精密注塑制品残余应力的试验研究及其计算

注塑残余应力对精密注塑制品的力学性能和光学性能等有重要影响,是精密注塑制品质量控制的关键指标之一。为研究注塑成形过程中残余应力的发展,以丙烯腈—丁二烯—苯乙烯共聚物(Acrylonitrile butadiene styrene,ABS)塑料为研究对象,对其模内蠕变行为进行试验研究。将热弹性模型计算的收缩应变与试验测量的收缩应变之间的差值定义为制件的模内蠕变,得到注塑工艺条件对模内蠕变的影响规律。在此基础上构建计算精密注塑制品残余应力的蠕变模型。模型中的材料弹性模量可由Tait方程计算得到,粘壶系数采用反演方法计算得到。利用该模型结合薄壳有限元法对ABS平板注塑件残余应力进行计算,对计算结果进行试验验证,并与普通的松弛模型计算进行比较。计算结果表明,该模型的计算精度高于普通的松弛模型,是解决精密注塑制品残余应力预测问题的新的有效方法。     

全三维注塑成形流动模拟有限元模型的研究

注塑制品往往具有复杂的几何形状，存在着壁厚的差异。三维流动模型比二维模型能更准确地模拟出熔体充模流动的情况。提出了一种基于全三维模型的注塑成形流动模拟的数学模型和数值实现方法，把速度和压力同次插值的方法成功地应用到三维注塑模拟的计算中，采用三维控制体积追踪塑料熔体的流动前沿，在温度场计算中，全面考虑了对流项在各个方向的影响，使模型的适用范围更广，结果更准确。在此基础上开发了相应的软件，可以计算熔体充模过程中的压力场、速度场和温度场等。实验验证和算例分析说明了三维流动模型的有效性。     

残余应力对碳纤维填充聚合物注塑制品电阻率的影响

为了研究残余应力对注塑导电高分子复合材料导电性能的影响,以碳纤维填充聚合物注塑成型为试验对象,采用剥层法计算制品的残余应力,测量退火前后制品各层的电阻率变化,得到注塑工艺、残余应力和制品电阻率之间的关系。为了提高计算结果的可靠性,采用连续追踪截面形貌测量各层的纤维取向,并将结果集成于制品残余应力计算中。研究结果表明,残余应力对制品电阻率的影响主要集中在表层,芯部影响较小。在退火处理过程中,受残余应力释放和高分子链动态回复运动的双重影响,碳纤维在基体中分布状态更加均匀,提高了导电网络结构的连续性,从而使制品电阻率下降。残余压应力越高,退火过程中高分子链动态回复越快,制品表层电阻率下降越多,制品导电性能越好。     

复合管液压成形装置及残余接触压力预测

针对现有复合管制造工艺中存在的问题，研制开发了一种焊接不锈钢衬里复合管液压成形装置，介绍了该装置液压成形系统的工作原理及技术特点。阐述了复合管液压成形过程的原理，并采用弹塑性理论分析了其在液压成形过程中内管及外管的应力应变状态。推导出了复合管残余接触压力与成形压力之间关系的理论计算公式，通过实验对公式进行了验证。结果表明该装置结构及其计算方法适于工程应用。     

考虑铣削残余应力的压弯成形仿真计算方法

针对铣削加工引起的残余应力影响工件压弯成形过程中弹塑性应力分布并最终影响成形工件形状精度的问题,提出考虑铣削残余应力的压弯成形仿真计算方法。首先基于弹塑性理论推导了压弯成形应力计算公式,然后建立了考虑铣削残余应力的压弯成形有限元模型,研究了铣削残余应力对压弯成形应力应变分布及回弹的影响规律,采用数值方法建立了考虑铣削残余应力的压弯成形应力计算公式。结果表明:该有限元模型可以用于研究压弯成形应力应变变化规律,低速铣削产生的残余压应力对压弯成形卸载前的应力分布和压弯卸载后上下表面的切向应变影响最大,高速铣削引起的铣削残余应力使得试件压弯卸载后弯曲角度最小,变形程度最大。     

某轴流风叶的注塑残余应力计算与模拟

介绍了注塑残余应力的形成机理和主要影响因素,建立注塑制件的二维温度场和残余应力计算模型,并进行了某轴流风叶的注塑残余应力计算模拟,验证了注塑残余应力计算模型的合理性和准确性。     

塑料注射成形过程仿真软件的开发和应用

智能型3维注射成形过程仿真系统HSCAE　3D解决了用3维实体／表面模型取代中性层模型的关键性技术难题，通过数值计算与人工智能技术的结合，使仿真软件由传统的被动式计算工具提升为主动式优化系统。实验和实践证明，HSCAE　3D为注塑制品与模具的虚拟制造奠定了坚实的理论和技术基础，构成了注塑制品成形质量全面控制的核心技术，已在模具行业中得到了很好的应用。     

基于Moldflow Insight 2010的残余应力优化分析

注塑制品的残余应力影响制品的形状、表面质量及使用性能。在分析残余应力产生机理和原因的基础上,应用软件模拟实验方法,介绍了降低残余应力的方法,结果发现冷却方式与熔体温度对残余应力的影响很大,其次是保压压力、保压时间和螺杆速度的影响,程度依次递减。得出的结论对工程实际有一定的指导意义。     

基于预应力计算模态的塑料支架的共振分析

介绍了计算模态的基本理论,将塑料支架的模态预应力划分为结构载荷预应力和注塑工艺产生的残余预应力,对注塑残余应力的产生机理进行了简要分析,并使用有限元程序准确计算出注塑残余应力,发现结构中存在两处较高的注塑残余拉应力分布区,说明注塑残余应力是模态预应力的重要组成部分.通过对比研究和试验验证,分析了注塑结构的注塑残余预应力对结构模态特性的影响规律,为塑料结构件的模态特性研究和结构强度设计提供了理论参考和应用指导.     

聚合物注塑内应力数值计算的黏弹性模型

在聚合物黏弹性理论和注塑蠕变实验的基础上,结合注塑成形的工艺特点,构建了注塑制品内应力计算的四元件串联力学模型,推导了相应的本构方程,提出了聚合物材料参数弹性模量和黏壶黏度系数的计算公式。为了验证模型的可靠性,利用该模型对聚合物平板注塑制件的内应力进行了模拟计算并与相关文献的实验结果进行比较。计算结果表明：模型对注塑内应力发展的表征可以用固体高聚物的结构和力学性能的相关研究进行解释,结果真实可靠。     

TC4管状零件内壁加工残余应力计算及其有限元分析

针对残余应力对加工零件使用性能有严重影响以及TC4材料难以用X射线法进行残余应力测量的现状,提出了一种通过测量外壁应变来计算TC4管状零件内壁加工残余应力的方法。为验证该方法的正确性,在有限元软件中对模型内壁进行分层施加预定的随深度变化的残余应力,并用生死单元技术将内层单元逐层“杀死”来模拟实际实验中应力层被腐蚀的过程。根据外层不断变化的应变以及推导出的计算公式来计算内壁随深度变化的残余应力,并将计算得到的残余应力与之前所施加的应力进行对比,可发现该方法求得的残余应力值准确度较高,由此可以得出结论：该方法可用于测量实际零件的残余应力。     

Improved analytical model for residual stress prediction in orthogonal cutting

The analytical model of residual stress in orthogonal cutting proposed by Jiann is an important tool for residual stress prediction in orthogonal cutting. In application of the model, a problem of low precision of the surface residual stress prediction is found. By theoretical analysis, several shortages of Jiann’s model are picked out, including: inappropriate boundary conditions, unreasonable calculation method of thermal stress, ignorance of stress constraint and cyclic loading algorithm. These shortages may directly lead to the low precision of the surface residual stress prediction. To eliminate these shortages and make the prediction more accurate, an improved model is proposed. In this model, a new contact boundary condition between tool and workpiece is used to make it in accord with the real cutting process; an improved calculation method of thermal stress is adopted; a stress constraint is added according to the volume-constancy of plastic deformation; and the accumulative effect of the stresses during cyclic loading is considered. At last, an experiment for measuring residual stress in cutting AISI 1045 steel is conducted. Also, Jiann’s model and the improved model are simulated under the same conditions with cutting experiment. The comparisons show that the surface residual stresses predicted by the improved model is closer to the experimental results than the results predicted by Jiann’s model.     

研磨工艺对工件表面粗糙度及残余应力的影响

通过试验探讨了研磨过程中磨料粒度、研磨压力和研磨速度等工艺参数对工件表面粗糙度及残余应力的影响。试验结果表明,磨料粒度和研磨压力对工件表面粗糙度的影响较大,而研磨速度的影响较小;研磨使工件表面产生残余压应力,日残余压应力随磨料粒度、研磨压力及研磨速度的增大而增大。     

钛合金铣削加工表面残余应力研究

金属切削加工引起的残余应力对零部件变形、疲劳性能有重要影响,通过选择合适的加工参数对其进行控制是可能的。目的在于研究钛合金铣削加工中铣削参数对已加工表面残余应力的影响,利用X射线衍射技术测量进给方向和铣削方向的残余应力。为保证X射线应力测量精度,采用摇摆法和峰拟合定峰方法。试验结果表明,钛合金顺铣加工表面残余应力表现为压应力,主要是由于刀具后刀面与已加工表面的挤光效应起主导作用所致。沿铣削方向和进给方向,切削参数对工件表面残余应力影响具有差异性。通过控制切削参数有可能生成定制化的应力。     

Failure analysis of rolling bearings by X-ray measurement of residual stress

Residual stress measurements were carried out for the failure analyses of rolling bearings. According to the survey of more than one hundred examples, some change in residual stress was observed in most cases.Compressive residual stresses peak below the surface and if present, represent the position of maximum shearing stress due to normal contact pressure. Unexpected overloading is confirmed by this method.However, bearings often fail without such overloading. Early failures were observed to be associated with the residual stress changes near the surface. The influences of sliding, vibration and surface roughness on residual stress changes are discussed.     

钎料对金属/陶瓷钎焊接头残余应力的影响

采用热弹塑性有限元方法,在考虑材料性能参数随温度变化的情况下,分析了采用Ag-Cu-Ti钎料钎焊Al2O3陶瓷与镍丝钎焊接头在钎焊过程中产生的应力大小和分布情况.结果表明：钎焊过程中,在钎料与陶瓷界面的陶瓷侧会产生较大的残余拉应力,影响了钎焊接头的连接强度.在此类连接结构中,钎料对接头残余应力的影响是主要的,而钎料性能参数及厚度是决定接头残余应力大小的重要因素.在选择金属/陶瓷钎焊用钎料时,为降低接头残余应力,除考虑钎料与陶瓷的润湿性和界面反应程度外,钎料的性能参数和厚度同样重要.     

基于三剪统一强度准则的厚壁圆筒自增强分析

基于三剪统一强度准则,考虑材料应变强化效应、包辛格效应、拉压异性及中间主应力的影响,采用双线性强化材料模型对厚壁圆筒进行自增强分析,得到了厚壁圆筒加载应力、残余应力和工作应力的解析解,提出了最佳自增强压力的计算方法,探讨了拉压比、强度准则变化参数的影响,比较了自增强处理和非自增强处理及双线性强化模型和理想弹塑性模型厚壁圆筒的应力分布差异。研究结果表明：厚壁圆筒的最佳自增强压力随半径比和强度准则参数的增大而增大;工作时的最大等效应力随半径比和强度理论参数的增大而减小,随拉压比的增大而增大;自增强等效应力的最大值在弹塑性分界面处,且应力沿壁厚的分布较均匀;与理想弹塑性模型相比,双线性强化模型所对应的弹塑性分界面半径和残余应力较小,且随着自增强压力的增大,两种模型的差值越来越大;等效应力随半径比的变化规律可为厚壁圆筒选择合理的壁厚提供一定的参考;自增强技术可改善厚壁圆筒工作时的实际应力分布,提高其极限承载能力。     

喷丸强化残余应力对疲劳性能和变形控制影响研究进展

作为机械表面强化技术之一,喷丸强化使工件表层发生形变硬化,引入较高的残余压应力,减少了疲劳应力作用下微裂纹的萌生并抑制其扩展,从而显著提高零件的抗疲劳断裂和抗应力腐蚀开裂的能力。基于喷丸残余应力解析计算模型,从余弦函数模型、接触应力模型和球腔膨胀模型三个方面介绍喷丸强化残余应力的产生,进而对喷丸残余应力的仿真预测及影响规律进行论述。为了提高试件疲劳强度而引入的残余压应力会带来影响形位精度的变形,基于此阐述了喷丸残余应力对疲劳性能的影响及其在疲劳过程中的演化,同时论述了喷丸残余应力变形预测及控制的研究现状,最后对喷丸残余应力未来的研究内容与发展方向进行展望。     

Investigation of the coupled distribution of initial and machining-induced residual stress on the surface of thin-walled parts

Residual stress on the machined surface and the subsurface is known to influence the distortion of thin-walled parts. Therefore, it is essential to predict the distribution of surface residual stress accurately. In this paper, the coupled distribution law of initial residual stress and machining-induced residual stress is investigated. Firstly, a model with initial residual stress is established and incorporated into thermal mechanical coupled finite element model of 2-D cutting. Then, a tensile fixture is designed to impose initial stress into a thin-walled part of Al-6061, and cutting experiments are carried out. The residual stress distribution is measured by X-ray diffraction/electropolishing method. The results of experiments and simulation show that in the plastic deformation zone, the initial residual stress has no significant influence on the distribution of the machining-induced residual stress. In the elastic deformation zone, the stress that linear grows along depth from zero to initial residual stress is superimposed on machining-induced residual stress. The mathematical model of stress coupling distribution on the surface of thin-walled parts is established by numerical method. Finally, it is found that the effect of coupled stress distribution on distortion is more significant with the decrease of thickness (from 3 to 0.5 mm) of the thin-walled parts.     

A simplified analysis of the effect of microstructure gradient on the stress relief of aluminum plates and extrusions

Many bulk forms of metal products are quenched after heat treatment in order to preserve material characteristics. Rapid quenching results in large thermal stress gradients that lead to high levels of residual stress. For products such as plates and extrusions, stretching by a few percent can reduce these stresses, but the stresses are not completely relieved. This report presents a simplified analytical model of the stress relief process illustrating the effects of through-thickness property gradients on residual stress after stretching. The basic conclusion is that for plates with uniform yield surface shapes through the thickness, the through-thickness residual stress range after stress relief is equal to the strength range in the direction of stretch. In extrusions, the bow after stress relief is proportional to this strength range. Cases are also considered in which the yield surface shapes range from isotropic to anisotropic through the thickness. Plastic anisotropy can perturb the effect of strength range on residual stress.