Distribution of contact loads in crushed zone between tunnel boring machine disc cutter and rock

The construction efficiency and quality of tunnel boring machines(TBMs)is largely determined by the service life of cutting tools,which is the result of contact loads in the crushed zone between cutter ring and rock.In this paper,a series of rock breaking tests were conducted with a 216 mm diameter disc cutter and concrete samples.Based on the superposition principle,the distribution of contact loads between disc cutter and rock were obtained by using the truncated singular value decomposition(TSVD).The results show that both the peak value and the whole numerical distribution of the radial strains on the cutter ring increase with the increase of the penetration.The distribution curves of the contact loads show an approximate parabola going downwards,which indicates contact loads are more concentrated.The front non-loading area with a ratio from 1.8%to 5.4%shows an increasing trend with the increase of penetration.However,the change of rear non-loading area is not obvious.It is believed that the conclusions have guidance for the study of rock breaking mechanism and manufacturing process of the disc cutter.

Variation in contact load at the most loaded position of the outer raceway of a bearing in high-speed train gearbox

For the fatigue failure and tribological property of a rolling element bearing,the contact load variation plays a significant role while the most loaded position of the bearing outer raceway takes the greatest risk of failure.This paper focuses on the variation in contact load on the most loaded position of the outer raceway of a gearbox bearing in high-speed train.Under operation conditions of different input speeds and torques,the dynamic contact load distribution in a gearbox bearing of high-speed train was measured by instrumenting the bearing with strain gauges.The most loaded position was identified accordingly and the features and reasons of the variation in contact load on this position were suggested.Three factors were found to have varying degrees of impact on the contact load variation under different gear meshing conditions:modal vibration of the cage or shaft,radial geometrical differences among the rollers and vibration of the gearbox housing.

Enhanced drug loading efficiency of contact lenses via salt-induced modulation

Low drug loading efficiency is one of the main obstacles hindering the application of contact lenses(CLs) as the carrier for extended ocular drug delivery. Here in this study, a simple and effective drug loading method based on salt induced modulation was proposed and demonstrated with mechanism elucidation. First of all, using poly(2-hydroxyethyl methacrylate)(p-HEMA) as the contact lens material, betaxolol hydrochloride, Diclofenac Sodium and Betaxolol Base as the model drugs with different solubility, influence of salt concentration,salt type(sodium salts of sulfate, chloride, and sulfocyanate) and drug properties in the loading solution on drug loading efficiency was investigated. Mechanism of enhanced drug loading in contact lens was further explored via studying the influence of salt on the absorption isotherm, drug solubility and water content of CLs. Applicability of this method to other CLs materials was also investigated. It was demonstrated that adjusting the ionic strength of loading solutions resulted in significant increase of drug loading in CLs. Type and concentration of the salts and solubility of the drug were the main factors influencing enhancement ratio of drug loading. The mechanism for improved drug loading was related to the reduced drug solubility in loading solutions and the reduced bound water content in contact lenses. Modulation of drug loading by adjusting ionic strength was also applicable to other CLs and the light transmittance was not affected. This method was more suitable for salt-form drugs with high solubility. In summary, adjusting ionic strength of loading solution is an economical and effective way to improve drug loading in CLs, and this simple method may also find application in other hydrogel based drug delivery systems.

Design of Non-contact On-load Automatic Regulating Voltage Transformer

At present, an automatic-mechanic contact tap-changer is widely used in power system, but it can not frequently operate. In addition, arc will occur when the switch changes. In order to solve these two problems, this paper presented an automatic on-load voltage-regulating distributing transformer which employed non-contact solid-state relay as tap-changer, and mainly introduced its structure, basic principal, design method of each key link and experimental results. Laboratory simulation experiments informed that the scheme was feasible. It was a smooth and effective experiment device, which was practical in application.

Dynamics of a Dual Power-split Transmission Based on Loaded Tooth Contact Analysis

In order to implement the dynamic characteristic of a dual power-split transmission, a dynamic me- chanics model is built. Firstly, according to the method of theoretical analysis of the tooth contact analysis （TCA） and loaded tooth contact analysis （LTCA）, the actual meshing process of each gear pairs is simulated, and the time-varying mesh stiffness excitations are obtained, which can improve the numerical precision. Second- ly, by using the lumped mass method, the bending-torsional coupling three dimensional dynamic model of the dual power-split transmission is established, and the identical dimensionless equations are deduced by elimina- ting the effect of rigid displacement and the method of dimensional normalization. Finally, by the method of the fourth order Runge-Kutta algorithm with variable step lengths, the responses of this system in a frequency domain and time domain are obtained, and the dynamic load change characteristics of each gear pairs are analyzed. The results show that the establishment, solution and analysis of the system dynamics model could provide a basis for the dynamic design, and have an important significance for the dynamic efficiency analysis and dynamic perform- ance optimization design of the dual power-split transmission.

Contact Force Distribution and Static Load-carrying Capacity of Large Size Double Row Four-point Contact Ball Bearing

Clearance not only affects the startup torque,rotation precision and stiffness of bearing,but also affects the load distribution,load-carrying capacity and life of bearing.A computational model in which the clearance of bearing is first included is presented for determining the contact force distribution and static load-carrying capacity of a double row four-point contact ball bearing which is subjected to the combined radial,axial and overturning moment loadings.The relation between the negative axial clearance and the contact force distribution is analyzed.The static load-carrying capacity curves are established,and the effects of the changes in negative axial clearance,curvature radius coefficient of raceway groove and initial contact angle on the static load-carrying capacity are analyzed.The results show that,with the increase in the absolute value of negative clearance,the maximum contact load decreases first and then increases.The clearance values in the range of 0.2 mme0 mm have little effect on the static load-carrying capacity of bearing.With the increase in the curvature radius coefficient of raceway groove and the decrease in the initial contact angle,the static load capacity of bearing decreases.

STUDY ON LOADS AND CONTACT STRESSES FOR TOROIDAL DRIVE

The load distribution and calculating formulae of the contact stresses in the rotor worm and stator helical surface for toroidal drive are given. The effecting factors on contact stresses and their effects are analyzed. The results is useful for reference purposes in manufacture and design of the drive.

面向双斜齿轮啮合接触的传动特性研究

针对双斜齿轮啮合特性,提出了一种考虑小齿轮轴向支承刚度的双斜齿轮三维加载齿面接触分析模型。该模型根据微分几何和力学分析,考虑了变形协调条件、力平衡条件、轴向力平衡约束,为了减小三维载荷传递误差以改善载荷分布,建立了双斜齿轮的多目标优化数学模型。最后,通过数值仿真研究了载荷、小齿轮轴向支承刚度和齿面修形对双斜齿轮径向载荷传动误差和轴向载荷传动误差的影响,结果表明所提模型可以准确地计算双斜齿轮的传动误差。最后通过实验对比分析了齿面修形前和修形后的振动加速度情况。

LOAD SHARING AND CONTACT OF HOURGLASS WORM GEARING

Based on solid modeling, the geometry and the FE model of the hourglass worm gearing are established. By the hybrid method of FEM and penalty function, the load sharing among tooth paris and the stress of contact teeth are calculated, the contact zones and the distribution of the contact pressure are investigated. The variation of the contact states with the load is investigated by comparision of its contact patterns under different loads.

沟曲率半径(密合度)对四点接触球轴承疲劳寿命影响研究

采用Romax Designer工程分析软件,应用ISO/TS 16281—2008寿命计算方法,根据经典的滚动轴承理论,对某电机轴四点接触球轴承内部载荷分布、接触应力、套圈滚道等效动态滚动元件载荷和ISO/TS16281—2008寿命等进行了大量的计算,重点研究滚道沟曲率半径对轴承内部载荷分布、接触应力、套圈滚道等效动态滚动元件载荷和ISO/TS16281—2008疲劳寿命的影响。研究结果表明,轴承型号和制造质量、载荷条件、润滑条件和可靠度等其他条件确定时,存在一个相对最优的滚道沟曲率半径(密合度);当载荷条件不同时,相应最优的滚道沟曲率半径(密合度)不同。在所研究的具体条件下,由于轴系中的2个轴承所承受的载荷不同,因而,2个轴承的最优滚道沟曲率半径(密合度)不同。研究结果可为四点接触球轴承的设计方案提供参考。

基于micro-CT实验的颗粒体系接触力计算及演化分析

三维颗粒体系颗粒间接触力计算是散体力学研究的重难点.以双弹性橡胶球为研究对象,开展显微CT(micro-CT)原位平压实验,基于Hertz接触理论和Tatara大变形接触理论,验证了弹性球接触模型,获得了基于实验的弹性球接触力理论公式.以三维颗粒体系为研究对象,开展了micro-CT原位探针加载实验,获取颗粒二维图像序列,经过系列数字变换得到数字体图像,获得了不同加载状态下三维颗粒体系接触力网络,分析了颗粒体系接触力分布及演化规律,探究了强接触数量及分布演化与颗粒体系稳定性的联系.研究结果表明:基于实验的弹性球接触力公式能合理有效表征两颗粒间的接触力;探针加载下颗粒间接触力呈现以探针压头接触点为起点,向下方和四周逐级传递接触力的网状分布;强接触数量占接触总数量的45%-50%,分布贯穿于整个颗粒体系内部,支撑起颗粒体系网络结构,较大值集中于压头下方呈现树杈状分布;加载过程中,z=14 mm处建立了平衡点,平衡点处,强接触数量达到顶峰,强接触力网络结构布满整个三维颗粒体系,建立起承受外载荷的主要骨架,随着加载继续,强接触力的整体数值更高,在颗粒体系内部分布也更加均匀.

微涡轮角接触球轴承打滑性能分析

在赫兹接触理论的基础上,通过拟静力学方程对高速旋转,承受联合载荷和角偏斜的微涡轮角接触球轴承进行计算,得到不同轴向预紧力、径向载荷及偏转角下的轴承受力及其打滑情况,并基于Hirano打滑准则得到轴承的打滑临界曲线。结果表明:为了防止球打滑,以较高转速运转的角接触球轴承需要较大的轴向预紧力;当不承受径向载荷且轴向预紧力低于100 N时,轴承在20000~70000 r/min转速内均发生打滑,当径向载荷增至2000 N时,轴承在20000~70000 r/min转速内均不发生打滑;随着转速的增加,轴承所受离心力增加,球与外圈间的接触载荷增加,球与内圈间的接触载荷减小,导致轴承在高速下的打滑加剧;随着轴承力矩载荷或轴向预紧力的增大,偏转角增大;存在角偏斜的情况下,随着轴向预紧力的增大,球受力增大,离径向载荷作用线越近的球受力更明显,球Hirano打滑系数增大,轴承越不易打滑。

超早强钢筋混凝土板抗接触爆炸试验研究

UR50超早强水泥基自密实高强材料具有固化时间短、早期强度发展快等优点,是战时关键设施快速修复和施工的理想材料。为研究UR50超早强水泥基自密实高强材料钢筋混凝土板(URCS)的抗爆性能,对其开展了系列接触爆炸研究。采用养护时长分别为28 d和24 h的超早强水泥基钢筋混凝土板,以及一块普通混凝土板(NRCS)作为对照。通过试验分析了不同养护时间下的混凝土板的破坏模式和破坏特征。结果表明:URCS相对于NRCS具有较强的抗爆能力,URCS在接触爆炸作用下的破坏模式为正面爆炸成坑和背面层裂震塌破坏,随着装药量的增加,其破坏模式逐渐转变为爆炸贯穿和爆炸冲切。URCS养护时间为24 h可以达到28 d时的抗爆性能。根据试验结果,划定了不同破坏模式的震塌系数范围,并对结构的毁伤参数进行了量化统计,建立了预测开坑直径和层裂直径的经验公式。

球轴承刚度斜弹簧计算方法

针对传统轴承刚度计算方法计算过程复杂,计算结果正确性存疑的问题,提出了一种斜弹簧计算方法,以角接触球轴承为例,推导了受联合载荷、高速运转和仅受中心轴向载荷、中低速运转2种极端情形下的轴承刚度计算公式,斜弹簧计算方法整个过程无需微分和矩阵运算,物理意义清晰,正确性能够自证,计算过程简洁,计算精度高。并与虚功原理法、刚度投影法、准静态模型的增量法进行对比,结果表明:与虚功原理法误差较小,进一步证明了斜弹簧计算方法的正确性;与刚度投影法、准静态模型的增量法误差较大,两者所依据的物理基础不实的计算结果正确性存疑。

基于Savitzky-Golay滤波器的有载分接开关振动信号包络线提取方法研究

分接开关切换过程中各触头依次分合碰撞产生振动信号,信号特征反映了碰撞能量和触头刚度。为进一步研究触头碰撞动力学特性,文中首先建立M型分接开关四触头的碰撞动力学模型,计算了静触头刚度对模型响应特性的影响规律;其次模拟了静触头弹簧松弛故障,获得了弹簧0.6 mm线径和1.0 mm线径对应的振动信号;然后提出基于Savitzky-Golay滤波器的包络线计算方法,提取奇—偶切换和偶—奇切换时振动信号的平均包络线;最后计算了2种线径静弹簧对应的平均包络线的相关系数。研究结果表明触头碰撞系统的固有频率随分接开关静触头刚度下降而下降,触头碰撞的响应速度降低,振动信号的第一个峰值出现的时刻推迟,且平均包络线的相关系数仅为1.6,说明触头刚度变化后振动信号出现了明显变化。研究结论可用于有载分接开关触头状况的诊断。

双列调心非对称球面滚子轴承接触应力计算方法

为实现双列调心非对称球面滚子轴承在径向载荷下的接触应力分析,基于该类轴承的内部几何关系及非赫兹接触理论,建立了轴承数值分析模型,采用牛顿法求解,并以某双列调心非对称球面滚子轴承为例,计算分析了径向载荷、径向游隙、内滚道半径、滚子轮廓修形半径、滚子轮廓峰值点位置对轴承接触应力的影响。结果表明:随着径向载荷、径向游隙增大,内滚道中央区域和边缘接触应力均增大;随着内滚道半径增大,内滚道中央区域接触应力增大,边缘应力减小;随着滚子轮廓修形半径增大,内滚道中央区域接触应力减小,边缘应力增大;随着滚子轮廓峰值点位置与滚子大端面距离增大,内滚道中央区域接触应力变化较小,边缘应力减小。

Geometry Design and Tooth Contact Analysis of Crossed Beveloid Gears for Marine Transmissions

Beveloid gears,also known as conical gears,gain more and more importance in industry practice due to their abilities for power transmission between parallel,intersected and crossed axis.However,this type of gearing with crossed axes has no common plane of action which results in a point contact and low tooth durability.Therefore,a geometry design approach assuming line contact is developed to analyze the tooth engagement process of crossed beveloid gears with small shaft angle for marine transmission applications.The loaded gear tooth contact behavior is simulated by applying a quasi-static analysis to study the effects of gearing parameters on mesh characteristics.Using the proposed method,a series of sensitivity analyses to examine the effects of critical gearing parameters such as shaft angle,cone angle,helix angle and profile-shift coefficient on the theoretical gear mesh is performed.The parametric analysis of pitch cone design shows that the dominant design parameters represented by the angle between the first principle directions（FPD） and normal angular factor are more sensitive to the shaft and cone angles than they are to the helix angle.The theoretical contact path is highly sensitive to the profile-shift coefficient,which is determined from the theoretical tooth contact analysis.The FPD angle is found to change the distribution of contact pattern,contact pressure and root stress as well as the translational transmission error and the variation of the mesh stiffness significantly.The contact pattern is clearly different between the drive and coast sides due to different designed FPD angles.Finally,a practical experimental setup for marine transmission is performed and tooth bearing test is conducted to demonstrate the proposed design procedure.The experimental result compared well with the simulation.Results of this study yield a better understanding of the geometry design and loaded gear mesh characteristics for crossed beveloid gears used in marine transmission.

Boundary slippage for generating hydrodynamic load-carrying capacity

Boundary slippage is used to generate the load-carrying capacity of the hydrodynamic contact between two parallel plane surfaces. In the fluid inlet zone, the fluidcontact interfacial shear strength on a stationary surface is set at low to generate boundary slippage there, while in the fluid outlet zone the fluid-contact interfacial shear strength on the stationary surface is set at high enough to prevent the occurrence of boundary slippage. The fluid-contact interfacial shear strength on the entire moving surface is set at high enough to prevent boundary slippage on the moving surface. These hydrodynamic contact configurations are analyzed to generate the pronounced load-carrying capacity. The optimum ratio of the outlet zone width to the inlet zone width for the maximum load-carrying capacity of the whole contact is found to be 0.5.

Generation Principle of Helix Tooth Profile in Hypocycloid Pinw heel Transmission and Its Contact Characteristics

The transmission characteristics of gear drive can be improved with the use of novel tooth profiles.A theoretical study on tooth profile of the hypocycloid pinwheel transmission and contact analysis of gear pair based on finite element method(FEM) are carried out,respectively.The line contact between mated tooth surfaces becomes point contact according to a plus movement.Through loaded tooth contact analysis(LTCA),the contact stress and load distributions for the proposed hypocycloid pinwheel transmission and the traditional one are discussed.The analysis results show that the developed tooth surfaces have anticipatory point contact characteristics under loads and contact fatigue dangerous area locates around the ultimate contact position.

浸渍石墨材料在不同法向载荷下的磨损性能研究

研究不同摩擦体系下法向载荷对浸渍石墨的摩擦磨损特性的影响,采用扫描电子显微镜和激光共聚焦显微镜分别表征摩擦表面磨痕形貌、磨痕轮廓,对浸渍石墨与对偶球(GCr15钢球和Si_(3)N_(4)陶瓷球)的摩擦磨损情况与机制进行评估分析。结果表明:磨损痕迹随着施加载荷的增加而加深加宽,磨损率与法向载荷呈负相关,而摩擦因数、磨损体积则与法向载荷呈正相关;小载荷作用下石墨的磨损机制为黏着磨损和磨粒磨损,大载荷下则主要表现为黏着磨损、氧化磨损以及疲劳磨损;GCr15/石墨摩擦副相比于Si_(3)N_(4)/石墨摩擦副磨损率较低,在摩擦过程中形成完整、连续性更好的“第三体”转移膜减轻了磨损,对石墨基体起到保护作用。