基于EBSD技术构建弹性各向异性粗晶材料超声仿真模型的研究

Research on Modeling of Ultrasonic Propagation in Anisotropic Coarse-grained Materials Based on EBSD Technique

针对弹性各向异性粗晶材料晶粒结构和取向定量描述困难,导致超声检测仿真结果与试验符合程度较差的问题,提出基于电子背散射衍射(Electron back-scatter diffraction,EBSD)技术确定晶粒形态及晶体取向的建模思路。利用EBSD技术实测得到了尺寸为96 mm×12 mm的离心铸造奥氏体不锈钢(Centrifugally cast austenitic stainless steel,CCASS)轴-径向截面的晶体取向图谱,选择15°取向相(差)角定义EBSD图谱的晶粒结构,并对晶体取向进行归一化处理。在此基础上借助Bond变换法赋以晶粒在对应晶体取向下的刚度矩阵,对模型中晶粒的弹性特征进行量化表征,建立CCASS超声检测模型。采用时域有限差分法进行数值计算,结果表明:利用该方法能够较好地重现CCASS超声检测特有的结构噪声和主频降低等现象,为揭示超声波在弹性各向异性粗晶结构中的散射机理提供了解决思路。

Due o the difficulty of the accurate description of thegrain structure and orientation, discrepancy occurs between the ultrasonic inspection simulation and experimental results for anisotropic coarse-grained materials. A modeling method based onelectron backscattered diffraction （EBSD） technique is proposed to quantitative describe the grain structure and orientation. A 96 mm×12 mm crystal orientation map for the radial-axial cross section of a centrifugally cast austenitic stainless steel （CCASS） specimen is acquired using the EBSD technique. A15° misorientation angle is selected for the grain “orientation unification”. The bond transformation is used to determine the stiffness matrix of the grains with different orientations in the model, thus realizing quantitative description of the complex elastic characteristics. A CCASS ultrasonic inspection model is built and numerically calculated by finite difference time domain method. The simulation results of CCASS ultrasonic testing reproduced typical structural noise and decrease of central frequency quite well. The modeling method provides effective solution to reveal the mechanism of ultrasonic scattering in the anisotropic coarse-grained structure.