Effect of shaft misalignment and friction force on time varying mesh stiffness of spur gear pair

Shaft misalignment and sliding friction between meshing teeth are considered as primary excitation to generate vibrations and extra dynamic loads on transmitting gear teeth. Time varying mesh stiffness (TVMS) is an important parameter to understand the dynamics of meshing gear pair. Potential energy method is one of the most acceptable methods to calculate TVMS. This paper proposes a computer simulation based approach to study the effect of shaft misalignment and friction on total effective mesh stiffness for spur gear pair. The results showed clearly that misalignment and friction affect TVMS of gear pair. The effect of misalignment and friction has also been studied for cracked gear pair and results are discussed.     

裂隙岩体冲击韧性及破坏模式实验

为研究裂隙对岩体冲击韧性及破坏模式的影响规律,以及裂隙岩体在高应变率下的动态破坏特征,采用摆锤式冲击实验机对裂隙及完整岩体进行了不同冲击速度、不同裂隙条件下的冲击实验。实验结果表明,对长度相同的完整试件而言,试件直径越大,即试件体积越大,试件破碎就越充分,断面也越不规整;试件中的裂隙长度越长,试件破坏时的吸收功就越小,冲击韧性也越小,试件吸收功和冲击韧性随裂隙长度的增加而减小;试件裂隙角度越大,试件破坏断面就越不规整,试件破坏后的块度也越不均匀,试件吸收功和冲击韧性随裂隙倾角的增大而减小。     

新乙烯回收技术扩大中试装置工艺路线

介绍了中试装置的布置、工艺路线及特点，并简要总结了工程建设过程中的经验。     

Buckling of cracked thin-plates under tension or compression

Plates are easily susceptible to buckling under compression, in particular when plate's thickness becomes sufficiently small with respect to others plate's sizes; such a mode of failure is often prevalent with respect to strength failure. The buckling phenomena under tension loading can also occur, especially in plates containing defects such as cracks or holes; when the buckling load is reached, complex wrinkling deflection patterns in compressed regions develops around such imperfections.In the present paper, the buckling analysis of variously cracked rectangular elastic thin-plates under tension and compression is considered. A short explanation of the buckling phenomena in plates is recalled and several numerical analyses, carried out by using the Finite Element Method (FEM), are performed in order to determine the critical load multiplier, both in compression and in tension, by varying some plates' parameters. In particular, the critical load multiplier is determined for different relative crack length, crack orientation and Poisson's coefficient of the plate's material which is made to range between 0.1 and 0.49.Moreover a simple approximate theoretical model to explain and predict the buckling phenomena in cracked plates under tension is proposed and some comparisons are made with FE numerical results in order to assess its reliability in predicting buckling load multipliers.Finally, the obtained results are graphically summarised (in dimensionless form) in several graphs and some interesting conclusions are drawn.     

具有两条裂纹的转子系统的振动研究

转轴裂纹是旋转机械的常见故障。文中采用数值模拟的方法研究具有两条裂纹的转子系统的非线性耦合振动响应。裂纹对轴段刚度的影响采用断裂力学理论得到,裂纹的开闭状态由裂纹面的应力决定。研究表日月,裂纹的存住引起系统横向、纵向、扭转振动相互耦合,两条裂纹之间的夹角对系统非线性耦合振动有明显的影响。     

深部铜矿破碎岩体巷道支护参数优化研究

通过分析深部铜矿破碎地段支护失效的原因,建立巷道开挖岩石力学分析模型,对巷道开挖后的破碎圈半径和应力分布进行了计算,根据计算结果,对破碎地段的巷道支护参数进行了设计,设计采用钢筋混凝土和锚杆联合支护方案,混凝土厚度95cm,锚杆长度2m。新的支护方案对破碎地段的巷道支护效果明显。     

Compliance based assessment of stress intensity factor in cracked hollow cylinders with finite boundary restraint: Application to thermal shock part I

The evaluation of mode I stress intensity factor associated with the creep-free thermal shock (TS) of finite length elastically/thermo-elastically restrained cracked hollow cylinders is a problem of interest. Among existing evaluation methodologies, the mechanical weight function approach is often perceived to be an optimal compromise between simplicity and accuracy for and more generalised K_I evaluation. However, to confidently apply a mechanical weight function methodology in such circumstances requires the derivation of different weight functions for each potential boundary restraint configuration, i.e. free, flexible or rigid boundary conditions. In this article, the traditional mechanical weight function philosophy is complimented with an elastic compliance analysis, enabling the mechanical weight function and geometry factors for an equivalent semi-infinite cracked hollow cylinder to be used to evaluate associated with a wide range of finite length elastically/thermo-elastically restrained cracked hollow cylinders. The need for deriving different weight functions is therefore removed and the proposed Compliance Adjusted Weight Function (CAWF) approach becomes more ‘user-friendly’. The targeted cracked hollow cylinders are assumed to exhibit an exterior circumferential edge crack or an exterior circumferential semi-elliptical surface crack.     

多自由度裂纹转子系统非线性动力学特性分析

大型旋转机械转轴裂纹具有复杂的高维非线性特征, 由此产生的机械故障时有发生。本文根据某航空发动机低压转子系统,利用拉格朗日原理建立了具有26个自由度的含有裂纹故障的高维非线性动力学模型。引进改进的POD方法成功将该系统降为具有两个自由度含有特征的低维非线性系统。数值模拟结果显示降维系统具有与原系统一致的非线性动力学特征,表明本方法对解决高维非线性问题具有较好的有效性。此外,本文还利用C-L方法对其进行分岔分析,讨论了系统参数与系统动态行为之间的关系,得到了裂纹转子各种不同分岔模式,得到了裂纹二分之一亚谐共振条件下的非线性动力学特性, 准确反映了裂纹转子的动力学特征。     

Compliance Based Assessment of Stress Intensity Factor in Cracked Plates with Finite Boundary Restraint: Application to Thermal Shock Part II

A Compliance Adjusted Weight Function (CAWF) approach has been recently developed to enable the estimation of stress intensity factor in thermal shocked cracked plates with finite boundary restraint. In this article the CAWF approach is used to analyse three case studies that collectively encompass the plate configurations, crack configurations and load configurations with which the CAWF is currently formulated. The results of these analyses highlight that the CAWF approach is suitable for estimates within 5–10% of benchmark fracture mechanics finite element values for a wide range of targeted cracked plate configurations and boundary restraint. An exception occurs for the semi-elliptical surface cracked plates where a free boundary effect can be observed at a free or near free boundary restraint condition.