<Emphasis Type="Italic">SH</Emphasis>-wave intromission concept

The existence of an SH-wave incidence angle for which the reflected amplitude is zero (SH-wave intromission angle) is established for the case of plane-wave scattering by a planar interface joining two homogeneous, isotropic, and linearly elastic half-spaces. Such an incidence angle is numerically shown to exist for two combinations of bimaterial interface properties. The SH-wave intromission angle is roughly parallel to the electromagnetic Brewster angle and the acoustic P-wave intromission angle, and the concept should find new applications for non-intrusive characterization of interfaces.     

基于 Matlab全自动装订机空间凸轮参数计算

目的研究影响全自动装订机空间圆柱凸轮机构的力与运动传递性能的压力角和曲率参数。方法应用共轭曲面啮合理论,推导凸轮压力角和曲率的计算公式,基于Matlab软件编程绘制压力角和曲率变化曲线,得出压铆各阶段压力角最大值和诱导主曲率值,并与许用压力角和临界曲率值作比较。结果在铆头上升过程中,最大压力角为15°;在压铆过程中,压力角接近0°;在铆头返回过程中,最大压力角为55°。每个点的诱导主曲率值均大于0。结论升程过程最大压力角低于许用压力角,可以满足要求;压铆过程凸轮机构的力传递性能良好;返回过程对动力要求很小,压力角变化较大,对机器的正常工作影响很小,曲率不发生干涉。     

直线空间角计算机辅助求解方法的研究

经空间关系分析,将三维空间角度的多种表达形式归纳为已知两方向角求一投影角,已知两投影角求一方向角,已知一方向角、一投影角求一方向角或一投影角三大类。根据画法几何原理,建立空间角计算的数学模型,并将 Visual LISP 与 Visual Basic 相结合开发空间角计算与显示系统,从而实现了空间角的计算机辅助求解,其特点是能精确、迅速和方便地解决复杂的空间角度计算问题。     

Formulation of new correlations in terms of extraterrestrial radiation by optimization of tilt angle for installation of solar photovoltaic systems for maximum power generation: case study of 26 cities in India

This paper deals with finding of optimum tilt angle for installation of optimized solar photovoltaic system in India. The optimization of tilt angles is performed using measured solar radiation data for 26 cities in India. The tilt angle is changed from 0° to 90° at step of 1° to find out optimum tilt angle for which monthly average solar radiation is maximum. It was found that the optimum tilt angle varies between 0° and 63° throughout the year in India. The monthly optimum tilt angle is maximum in December for all cities in India. It is found that increase in maximum solar radiation at monthly optimum tilt angle in comparison to latitude based tilt angle and annual optimum tilt angle varies from 5.85% to 8.08% and 5.95% to 8.34%, respectively, showing monthly optimum tilt angle is beneficial for maximum power generation for different cities in India. The novelty of this study is new correlations of optimum tilt angle in terms of extraterrestrial radiation are developed for estimating monthly optimum tilt angle for installation of photovoltaic systems at different sites in India. The root mean square error in correlation equations varies from 0.1256 to 0.9771.     

基于节点刚度的钢框架梁柱子结构抗倒塌性能试验研究

以钢框架中3种不同连接节点形式（栓焊连接、顶底角钢腹板双角钢连接和腹板双角钢连接）的两跨三柱型梁柱子结构为研究对象,通过对中柱施加静力荷载的大变形试验考察梁柱子结构在中柱失效连续倒塌条件下的破坏模式、力学形态和抗倒塌机理。结果表明:栓焊连接试件因梁柱节点处梁端受拉翼缘发生断裂而失效;顶底角钢腹板双角钢连接试件为梁柱相连的受拉角钢在螺栓孔处发生断裂,且因梁端腹板螺栓孔发生承压破坏而失效;腹板双角钢连接试件因腹板两侧角钢在螺栓孔处断裂而破坏。梁柱节点刚度对结构的抗倒塌性能影响较大,腹板双角钢连接试件主要通过悬链线机制提供抗力;而其他两类试件在加载前期主要通过梁机制提供抗力,进而转变由悬链线机制来抵抗外部荷载。其中,顶底角钢腹板双角钢连接试件在后期更能充分发展梁端节点转角和梁截面轴力,表现出更为富余的抗倒塌能力储备。     

一种异形多边形瓦楞纸箱的抗压性能研究

在传统瓦楞纸箱上增加了切角结构,以构成适用于衬垫外箱一体式快装包装箱的异形多边形瓦楞纸箱。通过试验研究了切角结构对纸箱抗压强度的影响,比较了不同切角尺寸、切角角度与切角数量对纸箱抗压强度的影响。结果表明:在其他结构参数保持不变的情况下,纸箱抗压强度在一定范围内随着切角长度的增加而增大;切角角度越接近45°,抗压强度越大;切角数量越多,抗压强度增加越明显。试验结果为该一体式快装包装箱的结构设计提供了理论依据,对利用切角提高纸箱抗压强度的结构设计也有一定参考价值。     

Self-rotatory performance of conical cutter interacted with rock material

Conical cutters work on high impact and stress condition, which easily results in failure. The percentage of failure due to wear is about 75%. More importantly, self-rotatory ability of conical cutters is the key factor on its wear. However, the mechanism of self-rotatory has not been further studied until now. Thus, firstly in this paper, three probable rotating states of cutter interacted with rock material were analyzed in theory, and the hypotheses about influence of rotary kinetic and resistance torque were proposed. Then, the influence of cutting types, working angle parameters and structural parameters on self-rotatory performance of cutter was studied using cutting test-bed for rock material. The experiment results indicate that, conical cutters really have self-rotatory ability when interacted with rock material, which owes to asymmetrical cutting load; the rotatory angle of cutter decreases gradually with cutting angle, and increases with incline angle; the change of rotatory angle caused by cutting angle is about 60°, while almost 360° for incline angle when the rotation angle of cutter is less than 360° in a certain cutting time; the rotatory angle almost shows a linear increasing trend with cutter-body length and the interval between cutter-handle and cutter-holder, decreases linearly with cutter-handle length, while increases at first and then decreases with cutter-handle diameter; among these four structural parameters, the influence of interval between cutter-handle and cutter-holder is greatest about 200°, followed by cutter-body length, and the last is cutter-handle length and cutter-handle diameter. At last, comparing the experiment results and hypotheses about influence of rotary resistance torque, it can be seen that, the dominant factor on self-rotatory ability of cutter is not friction resistance between cutter and cutter-holder but the duration that cutter with no rotary resistance torque.     

The influence of specimen's geometry on the crack extension angle

The objective of the present paper is to study the dependence of the angle at which a crack would propagate under mixed mode loading conditions on specimen's geometry. The centre-and edge-cracked specimens under tension and bending are examined. For each type of specimen the crack extension angle is determined for various values of the crack inclination angle and the ratio of the crack length to specimen's width. The minimum strain energy theory developed by Sih is used. Numerical results establishing the influence of specimen's geometry on the crack extension angle are given and useful conclusions are disclosed.     

Position-sensitive photodetector for rotation-angle transducers

A new position-sensitive photodetector (PSPD) for photoelectric transducers of rotation angle is described, which is based on a three-layer ring sector structure. The output voltage of the PSPD is a linear function of the angle of rotation of a light-emitting diode relative to the PSPD contacts. The proposed device is highly reliable and ensures angle determination to within 7 min of arc. Rotation-angle transducers based on this PSPD are compatible with any measuring, matching, and processing equipment.

     

Finite Element Analysis of Single-Particle Impact on Mild Steel and Spheroidal Graphite Cast Iron

Erosion of materials due to the impact of solid particles is strongly affected by the mechanical properties and microstructures of materials. The experiments in this study showed that maximum erosion occurred at impact angle of 20° for mild steel SS400 and 60° for spheroidal graphite cast iron FDI. This phenomenon has been referred to as the impact angle dependence of erosion in previous studies. In order to clarify the impact angle dependence of erosion on these two materials, 3D finite element (FE) models of single-particle impact on SS400 and FDI were built and analyzed. Considering that erosion occurs due to a combination of cutting and deformation effects, the experimental results were explained from the viewpoint of shear stress and plastic strain on the material surface of FE models. Simulation results showed that for FE models of SS400, plastic strain varied only slightly at different impact angles, whereas the shear stress changed significantly with impact angle, with the maximum value occurring at impact angle of 20°. Thus, shear stress was the main factor affecting the erosion of mild steel, which can explain the experimental observation of maximum erosion occurring at 20° for SS400. On the other hand, for FE models of FDI, shear stress changed little at different impact angles while plastic strain changed significantly with impact angle. The maximum value of plastic strain occurred at impact angle of 50° or 80°, which was also in accordance with the experimental result that maximum erosion occurred at impact angle of 60° for FDI.     

Effects of a Small Inclination Misalignment in Talbot Interferometry by use of Gratings with Arbitrary Line Orientation. I. Theoretical Analysis

We discuss the effects of a general small inclination misalignment, which is formed by rotation of the beam-splitter grating around an axis that is laid on the grating plane and that has an arbitrary angle with respect to the line direction of the grating, between the two grating planes on the moiré fringes in Talbot interferometry. It is shown that the small inclination angle has a significant influence on measurement results based on Talbot interferometry because both the period and the slope of the moiré fringes are sensitive to the angle, especially when the rotation axis is nearly parallel to the lines of the grating. Simple and practical detection methods for the small inclination angle are proposed, and the effects of the inclination angle on the contrast in the moiré fringes are also briefly discussed.     

纤维角度对变角度层合板减振性能的影响

自动铺丝技术可以实现复杂曲率曲线铺放,可极大提高角度设计的自由度。本文以改善复合材料层合板动态特性为目的,对变角度层合板的减振性能进行了研究分析。首先对不同角度变化变角度层合板进行自由衰减试验,研究了纤维角度变化与变角度层合板阻尼比的关系。然后对含相应角度变角度夹层板进行随机试验,研究了层合板随机激励条件下的振动响应,并采用共振峰处传递函数(Transition function,TF)和拾振点加速度总均方根(Root mean square,RMS)两种指标评价减振效果。结果表明:层合板阻尼比在纤维变化角度为±<45|60>时最大,纤维变化角度为±<73|88>时最小。基于RMS减振评价指标,±<45|60>夹层板较传统直线板减振性能提高27.13%;基于共振峰TF减振评价指标,纤维角度变化对不同共振峰减振效果规律差异明显。研究表明,变角度层合板减振性能明显优于传统直线层合板,相关实验结果将对变角度层合板减振设计及优化提供一定的参考意义。      

Ductility and fracture of copper bicrystals with boundary SiO2 particles

Abstract

High temperature deformation andfracture ofCu-SiO₂ bicrystals with [001] twist boundaries of various misorientation angles were investigated under the condition of non-activation of grain boundary sliding. As the misorientation angle increases, the bicrystals became more susceptible to intergranular brittle fracture. Clear intermediate temperature embrittlement was observed in bicrystals with a random high angle boundary. The boundary segregation of O atoms was found to enhance intergranular fracture. Although the boundary SiO₂ particles provide stress concentration sites which cause early formation of boundary cavities, the boundary dependent deformation and fracture behaviour is essentially determined by inherent boundary strength, which is afunction of the misorientation angle.

MST/1969     

Analytical study of the principal angle used in optical experiments

An analytical method has been developed for directly calculating the principal angle theta(p) at which the phase difference between the two reflection coefficients is equal to 90 degrees and at which the ratio of /r(p)/ to /r(s)/ is equal or close to a minimum. The equations given here can be used in many optical applications. For example, ellipsometric data measured at an incidence angle theta(p) will have higher precision than data measured at other incidence angles. theta(p) is the principal angle. Instead of three principal angles, there is only one principal angle, which can be found in the region of 0 < or = theta(p) < or = 90 degrees for most metallic materials used in applications. Results show good agreement between the measured and the calculated spectra of delta(p) and rho(po).     

扩底楔形桩抗压承载力理论计算分析

扩底楔形桩是一种可以有效发挥桩侧摩阻力和桩端承载力,提高单位材料承载力的新型桩;然而针对其竖向抗压承载力理论机理及计算方法的研究相对较少。在小倾角范围内(<5°),基于Randolph和Wroth荷载传递理论模型,建立考虑楔形角对荷载传递机理影响的扩底楔形桩桩侧摩阻力、桩端承载力计算方法;通过与数值计算模型和模型试验实测结果的对比分析,验证该文所建立的理论计算模型的准确性与可靠性;续而开展楔形角、扩大头直径以及桩体强度等因素对扩底楔形桩抗压承载力特性的影响分析。研究结果表明:该文所建立的扩底楔形桩理论计算方法可以准确、有效地计算其竖向抗压承载力;同等地质条件下,扩大头直径比楔形角对基桩竖向抗压承载力的影响更明显。     

Effect of texture and testing conditions on strain localization during cyclic deformation of copper polycrystals

Fatigue tests were performed on pure copper polycrystals with a crystallographic texture different from that produced by ‘standard’ thermomechanical treatments, which emphasize multi-slip 111–100 textures. The texture along the loading axis deviated by 10–15° from these two poles for the samples used here. The experiments were initiated by ramp loading as a mechanical pretreatment and the cyclic stress–strain curve (CSSC) was established by step tests using enough cycles at each step to insure saturation. Under these conditions, a plateau was observed in the CSSC at an appropriate stress level and in a reproducible fashion.     

超疏水表面融霜演化行为及排液特性

及时脱除热力除霜后冷表面残留液滴,可以延缓二次结霜。本文对室温环境下超疏水表面融霜演化行为进行了微观可视化观测,对比分析了表面倾角对裸铝表面(接触角88. 0°)及超疏水表面(接触角151. 1°)融霜排液的影响。实验结果表明,水平超疏水表面融霜过程存在单液膜卷曲收缩及多液滴合并两种行为,较大的静态接触角及较小的接触角滞后是促使多液滴合并的主要原因。与倾斜裸表面融霜过程存在大量残留液滴不同,超疏水表面融霜液可实现自排除;当表面倾角>30°时,超疏水表面排液率可达90%以上。结合表面润湿特性及表面倾角推导出表面液滴临界脱落半径,与实验结果吻合较好。     

Heterogeneous Mohr-Coulomb plastic material

We consider a heterogeneous medium which locally obeys a Mohr-Coulomb rigid-plastic behavior. We are interested in the macroscopic yield criterion based on an admissible stress formulation. We propose a two-dimensional analysis based on Airy potential formulation, using a first order perturbation. We first derive an upper bound for the macroscopic yield, and then construct explicitly an admissible stress field which reaches this bound. We finally show that within this framework, the macroscopic friction angle tends to the average of the local friction angle. Corrections to this value decay with the system size as [log(L)/L]^1/2, for all (narrow) distributions of local friction angle. Received: 26 June 1999     

On the effect of residual birefringence in anisotropic photoelastic materials

The effect of residual birefringence on isoclinic angle and fringe order is considered for mechanically and optically anisotropic materials. Toupin's⁴ theory of deformable dielectrics forms the basis of the investigation. Equations are derived for fringe order, stress fringe value and isoclinic angle in linear orthotopic photoelastic materials. The principal effect of residual birefringence relates to the determination of the isoclinic angle. This is particularly so for certain fibre–orientations. Unlike the isotropic case, the isoclinic angle depends on the stress at which it is measured.