Fracture of Functionally Graded Materials - Modeling, Synthesis and Experiments

该项目开发了基于物理的模型，可用于预测和优化FGM的力学性能。分别用边界积分方程和有限元法对离散和连续fgm进行了分析。通过数值模拟优化组分梯度，为材料合成提供了相关输入。在合成过程中使用了一种称为现场激活燃烧合成（FACS）的新技术。采用脆性FGM系统，MOSi2/SiC，由两层组成，由层间的成分渐变界面连接。在不同的外加电场作用下，得到了不同的组成曲线。通过电子探针分析确定了Mo和Si相浓度的空间分布。不同的样品，具有不同的成分剖面在分级界面，通过仔细放置一个裂纹在成分分级层内进行测试。对裂纹面平行于和垂直于性能梯度的fgm材料的断裂行为进行了实验和数值研究。通过断裂力学实验对数值模型进行了标定。研究了在力学和热载荷作用下，成分分布函数对fgm结构性能和裂纹萌生扩展力学的影响。该研究有助于理解MoSi，)/SiC和Ti3SiC2/SiC复合材料的力学行为和最优（或接近最优）成分分布函数，特别是对FGMs的实际设计。＊＊＊

9713798 Paulino Physically based models which can be used to predict and optimize FGM mechanical performance are developed under this project. Discrete and continuous FGMs are analyzed using the boundary integral equations and the finite element methods, respectively. Optimization of the compositional gradient by means of numerical simulations provides relevant input for material synthesis. A novel technique known as Field- Activated Combustion Synthesis (FACS), is used in the synthesis process. Brittle FGM system, MOSi2/SiC, consisting of two layers joined by a compositionally graded interface sandwiched between the layers is used. With different applied electrical fields, different compositional profiles are obtained for this system. The spatial distribution of the phase concentrations of Mo and Si are determined from electron microprobe analysis. The distinct samples, with various compositional profiles at the graded interface, are tested by carefully placing a crack inside the compositionally graded.layer. The fracture behavior of FGMs with crack faces parallel and perpendicular to the property gradient are investigated both experimentally and numerically. The numerical models are calibrated by fracture mechanics experiments. The influence of compositional distribution functions on the structural behavior and the mechanics of crack initiation and propagation in FGMs under mechanical and/or thermal loads is studied. The study contributes to the understanding of mechanical behavior and optimal (or near optimal) compositional distribution functions of MoSi,)/SiC and Ti3SiC2/SiC FGMs, in particular, and to the actual design of FGMS, in general. ***