自增强高压缸精加工残余应力及强度数值分析

基于弹塑性理论和材料的实际拉/压性能,用有限元软件ANSYS命令流及APDL语言建立了高压缸体的三维模型,将多载荷步分析及单元生死技术相结合,研究了缸体内外表面加工余量对其残余应力分布及弹性强度的影响。研究表明:当内壁发生反向屈服时,加工顺序影响残余应力的分布,这时先加工外圆,后加工内孔,有利于提高缸体的强度;精加工内孔,内壁处残余压应力增大,精加工外圆,内壁处残余压应力减小,应力变化量都与加工余量呈线性关系。以上方法及结论,可为自增强结构的设计加工提供依据。     

混烃球罐的开裂原因

在停车检验期间某混烃球罐下极带环焊缝处存在大量表面裂纹,采用X射线应力测定仪对裂纹集中部位的残余应力进行测试,并通过化学成分分析、力学性能测试、断口微观形貌观察等方法对球罐开裂的原因进行了分析.结果表明:球罐下极带环焊缝熔合线和热影响区处发生了硫化物应力腐蚀开裂;在腐蚀介质及较大的残余拉应力作用下,裂纹在残余拉应力最大...     

某四缸汽油机气缸盖气缸体组合结构有限元分析

建立了某四缸汽油机气缸盖、缸体、主轴承盖等零件的三维有限元组合模型。使用有限元分析软件Abaqus,在考虑各组件非线性接触关系的基础上,计算了该组合体在标定工况下的振动响应。对该发动机进行了表面振动测量,通过振动测点处实验数据与该点处计算数据的对比验证了有限元模型建立的合理性。分析了爆发工况下缸体、缸盖火力面及缸孔的振动变形。结果表明:缸体裙部刚度较弱容易产生变形;缸盖火力面鼻梁区变形较大,缸盖火力面与气缸盖连接处容易产生较大的应力;缸孔的变形量较小在工程允许的范围之内。     

M22机用丝锥产生裂纹的原因分析与探讨

在M22机用丝锥蒸汽处理后发现有批量的产品存在裂纹,经过分析认为:裂纹产生于机加工的磨槽工序,磨削过程中产生了加工变质层,导致产生了磨削应力。在机加工后,磨削应力转变成残余磨削应力,磨削应力以及残余磨削应力的本质是拉应力,应力在丝锥牙根处集中导致裂纹的产生和扩展。     

损伤轴面激光熔覆修复残余应力测量及分析

残余应力直接影响激光熔覆修复机械零件的结构强度和安全性能,为了掌握损伤轴面激光熔覆修复后的残余应力分布情况,以40Cr钢零件轴为基材,Ni60自熔合金粉末为熔覆材料,采用脉冲激光熔覆工艺制备零件轴表面修复试件,利用盲孔法对零件轴修复试件进行残余应力分布特性分析。结果表明,在轴面激光熔覆的镍基合金修复层中产生了不可忽略的残余拉应力,高应力区位于熔覆层始末两道上;轴线方向检测点上X方向残余应力呈"M"形分布,Y方向残余应力呈"Λ"形分布,σx值较高,接近基材屈服强度的45. 9%,而圆周方向检测点的X方向和Y方向残余应力相对稳定,最大拉应力约为200 MPa;激光扫描路径对轴面熔覆层的残余应力值的影响大、分布形状的影响小,螺旋路径熔覆产生的残余应力值较低,更适合圆周面修复,但熔覆层始末两道边沿处的残余应力比中间部位高,有必要采取适当措施进行消应力处理,以获得优良的修复效果。     

成型过程对焊管残余应力的影响

采用盲孔法对UOE、JCOE、HSAW焊管的残余应力进行了分析,重点对不同工艺条件下HSAW焊管的残余应力进行了分析。结果表明:UOE焊管厚度方向的双向(周向、轴向)平均拉应力水平较低,峰值拉应力出现在焊管的内表面;JCOE焊管的双向平均拉应力水平略高,但峰值拉应力出现在外表面;成型参数合适的HSAW螺旋焊管的平均残余应力可以达到(UOE或JCOE)直缝管的水平,但其内表面的峰值拉应力均明显高于直缝焊管的,且当螺旋焊管成型下压量过大时,将导致平均残余应力及峰值均有很大提高。     

盲孔除切屑机的研制与应用

1　现状　　发动机的缸体和缸盖上的盲孔多而且深,加工后的切屑沉积在孔的底部,经常是和油污一起粘附在螺纹槽内,切屑清理工作非常困难。一般采用压缩空气吹除或者高压水冲洗,这些方法使得切屑四处纷飞,既不安全又不卫生,更重要的是切屑清除不干净,造成发动机整机清洁度差,危害性特别大,直接影响产品性能。例如缸体主轴承螺纹孔(盲孔)内残余的切屑会使主轴承螺栓力矩存在假力矩现象,发动机运转一段时间后产生螺栓松动,切屑易进入主轴瓦背面,造成主轴承瓦挤瓦、烧瓦,甚至使曲轴断裂,以及发动机振动大等不良现象的产生。再如缸体顶平面上用于…     

只需贴片、打孔,无需人工计算,残余应力测量的新一代产品

ＹＣ Ⅲ型应力测量仪功能 :1.可用于盲孔法和环芯法两种方法的残余应力测量2 .显示释放应变数据和残余应力值3.对计算公式中的各个系数进行显示和修改4 .打印测量应变值和残余应力值5 .断电保护功能特点 :体积小 ,重量轻 ,操作简单 ,与钻孔装置配合使用 ,实现残余应力测量的自动化。ＺＤＬ Ⅱ型钻孔装置功能 :用手电钻在平面、曲面和角焊缝等处钻 1.0～ 3.0ｍｍ的盲孔 ,对中精度± 0 .0 2 5ｍｍ特点 :重量轻、携带方便、操作简单。拥有先进的非线性有限元结构分析程序和高精度多点数字应变仪 ,承接各种结构有限元计算分析、大型结构现场应…     

真空钎焊液冷模块残余应力研究

通过盲孔法,对真空钎焊液冷模块生产过程中产生残余应力的工序进行测试分析,测定了真空钎焊后模块、固溶处理和热时效后模块、真空钎焊前的组件、数控成型后未打压组件、打压测试后的模块、使用一段时间的模块、鼓包故障模块7种状态的液冷模块残余应力,对测试结果分析得出打压测试是造成模块最终残余应力较大,导致工作应力与残余应力叠加造成鼓包的结论。因此调整打压测试工艺的时机,或者打压测试后进行残余应力消除,是保证液冷模块安全使用的前提条件。     

基于盲孔法的齿轮残余应力的测试研究

为了解齿轮残余应力分布,应用盲孔法结合电测法,分别对感应淬火热处理后的齿轮进行了盲孔法残余应力测试。结果表明,热处理后齿轮残余应力有了较大改善,且残余主应力为压应力,试验表明热处理对齿轮起到了较好的强化作用。同时,详细介绍了盲孔法残余应力的测试方法和过程,为相关测试研究提供了较好的借鉴。     

激光熔覆工艺参数对铁基双层涂层组织和残余应力的影响

针对激光熔覆过程中剧烈的温度场变化伴随着应力、应变演化,进而导致零件具有高裂纹敏感性的问题,对不同激光扫描路径及工艺参数下残余应力演变规律进行研究。采用激光熔覆在Q345钢上制备了Fe基双层多道涂层,并以X射线衍射法结合电化学腐蚀剥层法测量沿涂层深度方向的残余应力分布,探究激光扫描路径、功率以及扫描速度对涂层显微组织和应力分布的影响。结果表明：涂层表面和内部为残余压应力,在涂层基体熔合线处残余应力发生突变,热影响区表现为残余拉应力;激光熔覆工艺对涂层残余应力的大小和分布规律有显著影响,当激光扫描路径为轮廓偏置式、激光功率为1.8 kW、扫描速度为0.02 m/s时,涂层具有最优的残余应力分布和成形质量;残余应力的产生主要与激光束对熔池的冲击作用以及熔覆层的非平衡凝固特性有关。     

轴承套圈强化研磨表面残余应力试验研究

结合疲劳裂纹扩展原理,分析残余压应力对材料表面的疲劳裂纹扩展速率的影响。采用电磁无心夹具对轴承套圈进行定位,利用新型轴承强化研磨机对轴承套圈表面进行加工,基于X射线衍射法测定轴承套圈加工后的表面残余应力。试验结果表明,强化研磨加工使轴承套圈表面的残余压应力增大,提高工件服役可靠性。     

塑性变形T8碳素钢中渗碳体相的残余应力

运用X射线残余应力测量法分析了含有球状渗碳体的碳素钢在拉伸塑性变形后铁素体相及渗碳体相的残余应力情况.结果表明:在经过拉伸塑性变形后,铁素体相呈现残余压应力状态,而渗碳体相呈现残余拉应力状态;当施加的塑性应变在边界应变点之前,渗碳体的残余应力随应变值的增加而增大,而在边界应变点之后,残余应力呈下降趋势.观察发现渗碳体颗粒内部的断裂及渗碳体与铁素体结合边界部分的分离是引起渗碳体残余应力下降的原因.为了更好地理解渗碳体相和铁素体相之间的相互作用,在Eshelby/Mori-Tanaka模型的基础上分析了两相各自的塑性应变及两相间的塑性应变失配.     

A case study on the effect of thermal residual stresses on the crack-driving force in linear-elastic bimaterials

The effect of thermal residual stresses in bimaterial structure with initial crack located near a sharp interface is discussed in this paper. Bimaterial compact tension (CT) specimen is used in the analysis, and the residual stresses are introduced by cooling of the specimen. The residual stresses affect the stress and strain fields near the crack tip, and the crack-driving force is different compared with that in the homogeneous material without residual stresses. This difference can be quantitatively expressed through an additional crack-driving force term—the material inhomogeneity term, Cinh. In this paper, it is evaluated using the post-processing procedure based on the concept of configurational forces, following a finite-element analysis. The results indicate that accurate numerical analysis of pre-cracked bimaterials should include the effect of thermally induced residual stresses. This effect cannot be neglected, even for bimaterials with homogeneous mechanical properties and inhomogeneity in thermal properties only (e.g. welded joints of ferritic and austenitic steel). Based on the obtained results, data from this study can be used in engineering practice to improve integrity and work safety of various inhomogeneous structures.     

Crack Propagation of Rolling Contact Fatigue in Ball Bearing Steel Due to Tensile Strain

Crack propagations or failure modes in rolling element bearings, which had been difficult to explain via conventional crack propagation mechanisms such as the orthogonal shear stress mechanism, were discussed from the viewpoint of a tensile strain mechanism. Contact stresses are compressive in three axes, whose values differ from each other; then strain can be tensile in one of these directions, acting at a right angle to the direction of maximum compressive stress. A crack is considered to propagate by this tensile strain. When contact stress is small, a crack produced by some cause can propagate by this elastic tensile strain. When contact stress is large, residual tensile strain is produced by plastic deformation, which can also influence the crack propagation. Several failure modes of rolling element bearings, which had been difficult to explain, were explained by tensile strain.     

Measurement of equivalent residual stresses generated by milling and corresponding deformation prediction

We introduce a method to measure the equivalent residual stresses and depths of the affected layers, which are generated in the workpiece during the milling process. These layers lie immediately under the milled surface. After machining, two material layers on the opposite side from the machined surface were chemically removed, and strain changes on the machined surface were measured after each layer removal. Based on the strain changes and the thickness of each removed layer, the equivalent residual stresses and depths of the affected layers in different directions were obtained. Based on the measured results, the corresponding deformations caused by the milling induced residual stresses can be predicted in workpieces with different rigidities. The predicted deformations were validated by the experimental results. We found that our measuring method can be successfully used in practice to evaluate the machined surface properties and predict the deformations caused by milling induced surface residual stresses accurately.     

齿轮接触安定分析

以Hertz理论为基础,建立齿轮的接触模型.针对齿轮接触表面层变曲率的特点,构造出局部坐标下残余应力应变场的分布状态,分析在此残余应力场分布状态下,齿轮接触的静力安定和机动安定的条件.采用应力应变释放的算法和不同啮合点局部坐标之间的转换法则,模拟齿轮在重复啮合过程中残余应力应变的累积过程,求解安定状态下残余应力的分布状况,确定齿轮接触的安定极限与摩擦因数和齿轮啮合位置之间的变化情况.     

环芯法测量深度方向上的残余应力分布

叙述了环芯法采用逐层铣槽方式测量残科应力的应力应变关系，并讨论了积分法和应变增量法两种方法测量主应力的误差问题。     

刀刃半径对不锈钢切削表面残余应力影响的模拟

建立了平面应变有限元模型，采用更新的Lagrange方法模拟了奥氏体不锈钢AISI316L的正交切削过程；研究了刀刃圆弧半径对已加工表面残余应力的影响，发现随着半径的增大，残余拉应力和压应力的数值都增大，压应力层厚度也增大，但是拉应力层厚度不变。将模拟结果与实验结果进行对比，发现二者是吻合的，从而验证了有限元模拟的可用性。     

The effect of plasticity on the ability of the deep hole drilling technique to measure axisymmetric residual stress

Mechanical strain relief covers a class of techniques for measuring residual stress in engineering components. These techniques work by measuring strains or displacements when part of the component is machined away. The assumption is that such strain or displacement changes result from elastic unloading; however, in components containing high magnitudes of residual stress elastic–plastic unloading may well occur. Such elastic–plastic unloading introduces errors into the measurement of the residual stresses and these errors may be large. This paper addresses the performance of the deep hole drilling technique, a mechanical strain relief technique particularly suitable for large section components. First a plane strain analysis is presented that quantifies the errors associated with plasticity for different magnitudes of residual stress. A three dimensional finite element analysis is then carried out that shows larger errors may be obtained than those suggested by the plane strain analysis. A method for reducing the magnitude of the error is investigated. Finally, the results of an experimental measurement of residual stress are presented where substantial plasticity occurs. The work demonstrates the potential vulnerability of mechanical strain relief methods to plasticity and introduces methods for quantifying the resulting errors. It also provides further evidence that modifications to the standard DHD technique can be made to make the technique less susceptible to error when plasticity occurs.