变速下差厚板变形域分布演化机制与冲压成形性能研究

Tailor Rolled Blanks(TRB) have the characters of non-uniform thickness and mechanical properties, which leads to inhomogeneous deformation and poor formability. And then plastic forming theory and forming method for same thickness sheet metal are not suitable for TRB. In order to improve formability of Tailor Rolled Blanks, variable-speed forming according with the features of key deformation domain in each forming phase is proposed. And universality flowing law of Tailor Rolled Blanks is obtained by using macro-meso method.The detail study contents include: (1)Based on micro method a hierarchical multilevel finite element model is created to study the effect of microstructure and its evolution on plastic forming behavior of Tailor Rolled Blanks, and reveal plastic flow law of polycrystal material with inhomogeneous microstructure, and the flow ability universality laws of TRB can be obtained. (2)Meso-damage mechanics theory combined with crystal plasticity finite element to analyze the micro defect growth and macro crack formation, reveal ductile damage mechanism, create the fracture criteria suitable for different strain paths, and the formability universality laws of TRB can be obtained.(3)Macro-Micro research methods are used to analyze effect of variable speed mode on distribution evolution of deformation domain and plastic flow, so the forming mechanism of TRB in variable speed forming can be revealed and then the general law for improving formability obtained.

差厚板厚度和材料性能的非均一性降低其冲压成形性能，基于单一厚度板构建的成形理论和成形技术不再适用于差厚板的成形。项目拟通过适合每一变形阶段关键变形域变形特点的变速成形来提高差厚板的整体成形性能；宏-细观耦合的研究方法建立非均一性板料普适性流动规律。主要研究内容为:（1）应用晶体塑性理论建立分层递阶多晶体塑性本构有限元模型，研究微结构及其演化对差厚板塑性行为的影响规律，揭示微观不均匀板料的塑性流动行为，建立差厚板流动性能的普适性规律;（2）引入细观损伤力学理论和晶体塑性有限元相结合的研究方法，分析差厚板内部微缺陷发展直至宏观裂纹产生的内在原因，揭示差厚板韧性损伤机理，建立适合不同应变路径的破裂准则，获得差厚板成形性能的普适性规律;（3）运用宏细观耦合的研究方法，分析变速对差厚板变形域分布演化和塑性流动的影响规律，揭示变速成形提高差厚板成形性能的作用机理，获得提高差厚板整体成形性能的一般规律。

轧制差厚板几何截面形状和力学性能的非均一性，降低了其冲压成形性能，且传统等厚板的成形理论和成形技术不再适用于差厚板的成形。本项目从微观和细观角度研究非均一性板材的塑性变形行为和韧性断裂机理，建立了晶体塑性本构有限元模型和韧性断裂准则，获得了差厚板塑性流动普适性规律和成形极限预测的普适性规律。在此基础上采用塑性理论、有限元数值模拟和实验研究相结合的方法，研究了变速成形影响变形域分布及其演化的规律，获得变速成形提高差厚板成形性能的一般规律。首先应用宏-细观耦合的研究方法，应用晶体塑性理论建立多晶体塑性本构有限元模型，研究微结构影响差厚板塑性变形行为的规律，结果表明差厚板等厚区晶粒大小分布均匀，且存在有利于滑移系开动的{111}<0-11>和{876}<-2-25>织构，而过渡区的组织均匀性差且存在不利于滑移系滑动的晶体取向。因此，差厚板塑性变形呈现非均匀性变形的特点，随着变形程度增加，板材薄区的应力集中和应变区域向过渡区转移，减薄或破裂等成形缺陷在薄区或薄区和过渡区的交界处产生，降低了差厚板的成形性能。为了表征差厚板的成形性能，进一步应用细观损伤力学理论建立了GTN细观损伤模型,研究结果表明，塑性应变首先在屈服强度低的板料一侧产生，当孔洞体积分数快速增加时，塑性应变向另一厚度区扩展，导致该厚度区应力集中，引起裂纹首先在屈服强度低的厚度区域产生和扩展，并逐渐向另一厚度区延伸。在上述研究成果基础上，采用有限元数值模拟技术和拉深工艺实验进一步研究了成形速度及速度模式对变形域分布及演化的影响规律，获得了变速提高差厚板成形性能的工艺设置规律。本项目的研究成果为今后采用变速方法，解决非等厚板和复杂零件的成形奠定了理论基础。