基于细观损伤理论的高强铝板成形性能研究

The deformation and instability of high-strength aluminum alloy sheet is different from ordinary metal sheet, and the influence of micro-cracks and pores development on the macroscopic mechanical properties of sheet metal are neglected in the classical plastic mechanics about tensile instability and defect theory. The forming properties under warm forming and heat treating cannot be analyzed by the above theory. So the technical problem of rupture instability and spring-back precise prediction in the warm forming and aging process urgent need to be solved. Based on above, this project in combination with the forming characteristics to carry out the following research: (1) To accurately describe the development rule of the coupling between elastic-plastic anisotropic and damage, the constitutive model of GTN meso-damage of elastic-plastic anisotropy with mixed hardening rule is established. (2) The prediction model of finite element simulation of forming limit is established. The cumulative damage caused by loading history is introduced into the forming limit analysis, and the forming limit criterion of damage evolution related to nonlinear strain path is proposed. (3) With mixed hardening characteristics and damage evolution, the simulation model of spring-back prediction of high-strength aluminum alloy sheet warm forming and heat treating is established, and the influence mechanism of spring-back of the residual stress and damage distribution is revealed. This study will provide theoretical and experimental supports for the development and application of high-strength aluminum alloy forming technology.

高强铝板变形和失稳行为异于普通金属板料，经典的塑性力学拉伸失稳理论和缺陷理论忽略了变形材料内部微裂纹和孔洞发展变化对板料宏观力学性质的影响，难以指导高强铝板在温热变形和热处理条件下的成形性能分析，破裂失稳和回弹变形的精确预判仍然是高强铝板温热成形和后继时效过程中亟待解决技术难题。基于此，本项目结合高强铝板成形技术特征开展以下研究：(1)建立遵循混合强化准则的弹塑性各向异性GTN细观损伤本构模型，准确描述板材的弹塑性各向异性行为和损伤耦合发展的规律；(2)建立基于GTN损伤模型的高强铝板有限元仿真成形极限预测模型，将加载历史导致的损伤累积效应引入成形极限分析，提出与非线性应变路径相关的损伤演化成形极限判据；(3)建立考虑混合强化特性和损伤演化的高强铝板成形及热处理全过程的回弹预测仿真模型，揭示残余应力和损伤分布对板材回弹的影响机理。本项研究将为高强铝板成形技术的开发和应用提供理论和试验支持。

高强铝板变形和失稳行为异于普通金属板料，经典的塑性力学拉伸失稳理论和缺陷理论忽略了变形材料内部微裂纹和孔洞发展变化对板料宏观力学性质的影响，难以指导高强铝板在复杂工艺条件下的成形性能分析与评判，破裂失稳和回弹变形的精确预判仍然是亟待解决技术难题。本项目结合高强铝板成形技术特征，基于细观损伤理论构建本构模型，探索了伴随损伤演化和累积的板壳弹塑性变形、断裂失稳和回弹机理，构建了板材各向异性屈服准则与细观损伤本构耦合的力学建模思路和技术实施框架，并开展了深入的研究。.以可热处理强化6系和7系高强铝板作为研究对象，基于Yld2000各向异性屈服准则和GTN损伤模型的研究，提出将平均应力三轴度与GTN损伤形核孔洞体积分数关系函数引入Yld2000-GTN模型，构建了与应力状态相关的Yld2000-GTN模型仿真平台，并绘制了高强铝板仿真成形极限图；建立了基于BP神经网络+遗传算法的韧性断裂准则判定策略及技术路线；开发了适用于多种工需条件的高强铝板低温形变热处理工艺路线和优化策略，揭示了固溶水淬、自然时效、人工时效等工艺步骤参数对成形性能影响的机理机制及控制策略，拓宽了高强铝板制备复杂构件的工艺窗口；建立了基于非线性弹性行为本构关系应变驱动的变弹性模量理论模型和仿真平台，有效提升了对高强铝板件扭转弯曲成形的回弹预测精度。本项目研究产生了20余篇学术论文和发明专利成果，衍生了3项国家级、省级科研项目，培养了10余名博士、硕士研究生。项目组应用本项开发的技术成果和相关经验成功解决了难成形、高精度航空高强合金板件橡皮囊胀形工艺的技术难题，以及大批量、高可靠性要求的民用薄板液压胀形球形制件工艺技术及配套产线的稳健性研发，为高强、轻质板材构件的应用领域的拓展提供了理论支撑和实践经验。