Springback analysis in torsion of rectangular strips

A theoretical analysis of the springback of narrow rectangular strips under torsional loading is presented. The theoretical analysis is supported by experimental results for different materials, different thicknesses and different lengths, keeping the width of the strips constant. Finally an analytical generalized expression relating angle of twist and twisting moment and residual angle of twist per unit length for rectangular bars under plastic torsion is obtained in non-dimensionalized form.     

Improved lateral force calibration based on the angle conversion factor in atomic force microscopy

A novel calibration method is proposed for determining lateral forces in atomic force microscopy (AFM), by introducing an angle conversion factor, which is defined as the ratio of the twist angle of a cantilever to the corresponding lateral signal. This factor greatly simplifies the calibration procedures. Once the angle conversion factor is determined in AFM, the lateral force calibration factors of any rectangular cantilever can be obtained by simple computation without further experiments. To determine the angle conversion factor, this study focuses on the determination of the twist angle of a cantilever during lateral force calibration in AFM. Since the twist angle of a cantilever cannot be directly measured in AFM, the angles are obtained by means of the moment balance equations between a rectangular AFM cantilever and a simple commercially available step grating. To eliminate the effect of the adhesive force, the gradients of the lateral signals and the twist angles as a function of normal force are used in calculating the angle conversion factor. To verify reliability and reproducibility of the method, two step gratings with different heights and two different rectangular cantilevers were used in lateral force calibration in AFM. The results showed good agreement, to within 10%. This method was validated by comparing the coefficient of friction of mica so determined with values in the literature.     

少模光纤倾斜光栅制备及扭转传感研究

设计了一种基于少模光纤倾斜布拉格光栅的反射型扭转传感器,小角度倾斜光栅中的纤芯基模与二阶模在光栅处发生互耦,通过测量该过程形成的反射峰强度变化实现扭转测量。分析了光栅倾斜角度对模式耦合效率的影响,采用相位掩模板法在线刻写光栅技术,在少模光纤上刻写了不同的小角度倾斜光栅;在此基础上选择倾斜角度为1°的光栅进行了单点、双点扭转传感实验,实验表明其反射光谱中基模与二阶模的互耦合峰(LP₀₁-LP₁₁)对光纤扭转敏感,可以实现对扭转角度大小的测量。在-50°～-150°逆时针扭转过程中,扭转灵敏度为0.52 dB/(rad·m^-1),而在40°～190°顺时针扭转的角度范围内,扭转灵敏度为0.34 dB/(rad·m^-1)。这种传感器具有在单根光纤上实现多点扭转传感的潜力,在多点扭转监测方面具有应用前景。     

基于多目标遗传算法的扭转梁式后悬架分析与设计

通过推导扭转横梁的剪切中心,建立了某扭转梁式后悬架等效侧倾运动学模型,计算得到了前束角、轮距以及侧倾中心随侧倾运动时轮跳的变化关系。利用多目标遗传算法,将悬架横梁的位置、衬套中心位置作为设计变量,以车轮运动的前束角、轮胎侧向滑移量以及静态侧倾中心高度为目标函数对数学模型进行了优化,一次性获得了所有的非支配解。通过获得的Pareto解的边界,选择合适的悬架侧倾运动学特性,可以指导扭转梁式后悬架的设计,大幅提高扭转梁式后悬架的设计效率。     

超声纵扭辅助铣削高强铝合金表面润湿性能研究

针对超声辅助加工在工件表面形成微刻划表面可以提高高强铝合金表面的微结构性能的现象,进行了单激励旋转超声纵扭复合铣削表面微观结构的试验,基于水接触角理论和纵扭铣削运动学理论分析了加工参数对水接触角的影响;搭建了单激励超声纵扭铣削试验平台,采用正交试验法研究了不同加工参数对表面粗糙度、铣削力以及表面润湿性能的影响。结果表明：超声振幅为4 μm时表面质量最佳,切削速度和进给量与表面粗糙度和水接触角呈正相关的关系;超声加工方式下的表面水接触角较普通方式更大,而在超声加工时低振幅加工比高振幅加工的表面水接触角大,当转速达到一定值时,高振幅和低振幅所加工的表面水接触角差别不大。合适的加工参数条件下超声纵扭加工方式可以降低加工表面的粗糙度,改变表面的润湿性。     

Analysis of plate drawing processes by the upper bound method using theoretical work-hardening materials

The present paper analyses the plate drawing processes carried out in converging dies using theoretical work-hardening materials. The analysis has been carried out by the upper bound method (UBM), modelling the plastic deformation zone by triangular rigid zones (TRZ) and considering that the processes occur under plane strain and partial friction conditions. Explicit expressions for the calculation of the necessary power and the non-dimensional total energy to carry out the process using theoretical work-hardening materials have been established. The results have been compared with those obtained using rigid-perfectly plastic materials. In spite of the fact that the energy involved in the process using a work-hardening material is higher than when a rigid-perfectly plastic material is used, the number of possible sets of variables (die geometries, cross-sectional area reductions and partial friction coefficients) increases, since the stability limit of the process increases as well.     

Novel torsion sensor using a polarization maintaining photonic crystal fiber loop mirror

A novel torsion sensor employing a short length of polarization maintaining photonic crystal fiber was inserted into the fiber loop mirror with an output probe. The sensing scheme was described theoretically by a Jones matrix and experimentally demonstrated. The results showed that the sensitivity of the intensity loss in response to the twist angle may be up to 0.0394 dB/° and a resolution of 0.025° was achieved. This torsion sensor is attractive due to its compact size, insensitivity to temperature, and suitability for longer distance transmission than conventional sensors.     

Predicting the oil cooler fan performance of large-sized diesel engines by changing the outlet and torsion angles

This study analyzed how the outlet and torsion angles of an oil cooler fan in large-sized diesel engines affect the performance of the fan using a numerical analysis method. The discharge flow rate, theoretical power, and efficiency were numerically calculated at the variable outlet and torsion angles. Results showed that the discharge flow rate slightly increased with increased outlet angle, leading to increased theoretical power and efficiency. The outlet-side blade also came closer to a vertical position with smaller torsion angle for higher performance of the fan. To verify the numerical analysis results, an experiment was conducted according to AMCA Standard 210–99 and the results were compared. The performance curve of the experimental and numerical analysis results indicated about 3% error.     

Bending and torsion of anisotropic cantilevers

A mathematical formulation is developed for bending and torsion of an inhomogeneous cantilever constructed of anisotropic composite materials. It is shown that anisotropic beams do not have a constant rate of twist. Hence the shear centre requires redefinition, and design for specified rate of twist is possible. A numerical solution is obtained using the finite element method, and the lateral or pinching stresses are shown to be two order of magnitude smaller than the other stresses. Since most practical composite material beams are constructed from nearly symmetric laminates, this confirms that traditional orthotropic stressing yields quite reasonable results.     

多维性能极限状态平面不规则结构易损性分析

针对平面不规则框剪结构,在引入最不利输入角度的基础上,提出多维性能极限状态的易损性分析方法。首先,利用Matlab中小波变换系数法,判别地震动的最不利输入方向;然后,采用层间位移和层间扭转角作为性能量化指标并考虑量化指标间的相关性,计算超越概率,从而得到二维性能极限状态下结构的易损性曲线。利用该方法对平面不规则框剪结构进行分析得到结构在正常使用、可以使用、生命安全、防止倒塌4个性能水平下的易损性曲线。结果表明:对于平面不规则结构,地震动输入角度对结构的抗震性能有不可忽略的影响;对平面不规则结构进行易损性分析时,应同时考虑层间位移和层间扭转角双指标的影响,防止高估这类结构的抗震性能。基于多维性能极限状态的易损性分析方法对平面不规则结构抗震性能的评估更为安全、可靠。     

Free vibrations of continuous rectangular plates on oblique supports

The Finite Strip Method has been employed in the vibration problem of continuous rectangular plates on oblique supports. The structure has been divided into quadrilateral finite strips. The various properties of a quadrilateral finite strip have been derived using the displacement approach. The results are obtained for a two span rectangular plate with an oblique support at various angles and compared with other solutions. The results obtained due to various layouts of finite strips in the structure have been compared.     

A modeling and analysis of spring-shaped torsion micromirrors for low-voltage applications

An electrostatic torsion micromirror is designed using the optimized spring-shaped torsion beams and U-shaped groove supporters. The main advantages of this design will be a reduction in the pull-in voltage for low-voltage applications and the function as a switch of the instability mode by adjusting the effective bending stiffness of the torsion beam. In this design, a theoretical model is developed to demonstrate the static characteristics of the electrostatic torsion micromirror. The pull-in effect is investigated specifically to predict the pull-in voltage, pull-in angle, and pull-in displacement. These parameters depend significantly on the electrode size and position, position of the groove, and ratio of the bending and torsion effect of the torsion beam. In addition, the effective torsion and bending stiffness model is provided using the energy method with the objectives to optimize the spring-shaped geometries of the torsion beams and to decrease the pull-in voltage below 2 V. The U-shaped groove supporters are applied in the theoretical model to adjust the effective bending stiffness of the torsion beam and to switch the instability mode of the torsion micromirror. The theoretical analysis is consistent with the numerical simulation using MEMCAD and experimental results measured by an optical projection method.     

S135钻杆钢的单轴疲劳性能对比

通过疲劳试验测定了S135钻杆钢在单轴对称拉-压和扭-转加载条件下的疲劳寿命,应用回归分析方法得到了单轴疲劳寿命的定量公式,并对疲劳断裂的机制进行了分析。结果表明:在双对数坐标中,疲劳寿命与有效应力幅呈良好的直线关系;扭-转疲劳极限与拉压疲劳极限之比为0.682;拉-压加载和扭-转加载下的裂纹均萌生于试样表面;拉-压疲劳试样的裂纹扩展以疲劳条带为主要特征;扭-转疲劳试样的裂纹扩展以剪切型涟波花样为主要特征。     

The press-brake bending of rigid/linear work-hardening plates

The analogy between the deformation of the rigid/linear work-hardening beam beyond yield and the linear elastic beam is successfully applied to analyse press-brake plate and sheet bending. Some of the results obtained cannot be obtained by using more elementary theories. Compared with an analysis by the finite element method[4], the solution in this paper not only needs much lesss computing storage and time, but also provides a clearer insight into the physical mechanisms which operate. The springback effect is considered.     

A study on radial flow field for extrusion through conical dies

A generalized expression for the radial flow field for extrusion through a conical die is suggested. The upper bound to the extrusion pressure for a rigid-perfectly plastic material is obtained. Other energy methods which include solutions for work-hardening and composite billets are also obtained for the generalized radial flow field. The results are used to analyse the hydrostatic extrusion of Al, Cu and Al-Cu composite billets. The extrusion pressure and hardness distribution of the product were measured in experiments and they are compared with theoretical results.     

Research on the piezoelectric torsional effect of a rectangular quartz disc and a novel drilling dynamometer

The theoretical foundation of a new-type drilling dynamometer (i.e. the torsional effect of a rectangular piezoelectric quartz disc), the structure design and calibration of the drilling dynamometer are investigated in this paper. By using the theory of anisotropic elasticity and the Maxwell electromagnetism, the torsion stress and the distribution of surface charge densities of a rectangular quartz disc are calculated. According to the theoretical analyses of the bound charge densities, the detection electrodes are effectively disposed on the surface of the piezoelectric disc. The experimental results show that the torsional effect exists in the rectangular quartz disc and the bound charges are linear with the torque applied. Based on the torsional effect, a new type of drilling dynamometer is designed, in which only four quartz discs are used. The axial force measuring cell consists of two X0°-Cut quartz discs, and by the partitioned electrode method only two Y0°-Cut quartz discs can simultaneously sense the radial force and torque. After static calibrations, the torque sensor has full reached the dynamometer standard stipulated by CIRP-STCC. Undoubtedly the drilling dynamometer will provide a new method for measuring the drilling force and monitoring the drilling process.     

Investigation of a new-type precision cropping system with variable-frequency vibration

To investigate a new-type precision cropping system with variable-frequency vibration, it is necessary to obtain the characteristics of vibrating force and displacement of shearing die in different exciting frequencies. The model and equations of a six-degree-of-freedom vibrating system are established, and the six natural frequencies of the system are achieved by means of classical analysis method, the amplitude-frequency characteristics are described according to Cramer's rule, and the theoretical analysis results are verified by experiments. The approximate relationship between the vibrating force and exciting frequency are achieved and the experimental results show that crack will propagate along z direction, which is in agreement with the theoretical results. The work-piece cross-section obtained by the experiments has no radial distortion and deviation angle, moreover, the cutting force is lower and the die lifetime is longer compared with common bar cropping method. A new cross-section quality assessment method is proposed for the work-piece obtained under the control of different frequency-time characteristic curves. The assessment results show that the linear decrement control mode is better for producing good-quality work-piece.     

Influence of Poisson's ratio variation on lateral spring constant of atomic force microscopy cantilevers

Atomic force microscopy (AFM) can be used to measure the surface morphologies and the mechanical properties of nanostructures. The force acting on the AFM cantilever can be obtained by multiplying the spring constant of AFM cantilever and the corresponding deformation. To improve the accuracy of force experiments, the spring constant of AFM cantilever must be calibrated carefully. Many methods, such as theoretical equations, the finite element method, and the use of reference cantilever, were reported to obtain the spring constant of AFM cantilevers. For the cantilever made of single crystal, the Poisson's ratio varies with different cantilever-crystal angles. In this paper, the influences of Poisson's ratio variation on the lateral spring constant and axial spring constant of rectangular and V-shaped AFM cantilevers, with different tilt angles and normal forces, were investigated by the finite element analysis. When the cantilever's tilt angle is 20 degrees and the Poisson's ratio varies from 0.02 to 0.4, the finite element results show that the lateral spring constants decrease 11.75% for the rectangular cantilever with 1muN landing force and decrease 18.60% for the V-shaped cantilever with 50nN landing force, respectively. The influence of Poisson's ratio variation on axial spring constant is less than 3% for both rectangular and V-shaped cantilevers. As the tilt angle increases, the axial spring constants for rectangular and V-shaped cantilevers decrease substantially. The results obtained can be used to improve the accuracy of the lateral force measurement when using atomic force microscopy.     

Bending collapse of rectangular and square section tubes

The bending collapse behaviour of rectangular and square section tubes is studied theoretically and experimentally. A limit analysis technique was employed and a set of formulae relating the hinge moment and associated angle of rotation was derived. The theoretical predictions were verified by comparison with 56 quasi-static bending tests on 27 different sections having aspect ratios ( ) varying between 3.0 and 0.33 and with width to wall thickness ratios ( ) between 128 and 9.14. Very good agreement was found between the theoretical predictions and experimental results for the whole range of sections.