Numerical Simulation of Heat Transfer and Deformation of Initial Shell in Soft Contact Continuous Casting Mold Under High Frequency Electromagnetic Field

Heat transfer and deformation of initial solidification shell in soft contact continuous casting mold under high frequency electromagnetic field were analyzed using numerical simulation method; the relative electromagnetic parameters were obtained from the previous studies. Owing to the induction heating of a high frequency electromagnetic field （20 kHz）, the thickness of initial solidification shell decreases, and the temperature of strand surface and slit copper mold increases when compared with the case without the electromagnetic filed. The viscosity of flux de- creases because of the induction heating of the high frequency electromagnetic field, and the dimension of the flux channel increases with electromagnetic pressure; thus, the deformation behavior of initial solidification shell was different before and after the action of high frequency electromagnetic field. Furthermore, the abatement mechanism of oscillation marks under high frequency electromagnetic field was explained.

Gaps,challenges and possible solution for prediction of wheel-rail rolling contact fatigue crack initiation

The prediction of wheel/rail rolling contact fatigue(RCF)crack initiation during railway operations is an important task.Since RCF crack evolution is influenced by many factors,its prediction process is complex.This paper reviews the existing approaches to predict RCF crack initiation.The crack initiation region is predicted by the shakedown map.By combining the shakedown map with various initiation criteria and the critical plane method,the crack initiation life is calculated.The classification,methodologies,theories and applications of these approaches are included in this paper.The advantages and limitations of these methods are analyzed to provide recommendation for RCF crack initiation prediction.This review highlights that wheel/rail dynamic characteristic,complex working conditions,surface defects and wear all affect the RCF crack initiation.The optimal selection of criteria is essential in the crack initiation prediction.Based on the research gap regarding the challenging process of crack initiation prediction detailed in this review,a proposed prediction process of RCF crack initiation is proposed to achieve a more accurate result.

Optimization design method of contact bounce and breakaway initial velocity for aerospace electromagnetic relay

Aerospace electromagnetic relay is an electric component that has been widely used in aerospace industry.Contact bounce and contact breakaway for initial velocity are the key parameters that have strong influence on reliability and electric life of the relay.Generally,it is difficult to optimize these two parameters simultaneously.In this paper,according to kinetics theory and structural mechanics,a dynamic reaction calculation model of the relay that describes contact bounce and breakaway for initial velocity is proposed.Under the constraints of contact gap and contact force,the optimal combination of debugging parameters is obtained by the application of orthogonal design.It considers the reduction of contact bounce and the augmentation of breakaway for initial velocity as the optimization objectives,and takes the debugging parameters as the optimization variables.All these above ensure the increase of contact breakaway for initial velocity and the decrease of contact bounce simultaneously,and contact arc erosion is also reduced.

A Spring-Layer Model for a Bi-Layered Plate-Strip with Initial Stress Through Imperfect Contact Interface

In this paper,we present our report on the forced vibration of a bi-layered plate-strip with initial stress resting on a rigid foundation induced by a time-harmonic force.The investigation is carried out according to the piecewise homogeneous body model with utilizing the three-dimensional linearized theory of elastic waves in initially stressed bodies(TLTEWISB).The materials of the body are chosen to be linearly elastic,homogeneous,and isotropic.The interface between the layers is assumed to be imperfect,and is simulated by the spring-layer model.A similar degree of imperfection on the interface is realized in the normal and tangential directions.The mathematical model for the problem under consideration is designed,and the system of the equations of motion is approximately solved by employing the finite element method(FEM).The numerical results explaining the influence of the parameter that characterizes the degree of corresponding imperfectness on the dynamic response of the plate-strip are presented.In particular,we demonstrate that the distributions of the normal stress become flat,as the normal-spring parameter increases.

Life prediction for rolling contact fatigue crack initiation of kiln wheels

这份报纸关于轴行偏转调查火炉车轮的滚动接触疲劳，它与车轮上的应用支持的负担是线性的。为有弹性的临时的便床，塑料临时的便床和 ratcheting 材料回答的疲劳裂缝开始标准被使用与轴的行偏转的二个集合估计车轮回答。有限元素模拟被使用双线性的材料模式为执行非线性、运动学在 ANSYS 11.0 变硬。由从不同 critera 比较结果，低周期的疲劳是支配的失败，这被显示出。从不同的轴的线偏转的结果显示最佳调整罐头极大地提高支持的结构的整个生活。

炮膛间距对枢轨初始接触状态的影响分析

电磁轨道炮炮膛间距直接影响到发射过程中枢轨滑动电接触状态,尤其是起始段炮膛间距变化对电枢烧蚀具有较大影响,将炮膛等效成呈一定角度张开的两条直线,利用角平分线相关特性开展炮膛间距测量,根据炮膛间距实测数据,结合工程实际分析起始段炮膛变化形态并建立对应形态下的枢轨初始接触模型,分析了炮膛装配精度对枢轨初始接触性能的影响,分析结果表明起始段炮膛间距是造成电枢静态受力不均、枢轨接触面积及接触力非对称分布的主要原因,通过不同炮膛变化形态的静态接触试验,进一步验证了理论分析结果。通过分析炮膛间距对枢轨初始接触的影响作用,为枢轨匹配性设计提供理论依据。

基于晶体塑性模型与内聚力单元模拟的接触疲劳亚表面原奥晶界裂纹萌生

材料在接触疲劳载荷下亚表面裂纹的萌生是其主要损伤模式之一.采用晶体塑性模型耦合内聚力单元,模拟高强钢在滚动接触疲劳载荷下亚表面原奥氏体晶界处的疲劳裂纹萌生.基于内聚力模型的损伤起始准则和疲劳损伤演化规律,并利用USDFLD子程序将内聚力单元的疲劳损伤与晶体塑性模型结合,计算了滚动接触疲劳加载下的损伤随循环次数的累积.对Voronoi模型下的疲劳裂纹萌生进行了模拟,研究了晶体取向对裂纹萌生的影响.结果表明,裂纹的萌生受剪切应力主导,萌生位置在最大剪切应力范围内,模拟结果和试验观察一致.晶粒取向对裂纹萌生位置与萌生寿命有显著影响.

横磁触头真空电弧起始运动的临界触头开距实验研究

起始桥柱状真空电弧运动的临界开距是对应于横磁触头大电流真空电弧运动模式演变的标志性物理量,对横磁触头真空断路器大电流开断性能具有重要影响。本文的研究目标是实验研究横磁触头开槽方式、燃弧时间和电弧电流等因素对横磁触头起始桥柱状真空电弧运动临界开距的影响规律。研究结果显示在燃弧时间0 ms~10 ms、电流有效值5 kA~31.5 kA的实验条件下,3种结构的横磁触头的起始桥柱状电弧有越靠近电流峰值起弧,停滞时间越长的趋势。直角槽型卐字形横磁触头(CuCr40)、螺旋槽型横磁触头(CuCr25)和曲线槽型卐字形横磁触头(CuCr50)的电弧运动临界开距分别在0.96,1.1 mm和1.7 mm有概率最大值点。相关研究结果对横磁触头大电流真空电弧的发展和演变特性的理解提供基础。

CONTACTING FATIGUE FAILURE OF Cu-22%Pb PLAIN BEARING ALLOY

The results of the contacting fatigue tests for Cu-22%Pb plain bearing alloy show that the fa- tigue failure behavior of the alloy is related to the distribution of Pb particles.Both the addi- tions of mischmetal and sulphur can refine the Pb particles.However,mischmetal improves and sulphur deteriorates the fatigue property of the alloy.

Study on drying rate in contact drying with flexible screen

The moisture contents (MC) of popular veneers were tested in Composition Board Laboratory of Northeast Forestry University by contact drying with flexible screen. The influence factors considered included temperature, initial moisture contents (IMC), and veneer thickness. Veneer-drying laws under different hot press conditions were analyzed. The results showed that the drying rate increased with temperature rising. 160°C was considered to be more efficient than 140°C and 180°C because excessive high temperature has no significant contribution to drying rate. IMC had significant effect on drying rate. The veneer with high IMC had a higher drying rate at above fiber saturation point (FSP) and a lower drying rate at below FSP, compared to the veneer with low IMC. Average drying rate also varied with thickness in power law.

高速铁路钢轨上拱不平顺对波磨萌生的影响研究

高速铁路钢轨波磨是近年来致力于解决的一种极其复杂的轮轨关系问题。武广高铁胡家湾大桥存在钢轨上拱不平顺并伴随钢轨波磨病害,有必要通过理论与实践研究寻找钢轨上拱和波磨相伴相生的证据并诠释其机理。首先建立涵盖钢轨上拱-大幅值轮载-轮轨接触力统一数力学模型,采用能量法、轮轨接触理论和安定极限法进行解析计算,研究钢轨上拱矢度、列车参数和轨道参数的影响规律。然后阐释钢轨上拱、轮载与轮轨接触力之间的相互作用对理解钢轨波磨的萌生机理和减磨措施以及提出车轮多边形发生机理猜想所具有的启示意义,最后简要总结钢轨上拱引发波磨需要进一步研究的前沿问题。计算结果表明:钢轨上拱矢度对轮轨接触力影响显著,如以CRH2型动车组和弹性支撑块式无砟轨道组合为例,当钢轨上拱0.2 cm时,动轮载为21.45 t,相较平顺时增大3.1倍,切向力为15.86 kN,增大2.1倍,法向应力为1 131.6 MPa,增大1.5倍,超出安定极限值20.1%;轮轨接触力随着静轮重、簧下质量和轨道垂向刚度的增加而增大,随着轨道阻尼的增大而减小。研究发现,钢轨上拱激励轮轨系统高频共振导致了钢轨波磨的萌生与发展。防止或抑制此类型波磨的主要措施有:控制钢轨上拱不平顺、防止轮轨系统共振、减小轮载变化幅值、提高钢轨材质强度与耐磨性能以及采取预防性和修复性打磨等。

钢轨打磨对小半径曲线钢轨滚动接触疲劳的影响研究

为研究钢轨打磨对小半径曲线钢轨滚动接触疲劳的影响,基于国内某重载铁路小半径曲线和运行车辆建立实参数轨道-车辆多体动力学仿真模型,对钢轨打磨前后轮轨接触几何关系、轮轨接触应力和轮轨蠕滑力进行分析,现场测试打磨前后车辆通过该曲线的轮轨力,结合Burstow钢轨损伤函数模型对该曲线轨面裂纹萌生寿命进行分析。结果表明:钢轨打磨后,轮轨接触点集中问题得到缓解,轮轨接触应力、轮轨蠕滑力减小和轨面裂纹法向分力减小,实测轮轨力减小,相同载荷下对应的载荷循环数增大。各项指标较打磨前更有利于抑制钢轨滚动接触疲劳的萌生及扩展,轨面裂纹萌生寿命明显延长。打磨后3.5个月轨面裂纹未见明显发展,仿真计算结果与实际情况吻合良好。

液氮冻融-微波注热急速冷热冲击下饱水煤力学及渗流特征研究

为研究饱水、冻融与温度因素耦合作用下煤岩力学及渗流特征,以王庄煤矿9105工作面原煤为研究对象,采用非接触式数字图像处理技术开展液氮冻融与微波注热条件下煤岩三轴加载实验。研究结果表明:原始煤岩经液氮冻融、液氮饱水冻融、液氮饱水冻融不同温度处理后,煤岩抗压强度、弹性模量降低,泊松比升高,剪切应变值增大;原始煤岩在压密、弹性、屈服和破坏4阶段应力集中现象无明显变化,但经3种条件处理后,煤岩局部应力集中在破坏阶段出现明显扩增现象;相比于原始煤岩初始渗透率,经冻融处理后煤岩初始渗透率为1.44×10^(-3)μm^(2),增幅较小;经饱水冻融、饱水冻融后50℃、100℃温度处理,煤岩初始渗透率增幅较为明显;经饱水冻融后150℃温度处理后煤岩初始渗透率为7.40×10^(-3)μm^(2),增幅显著提高。研究结果可为深部低渗透煤层瓦斯增透提供指导,对提高井下瓦斯抽采效率具有参考意义。

论皖南泾县吴语古影母非开口平声字归上的音变原因

本文尝试从外部接触和内部结构相结合的角度来分析皖南泾县宣州吴语影母非开口平声字归上这一典型的由内外因共同作用导致的音变现象。研究认为该音变的外因是与明清官话标准音阴平调值趋同;音变内因是方言阴阳平调值接近,当在非开口呼前,奉、微、疑、喻、匣等浊声母变为零声母,与影母字声韵相同时,阴阳平字就有混同的趋势,为保持阴阳平字的区别这一汉语方言中的强势规则,从而推动影母非开口平声字的声调发生变化。

卷烟接装胶的吸收性及对粘合性能的影响

本研究在对比分析接装胶性能基础上,通过动态接触角法、动态渗透法、斜面滚球法和90°剥离强度实验法等,对接装胶在接装纸表面的吸收性、渗透性、初粘性和粘合强度进行了研究。结果表明,接装胶在接装纸非印刷面的接触角随时间的变化及动态渗透情况与水不同,高黏度接装胶在多孔性接装纸非印刷面的吸收速率低,高固含量接装胶的动态渗透特征参数t_(max)和t_(95)小。上胶开放时间对接装胶的初粘性和最终粘合强度均有影响,随着上胶开放时间延长,因接装纸表面对接装胶的吸收,初粘性呈现先上升后下降的趋势,即存在一个最大初粘性的开放时间窗口,低于该时间点封合,不会影响粘合强度,但高于该时间点封合,可能会发生粘合不良问题。

紫外光引发TPU薄膜亲水改性研究

以热塑性聚氨酯弹性体(TPU)薄膜为基体,采用紫外光引发接枝对其表面进行亲水改性。探究泊洛沙姆407及其与PVPK-90配比对亲水性的影响,采用接触角测试仪测定接触角,采用电子万能试验机和扫描电镜分别测试其力学性能和表面的微观结构。结果表明:当PVPK-90含量为2%时,随着洛沙姆407含量增加,接触角呈现先减小然后增大的变化趋势;当泊洛沙姆407与PVPK-90的比例为3:1时,随着亲水剂泊洛沙姆407和PVPK-90的含量增加,接触角平均值呈现先减小后增大的变化趋势;在紫外灯波长568.7nm、光引发时间4min条件下的最佳配方为:PVPK-90浓度2%、泊洛沙姆407浓度6%、光引发剂6976浓度10%,此时亲水改性TPU薄膜接触角最小为25.10°,亲水性能优异;力学性能保持良好;SEM照片证实亲水单体接枝到材料表面。

C型电枢-轨道初始接触特性分析

针对C型电磁发射器的结构特点,设计了基于过盈配合的电枢-轨道初始接触有限元模型,对发射装置进行装配并分别进行结构和电磁-结构分析,选取电枢臂路径a、b,探究了电枢臂不同过盈量对电枢始接触特性的影响。分析研究了发射装置通入不同电流时对电枢应力、接触压强的影响规律。结果表明,改变电枢过盈量、电流的大小只影响接触参数的大小,没有改变其变化规律,电枢-轨道装置初始阶段所需的预紧力是由电枢臂的过盈量所决定的。

An analytical method for assessing the initiation and interaction of cracks in fused silica subjected to contact sliding

Understanding the fracture behavior of fused silica in contact sliding is important to the fabrication of damage-free optics.This study develops an analytical method to characterize the stress field in fused silica under contact sliding by extending the embedded center of dilation(ECD)model and considering the depth of yield region.The effects of densification on the stress fields were considered by scratch volume analysis and finite element analysis.Key mechanisms,such as crack initiation and morphology evolution were comprehensively investigated by analyzing the predicted stress fields and principal stress trajectories.The predictions were validated by Berkovich scratching experiment.It was found that partial conical,median and lateral cracks could emerge in the loading stage of the contact sliding,but radial and lateral cracks could be initiated during unloading.It was also found that the partial conical crack had the lowest initiation load.The intersection of long lateral cracks makes the material removal greater.

大锥角新型裙座结构设计及其接触特性和应力分析

为满足裂解反应器下封头复杂的工艺配管要求,设计了一种带温箱和垫板的新型裙座结构。利用有限元法,对裙座结构在温度场、温度-内压耦合作用和不同初始间隙尺寸下的应力状况、接触特性、应力分布变化规律进行了分析。裙座筒体存在两个由温差产生的高应力环状区,主要应力类型为弯曲应力,其应力状态基本不受内压和初始间隙变化的影响。接触压力和内压的增加会显著加强垫板下焊缝附近的应力集中。初始间隙对垫板应力分布的影响存在临界值,当间隙长度超过垫板宽度的80%时,裙座结构应力最大位置由裙座筒体转移至垫板半锥顶角对侧,应力最值随间隙尺寸增加持续增大,威胁裙座结构完整性。

基于Lankarani赫兹接触模型的弓网动力学仿真研究

该文通过有限元方法建立简单链型悬挂接触网模型并对其进行模态分析,通过使用Lankarani赫兹接触模型,运用显式中心差分法对弓网耦合动力学方程进行求解,基于上述理论创建弓网动力学仿真平台,采用模块化的思想进行弓网动力学的仿真分析。在此基础上,采用EN50318标准对弓网仿真平台的正确性进行验证。最后,通过对考虑迟滞阻尼效应的Lankarani赫兹接触模型进行动力学仿真,分析Lankarani赫兹接触模型中重要参数对仿真结果的影响。