Buckling behavior of Kelvin open-cell foams under [0 0 1], [0 1 1] and [1 1 1] compressive loads

This paper describes buckling modes and stresses of elastic Kelvin open-cell foams subjected to [0 0 1], [0 1 1] and [1 1 1] uniaxial compressions. Cubic unit cells and cell aggregates in model foams are analyzed using a homogenization theory of the updated Lagrangian type. The analysis is performed on the assumption that the struts in foams have a non-uniform distribution of cross-sectional areas as observed experimentally. The relative density is changed to range from 0.005 to 0.05. It is thus found that long wavelength buckling and macroscopic instability primarily occur under [0 0 1] and [0 1 1] compressions, with only short wavelength buckling under [1 1 1] compression. The primary buckling stresses under the three compressions are fairly close to one another and almost satisfy the Gibson–Ashby relation established to fit experiments. By also performing the analysis based on the uniformity of strut cross-sectional areas, it is shown that the non-uniformity of cross-sectional areas is an important factor for the buckling behavior of open-cell foams.     

Computer simulations of nanoindentation on Cu (1 1 1) with a void

This paper employs static atomistic simulations to investigate the effect of a void on the nanoindentation of Cu (1 1 1). The simulations minimize the potential energy of the complete system via finite element formulation to identify the equilibrium configuration of any deformed state. The size and depth of the void are treated as two variable parameters. The numerical results reveal that the void disappears when the indentation depth is sufficiently large. A stress concentration is observed at the internal surface of the void in all simulations cases. The results indicate that the presence of a void has a significant influence on the nanohardness extracted from the nanoindentation tests.     

M-lump and interactive solutions to a (3 $${+}$$ + 1)-dimensional nonlinear system

Nonlinear Dynamics - This paper aims at computing M-lump solutions for the $$(3+1)$$ -dimensional nonlinear evolution equation. These solutions in all directions decline to an identical state...     

Rational solutions for a combined (3 + 1)-dimensional generalized BKP equation

Nonlinear Dynamics - In this paper, we focus on the rational solutions for a combined (3 + 1)-dimensional generalized BKP equation. By using the symbolic computation with Maple,...     

一种惯性测量组件实时测温电路的研究及设计

介绍了一种采用三极管作为测温元件的惯性测量组件（IMU）实时测温电路的工作原理。该电路采用自闭环的工作方式，将温度值转换为二进制并行代码，具有电路体积小，响应快，对计算机时序要求低，构思巧等特点，在某型号空空导弹惯导系统中已经得到实际应用。     

Design and Simulation of a Novel Multi-Axial Fatigue Test Rig

This research covers the design and simulation of a novel experimental concept for multi-axial fatigue analysis of cylindrical specimens. The resulting design allows a combination of bending and torsional stress to test specimens with critical diameters ranging from 5 to 15 mm at test frequencies up to 50 Hz. Furthermore, the amplitude and frequency of both loadcases can be controlled independently. The test rig will be used to study and validate fatigue criteria for synchronous and asynchronous loading conditions and to analyze the effect of size on the fatigue life of metal and plastic components. The test setup consists of a closed mechanical loop. The primary shaft contains the cylindrical test specimen and is modified to impose rotating bending loads. The secondary shaft is adjusted to introduce fluctuating torque in the transmission loop. Both shafts are connected by means of two double link mechanisms to minimize the clearance and the inertia of the system. The time-varying multi-axial stress state in the cylindrical specimen is analyzed as a function of the amplitudes and frequencies of both bending and torsional loadcases. This is verified by a numerical fatigue analysis in MSC-Patran and MSC-Fatigue. Finally, the dynamical behavior of the test system is studied using a 5 DOF torsional mass-spring representation and the Lagrangian method. A more complex model with 20 DOF is implemented in SimDriveLine and solved via Matlab to analyze the kinematical and dynamical properties more accurately. Both studies take the mechanical properties of steel and plastic test specimens of different sizes into account.     

Draftability of a 8.95 kW walking tractor on tilled land

A 8.95-kW walking tractor was evaluated for draft and drawbar power on tilled land. Empirical equations were developed to correlate the relationship between draft and wheel slip, drawbar power and wheel slip and drawbar power and fuel consumption. The values of draft, drawbar power and specific fuel consumption were calculated at 25% wheel slip. The results indicated that the values of draft on tilled land with pneumatic wheels at engine speed of 2000 rpm were 803 and 773 N in second low and third low gears, respectively. The respective draft values at engine speed of 1500 rpm were 748 and 735 N in second low and third low gears under slightly loose soil conditions. Mounting of a 40-kg wheel ballast increased the value of draft to 901 and 921 N at an engine speed of 2000 rpm and 872 and 888 N at an engine speed of 1500 rpm in second low and third low gears. Replacement of pneumatic wheels by steel wheels further increased the draft readings to 1034 and 999 N at an engine speed of 2000 rpm and 913 and 935 N at engine speed of 1500 rpm in second low and third low gears, respectively, indicating significant increase in drawbar power both at 2000 and 1500 rpm in second low and third low gears with the use of steel wheels. The specific fuel consumption decreased by about 28% and 27% at engine speed of 2000 rpm and about 17% and 21% at engine speed of 1500 rpm in second low and third low gear with the use of steel wheels over pneumatic wheels without wheel ballast. The specific fuel consumption decreased by about 4% and 14% at engine speed of 2000 rpm and 7% and 23% at engine speed of 1500 rpm in second low and third low gears, respectively, with the use of steel wheels over pneumatic wheels with 40 kg wheel ballast.     

Wave propagation in a piezoelectric rod of 6 mm symmetry

The wave propagation in a piezoelectric rod of 6 mm symmetry is investigated by applying a 3-D piezoelectric elastic model. A self-adjoint method is introduced to solve this problem, this method avoids calculating the generalized eigenvalue equation, it completely draws the dispersion curves in the forms of Quasi-P wave, Quasi-SV wave and Quasi-SH wave under the self-adjoint boundary condition, and it can evaluate the dispersion curves of all kinds of boundary conditions. As an example, the dispersion curves of PLT-5H are completely drawn, we also found the Quasi-SV wave has standing wave phenomenon in the PLT-5H rod. In addition the relation of dispersion curves among different boundary conditions is discussed, and an experiment method is introduce to decide the dispersion curves for another boundary conditions.     

Antidark solitons and soliton molecules in a (3 + 1)-dimensional nonlinear evolution equation

Nonlinear Dynamics - We investigate a (3 + 1)-dimensional nonlinear evolution equation which is a higher-dimensional generalization of the Korteweg–de Vries equation. On the...     

Nonlocal instability analysis of FCC bulk and (1 0 0) surfaces under uniaxial stretching

The objective of this paper is to examine the instability characteristics of both a bulk FCC crystal and a (1 0 0) surface of an FCC crystal under uniaxial stretching along a 〈1 0 0〉 direction using an atomistic-based nonlocal instability criterion. By comparison to benchmark atomistic simulations, we demonstrate that for both the FCC bulk and (1 0 0) surface, about 5000–10,000 atoms are required in order to obtain an accurate converged value for the instability strain and a converged instability mode. The instability modes are fundamentally different at the surface as compared to the bulk, but in both cases a strong dependence of the instability mode on the number of atoms that are allowed to participate in the instability process is observed. In addition, the nonlocal instability criterion enables us to determine the total number of atoms, and thus the total volume occupied by these atoms, that participate in the defect nucleation process for both cases. We find that this defect participation volume converges as the number of atoms increases for both the bulk and surface, and that the defect participation volume of the surface is smaller than that of the bulk. Overall, the present results demonstrate both the necessity and utility of nonlocal instability criteria in predicting instability and subsequent failure of both bulk and surface-dominated nanomaterials.     

链条抽油机机架的结构优化设计

随着深井和稠油井的发展，长冲程的链条抽油机越来越受到重视，为提高经济效益对其进行结构优化设计是石油生产的需要。链条抽油机机架是个封闭的空间结构，不能象传统设计中那样被简化为压杆和梁。本文将其简化为由板和梁组成的结构，目标函数为结构质量，约束条件为应力约束、位移约束、疲劳寿命的约束、局部稳定的约束和频率约束。本中用满约束准则与最优性条件相结合的方法处理不同的约束。优化后的机架结构是分块变厚度的，明显地节省了材料。     

静电陀螺测试转台电气部分方案设计

叙述了静电陀螺三环测试转台电气部分的方案设计要点。该电气部分包括静电陀螺启动与控制系统，转台控制系统，计算机三大部分，测角分系统采用粗精耦合式角位置传感器。双轴伺服分系统采用带有纯积分环节的一阶无差控制系统，三轴位置控制分系统采用一阶无差数字控制的方案，从而确保转台满足精度指标。     

微结构片外弯曲测试装置及试样设计

硅是微电子机械系统（简称微机电系统）中最常见的功能结构材料,可靠性是制约硅微构件小尺度加工和大规模制造的瓶颈问题．为研究硅微构件的力学特性,本文开发了一套以压电驱动、微力测量、位移检测为核心组件的片外测试系统．设计了一种将四个弯曲测试梁集于一体的微结构,借助有限元方法确定其尺寸,并用理论方法验证有限元分析的合理性．本文着重确保了四个关键设计目标：一、每根测试梁最大应力应位于其与外框架结合处;二、未断裂测试梁的最大应力受其他梁的断裂的影响应足够小;三、各个测试梁的最大应力的差别应足够小;四、支撑梁的最大应力应明显小于测试梁．最后测试了试样的弯曲强度,实验加载曲线和有限元分析基本吻合,表明测试装置和试样设计是合理的,为后续的硅微构件可靠性测试奠定了基础．     

离心机上辨识加速度计模型参数的优化试验设计

本文针对离心机上测试加速度计时可以在多个球面上布测试点的特点,研究了双球面组合试验计划的优化设计问题,得出了Ｄ 最优准则下一个优化的组合试验计划测度比,并进行了工程简化,得到了一个实用的准Ｄ 最优组合试验计划。     

A mode III crack in a piezoelectric semiconductor of crystals with 6 mm symmetry

A finite mode III crack in a piezoelectric semiconductor of 6 mm crystals is analyzed. Fourier transform is employed to reduce the mixed boundary value problem to a pair of dual-integral equations. Numerical solution of these equations yields coupled electromechanical fields, the intensity factor and the energy release rate near the crack tip. Numerical results are presented graphically to show the fracture behavior which is affected by the semiconduction.     

加速度计自动测试系统的设计与实现

介绍了一种采用分布式计算机测试与控制方式的加速度计自动测试系统，它实现了转台自动控制和加速度的程控测试。通过实验测试表明：它不但可以提高了测试系统的自动化程度，而且还降低了劳动强度，极大地提高了劳动效率。     

倾斜仿生刚毛的设计?制备及黏附性能研究

依据JKR理论,从几何仿生角度出发设计并制备了2种具有斜截面的倾斜人工刚毛.理论计算表明:刚毛支杆倾斜20°,斜截面为45°时,刚毛具有较为理想的黏附性能,且具有这种结构的刚毛可便利地调控吸附和脱附.利用微摩擦试验机测试了人工刚毛表面的黏附性能,结果表明:在无滑移的平面接触下,刚毛阵列的黏附力随法向载荷增加而增大,当法向载荷超过一定值后,黏附力增加缓慢并趋于饱和;法向载荷为30mN时,刚毛无滑移卸载所产生黏附强度约为2.4kPa,略高于逆向滑移后卸载所产生的黏附强度2.2kPa,而正向滑移后卸载所产生的最大黏附强度较逆向滑移后卸载有明显增加,达3.1kPa,增加了近41%;短距离的滑移可增加黏附力,但随着滑移距离加大,黏附力随之下降.