激光冲击波诱导轻质合金的多尺度塑性变形效应研究

For the requirements of high fatigue performance and high accuracy of assembly on the critical area of aeronautical light alloy (titanium alloy and aluminum alloy), a common problem-multi-scale plastic deformation effects was extracted on the processes of laser shock peening (LSP) and laser peen forming (LPF). In this project, spall strength, spall mechanism and spall threshold value, and spall prevention mechanism of thin-walled samples induced by laser shock were studied through Photon Doppler Velocimetry (PDV), ultrasonic non-destructive evaluation and scanning electron microscope. Simulated blade samples were designed to approximate a typical leading edge of blades. And then the control of macro and micro-plastic deformations of simulated blade samples with LSP and anti-foreign object damage fatigue extension life mechanism were studied by advanced measurement methods. Further, inherent relevance between laser process parameters, surface morphology, compressive residual stress and microstructure, and fatigue life was built to achieve the online nondestructive quality detection of blades with LSP. Moreover, the orthogonal experiment designing method was used to study the forming rules and forming mechanism of plates with LPF in order to build the inherent relevance between laser process parameters, curvature radius, plate thickness, and compressive residual stress distribution. Finally, on the basis of continuous shell element, equivalently numerical model of plates with LPF was established by the equivalent carrier of bending moment and stretching force. Research results are very important to improve the performance analysis and evaluation criterion of aviation key structures, reliability and safety of engine and wing structures.

针对航空轻质合金（钛和铝合金）关键区域的高疲劳性能和高配合精度需求，本项目提炼强化/成形的共性问题-多尺度塑性变形效应，采用光子多普勒测速技术、超声波无损检测技术和扫描电镜，研究激光冲击薄壁件的层裂强度、层裂机理和层裂阈值及其防层裂机理；设计截面形状近似叶片前缘的叶片模拟件，采用先进测试分析方法，研究激光冲击强化叶片模拟件的宏微观塑性变形调控和抗异物损伤疲劳延寿机理，建立激光工艺参数-表面形貌-残余压应力和微观组织-疲劳寿命的内在关联性，实现激光冲击强化叶片的在线无损质量检测；采用正交试验设计，研究激光喷丸成形板料的成形规律和成形机理，建立激光工艺参数-曲率半径-板厚-残余压应力的内在关联性；基于连续壳单元，以弯矩和延伸力为等效载体，构建激光喷丸成形板料的等效数值模型；本项目研究对完善航空关键结构的性能分析和评价标准、提高发动机和机翼结构的可靠性和安全性具有重要工程意义。

铝合金、钛合金等轻质合金是航空航天结构广泛使用的结构材料，本项目针对航空轻质合金（钛和铝合金）关键区域的高疲劳性能和高配合精度需求，提炼强化/成形的共性问题——多尺度塑性变形效应，形成“激光冲击波诱导轻质合金的多尺度塑性变形效应研究”研究课题。. 项目主要研究内容分三个方面，一是激光冲击薄壁件的层裂阈值和防层裂机理研究，二是激光冲击强化叶片模拟件的宏微观塑性变形调控和疲劳延寿机理研究，三是激光喷丸成形壁板材料的成形规律和成形机理研究。激光冲击薄壁件的层裂阈值和防层裂机理研究方面，通过激光冲击薄壁件的层裂阈值和防层裂机理研究，实现了薄壁结构激光冲击强化防层裂工艺实施。基于冲击波在材料中传播反射规律分析，通过在叶片（或薄壁铝合金壁板）背面粘贴铝箔胶带和喷水方式形成多层吸波层材料，可以有效避免叶片激光冲击强化产生的层裂。激光冲击强化诱导的残余压应力能够使部件实际应力比减小或疲劳裂纹尖端应力强度因子幅值下降，从而使得疲劳裂纹扩展速率降低。激光冲击强化诱导TC17合金强化层的晶格缺陷（位错、孪晶和纳米晶）在疲劳性能改善中起到重要作用。研究成果还形成《有色金属零件激光冲击强化技术》的中国航空工业集团公司标准，该标准用于指导飞机机身框梁结构、发动机钛合金整体结构的激光冲击强化，是航空制造领域抗疲劳关键技术，对飞行器目标寿命和安全性提升具有重要意义。