompanying the diffusion processes is taken into account as well as the effect of the stresses on the mass transfer. The exact solution of the mechanical equilibrium problem has allowed us to reduce the model to a nonlinear diffusion problem with a convective term responsible for mass transfer under the action of stresses. We have found that the external loading significantly affects the process if the magnitude of the distributed load is greater than that of the internal stresses, which, in turn, depends on the material properties and the diffusant type. The time-dependence curves of the average strains in the direction of the acting load are typical of the phenomena of diffusion creep.     

Shakedown of an Elastic-Plastic Arch Under Moving Load

Abstract

The problem considered consists in calculating the maximum value of a shakedown load which moves slowly across an arch according to a prescribed loading program. Sandwich cross section of the arch and elastic-plastic material with linear strain-hardening and ideal Bauschinger effect are assumed. Both current residual stress distribution and yield limits are evaluated for selected cross sections and for every load crossing.

In most cases the first crossing is decisive, and shakedown loads can be computed on the basis of the results of the first and second crossing     

Chaos in an embedded single-walled carbon nanotube

Considering the geometrical nonlinearity of an embedded single-walled carbon nanotube, the analytical condition and the numerical results of chaotic vibration of the carbon nanotube are presented in this paper. Firstly, based on the Galerkin approximation method, a Duffing-type model is derived from the equation of motion that describes the oscillation of the embedded single-walled carbon nanotube clamped at both ends under a transverse load. And then, the Melnikov function of the Duffing-type model is derived. From the Melnikov function, the analytical condition of the chaos in the nanotube is obtained. Finally, a structure-preserving difference scheme for the original oscillating model is constructed based on the generalized multi-symplectic framework and the chaotic vibration of the nanotube is reproduced to verify the accuracy and the validity of the analytical condition. The analytical condition obtained in this paper gives some guidance on the property studying and the structure designing of some carbon nanotube devices.     

滑坡支挡结构荷载取值问题研究

当前,在我国工程界,滑坡支挡结构上的荷载取值普遍以传递系数法的条间力(即剩余下滑力)为基础,本文对这种荷载取值方法存在的问题进行了分析,提出了以稳定性为基础确定滑坡支挡结构上荷载的方法,该方法能弥补现行荷载取值方法的不足。     

Ultimate kinematic characteristics of rail electromagnetic launchers with metal armatures in an external magnetic field

This paper presents the results of numerical simulation of the Joule heating of the armature and rails in rail launchers of metal bodies with one or two augmenting rails generating an external magnetic field. The ultimate projectile velocity is calculated under the assumption that the Joule heating of the armature and rails during acceleration does not exceed the melting temperature of the materials of which they are made. It is shown that, with an appropriate choice of the position of the coils generating the augmenting magnetic field with respect to the launcher channel and the current magnitude in them, the heat load on the rails and armature in electromagnetic launchers of solids can be substantially reduced and the ultimate kinematic characteristics of these launchers in crisis-free regimes can be considerably increased.