残余应力对航空整体结构件加工变形的影响分析

基于理论计算和有限元模拟,研究了毛坯的初始残余应力对大型整体结构件数控加工变形的影响,对单向 应力作用的矩形截面梁在剥层过程中的变形挠度值进行了求解。结果表明,理论解与有限元计算值是一致的。面 向工程应用,采用ABAQUS有限元软件模拟了残余应力对隔框类整体结构件加工变形的影响,并进行了试验验证。 有限元仿真结果与试验数值非常吻合。最后,根据工件加工变形的有限元模拟结果,提出了提高整体结构件制造 精度的工艺措施。     

焊接顺序对中厚板对接焊残余应力的影响

针对同种材料,但几何结构不同的中厚板结构件之间的对接焊,运用有限元软件进行模拟,分析多层多道焊各层焊缝的焊接顺序对焊缝区域横、纵向残余应力的影响。采用内生热的加载方式模拟热源,采用生死单元法模拟多层多道焊缝的焊接过程。模拟结果表明,从几何尺寸小的一边向几何尺寸大的一边焊,沿焊缝底部和顶部中心线方向产生的横纵向残余应力峰值最小;底层的几道焊缝的焊接顺序对焊缝底部和顶部中心线方向所产生的横纵向残余应力的影响不大。     

钢制压力容器残余应力的Mises屈服条件确定法

利用Mises屈服条件建立了确定钢制压力容器焊接残余应力的方法,即只要测点进入屈服状态,就完全可以确定该点两个主应力方程的残余应力。并指出该方法是一种确定钢制压力容器残余应力的简易方法,具有实用和推广价值。     

工程陶瓷磨削表面残余应力的数学模型

作为特殊的硬脆工程材料，陶瓷零件的断裂强度和韧性对表面应力状态异常敏感，建立相应的数学模型是研究残余应力的理论基础。本文阐述了陶瓷材料在磨削过程中的弹塑性变形数学模型，建立了磨削温度模型，介绍了利用磨削参数进行编码的二次回归模型，从而为预测和控制残余应力数值及性质提供指导。     

Prediction of residual stress distribution after turning in turbine disks

The state of a surface region after machining is definitely affected by cutting parameters, such as cutting speed, feed rate, tool nose radius, tool rake angle and the presence of a cutting fluid, which plays a major role in determining friction at the tool–chip interface. The aim of the present study is to develop a finite element model based on the general-purpose nonlinear finite element code MSC.Marc by MSC.Software Corporation. This software is capable of simulating the cutting process of low-pressure turbine disks of aircraft jet engines from its very beginning to steady-state conditions. Basically, the present analysis is a coupled thermo-mechanical dynamic-transient problem, based on the update Lagrangian formulation; no pre-defined path is given for the separation of the chip from the workpiece, since material deformation occurs as a continuous indentation performed by the rigid tool. In addition to the cutting parameters, the main inputs in this analysis are material constitutive data, the friction coefficient at the toolchip interface and the cutting tool temperature. All the relevant variables, like stresses, strains, temperatures, chip shape and residual stresses, are predicted in a wide range of cutting conditions. The results from the model are compared to some basic theories of metal cutting and to an experimental study, concerning orthogonal cutting of steel AISI 316L. Concerning the specific case of turning process of nickel alloy Inconel 718 low-pressure turbine disks, the calculated residual stress are compared to experimental measurements from real machined disks.     

Measurement of residual stress in thick section composite laminates using the deep-hole method

The deep-hole method is a method of measuring residual stress in large metallic components. In this paper, an extension to the deep-hole method is described to allow the residual stresses in thick section composite laminated plates to be evaluated. The method involves first drilling a small hole through the laminate perpendicular to the surface. The material around the hole is then machined away, resulting in a change in diameter of the hole due to the release of residual stress. This change in diameter is measured and used to calculate the residual stress. The calculation requires the evaluation of coefficients that depend on the properties of the composite. In this work, the finite element method is used to evaluate these coefficients. Using this method, the residual stresses in a 22 mm thick carbon/epoxy composite plate are measured and reported.     

矫直对H型钢残余应力影响规律的研究分析

根据实测温度场的数据,模拟了H型钢H700×300的轧后冷却温度场,计算得到了冷却过程中产生的热应力分布.以冷却2400s时的热应力做为H型钢矫前的初始残余应力、引入到九辊矫直模型中,研究分析了矫直过程中型钢内残余应力的遗传演变规律.经过多辊矫直,翼缘高度方向呈抛物线状分布的初始纵向残余应力基本没有改变;腹板宽度方向大部分的初始残余应力仍然遗传到矫后,只有腹板根部的应力分布与矫前明显不同.就目前生产采用的矫直工艺参数而言,矫直过程对改善残余应力分布的效果并不明显,因此要提高产品性能,应从H型钢的轧制及冷却方面的控制入手.以保持较低水平的初始残余应力才是根本.     

GH761合金拉削残余应力研究

这里分析了GH761合金拉削时，速度、齿升量、拉刀前角对拉削表面残余应力的影响。试验结果表明，沿拉削速度方向的表面残余应力为拉应力，最大残余应力在表面层下。     

孔挤压强化和工艺参数研究

孔挤压强化可以显著提高机械连接的疲劳强度。采用有限元方法建立了孔挤压强化轴对称模型,得到了孔壁残余应力分布状态,建立了孔壁残余应力和孔径、板件厚度、挤压强化过盈量等工艺参数之间的关系曲线。结果表明,周向残余应力和孔径、挤压强化过盈量之间为对数关系,和板件厚度之间为线性关系;径向残余应力和孔径、挤压强化过盈量之间为对数关系,和板厚(以2.5mm为分界线)之间为线性关系,为孔挤压强化效果的定量化认识奠定了基础。     

Investigation of bending creep tests. Part I: Effect of residual stress

Bending creep test (based on overhang beam geometry) is investigated by incorporating the important contribution of residual stress. Finite element simulations considering the residual stress is employed to investigate the residual stress behavior of bending creep specimen. We propose several methods to determine the creep parameters directly from the bending creep tests. We considered two cases of residual stress, one is tensile residual stress. The other is compressive residual stress. The present work may shed some light on the influences during bending creep, as well as provide an efficient way to determine material residual stress characteristics.     

Application of quenching to create highly triaxial residual stresses in type 316H stainless steels

It has been proposed that highly triaxial residual stress fields may be sufficient to promote creep damage in thermally aged components, even in the absence of in-service loads. To test this proposal, it is necessary to create test specimens containing highly triaxial residual stress fields over a significant volume of the specimen. This paper presents results from an experimental and numerical study on the generation of triaxial residual stresses in stainless steel test specimens. Spray water quenching was used to generate residual stress fields in solid cylinders and spheres made from type 316H stainless steel. A series of finite element simulations and measurements were carried out to determine how process conditions and specimen dimensions influenced the resulting residual stress distributions. The results showed that highly compressive residual stresses occurred around the surfaces of the cylinders and spheres and tensile residual stresses occurred near the centre. Surface residual stresses were measured using the incremental centre hole-drilling technique, while internal residual stresses were measured using neutron diffraction. Overall there was good agreement between the predicted and measured residual stresses. The level of triaxiality was found to be very sensitive to the heat transfer coefficient, and could be controlled by adjusting the cooling conditions and changing the dimensions of the steel samples. This differed from other processes, such as welding and shot-peening, where the magnitudes and distributions of residual stresses are ill-defined and the volume of material subjected to a triaxial residual stress state is relatively small.     

Thermo-viscoelastic residual stress analysis of metal liner-inserted composite cylinders

One of the most significant problems in the processing of composite material is residual stress. The high residual stress may cause cracking in the matrix without external loads and degrade tile integrity of composite structures. In this Study, thermo-viscoelastic residual stresses occurred in an aluminum liner-inserted composite cylinder are investigated. This type of the structure is used for rocket fuselage due to the convenience to attach payloads and equipment to the metal liner by machining. The time and degree of cure dependent thermo-viscoelastic constitutive equations are developed and coupled with a thermo-chemical process model. Thee equations are solved with the finite element method to predict the residual stresses in the composite cylinder and also in the interface between the liner and file composite dining cure.     

采用马赫-曾德尔干涉法测量单晶硅在线应力损伤

开展了毫秒脉冲激光辐照单晶硅的实验研究,基于马赫-曾德尔干涉技术测量了毫秒脉冲激光与单晶硅相互作用过程中的在线应力损伤。用COMSOL Multiphysics有限元仿真软件建立了毫秒脉冲激光辐照单晶硅的数值仿真模型。从理论和实验两方面探讨了毫秒脉冲激光与单晶硅作用时,相同脉宽不同能量密度下应力场随时间的演变规律。进一步研究了干涉条纹的处理方法,基于传统x轴投影法提出了用45°投影法来计算材料各方向上的应变,并对两种处理方法得到的实验结果进行了对比。结果显示:与仿真结果相比,x轴投影法实验结果的误差为9.5%~29.3%,而45°投影法实验结果的误差为0.1%~22.6%,表明用马赫-曾德尔干涉法测量激光辐照单晶硅产生的在线应力损伤时,采用45°投影法计算材料各方向上的应变结果更为准确。该实验和计算方法为单晶硅在线应力损伤的研究提供了理论和实验上的指导。     

Effects of initial condition of steel plate on welding deformation and residual stress due to welding

The effects of initial deflection and initial residual stress in steel plate on the out-of-plane deformation and residual stress due to welding are investigated from analysis results of thermal elastic-plastic FEM modeling with large deflection theory. Initial residual stress due to plate forming has very little effects on welding deformation and welding residual stress. For initial deflection, with concave profile (Type I), welding induced deformation has the same type as initial deflection and its magnitudes are small. When initial deflection is in the direction parallel to weld Une (Type II), welding induced deformation has minor variations. When initial deflection is bended in the direction normal to weld line (Type III), welding deformation was largely generated along the width direction of the steel plate. On the other hand, the variation in type of initial deflection does not affect the residual stress and plastic strain.     

热障涂层在多次热循环作用下残余应力的模拟

采用热弹塑性有限元方法,对热障涂层多次热循环降温过程中由于热梯度和材料参数不匹配而产生的残余应力进行了数值模拟,分析了平面和曲面的界面形貌对界面残余应力的影响.结果表明,在相同材料参数情况下,陶瓷层与粘接层的界面形状对残余应力及结构稳定状态有显著的影响,凹凸不平的界面将会使界面残余应力发生突变,不利于增强界面结合强度和涂层结构的热稳定性.该结果对分析涂层寿命及失效机制有指导意义.     

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.     

Evaluation of surface characteristics of ground CVD-SiC using cast iron bond diamond wheels

The precision and efficient machining of CVD-SiC ceramic to required quality has not been well established yet. In this paper, a comparative study was conducted to investigate the special aspects in grinding of CVD-SiC ceramic, with ELID method or rotary dressing method. The stability of surface roughness, effects of material properties and dressing methods on grinding results, effects of material properties and dressing methods on surface stress state, and microscopic analysis of ground CVD ceramics by both methods were well analyzed. In addition, a wheel-workpiece interaction model was proposed for the two dressing methods.     

Formation of tangential pre-stress as a residual stress and its influence on the tribological performance of nodular cast irons

Since any state of residual stress influences the service behavior of a material, it is of particular interest for engineers and designers to know its benefits to machine parts, and where it can be utilized successfully. From this point of view, mechanical tangential pre-stress as circumferential compressive residual stress has been investigated for wear performance. For this purpose, a thick walled cylinder specimen model was established as a tribo-element, and the force, which will form the desired tangential pre-stress representing residual stress, has been calculated by the rules of elasticity theory. In order to compare the effect of residual stress on the wear performance under dry and lubricated conditions, 0.8 R_e (R_e: unidirectional yield strength) were applied to the nodular cast iron (DDK-40, DDK-60) specimens. Wear test results have been evaluated in terms of two different stress levels, 0 R_e and 0.8 R_e, formed on the specimen.     

General approach to residual stresses determination in thin-walled structures by combining the hole drilling method and reflection hologram interferometry

Main questions, which are connected with a determination of residual stresses by combining the hole-drilling method and whole-field displacement measurements, are considered in detail. The relations, which are needed for converting initial experimental data into stress values of interest, are presented for thin-walled plane structures. Required input data are obtained by simultaneous measurements of probe hole distortions in two principal strain directions on opposite sides of thin plane specimen. Emphasis is made on a careful quantitative formulation of the inverse problem, a solution of which is capable of deriving both membrane and bending residual stress components with the highest possible accuracy. It is shown that an availability of two-side initial data is both an essential and a necessary condition of such formulation. Detailed analysis of accuracy of the results obtained is performed proceeding from three different criteria. All presented considerations are supported with a set of high-quality actual interferograms and analogous reference fringe patterns related to weld-induced residual stress fields.     

残余应力与边界条件耦合作用对H型钢柱构件承载能力的影响

H型钢构件在生产过程中将不可避免的产生残余应力,而残余应力的存在将极大地影响构件的承载能力。采用盲孔法测试了大H型钢构件的残余应力分布,根据对大型H型钢构件的残余应力测试结果在有限元模型中引入不同残余应力分布和边界条件,讨论了残余应力与边界条件耦合作用对构件承载能力的影响。结果表明对于不同的边界条件和残余应力分布,H型钢柱构件的承载能力表现出不同的敏感性,该结果对H型钢结构设计具有一定的指导作用。