【作者】 李宏伟；

【导师】 杨合；

【作者基本信息】 西北工业大学 ， 材料加工工程， 2005， 硕士

【摘要】 环件冷辗扩工艺是一种先进的连续局部回转塑性成形技术,具有省力、节能、节材、高效、低成本的技术优势,在航空、航天、汽车、火车、能源等领域获得了越来越广泛的应用。材料性能及其在加工过程中的演化对环件冷辗扩工艺的影响已经成为环件冷辗扩成形理论与技术发展迫切需要研究的重要课题。为此,本文从材料宏观和细观本构关系出发,基于有限元软件ABAOUS开发了材料模型子程序,进而对环件冷辗扩工艺进行了有限元模拟研究。本文的主要研究内容和结果有以下几个方面。 采用J2塑性理论,引入等向强化系数,提出了基于弹性张量的应力补偿更新算法,提高了本构计算的精度和效率。基于此算法在ABAQUS/Explicit平台开发了混合硬化弹塑性本构子程序,从而在ABAQUS/Explicit中成功实现了材料加工硬化各向异性行为的宏观描述。 引入晶体塑性本构理论的时间增量列式,对数值计算实现的关键技术提出了合理的处理方法,采用自动修改同伦的离散型延拓算法,开发了晶体塑性本构子程序,从晶体材料冷变形位错滑移的物理本质上描述了宏观变形的细观响应。单个单元压缩成形模拟的结果验证了该本构子程序的可靠性。从而实现了在ABAQUS/Explicit中晶体材料塑性各向异性行为的细观描述。 结合所开发的本构子程序,在ABAQUS/Explicit平台上对环件冷辗扩成形进行三维有限元模拟,研究了材料参数对该成形过程的影响规律。结果表明:①等向强化系数、硬化指数和初始屈服应力的增大都使得金属流动变得困难,但变形却越来越均匀,成形件截面质量提高;同时使得辗扩力、辗扩力矩增大,从而导致环件和驱动辊打滑且越来越严重;弹性模量主要影响材料的塑性流动,其值越大塑性流动越容易。②基于虚拟正交试验获得材料参数对辗扩力和鱼尾形状系数影响的显著性由大到小顺序为:初始屈服应力、硬化指数、等向强化系数、弹性模量。这些结果为环件冷辗扩成形的选材提供了依据。更多还原

【Abstract】 Cold ring rolling is an advanced plastic forming technology with continuous revolving local deformation, which has significant advantages in labor saving, energy conservation, material saving, high efficient and low cost. The technology has received an increasing application in the fields of aerospace, automobile, train and energy etc. To consistent with the development of cold ring rolling theory and technology, the research on the effect of material properties as well as their evolution in processing on the forming technology is becoming an important issue. So this paper pays more emphasis on the study of macro-micro constitutive relations. Then user’s material subroutines were developed based on ABAQUS/Explicit platform, and further 3D-FEM simulation of cold ring rolling was fulfilled. The main achievements in this paper are as follows:J2 plastic theory was employed with isotropic hardening coefficient introduced. A stress offset updating algorithm was put forward on the basis of elasticity tensor, and the results demonstrate the improved computational accuracy and efficient of constitutive equation. Based on the algorithm, the subroutine of elastic-plastic constitutive relation with hybrid hardening was developed on ABAQUS/Explicit platform. It fulfills the macroscopic description of anisotropic behavior in strain-hardening in ABAQUS.Time incremental formulas of crystal plastic constitutive relation were employed, and optimization for the key problems as the simplifying and solving of nonlinear equations set and even the iterative initial values’ confirming was treated. Based on the homotopy auto changing discrete-type continuation method, the subroutine of crystal plastic constitutive relation was developed. It enables the description of material’s microscopic responses during macroscopic deforming process from the point of view of dislocation slip. Further the accuracy of the subroutine was evaluated by the results of single element compression simulation. Thus it expands the application of crystal microscopic plastic anisotropic property in ABAQUS/Explicit.To study the effect of material parameters on the deforming process, 3D-FEM simulation of cold ring rolling was performed on ABQUS/Explicit platform with user’s materials subroutines developed. The results show that: ①The metal flows difficultly, the material deforming becomes uniform, and the cross-section of ring becomes smooth, as well as the draught pressure and roll torque augment, associated trackslip between the ring and the driver arises and turns severer with increasing isotropic hardening coefficient, hardenability value and initial yield stress; Young’s modulus mainly affects metal’s plastic flow. The metal flows easier as Young’smodulus turns larger. (2) On the basis of virtual orthogonal test, the effect of material parameters on draught pressure and fishtail coefficient obeys the following order: initial yield stress, hardenability value, isotropic hardening coefficient and Young’s modulus. These results obtained above will provide a valuable reference for choosing ring material.更多还原