硼钢热冲压热模拟实验与损伤演化建模仿真研究

发布时间：2018-01-21 20:36

  本文关键词： 热冲压 硼钢22MnB5 热模拟 损伤 本构模型　出处：《北京科技大学》2015年博士论文　论文类型：学位论文

【摘要】：安全和环保成为当前汽车制造业的发展主题,采用超高强度钢板制造车身不仅可以减轻车身重量、降低油耗,而且可以提高车身碰撞安全性。超高强度钢板在传统冷冲压中易出现破裂、回弹等成形缺陷,而硼钢热冲压工艺可以有效地解决这些问题。硼钢热冲压工艺主要流程：加热钢板至奥氏体化温度并保温一段时间,随后板料被迅速转移到安装在快速压力机的模具上,利用配有冷却系统的模具成形后,保压一段时间,在模具中淬火获得完全马氏体组织并使零件形状尺寸趋于稳定,淬火后零件抗拉强度达到1500MPa级别。 硼钢热冲压工艺是典型的零件成形成性一体化技术,能在保证零件成形的基础上,同时提升零件性能,属于零件成形研究领域前沿。热冲压工艺中存在很多工程科学问题需要被解决：热冲压工艺对板料力学性能和微观组织的影响规律,板料加热和模具淬火过程中相变问题,板料热成形条件下高温变形行为,板料高温成形性能和成形极限,板料与模具之间的传热、摩擦行为等。本文借助热物理模拟技术摸索硼钢热冲压工艺对板料力学性能和微观组织的影响规律和板料热成形条件下高温变形行为,并重点研究硼钢热冲压成形过程中板料损伤演化、建模和模拟。 利用Gleeble热模拟实验机开展硼钢热冲压工艺影响规律热模拟实验研究。研究不同加热曲线对22MnB5高温成形性能和淬后力学性能的影响,结果表明组合式加热曲线最优；进行连续加热相变实验,建立22MnB5奥氏体化Johnson-Meh1-Avrami方程；进行热冲压工艺流程热模拟实验,探索工艺参数对22MnB5力学性能和微观组织的影响规律,获得了最优的热冲压工艺参数。实验结果将为热冲压工艺制定和工艺参数选择提供实验依据和理论指导,并揭示了热冲压工艺中22MnB5微观组织演化规律。 通过Gleeble热模拟实验机进行高温拉伸实验研究热成形条件下22MnB5高温变形行为。建立了考虑应变的Arrhenius型本构方程,该方程使用双曲正弦函数,考虑高温变形热激活过程,能够较好地描述22MnB5热变形真应力-应变关系。建立了基于位错密度的统一粘塑性本构模型,通过遗传算法优化求解模型材料常数,该模型考虑加工硬化、位错密度、应力、应变率、温度等内变量之间内在关系,能够反映22MnB5高温变形本质规律。 利用SEM观察高温拉伸试件断口附近微观组织与断口形貌,分析损伤产生和演化机理,揭示了22MnB5高温单轴拉伸损伤演化过程：夹杂颗粒剥落→微孔洞形成→微孔洞汇聚→较大的微孔洞→微裂纹形成→材料接近破坏。基于连续介质损伤力学建立耦合损伤统一粘塑性本构模型,模型可以描述高温拉伸变形中加工硬化、稳态流动、损伤破坏三段过程,实现了真应力-应变曲线陡降段预测。编写VUMAT子程序并进行单轴拉伸有限元模拟,验证模型准确性和VUMAT子程序有效性。 由热态凸模胀形试验获得22MnB5高温成形极限曲线。引入多轴损伤因子,把单轴状态耦合损伤统一粘塑性本构模型推广至平面应力状态,利用成形极限曲线数据优化求解模型参数,由所建立的平面应力状态损伤本构模型预测不同变形条件下22MnB5高温成形极限。分析了模型参数对成形极限曲线预测效果的影响。编写VUMAT子程序并进行比例拉伸有限元模拟,验证模型准确性和VUMAT子程序有效性。 采用弹性预测、塑性迭代修正应力更新算法编写耦合损伤统一粘塑性本构模型VUMAT子程序。利用开发的VUMAT子程序,进行高温单轴拉伸有限元模拟分析,利用实验数据验证了有限元计算的断裂位移和载荷-位移曲线。进行杯形热拉深试验及其有限元模拟,验证了模型对热冲压成形中破裂现象的预测效果,并摸索了工艺参数对杯形热拉深成形极限的影响。利用二次开发的有限元模拟M形截面零件热冲压成形过程,分析了M形零件成形过程的应变场、应力场、温度场和损伤分布,对比了M形零件实际厚度与有限元计算厚度。通过以上三种有限元模拟及相关验证,说明所建立的耦合损伤统一粘塑性本构模型对热冲压成形过程中损伤演化计算的准确性和破裂预测的有效性,能够把该模型运用至实际零件热冲压数值模拟过程中,以预测实际零件的成形极限并避免破裂缺陷的产生。
[Abstract]:Safety and environmental protection has become the theme of development of automobile manufacturing industry at present, using ultra high strength steel body manufacturing can not only reduce body weight, reduce fuel consumption, but also can improve the vehicle collision safety. Ultra high strength steel is easy to appear in the traditional cold stamping springback rupture, forming defects, and boron steel hot stamping process can be effectively solved these problems. The main process of boron steel hot stamping process: heating plate to the austenitizing temperature and holding time, then quickly transferred to the panel is installed in the mould fast press on the use of the mold is equipped with cooling system after forming pressure for a period of time, in the die quenching martensite and get completely the shape size tends to be stable, the tensile strength of parts reach 1500MPa level after quenching.
Boron steel hot stamping process is a typical form of parts into integration technology, can guarantee the basic parts forming, and improve the performance of the parts forming belongs to the frontier research areas. Many engineering problems need to be solved in hot stamping process: the influence of hot stamping process of sheet microstructure and mechanical properties, phase transformation the problem of sheet heating and quenching process, the deformation behavior of sheet metal under the condition of high temperature, high temperature of sheet metal formability and forming limit, the heat transfer between the blank and die, friction behavior. The heat physical simulation and influence of sheet heat exploration hot stamping process of sheet steel and mechanical properties the microstructure forming deformation behavior under high temperature conditions, and focus on the hot stamping process of boron steel plate material damage evolution, modeling and simulation.
In order to carry out hot stamping process effect of thermal simulation experiments with Gleeble thermal simulation testing machine. The effect of different heating curve of 22MnB5 high temperature formability and mechanical properties after quenching. The results show that the combined optimal heating curve; continuous heating transformation experiment, establish 22MnB5 austenitised Johnson-Meh1-Avrami equation; simulation of hot stamping process the thermal effect, explore the law of process parameters on the microstructure and mechanical properties of 22MnB5, the hot stamping process parameters. The optimal experimental results for hot stamping process and process parameters, to provide experimental basis and theoretical guidance, and reveals the evolution of microstructure in hot stamping process 22MnB5 law.
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