题目：Texture determination from ultrasound for HCP and cubic materials　

　　报告人：兰波博士

　　        帝国理工学院

　　时间：2015年8月26日（周三），下午13:30

　　地点：李薰楼468会议室

　　Abstract:

Crystallographic texture in polycrystalline HCP and cubic materials has profound effects on properties at the macroscopic or component level. This research aims to develop a non-destructive, three-dimensional bulk texture detection method for these materials through systematic studies on the relationship between ultrasonic wave velocity and texture.

The feasibility of such development is firstly demonstrated via the combination of computational and experimental studies on exemplary HCP materials, where numerical and experimental results reveal that the wave speed varies progressively and significantly with changing texture. Then, a novel convolution theorem is presented, which couples the single crystal wave speed (the kernel function) with polycrystal orientation distribution function to give the resultant polycrystal wave speed function. Firstly developed on HCP and then successfully extended to general anisotropic materials, the theorem expresses the three functions as harmonic expansions, thus enabling the calculation of any one of them when the other two are known. Hence, the forward problem of determination of polycrystal wave speed is solved for all crystal systems with verifications on varying textures showing near-perfect representation of the sensitivity of wave speed to texture as well as quantitative predictions of polycrystal wave speed. More importantly, the theorem also presents a solution to the long-standing inverse problem for HCP and cubic materials, with proof of principle established where groups of HCP and cubic textures are recovered solely from polycrystal wave velocities through the theorem and the results show good agreements with the original textures. Therefore the theorem opens up the possibility of developing a powerful technique for bulk texture measurement and wave propagation studies in HCP, cubic materials and beyond.

　　兰波博士简介：

　　帝国理工学院博士后研究员，本科毕业于上海交通大学机械工程学专业，硕士毕业于清华大学机械工程学专业，博士毕业于牛津大学工程学专业。博士期间主要研究六方紧密堆积型金属（如钛、锆、镁及其合金）和立方晶系金属（如铁、铜、铝等），其宏观力学性能与微观晶向分布（织构）之间的关系，并致力于开发一种利用超声波来实现对这些金属内部的三维织构进行无损检测的技术，从而实现立体织构检测的实验室化或者工业化。目前技术的开发已经完成理论建模和仿真的验证，其结果非常良好，现正进行实验验证和器材的开发。

　　博士期间研究课题：Heterogeneous behaviours of Industrial Hexagonal Materials，是一个集结了英国牛津大学、帝国理工学院、曼彻斯特大学等大学和 Rolls-Royce、Westinghouse和Timet等大型工业公司的综合性研究课题。

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