基于损伤力学的轴承钢旋弯疲劳寿命预测

基于连续损伤力学理论,提出了考虑真空化学热处理工艺影响的疲劳损伤模型及数值计算方法,研究了M50NiL轴承钢的旋弯疲劳损伤分析及寿命预测方法。给出了本构模型、疲劳损伤演化方程和理论模型中的材料参数标定方法,基于ABAQUS平台,通过编写UMAT子程序,实现了基于硬化层影响的疲劳损伤分析的损伤力学-有限元数值计算方法;对淬火回火、渗碳及碳氮复渗2种真空化学热处理的M50NiL轴承钢,开展了旋弯疲劳试验,分析了热处理工艺对疲劳性能的影响;基于提出的疲劳损伤模型及数值计算方法,预测了M50NiL轴承钢的旋弯疲劳寿命,并与试验结果进行对比,验证了所提方法的适用性。

铝合金变直径管材旋弯渐进成形规律有限元模拟研究

研究设计了一种用于旋弯渐进成形的双辊柔性弯曲模,其可对管材施加较强周向约束,且成形中可自适应转动。相比传统圆弧型单辊弯曲模,新型双辊柔性弯曲模能够有效降低旋弯渐进成形弯曲力,提高成形稳定性,并抑制管材截面畸变。在此基础上,建立了铝合金管材旋弯渐进成形-回弹全过程有限元模型,并通过与柔性弯曲成形对比,分析获得了旋弯变形耦合对成形结果的影响规律,发现在旋压基础上引入弯曲工步,会引起一定程度的截面变形和壁厚不均匀现象;在弯曲基础上引入旋压工步,会减小弯曲段截面变形量,增加内外脊线壁厚差异,加剧起皱风险,减小成形后的回弹变形。

旋弯疲劳断料机设计中的几个基本问题

金属棒料在旋弯交变应力作用下会发生疲劳断裂。将这一原理应用于断料行业 ,就发明了旋弯疲劳应力断料机。主要探讨旋弯疲劳断料机设计的基本原理、切口参数对疲劳断裂的影响、断料效率和断面质量的主要影响因素、旋弯疲劳断料的特点及适宜参数等基本问题。

碳化物对8Cr4Mo4VE高温轴承钢旋弯疲劳性能的影响

采用双真空熔炼制备了8Cr4Mo4VE轴承钢并对其进行均匀化处理,以控制其碳化物的数量、大小、形态及分布。利用旋转弯曲疲劳试验测试了8Cr4Mo4VE轴承钢的旋弯疲劳性能,采用扫描电镜、体式显微镜和能谱仪等分析了其旋弯疲劳试样的断口形貌和起裂源成分。结果表明:8Cr4Mo4VE轴承钢疲劳极限达到915 MPa。断口观察表明,其疲劳损坏方式主要有表面起裂和次表面碳化物起裂。次表面碳化物起裂扩展模式有3种:碳化物起裂快速扩展断裂、碳化物起裂扩展形成鱼眼区(FIE)、碳化物萌生微裂纹形成光学黑区(Optical dark area,ODA)后扩展形成鱼眼区。碳化物周围萌生裂纹及扩展时其扩展速率da/dN同应力强度因子ΔK满足Forman公式。碳化物应力强度因子ΔK_(carb)远小于光学黑区应力强度因子ΔK_(ODA)时,碳化物周围出现ODA,其裂纹扩展速率约为(1.84~2.10)×10^(-12) m/cycle。8Cr4Mo4VE轴承钢中的碳化物形状及所受应力对其疲劳寿命循环次数具有显著影响。

金属材料旋弯—热疲劳的试验研究

在普通旋弯疲劳试验机上,对金属材料进行了旋弯—热疲劳的复合试验,测试了球铁轧辊材料的热疲劳性能,分析了其失效行为和破坏机理.

M50轴承钢旋弯断口分析

采用扫描电镜和旋弯疲劳试验机等设备对经双真空熔炼后M50轴承钢的疲劳寿命和旋弯断口形貌进行分析。结果表明,S-N曲线分为两个阶段且旋弯应力分布较为集中。起裂模式为次表面单个碳化物起裂、次表面聚集碳化物起裂、表面起裂三种方式。

芯轴旋弯式JCOE成形过程数值模拟试验

在钢板旋弯式JCOE成形过程中,板边缘容易产生"直边",影响直缝埋弧焊管质量。文章设计一种新型的可移动芯轴夹具装置,能够有效缓解直边呈现程度。采用数值模拟方法,并进行实际的预示改进装置的使用效果,试验验证结果表明,改进后的芯轴活动夹具装置对减小制品"直边"很有效,而且可行。

多楔轮毂缘多道次旋压成形工艺研究

针对传统锻后切削工艺生产多楔轮存在材料利用率低、切断齿形金属流线等问题,以某多楔轮零件为研究对象,基于旋压近净成形原理,对多楔轮毂缘制定了多道次旋压工艺方案。基于SIMUFACT软件平台建立了多道次旋压成形全流程三维有限元模型,通过数值模拟研究了各道次旋压成形过程中的毂缘区材料流动规律及增厚情况。模拟结果表明,旋压预制坯外缘在第1道次旋弯轮弧挤压作用下发生明显的弯曲和增厚,板坯整体呈“半弧形”结构,后经过第2道次旋平轮镦挤推平,板坯整体发生二次增厚并成形出满足旋齿厚度要求的毂缘筒壁;通过第3道次和第4道次旋齿工艺使毂缘筒壁金属发生转移,形成满足尺寸要求的齿形结构。根据模拟结果进行试验研究,成功试制出质量合格的多楔轮零件,验证了该成形方案的可行性。

应力场强法在旋弯及扭转疲劳极限分析中的应用

应用应力场强法对旋弯疲劳和扭转疲劳极限进行了分析,并通过3种金属材料的旋转弯曲和扭转疲劳试验加以验证,结果表明,旋转弯曲疲劳极限和扭转疲劳极限之间的关系同解析表达式给出之间的吻合得非常好,因此得到结论,应力场强法能够比较好的描述两种疲劳强度极限之间的关系。

采用ASPEX和旋弯疲劳法表征GCr15轴承钢夹杂物

为了探索ASPEX检测法与旋弯疲劳试验法的最佳适用条件,全面了解轴承钢中夹杂物的信息,对真空脱气冶金工艺制备的GCr15轴承钢分别应用上述两种方法对试验钢中夹杂物进行了类型、形状、尺寸、分布方面的表征。结果表明,在夹杂物类型检测方面,两种检测方法结果基本一致。该轴承钢中富含钙、铝、硫等元素的球型复合夹杂物,同时也存在少部分边缘锋利的TiN型夹杂物;利用ASPEX进行多面多次扫描,发现检测出的最大球型B类氧化铝夹杂物大小分布结果基本与旋弯疲劳法符合。根据试验结果以及两种检测方法的原理得出,ASPEX法对钢中夹杂物的尺寸、形状、类型、分布等信息的整体分析更为有效,而应用疲劳法对大尺寸刚性夹杂物的检测更为有利。

低碳钢丝类环形弯曲件螺旋式弯曲模设计

介绍了钢丝类环状制件一般弯曲方法。着重分析了一种简单、高效、适用的弯曲方法——螺旋式弯曲。论述了其模具结构特点、工作过程、参数确定、设计和技术要求。

旋耕弯刀切土能耗理论分析及降低能耗的途径

对r=195mm旋耕弯刀侧切面、正切面切土能耗进行理论计算表明:正切面切土能耗大于或接近于侧切面切土能耗。增大旋耕刀安装角可以改变土壤破坏形式,减少切土阻力,建议:r=195mm普通旋耕刀安装角可取65°左右;曲母线正切面旋耕刀安装角可取70°左右;其它类型旋耕刀的安装角亦可参照此结论相应增大。

基于电阻变化的高周疲劳寿命预测

研究金属材料在不同损伤机理时的基于电阻变化的损伤定义 ,在传导电流的导电截面与承载截面等价的假设条件下 ,其与有效截面的损伤定义等价。针对纯弯旋转高频疲劳试验 ,分析考虑材料损伤分布不均匀及电阻率变化的损伤最大值的测量公式 ,其具有超几何函数的形式 ;分析表明在材料损伤为 0～ 0 .6时其与假设损伤均匀且不计电阻率的情况差别不大 ,并提出一种近似公式。对结构钢的高周疲劳进行测量 。

不同加载方式下疲劳极限之间的关系

依据应力场强度法分析了同种材料在不同加载方式下各疲劳极限之间的关系，并讨论了弯扭、拉扭疲劳极限图，分析了一些疲劳实验数据，表明本文的分析方法是合理可行的。

压气机整流叶片开裂的原因

某型发动机在厂内试车20h后,其压气机整流叶片在叶身中部出现纵向裂纹。对开裂叶片进行外观检查、显微组织和断口形貌观察、硬度测试,研究了在发动机工作转速下叶片的振动情况,分析了裂纹成因。结果表明:整流叶片的开裂性质为高周疲劳开裂,裂纹是由于在发动机工作转速范围内存在由后排转子激起的旋弯共振而形成的;采取将叶片整体加厚的调频方案,将后排转子叶片激起旋弯共振的转速调至发动机最高转速以上,可以防止压气机整流叶片裂纹的产生。

Study and Design of Spiral Bent Waveguide Configuration

A new version of the scalar transverse electric(TE) wave equation in the bent waveguide is introduced. Then, TE polarized field in curved single-mode waveguides is analyzed by using the finite-difference beam propagation method(FD-BPM). The bending loss in bent waveguides is gotten for the optical fields obtained from BPM and comparisons are made among losses of the waveguides with various curvature radiuses, refractive index differences and cross sections. Based on the results, the design of spiral bent waveguide configuration is proposed as follows: refractive index difference being of 0.007, both width and thickness of waveguides being of 6 μm, the curvature radius in the spiral centre being of 4 mm, and the bending loss coefficient of the designed spiral bent waveguide being of 0.302 3 dB/cm.

Microstructure and mechanical properties evolution of 65Cu-35Zn brass tube during cyclic rotating−bending process

The cyclic rotating−bending(CRB)processes under different deformation conditions were carried out to refine the microstructure and improve the mechanical properties of the 65Cu−35Zn brass tubes.The microstructure and the mechanical properties in the axial direction of the tubes after the CRB process were studied with the OM,EBSD and conventional tensile test.To obtain the accumulated effective plastic strain of the tube during the CRB process,the FEM simulation was also executed.The results show that the average grain size decreases with the increase of rotation time at RT,and with the decrease of bending angle at 200℃.With the increase of accumulated effective plastic strain during the CRB process,the reduction rate of average grain size of the brass tube increases,the tensile strength of the brass tube increases in wave shape and the elongation increases first and then sharply decreases.

Aerodynamic performance of high-turning curved compressor cascade with boundary layer suction

The impact of boundary layer suction on the aerodynamic performance of a high-turning compressor cascade was numerically simulated and discussed.The aerodynamic performance of a curved and a straight cascade with and without boundary layer suction were comparatively studied at several suction flow rates.The results showed that boundary layer suction dramatically improved the flow behavior within the flow passage.Moreover,higher loading over the whole blade height,lower total pressure loss,and higher passage throughflow were achieved with a relatively small amount of boundary layer removal.The integration of curved blade and boundary layer suction contributed to better aerodynamic performance than the cascades with only curved blade or boundary layer suction used,and the more favorable effect resulted from the weakening of the three dimensional effects of the boundary layer close to the endwalls.

New extrusion process of Mg alloy automobile wheels

The recent research and development of forged magnesium road wheel were reviewed.Methods of flow-forming,spin forging of manufacturing a forged magnesium alloy wheel were introduced.A new extrusion method was investigated especially. Extrusion from hollow billet was proposed in order to enhance the strength of spoke portion and reduce the maximum forming load. By means of the developed technique,the one-piece Mg wheels were produced successfully by extrusion from AZ80+alloy.At the same time,the existing problems on the research and development of forged magnesium road wheel were analyzed.The impact testing,radial fatigue testing and bending fatigue testing results show that AZ80+wheel can meet application requirement in automobile industry.

Stability margin of the quadruped bionic robot with spinning gait

Spinning gait is valuable for quadruped robot,which can be used to avoid obstacles quickly for robot walking in unstructured environment. A kind of bionic flexible body is presented for quadruped robot to perform the spinning gait. The spinning gait can be achieved by coordinated movement of body laterally bending and legs swing,which can improve the mobility of robot walking in the unstructured environments. The coordinated movement relationship between the body and the leg mechanism is presented. The stability of quadruped robot with spinning gait is analyzed based on the center of gravity( COG) projection method. The effect of different body bending angle on the stability of quadruped robot with spinning gait is mainly studied. For the quadruped robot walking with spinning gait,during one spinning gait cycle,the supporting polygon and the trajectory of COG projection point under different body bending angle are calculated. Finally,the stability margin of quadruped robot with spinning gait under different body bending angle is determined,which can be used to evaluate reasonableness of spinning gait parameters.