第三代先进高强度镀锌钢板冲压成形动态摩擦与表面损伤模型研究

The third generation advanced high strength galvanized steel with high comprehensive mechanical properties has a vast application prospect in the field of automobile stamping parts with complex shape and high strength. However, the influence of the high strength and galvanized layer, complex changes in the friction on sheet metal and model die surface because of higher forming force that are susceptible to damage, and the damage mechanism which has not yet been fully elucidated, make the prediction precision of sheet deformation and surface damage still unreliable at present. The study is carried out to investigate dynamic friction mechanism and surface damage of ultra-thin zinc layer in the application of the typically third generation advanced high strength galvanized steel -QP980 at present. The rule of interface damage evolution and interface friction under the conditions of various stamping process parameters is revealed. The establishment of dynamic friction model under multi-factor coupling is used to improve the accuracy and surface quality of stamping parts. The deformation behavior of galvanized layer under the complex loading path is investigated based on strain gradient plasticity theories in micro scales. A contact model of sheet metal and model die surface on the basis of fractal theory is realized. And combined with the calculation of frictional power in the contact area on the dynamic friction model, a surface damage model is developed to achieve dynamic prediction of interface damage. The successes of the study have important scientific significance on developing the theory in stamping and enriching tribology for plastic working.

第三代先进高强度镀锌钢板具有高综合力学性能，在外形复杂、强度高的汽车冲压件上有广阔应用前景。但由于受高强度和镀锌层的影响，成形力大导致板料和模具表面间摩擦变化复杂，易产生损伤，其损伤机理尚未得到充分揭示，使得目前对板料变形和表面损伤的预测精度还较低。项目拟研究目前典型的第三代先进高强度镀锌钢板-QP980冲压成形过程中的动态摩擦机理及摩擦过程中超薄镀锌层与模具表面接触所产生的损伤问题，旨在揭示冲压成形工艺参数对摩擦的影响及表面损伤的变化规律，构建多因素耦合的动态摩擦模型，提高冲压成形精度和产品表面质量。项目将采用应变梯度塑性理论从微尺度研究镀锌层在复杂加载路径下的变形行为，在此基础上采用分形理论构建板料与模具表面的分形接触模型，结合动态摩擦模型计算冲压过程中的接触摩擦功，以此建立表面损伤模型，实现表面损伤的动态预测。项目的成功研究，对于发展冲压成形理论、丰富塑性加工摩擦学具有重要科学意义。

先进高强度镀锌钢板因具有强度高、材质轻、耐腐蚀性等优良的综合性能，已成为现代汽车覆盖件的主要材料之一。然而，在较大成形力下镀层会出现开裂、粉化等损伤行为，冲压摩擦会因此变得更加复杂。镀层的力学特性对先进高强度镀锌钢板冲压成形与摩擦影响的研究已成为改善其成形质量的关键性问题。项目通过拉伸实验对先进高强度镀锌钢板镀层的力学特性及其变形行为进行了研究，基于纳米压痕实验构建了微尺度下镀锌层的材料本构模型，并通过引入粘附层构建了镀锌钢板基体和镀锌层之间的界面结合模型。通过销-盘实验研究了镀锌层、载荷、滑动速度、行程、摩擦副粗糙度和硬度对摩擦系数的影响规律，以此提高镀锌钢板的数值模拟精度。基于划痕实验和内聚力模型构建了镀层的损伤模型，并且结合界面结合能对镀锌钢板冲压成形过程镀层的损伤现象实现了动态预测。项目最后以杯突拉深成形零件为模型，对先进高强度镀锌钢板进行了有限元数值模拟，考虑镀锌层的材料模型、界面结合能、摩擦因素和内聚力模型，将界面结合能应用到内聚力单元模型中，模拟镀层与基体分离状态，并与实验结果进行了对比。结果表明，本研究项目提高了先进高强度镀锌钢板冲压成形的数值模拟精度。该项目的研究成果对于发展先进高强度镀锌钢板冲压成形理论、摩擦学及其镀锌层损伤预测具有重要科学意义和实践意义。