残余应力作用下的航空整体结构件加工变形仿真

铝合金预拉伸板在成型过程中会产生较大的残余应力,在切削过程中毛坯的初始残余应力的释放对整体结构件的宏观变形有重要的影响。在弹塑性力学的基础上,综合运用Hypermesh和ABAQUS建立残余应力单因素作用下的三维铣削仿真加工变形场的有限元模型,利用生死单元技术模拟了材料的去除,分析了铝合金板材材料去除过程中残余应力释放引起的加工变形规律。并且运用Hypermesh提高了有限元前处理的速度,解决了复杂模型的残余应力加载困难与单元去除困难的问题。     

残余应力对加工变形的影响规律

为了研究材料去除过程中残余应力所引起的加工变形,采用试验测量和有限元模拟方法对含有已知残余应力情况的矩形板加工的变形规律进行了研究.试验与仿真结果表明,实测变形规律与有限元解获得极好的吻合,从而为提出减小变形的技术措施奠定了基础.     

航空结构件残余应力释放引起加工变形的数值模拟

航空铝合金结构件毛坯在成形过程中产生很大的残余应力,使其在后续机械加工过程中极易发生翘曲变形,采用有限元数值模拟技术,建立了航空铝合金板材残余应力释放引起加工变形的力学模型,分析了在7075T7351铝合金板材材料去除过程中残余应力释放引起的加工变形规律,并针对7075T7351隔框零件进行铣削加工变形实验研究,并与有限元模拟结果进行比较,验证了数值模拟结果具有较高的精确度。     

切削中残余应力释放对工件加工变形影响研究

为了研究加工过程中毛坯初始残余应力的释放对加工变形的影响,在弹塑性理论的基础上,建立了三维铣削仿真加工变形场的有限元分析模型,利用位移约束转换和"单元生死"技术仿真了加工过程中工件装夹和材料的去除。通过仿真数据与实验数据相比较,结果表明:工件毛坯残余应力在铣削加工过程中对称释放有利于减小工件加工后变形。     

残余应力重分布引起的结构件铣削变形研究

航空铝合金结构件毛坯在成形过程中产生很大的残余应力,使得其在后续机械加工过程中极易发生翘曲变形,这已经成为国防武器快速开发和高效加工的瓶颈.采用有限元数值模拟技术,建立了航空铝合金板材残余应力释放引起加工变形的力学模型,分析了在7050T7451铝合金板材材料去除过程中残余应力释放引起的加工变形规律,并针对7050T7451隔框零件进行铣削加工变形实验研究,并与有限元模拟结果进行比较,验证了数值模拟结果具有较高的精确度.     

航空薄壁结构件铣削加工变形数值模拟分析

针对广泛应用于航空航天制造业中的整体薄壁结构件刚性差、易产生加工变形,从而难以保证其加工品质的问题,基于金属切削原理的物理仿真,采用Production Module 3D仿真软件对工件的加工变形进行数值模拟,并与相同条件下的试验数据进行了对比验证,仿真结果与试验数据基本相符.在验证了仿真模型的有效性前提下,研究了走刀路径、切削用量和刀具结构参数对薄壁零件加工变形的影响,获得了其加工变形的规律.所做研究为通过改善加工工艺、优化切削参数和优选刀具来控制加工变形提供了理论依据.     

弱刚度结构件切削加工残余应力的研究

弱刚度结构件具有刚度差和材料去除量大等特点,加工过程中产生的残余应力容易导致其加工变形,尤其对于精度要求高且厚度不均匀的弱刚度结构件,更有必要研究切削加工残余应力的影响因素,从而为控制弱刚度结构件的加工变形提供基础。根据正交切削理论和热弹塑性有限元理论建立了切削加工的三维有限元模型,对材料为40CrNiMo的变厚度弱刚度结构件进行了切削加工模拟,对切削过程中的残余应力进行了有限元计算。通过对比不同切削参数情况下残余应力的分布,得到了残余应力随切削参数的变化规律;将变厚度弱刚度结构件的加工分为二次等厚度的切削加工,通过与一次加工得到的残余应力进行对比,得到了2种不同加工工序对变厚度弱刚度结构件的残余应力影响规律。     

航空薄壁结构件数控加工变形控制研究

数控加工中影响工件变形的因素很多,目前国内外的研究多采用数值模拟技术分析加工的不同侧面。相对已经 比较成熟的数控加工几何仿真系统,涉及力学模型的物理仿真系统还只有初步概念。选择航空弧形结构件和长梁两种 典型易变形的零件为例,通过具体分析加工变形情况及其影响因素,针对其中三个方面:切削力、装夹布局和残余应力建 立相应的物理仿真模型,模拟加工变形情况,并提出相应的解决方案。     

面向加工变形控制的航空整体结构件拓扑优化设计方法

在毛坯制造过程中,材料力学性能的非均匀性导致铝合金厚板内产生残余应力,以致在后续的高速切削加工过程中,随着材料的大量去除,残余应力的释放使得整体结构件发生变形,严重影响着整体结构件的尺寸稳定性。当初始残余应力水平及状态一定时,随着从毛坯上去除材料切削成形为不同的零件结构,零件变形会表现出不同的形式。因此,研究零件变形与零件结构形式之间的关系对于实现加工过程的高效化和精密化至关重要。首先,通过铝厚板的材料去除等效为残余应力的释放,利用弯曲变形理论建立铝厚板厚度方向上加工变形的解析分析模型及有限元分析模型。通过航空企业现场加工、测试零件后可知：加工变形的解析值、仿真值与测量值相比,无论是幅值水平还是变形曲线,解析值与仿真值完全吻合,而两者与实验值之间仅存在不到10%的幅值误差。其次,为了使得加工变形达到最小,构建以结构体积为约束的拓扑优化设计模型,通过利用一系列凸显式子问题逼近目标和约束函数,构建拓扑优化模型的MMA求解技术。最后利用所提出的优化方法计算出C919直梁件的结构,优化前、后的加工变形分别为22.02 mm与0.7414 mm,在相同的材料去除量情况下,通过优化结构可以使得加工变形减小96.63%。     

关于初始残余应力对薄壁回转件加工变形的影响探究

近年来,伴随着我国综合实力的提升,航空工业发展随之也得到了不错的发展。由于飞机与人们的出行安全有着密切的联系,所以,在现代化社会中人们逐渐提高了对飞机性能的要求。薄壁件作为飞机制造的元素之一,虽然薄壁件自身的优势能给飞机制造带来诸多好处,但不可否认的是,其在加工的过程中仍会受到残余应力等因素影响导致变形。基于此,加大对初始残余应力对薄壁回转件加工变形造成的影响研究极为迫切。     

薄壁铝合金结构焊接应力变形数值模拟

实际结构焊接过程的三维数值模拟因为计算量大而往往难以进行。为了采用三维热弹塑性有限元方法对薄 壁铝合金结构的焊接过程进行数值模拟,提出了粘贴单元和混和单元两种网格划分技术相结合的单元划分方案进 行有限元建模,通过薄板对接模型试验验证了此方案的可行性,并研究了不同建模方案对计算效率的影响。将这 种单元划分方案应用到实际薄壁筒体结构焊接过程的数值模拟中,对焊接过程产生的残余应力和变形进行了成功 地预测。结果表明:对于薄壁构件,采用粘贴单元和混合单元相结合的单元划分方案可以在保证一定精度的前提 下,可大大减少有限元网格划分工作量,同时可降低计算规模,提高计算效率。     

Finite element modeling of residual stresses in machining induced by cutting using a tool with finite edge radius

A thermal elastic-viscoplastic finite element model is used to evaluate the residual stresses remaining in a machined component. An improvement in the accuracy of the predicted residual stresses is obtained by: (a) using a modified Johnson–Cook material model that is augmented by a linearly elastic component to describe the material behavior as non-Newtonian fluid; (b) using a remeshing scheme to simulate the material flow in the vicinity of the rounded cutting tool edge without the use of a separation criterion; (c) properly accounting for the unloading path, and (d) considering the thermomechanical coupling effect on deformation. Case studies are performed to study the influence of sequential cuts, cutting conditions, etc., on the residual stresses induced by orthogonal machining.     

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.     

A new stress-based model of friction behavior in machining and its significant impact on residual stresses computed by finite element method

Friction modeling in metal cutting has been recognized as one of the most important and challenging tasks facing researchers engaged in modeling of machining operations. To address this issue from the perspective of predicting machining induced residual stresses, a new stress-based polynomial model of friction behavior in machining is proposed. The feasibility of this methodology is demonstrated by performing finite element analyses. A sensitivity study is performed by comparing the cutting force and residual stress predicted based on this new model with those based on a model using an average coefficient of friction deduced from cutting forces and a model using an average coefficient of friction deduced from stresses. The average coefficient of friction computed based on the measured cutting forces is the conventional approach and is still widely used. The average coefficient of friction due to stresses can be considered as a simplified version of the proposed model. Simulation results show significant difference among the predicted residual stresses. As the proposed model is able to capture the relationship between the normal stress and shear stress on the tool rake face better than the conventional approach can, it has a potential for improving the quality of the prediction of the residual stresses induced by machining.     

Computer simulation and experimental study of machining deflection due to original residual stress of aerospace thin-walled parts

Aerospace thin-walled parts have a complex structure and high accuracy. Factors such as original residual stress, fixing, and machining may make low-rigidity parts deform easily, which is difficult for traditional craftwork to forecast and control. Especially in machining big aerospace parts, original residual stress has a great effect on machining deflection. In this paper finite element model of original residual stress is established to analyze the corresponding deflection by machining aerospace thin-walled parts. Simulation results are validated consistent with experimental results approximately. At last the paper puts forward the corresponding mend methods to control the deflection caused by original residual stress during the actual machining process.     

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.     

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。     

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.