计及齿面摩擦的直齿轮动力学分析

建立了考虑齿面摩擦影响的六自由度非线性直齿轮动力学模型,以FZG试验专用A型齿轮为研究对象,计算了实际时变啮合刚度,基于混合润滑模型分析了不同齿面粗糙度对应的时变摩擦系数,利用数值仿真方法研究了齿面粗糙度改变对齿轮啮合力、摩擦力、轴承力以及动传动误差等信号的时频特征的影响,并利用FZG试验台对A型齿轮具有完好齿面和损伤齿面两种状态下的多个振动加速度时频信号进行比较分析,验证了仿真结果。结果表明：齿面摩擦力会抑制啮合线方向的振动,齿面粗糙度增大会减小动传动误差,但加剧摩擦力方向振动,从而导致系统振动幅值增加,结论对齿面微损伤的故障诊断有实用参考意义.     

Stability analysis of the tunnel face in the cohesive-frictional soils considering the arch effect and rotational mechanism

ABSTRACT

This article proposes a new 3D failure mechanism to analyze the stability of the tunnel face driven by a closed shield in cohesive-frictional soils. The failure mechanism consists of a single block in the lower part defined by logarithmic-spiral and a distributed force caused by the weight of a half-ellipsoid in the upper part. The logarithmic-spiral surface represents the shear band and the distributed force is applied to simulate the arch effect. The arch effect and rotational mechanism are considered simultaneously. Comparisons among the proposed mechanism, numerical simulation and existing mechanism are conducted. The results show that the proposed mechanism provides improved limit support pressure values, and the failure patterns of the proposed mechanism agree well with those of the numerical simulation and experimental tests. This verifies that the proposed mechanism is effective and reasonable.     

Investigation of oscillating flow friction factor for cryocooler regenerator considering cryogenic temperature effect

In this paper, experimental results and correlations on the friction factor of screen regenerators are presented, being focused on the effect of cryogenic temperature. Cryogenic environment of helium gas is simulated by performing a simple room-temperature experiment using a higher density gas. Based on the experimental results, the proper correlations are proposed with several non-dimensional parameters. Numerical simulation results from the model with the proposed friction factor are compared to the experimental data under actual operating condition of cryocoolers. The experimental data confirm the accuracy and the availability of the proposed friction factor.     

基于事故树的深孔爆破边坡稳定性分析

为了能够对爆破后形成的露天边坡稳定性进行合理的分析评价,结合大小鱼山岛露天爆破边坡失稳的情况,采用事故树分析方法,建立了工程爆破现场露天边坡失稳事故树模型。计算出事故树的最小割集96个,最小径集3个以及基本事件的结构重要度系数,并得到基本事件结构重要度排序,找出了导致边坡失稳的主要原因是边坡监测和边坡支护。然后根据基本事件结构重要度的排序,制定合理有序的预防措施。事故树分析方法可以全面阐述露天矿边坡失稳的各种因素和逻辑关系,并通过对结构重要性分析,提出合理预防措施,为爆破露天边坡的安全管理提供参考依据。     

基于事故树的深孔爆破边坡稳定性分析

为了能够对爆破后形成的露天边坡稳定性进行合理的分析评价,结合大小鱼山岛露天爆破边坡失稳的情况,采用事故树分析方法,建立了工程爆破现场露天边坡失稳事故树模型。计算出事故树的最小割集96个,最小径集3个以及基本事件的结构重要度系数,并得到基本事件结构重要度排序,找出了导致边坡失稳的主要原因是边坡监测和边坡支护。然后根据基本事件结构重要度的排序,制定合理有序的预防措施。事故树分析方法可以全面阐述露天矿边坡失稳的各种因素和逻辑关系,并通过对结构重要性分析,提出合理预防措施,为爆破露天边坡的安全管理提供参考依据。     

Checking the slope angle of helical gear teeth

Conclusions The above method of checking has provided the plant, which has no special instruments for this purpose, with the means of discovering and elminating large errors which arise during the setting or resetting of machines, and also provided it with a better control of the cutting tools by their geometrical parameters thus greatly improving the machining quality of helical gears.     

Finite element analysis of punch height effect on V-bending angle

Considering the advantages of the V-bending die, the economical set-up time and the fabrication of a wide range of part size and complex shape, the V-bending die is generally used, especially in the Press Brake machine. However, the punch heights in the partial V-bending die affected the bending angle. In this study, the finite element method (FEM) was used to investigate the effects of punch height. The FEM simulation results revealed that the effects of punch height on the bending angle were clearly theoretically clarified based on the material flow analysis and stress distribution. The punch height affected the gap between the workpiece and the die, as well as the reversed bending zone, which resulted in a non-required bending angle. Therefore, applying a suitable punch height created a balance of compensating the gap between the workpiece and the die, and the stress distribution on the bending allowance and the reversed bending zone. This resulted in achieving the required bending angle.     

一种考虑应变率效应的结构非线性时程分析方法

提出了一种在非线性时程分析中考虑材料应变率效应的近似方法：首先,对结构进行不考虑应变率效应的非线性时程分析;然后,根据第一次分析的结果可以得到关键位置在与结构最大顶点位移对应的前1/4循环内的平均应变率,根据这些点的平均应变率对进入非线性构件材料的本构关系进行修正;最后,对结构进行第二次分析。文中给出了该方法的力学解释,并通过数值模拟对该方法进行了验证。结论：本文提出的方法具有较高的精度,可以作为一种在非线性时程分析中考虑应变率效应的有效方法。     

最终边坡预裂爆破技术参数及应用效果分析

为了保证边坡稳定性及减小爆破振动效应,对大宝山矿区889～877 m平台最终边坡采用了深孔台阶爆破、缓冲爆破与预裂爆破相结合的技术方案。根据边坡预裂爆破中预裂缝的形成是爆炸应力波和髙压气体联合作用的分析结果,和889～877 m平台最终边坡的主爆孔、缓冲孔、预裂孔相关的爆破参数,进行了现场实验。结果表明:爆破实施后,889～877 m平台最终边坡的半孔率高达85%,不平整度较低,较好地保证了最终边坡的稳定性,并将爆破振动的影响控制在安全范围之内。     

Stability of some mechanical systems with dry friction

Mechanical systems subjected to dry friction forces can be studied by differential equations with discontinuous vector fields. The stability of equilibria of some such systems is considered     

基于模态耦合的摩擦自激振荡系统稳定性研究

模态耦合是摩擦引起系统自激振荡的主要不稳定性机理之一.针对此类问题,构建了两自由度非线性质量一传动带系统.首先,通过劳斯判据分析系统的稳定性,给出了计算Hopf分岔点的数学表达式以及系统参数改变时分岔点和特征值分岔图的变化状态.其次,将扩展谐波平衡法加以利用和延伸,得到了自激振荡系统极限环幅值的解析解,进而研究了系统外界参数和结构参数变化对极限环幅值的影响.外界参数(带速和摩擦系数)变化可造成极限环幅值的规律性变化,而结构参数(阻尼比和固有频率)的改变会引起极限环幅值复杂的动力学行为.研究方法及结果可为机械系统结构设计和减振等方面提供理论分析参考.     

考虑剪切变形的圆弧深拱参数共振稳定性分析

基于结构弹性稳定理论,根据能量法推导出以位移为基本未知量的圆弧深拱总势能,从Hamilton原理出发,建立了考虑剪切变形的圆弧深拱的动力稳定微分方程。 利用Galerkin方法将该方程转化为二阶常微分Mathieu型参数共振方程,推导出圆弧深拱主参数共振的临界频率方程式,从而求得周期解所包围的动力不稳定区域。通过分析剪切变形、圆弧半径、圆心角等参数对圆弧深拱动力稳定性的影响,探讨了圆弧深拱发生参数共振的动力稳定性问题,为拱型结构动力分析与设计提供参考依据。     

Numerical analysis of panels’ dent resistance considering the Bauschinger effect

The Bauschinger effect should be considered in the analysis of panels’ dent resistance, because sheet metal experiences a complex loading history from stamping to denting. This paper studies the modeling and simulation of panels’ static dent resistance, taking the Bauschinger effect into consideration. Our work covers two parts: simulation and experiment. Procedures of drawing, springback I, indenting and springback II are simulated in a multiple step analysis. Different hardening models, including the isotropic hardening model, the linear kinematic hardening model and the nonlinear combined hardening model are used, respectively, in simulation. Comparing the simulation results with the experiment results, we find that the Bauschinger effect has a great influence on panels’ dent resistance. When panels are made of high strength steel or stamped with a high Blank Holder Force (BHF), the Bauschinger effect on panels’ dent resistance is more severe. Considering the effect in numerical analysis would improve the simulation accuracy effectively. The work of this paper is beneficial to material selection and processing optimization for automobile exterior panels.     

考虑时变效应的水电工程运行安全风险分析方法

针对水电工程风险因子的时变特性,用随机过程的方法模拟结构抗力与荷载作用,分析水电工程结构特性与运行方式,综合运用改进层次分析法、时变可靠度理论和风险率阈值,建立水电工程运行安全风险率评估模型。以土石坝工程为算例,详细展示时变风险率评估方法的分析流程。算例表明,工程运行安全风险率与服役时间及设计标准有着密切关系;考虑时变效应,风险率随时间推移而逐渐增大,其与设计标准的交点反映结构技术性使用寿命。应用本文提出的评估模型,预测运行期风险率变化趋势,可为水电工程的安全运行和风险决策提供科学依据。     

东露天选煤厂槽仓高边坡稳定性与变形分析

平朔东露天槽仓为目前亚洲最大规模的储煤槽仓。采用极限平衡方法和有限元法,开展了边坡在支护前后不同工况下的稳定性计算和应力与变形分析。结果表明,边坡支护前无法达到使用要求,斜壁与直壁转角处和仓底坡脚处为应力集中和变形最大处,是加固的重点部位。边坡采用土钉墙复合结构和灌注桩+钢内撑复合结构支护后,稳定性满足使用要求,变形在正常范围内,该支护方案非常适合该边坡。     

入射角对微波在面内各向异性磁性薄膜中传播特征的影响

基于Maxwell方程组，探讨了面内各向异性磁性薄膜内磁导率的旋磁特性对微波在膜内传播性质的影响，揭示出不同角度入射的微波在膜内的传播性质具有显著差异。     

Sensitivity series and friction surface analysis of non-metallic friction materials

Nine non-metallic friction material formulations contained fibers, fillers and binder without strong abrasives were designed using Golden Section sequence combined with least-square method. Seven ingredients used without strong abrasives were selected based on the combinatorial approach. Wear (w) and coefficient of friction (μ) are expressed as a function of volume fraction of the ingredients selected as and . The formulations were optimized using the sensitivity series obtained from least-square method. An optimized formulation (S-10) was obtained with a total wear loss of 6.69 wt% and an average μ of 0.375. Friction surface of both brake pad and disc was observed using SEM, EDX and XRD. The non-metallic friction materials without abrasives exhibit unique friction performance and phenomena compared with the non-metallic friction materials with abrasives and semi-metallic brake linings. The temperature measured during friction is lower and the oxidation of the cast iron disc is not rigorous.