基于云纹法的虚位移场力学参数表征技术研究及应用

Virtual Fields Method (VFM) is a novel characterization method of constitutive parameters based on the full-field deformation information, possessing the advantages of multi-parameters measurement, high efficiency and low cost. The available results demonstrate that the acquisition of accurate deformation field is crucial for the successful utilization of VFM, but the common used grid method and digital image correlation are difficult to satisfy the requirement, and thus an accurate full-field deformation measurement method is in urgent requirement. Moiré method, owing to its superiorities of high sensitivity and large testing area, has a great potential to offer the desired deformation information for VFM. However, the moiré grating becomes a technical bottleneck which limits the development and application of moiré method, because of the complicated fabrication process and expensive cost. Focusing on the above mentioned challenges, this project is going to establish the moiré-VFM by combine the moiré method with VFM creatively, and solving the difficulty on moiré grating through developing new grating fabrication techniques based on the soft lithography. Furthermore, in this project, we will study the principle of moiré-VFM and relative measurement techniques, establish the design and optimization technique for virtual fields, minimize the disturbance of test error on the reversed constitutive parameters, determine the optimal specimen type and loading mode, develop the process software for moiré-VFM measurement, and apply the moiré-VFM to the room/high temperature constitutive parameters characterization of the directionally-solidified superalloy and its welding zone.

虚位移场法是一种基于全场变形信息表征材料力学参数的新方法，其具有单次实验可实现多参数测量、测量效率高、实验成本低等优点。研究表明，准确的试件变形场是虚位移场法应用的关键，但目前的网格法和数字图像相关法均难以满足上述需求，迫切需要引入高精度的全场变形测量技术。云纹法测试灵敏度高，测试区域大，具有为虚位移场法提供准确变形场的巨大潜力。但在云纹法测试中，高频云纹栅的制备已成为限制其发展的技术瓶颈。本项目将研究基于云纹法的虚位移场法表征方法和测试技术（云纹虚场法），拟解决虚位移场法表征中高精度变形数据获取的难题；发展基于软压印的新型云纹栅制备和评价技术，突破云纹栅制备的技术瓶颈。研究云纹虚场法测量理论，发展虚位移场优化设计方法，抑制实验误差对参数反演的干扰，研究云纹虚场法的最优试件类型和加载方案，编制云纹虚场法数据处理软件，并应用于高温定向凝固合金及其焊接区域的常温/高温力学参数表征中。

随着光学变形场测量技术的发展，与全场变形信息相结合的材料力学参数反演方法发展迅速并成为实验力学学科的热点研究方向之一。虚位移场法作为一种结合全场变形信息进行材料力学参数反演的新方法，其对变形场的精度要求较高，但是已有的网格法和数字图像相关法等均难以满足变形场的高精度测量需求。本项目研究了基于云纹法的虚位移场表征方法(云纹虚场法)及其测试技术，解决了虚位移场法表征中高精度变形数据获取的难题。为突破高频高温云纹栅制备的技术瓶颈，结合软压印技术发展了一种新型复合模板制备工艺，实现了微米/亚微米高温试件栅的制备；建立了压印试件栅的质量评价方法，分析了转移栅的剪切滞后效应，并利用云纹干涉法表征了高频光栅在转印工艺过程中的压印畸变、压印缺陷等。此外，研制了多功能软压印制栅系统及转移栅切割仪，实现了高频高温光栅的高效快速制备。.发展了基于三点弯曲梁和圆盘对径压缩加载构型的云纹虚场法测试技术，通过仿真实验和典型实验验证了云纹虚场法的可行性及其测量精度；为分析条纹处理技术对反演结果的影响，提出了一种基于条纹场的本构参数反演方法。同时，开发了云纹虚场法和基于条纹场的反演分析软件，实现了材料力学参数的高效、高精度表征。针对各向异性金属力学参数表征需求，发展了针对单晶镍基合金材料的晶向识别云纹虚场法，其晶向角度的反演误差在0.6度以内，三个面内弹性参数的反演误差均小于1 GPa；结合高温极端环境下材料力学行为研究的需求，发展了高温采样云纹虚场法，实现了镍基合金材料在1000℃范围内的高温力学参数测量与表征。本项目结合实验、理论、计算方法，系统地研究了软压印光栅制备技术及云纹虚场法参数反演理论，在定向凝固高温合金及其焊接区域的常/高温力学参数表征中取得了重要进展和创新性成果，为高效、高精度表征材料在常/高温环境下的力学性能参数提供了新的测试方法与技术。