连续激光热辅助增强短脉冲激光喷丸成形复合能场耦合作用机理与工艺控制研究

Laser Peen Forming uses the same technology of conventional Peen Forming process to bend and stretch metal, and then shape complex curvature of flat or integrated stiffened panels. Conventional Peen Forming is used today on many aircraft, however it has limitations primarily in the thickness of metal that can be altered by the peening effect. Laser Peen Forming, which has the ability to induce depths of compressive residual stress much deeper than that of conventional peening, with virtually no surface roughening, expands the potential of using this method on a wider range of structures. This research to be conducted is on improving the forming-limit of laser peen forming under the stress gradient mechanism by laser local warm-assisted method. With this method, two laser beams, one is short pulsed for laser peening, and the other one is continuous for heating, are integrated together in the forming process of large parts. The laser heating is used to induce the local pre-stress and decrease the strength in the plate to improve the formability. The effect of heat-induced elastic initial stress and softening on the downward bending deformation will be concerned and investigated by both experiments and numerical simulation to find the reason for the improvement of formability. Besides, dynamic strain ageing existed in the high-strain-rate plastic deformation after heating will also be analyzed by microcosmic observation after experiments. The process parameters for two laser beams including laser power density, spot size, and scanning velocity, etc, will be investigated to achieve the process optimization using the response surface method. This research will propose a new methodology for the forming of some key large parts with the precise geometry and high anti-fatigue properties. And the research outcome would also to help develop the process theory for the laser-shock based process.

面向整体壁板等大型复杂形状零件对提高喷丸成形弯曲能力的应用需求，本项目提出采用连续激光与短脉冲激光复合能场，实现激光局部热辅助增强激光喷丸成形能力的新工艺方法。针对双激光束能场复合作用特征，基于热弹塑性力学、高应变率冲击动力学、材料位错动力学理论，实验分析与数值模拟结合，重点解决双激光能场复合作用下，激光热预应力和热"软化"双重效应增强激光喷丸高应变率动态塑性变形的力学机理，阐明热动态应变时效影响激光喷丸成形能力与残余应力的物理机制，掌握激光加热工艺参数对不同条件下激光喷丸成形弯曲变形与表层残余应力场的影响规律；通过双激光束参数的协调控制，实现以金属板材高性能精确成形为目标的成形工艺参数匹配。通过本项目研究，有望显著提高激光喷丸成形中厚板的能力与效率，提高成形件抗疲劳性能，推动和完善激光复合能场制造原理与高应变率变形理论的发展，在技术上满足整体壁板等关键零部件高性能精确成形的迫切要求。

大型金属板材柔性无模成形技术，在航空航天领域有着非常广阔的应用前景与价值。由于现有高功率短脉冲激光器的单脉冲能量和重复频率的限制，通过提高单脉冲能量和重复冲击次数增加弯曲变形的方法，成本和效率难以满足工业应用需求。如何进一步增强其成形能力仍是激光喷丸成形工艺进一步发挥其应用价值的挑战。.本项目提出了采用激光局部热辅助增强激光喷丸成形能力的复合能场制造新工艺方法，显著提高激光喷丸成形能力和成形效率，为整体壁板等关键大型零部件的抗疲劳精确成形制造提供一种的新工艺途径。围绕热辅助激光喷丸成形工艺双激光束复合能场共同作用特征，从工艺方法与规律、耦合效应建模方法与工艺机理、整体壁板成形工艺方法三方面开展研究工作。完成的研究工作和结论包括：. （1）连续激光热辅助激光喷丸成形工艺方法与规律研究：研制了连续激光热辅助激光喷丸成形实验平台；揭示了水约束层作用下连续热辅助动态加热过程中温度场的稳态特性；掌握了不同激光热辅助加热功率作用下，钛合金板的弯曲变形规律及其对表面微观组织性能的影响；. （2）连续激光热辅助激光喷丸成形复合能场耦合效应建模仿真与机理：针对纳秒级别冲击压力的时空分布难以直接准确预测的难题，提出了基于激光冲击微坑几何形状特征的冲击压力模型多参数标定方法；建立了激光加热与动态冲击热力顺耦合建模方法；揭示了激光加热产生的热应力、热塑性应变、温度场对激光动态冲击过程的影响机制及其耦合增强效应；. （3）大型整体壁板激光喷丸成形工艺规律与工艺系统：针对大型整体壁板激光喷丸成形应用，建立了大型整体壁板固有应变壳单元建模方法，解决直接采用动态仿真模型计算成本巨大难以实现的问题；并以固有应变模型为基础建立条带激光喷丸成形模型，分析弯曲变形规律和条带参数优化方法；提出大型整体壁板激光喷丸成形大幅面扫描光路系统，研制大型整体壁板激光喷丸成形工艺系统。