基于损伤力学的锤锻模疲劳断裂分析及再制造工艺研究

发布时间：2018-09-13 10:47

【摘要】：锤锻模是热锻模的一个重要分支,能够通过较小吨位的锤锻设备加工出难以成型的复杂结构件。服役过程中除了受到普通热锻模机械及热的双重负荷,还要承受锻锤的高频次冲击载荷,因此相较于普通热锻模更容易出现底角疲劳断裂、磨损、塑性变形等失效。本文特别针对该类锤锻模极为严重的底角疲劳断裂问题,以某超超临界汽轮机叶片用锤锻模为研究对象;从连续介质损伤力学、断裂力学入手,对模具材料内部损伤的演化、裂纹的扩展,直至失效的过程进行深入研究并实现了有限元模拟;同时结合力学性能、断口分析等常规手段对疲劳断裂失效问题进行了系统的分析。本文提出了基于不同失效模式的梯度堆焊再制造工艺方法,并最终运用于该汽轮机叶片用锤锻模的再制造生产实践中。本文主要展开了以下方面的研究:(1)锤锻模服役状态分析采用金属塑性成型有限元方法对本文的研究对象-某汽轮机叶片用锤锻模的应力、应变、温度、磨损等服役状态进行了模拟分析,为后续疲劳断裂失效分析及再制造该类锤锻模提供支持;同时从减少锤锻模应力的角度出发,对模具的设计及使用工艺方法做了一些改进。(2)循环塑性损伤本构模型的建立及有限元实现针对锤锻模服役过程中容易引起材料劣化并出现内部宏观裂纹的问题。运用连续介质损伤力学(CDM)建立了一个循环塑性损伤本构模型,借助ABAQUS中UMAT子程序将该模型程式化,实现了有限元模拟。引入实验获得的5Cr Ni Mo相关材料参数,完成了试样拉伸过程的损伤演化模拟。从疲劳累积损伤角度对循环载荷条件下服役的锤锻模内部损伤的演化以及宏观裂纹的产生情况进行了预测分析,并获得了一些关于材料损伤演化的结论。(3)锤锻模疲劳断裂分析针对锤锻模在服役过程中出现的底角疲劳断裂问题。本文通过在连续介质力学的大框架内,从损伤力学开始再延伸到断裂力学的方法,来对循环载荷下的锤锻模疲劳断裂全过程加以研究;并结合材料力学性能、微观结构、断口分析等分析方法实现了对该类问题更为系统的分析。获得了裂纹扩展过程中的裂纹三维形貌、尖端应力场、应力强度因子、剩余寿命,模具材料力学性能、微观组织结构、断口情况等结果,进而分析出该锤锻模型腔底角疲劳裂纹形成及扩展的机理。(4)锤锻模再制造工艺的研究介绍了双金属梯度堆焊再制造热锻模工艺方法,并针对双金属梯度堆焊制造热锻模工艺方法难以同时解决锤锻模易出现的疲劳断裂、疲劳磨损、塑性变形等典型失效问题,特别是疲劳断裂问题。分析了该方法存在的局限性,针对性的提出了基于不同失效模式的梯度堆焊再制造工艺方法,给出了解决疲劳断裂失效等问题的对策。(5)某汽轮机叶片用锤锻模的再制造应用将提出的基于不同失效模式的梯度堆焊再制造工艺方法应用于某汽轮机叶片用锤锻模的再制造中。基于获得的锤锻模服役状态、失效分析、寿命预测信息,分析了锤锻模不同区域的堆焊材料需求;结合微观组织、力学性能等基础性实验,针对性的设计了三种焊材及其组合,优化的焊材分布方案;完成了对该锤锻模的再制造工作。经生产验证,该再制造锤锻模与原新制锤锻模相比较,成本降低了约1/2(含首次再制造设计费用),周期缩短了约2/3,寿命提升了约100%。
[Abstract]:The hammer forging die is an important branch of the hot forging die, which can be processed by the hammer forging equipment with smaller tonnage into complex structural parts which are difficult to form. In this paper, aiming at the extremely serious bottom angle fatigue fracture problem of this kind of hammer forging die, the hammer forging die for a certain ultra-supercritical steam turbine blade is taken as the research object, and the evolution of internal damage, crack propagation and failure process of the die material are studied from the continuum damage mechanics and fracture mechanics. The finite element simulation is studied and realized, and the fatigue fracture failure problem is analyzed systematically by combining mechanical properties and fracture analysis. A gradient surfacing remanufacturing process based on different failure modes is proposed and applied to the remanufacturing practice of hammer forging die for turbine blade. The following aspects are studied: (1) The service state analysis of the hammer forging die is carried out by using the metal plastic forming finite element method. The stress, strain, temperature and wear of the hammer forging die for a steam turbine blade are simulated and analyzed. From the point of reducing the stress of the hammer forging die, some improvements have been made in the design and application of the die. (2) Establishment of cyclic plastic damage constitutive model and Realization of finite element method. A series of cyclic plastic damage constitutive models are formulated by means of UMAT subroutine in ABAQUS, and finite element simulation is realized. The damage evolution of the specimen during tensile process is simulated by introducing the experimental 5Cr Ni Mo related material parameters. The damage evolution of hammer forging dies serving under cyclic loading is studied from the point of view of fatigue cumulative damage. (3) Fatigue fracture analysis of hammer forging dies aims at the problem of fatigue fracture at the bottom angle of the hammer forging dies in service. This paper extends from damage mechanics to fracture mechanics within the framework of continuum mechanics. The whole process of fatigue fracture of hammer forging dies under cyclic loading was studied by using the method of mechanical properties, microstructure and fracture analysis. The mechanism of fatigue crack formation and propagation in the bottom corner of the hammer forging die was analyzed by the results of mechanical properties, microstructure and fracture of the material. (4) The technology of bimetal gradient surfacing and remanufacturing hot forging die was introduced, and the technology of bimetal gradient surfacing was difficult to be used in manufacturing hot forging die. Some typical failure problems such as fatigue fracture, fatigue wear and plastic deformation, especially fatigue fracture, which are easy to occur in hammer forging dies, are solved. The limitations of this method are analyzed, and a gradient surfacing remanufacturing process based on different failure modes is proposed. The countermeasures to solve the problems such as fatigue fracture failure are given. (5) A steam The remanufacturing application of hammer forging die for turbine blade will apply the gradient surfacing remanufacturing process based on different failure modes to the remanufacturing of hammer forging die for turbine blade. Three kinds of welding materials and their combinations were designed to optimize the distribution of welding materials. The remanufacturing of the hammer forging die was completed. Compared with the original hammer forging die, the cost of the remanufacturing hammer forging die was reduced by about 1/2 (including the design cost of the first remanufacturing), and the period was shortened by about 2%. /3, lifespan has increased by about 100%.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG315.3

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