叠层功能梯度材料细观损伤演化机理实验研究

Due to the lack of experimental results in meso-scale, the damage evolution mechanism of functionally graded materials (FGMs) is still unclear, and the optimization design as well as effective fabrication of FGMs is affected. On the basis of former preparation and performance measurement,the evolution of meso-damage of layered FGMs under mechanical/thermo-mechanical load will be studied by experiments following the outline of preparation technique, meso-structure and macro-properties in this project. The initiation and the evolution of meso-damage of FGMs, such as debonding of particles, fractured particles, slip bands, the initiation and the growth of micro-cracks, will be in-situ measured. Digital image correlation measurement under scanning electron microscope will be improved. The strain field around the macro-cracks' tip will be in-situ measured and the mechanical parameters will then be obtained. The strain field of different micro-zone corresponding to different material's gradation,the path and velocity of micro crack growth will be in-situ measured. The evolution mechanism of meso-damage of FGMs, the effect of microstructure and gradation on the fatigue performance of micro-crack, and the intrinsic relationship between macro- and meso- damage mechanism will be investigated. The research results can be used to analyze and to modify the corresponding theoretical and simulated results. The results of this project will improve the experimental method of meso-mechanics, promote understanding the mechanism of meso-damage, and provide reference for optimizing the design and the performance evaluation of FGMs.

由于细观尺度下实验成果的缺乏，目前我们对功能梯度材料（FGMs）的损伤演化机理尚不十分清楚，影响了材料的优化设计和有效制备。本项目在前期材料制备和宏观性能测试的基础上，围绕制备工艺、细观结构及其演化和宏观性能这一主线，针对叠层功能梯度材料在力/热-力作用下的细观损伤演化开展实验研究，包括：材料细观损伤萌生和演化的原位观测，如，颗粒脱粘、颗粒开裂、滑移带、裂纹的形成与扩展等；扫描电镜下数字图像相关方法的改进；宏观裂纹尖端应变场的原位测量和力学参量的提取；细观尺度下不同梯度微区域应变场、微裂纹扩展路径和扩展速率的原位测量，探讨FGMs的细观损伤演化机理，细观结构和材料梯度对微裂纹疲劳特性的影响，以及宏细观损伤断裂机理的内禀关联机制，分析修正相关理论和数值模拟结果。研究成果将改进细观力学的实验表征方法、加深对FGMs细观损伤机理的认识，同时为FGMs的优化设计以及性能评价提供参考。

功能梯度材料的损伤演化机理对于其设计、制备和应用具有重要的指导意义，但在这方面开展的实验研究工作还比较少。本项目研究团队围绕叠层功能梯度材料的细观损伤演化机理，开展了细观损伤原位测试方法、功能梯度材料宏细观损伤断裂和应用于功能梯度材料损伤断裂测试的三维实时数字全息测量方法等研究工作。提出了平均灰度二阶导数这一新的散斑图质量评价参数，将数字图像相关方法与扫描电子显微镜相结合，实现了对颗粒增强复合材料的微区变形场的定量测量；应用DIC方法测量了Cu/WC复合材料和叠层功能梯度材料在高温下的断裂韧性，得到了断裂韧性指标随材料成分、结构及温度的变化规律；开展了Cu/WC复合材料和叠层功能梯度材料的宏观裂纹扩展行为研究，结合实验、数值模拟和SEM观测等手段，给出了材料细观结构、梯度组成对裂纹扩展行为的影响机制；开展了Cu/WC复合材料在力/热-力耦合作用下的原位SEM疲劳实验，研究了该材料在力/热-力耦合作用下的损伤机理；研究了Cu/WC均质复合材料和叠层材料的动态压缩力学性能，分析了其微观损伤机制；提出了基于最小二乘、迭代和相位梯度校正的相位解包裹算法，构建了基于彩色数字全息的三维变形测量系统，为功能梯度材料的损伤断裂研究提供了一种新的方法。本项目完成了计划书规定的研究任务，实现了预期目标，对功能梯度材料的设计、制备和应用具有重要的学术价值和指导意义。