先进高强钢板损伤断裂行为的多尺度研究及其非二次型各向异性细观损伤模型

Advanced high-strength steel (AHSS) is an important material for automotive weight reduction. Its fracture failure is difficult to predict, and it brings severe challenges to the design of the forming process. Deformation experiments under conditions of different stress triaxiality and strain rate will be carried out to study the rupture behavior of AHSS sheets, analyze the microstructure evolution characteristics in the deformation, explore the evolution process of voids and its relationship with deformation, damage and fracture, reveal macroscopic and microscopic mechanism of fracture failure of AHSS sheet. In view of low accuracy of the quadratic isotropy constitutive model describing AHSS sheet deformation, based on the experimental study and representative volume element (RVE) model, the plastic potential function of non-quadratic anisotropic porous model will be deduced. The void evolution equation will be introduced to establish a macro-microscopic coupled ductile damage fracture model, and the in-situ tensile and uniaxial tensile tests will be used to determine the model parameters. The key technologies for integrating the model and the finite element method will be solved and the typical forming process and rupture behavior of AHSS will be studied. This project aims to develop the macroscopic and microscopic damage fracture theory model of AHSS sheet, providing a theoretical basis for the accurate prediction of fractures in AHSS sheet forming.

先进高强钢（AHSS）是汽车轻量化的重要材料，其破裂失效难以预测，给成形工艺设计带来严峻挑战。本项目开展不同应力三轴度与应变率等条件下的变形实验，研究AHSS板材的破裂行为，分析变形中微观组织演化特征，探索孔洞演化过程及其与变形、损伤和断裂的关系，揭示AHSS板材断裂失效的宏微观机理。鉴于二次型各向同性本构模型描述AHSS板材变形行为精度低的问题，在实验研究基础上，基于代表体积元（RVE）模型，推导非二次型各向异性多孔介质塑性势函数，进而引入孔洞演化方程，建立宏微观耦合型韧性损伤断裂模型，结合原位拉伸、单向拉伸试验确定模型参数。解决所建模型与有限元集成的关键技术，对AHSS典型成形工艺过程及破裂行为进行模拟。本项目旨在发展AHSS板材宏微观结合的损伤断裂理论模型，为AHSS板材成形中断裂的准确预测提供理论依据。

通过对双轴加载试验机结构优化，以及数字图像相关算法（Digital Image Correlation ，DIC）研究，建立了单拉、双拉以及板材成形试验机与DIC测量技术无缝结合的试验系统，采用纯剪切、单向拉伸、平面应变以及双向拉伸试验，获得了较大应力三轴度范围内超高强钢板的等效断裂应变，获得了可靠的试验数据。.基于弹塑性力学基本理论推导零应变转角与应变形态角之间的关系，建立了基于应变形态角演化的失稳判据；在此基础上提出了一种基于相对漂移因子准则的板材成形极限确定方法，实现了采用单一应力三轴度试验即可获得整条成形极限曲线。.提出了变n值的Hollomon-Var流动应力模型，利用ABAQUS平台开发了基于Hollomon-nVP的二次开发子程序；.基于修正的混合物模型，推导了宏观损伤变量和细观损伤变量的演化模型，建立了宏-细观损伤演化的跨尺度联系，结合先进高强钢细观RVE模型，建立了基于颈缩损伤的成形极限图。.提出了基于破裂时应变形态角演化的破裂判据，确定了分别采用标准单拉试验和等双拉试验快速预测FLC的单拉区和双拉区极限应变值的方法。.基于RVE模型推导了非二次各向异性基体多孔介质塑性势函数，考虑空洞演化过程，建立了宏微观耦合型韧性损伤断裂模型，并通过编制用户自定义材料模型程序（VUMAT）引入有限元模型框架并进行了试验验证，建立了基于实际材料微观结构的RVE数值模型，通过宏观有限元分析和RVE数值模拟相结合，针对先进高强钢成形过程中的成形极限进行了多尺度分析和预测。为AHSS 板材成形中断裂的准确预测提供理论依据。

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