Experimental Studies of Diffuse Ultrasonics and Materials Characterizations

9701142 韦弗 一 项目 是为了进一步 我们 了解线性随机波场、波 已经遭受了足够的随机散射，或者 反射，失去了大部分的连贯性。 这些领域是 在许多现代超声技术的应用中， 异质材料 拟议工作主要 关切 的 多晶扩散超声 材料，以期最终应用于 对微结构进行稳健的超声表征， 在谷物噪音中进行探伤。 主要 重点 将对超声波的验证 辐射 多重传递公式 弥漫性 多晶体中的散射 特别感兴趣的是 从简单单散射极限模型的过渡 许多人使用，通过复杂的制度， 典型的射线已经散射了几次，再一次 简单 典型射线的扩散极限 有 分散了很多次。 广泛的工业兴趣在材料表征 传统的衰减和速度测量 困难或失败，因此， 项目将有应用，包括粒度和 通过粗糙表面的纹理表征（ 关于断裂韧性的相关推论， 可成形性），检测低水平的孔隙率， 厚截面声（颗粒）噪声材料 (i.e.粉末冶金铁中的孔隙度）， 微裂纹 和微裂纹的监测 后 服务， 检测 和 监测 的 脆化 条件， 检测 的 残余 压力， 和 高度不均匀材料的表征，例如 烧结材料或金属泡沫。 虽然主要关注和设想的是， 应用于扩散超声学、这类领域 也存在于足够长的时间尺度上， 地震学，在混响室，在振动的 大型不规则的建筑结构，在电子 中尺度器件和混浊介质中的光学器件。 的 因此，预计该项目还将有助于 这些其他领域。 拟议的项目包括理论，数值， 实验 超声波方程 辐射 如有需要，转拨时间会延长。 他们将 应用于特定的实验配置， 样品 在实验室里进行研究。 的 所得 扩散超声的数值生成预测 强度将与实验室测量值进行比较 并通过二维直接数值模拟 异构 弹性 媒体 广泛 超声 具有良好控制的金属样品的浸没测试 多晶微结构将在 各种配置，旨在优化 说明和测试辐射的主要预测 转移 两个次要但相关的推力将进行 also. 一个是关于超声波在材料中的应用， 强散射微结构将有助于 对波动和运输的基本认识 具有波数量级衰减的材料。 另一个是在很晚的时候， 将研究那些可能非常敏感， 全球 性能 样品 在 这 他们 回响 预计所提出的方法将揭示 材料 不属于 否则 容易 得到了 这是一个合作项目，其中理论和 数学将主要在大学进行， 伊利诺伊州，实验将主要进行 在密苏里州的大学。

9701142 Weaver A project is to be undertaken to further our understanding of linear stochastic wave fields, waves which have suffered sufficient randomizing scatterings or reflections as to lose most coherence. Such fields are present in applications of ultrasonics in many modern heterogeneous materials. The proposed work primarily concerns the diffuse ultrasonics of polycrystalline materials with a view towards ultimate applications in robust ultrasonic characterization of microstructures and flaw detection in the midst of grain noise. The main focus will be towards the validation of ultrasonic radiative transfer formulations of multiple diffuse scattering in polycrystals. Of particular interest is the transition from the simple single scattering limit model used by many, through the complicated regime in which typical rays have scattered a few times, to the once again simple diffusion limit in which typical rays have scattered many times. Broad industrial Interest in materials characterization where conventional attenuation and velocity measurements are difficult or fail, and where therefore the proposed project will have application, includes grain size and texture characterization through rough surfaces (with associated inferences in regard to fracture toughness and formability), detection of low levels of porosity in acoustically (grain-)noisy materials with thick sections (i.e. porosity in powder metallurgical iron), detection of microcracking and monitoring of microcracking after service, detection and monitoring of embrittling conditions, detection of residual stresses, and characterization of highly inhomogeneous materials such as sintered materials or metallic foams. While the primary concern and envisioned Immediate application i s in diffuse ultrasonics, fields of this kind are also present on sufficiently long time scales In seismology, in reverberation rooms, In the vibrations of large Irregular built structures, In the electronics of mesoscale devices and for optics in turbid media. The project Is also, therefore, expected to contribute to these other fields. The proposed project consists of theory, numerics, and experiments. The equations of ultrasonic radiative transfer will be extended where necessary. They will be applied to the specific experimental configurations and samples to be studied in the lab. The resulting numerically generated predictions for diffuse ultrasonic intensity will be compared with laboratory measurements and with direct numerical simulations of two-dimensional heterogeneous elastic media. Extensive ultrasonic Immersion testing of metal samples with well controlled polycrystalline microstructures will be carried out in a variety of configurations designed to be optimal for illustrating and testing the main predictions of radiative transfer. Two secondary but related thrusts will be carried out also. One on ultrasound in materials with extremely strongly scattering microstructures will contribute to a basic understanding of fluctuations and transport in materials with attenuations of the order of wavenumbers. The other on reverberant ultrasound at very late times will study fields which are potentially very sensitive to global properties of the samples in which they reverberate. The proposed methods are expected to reveal material properties that are not otherwise easily obtained. This is a collaborative project In which the theory and numerics will be conducted primarily at the University of Illinois, and the experiments will be conducted primarily at the Uni versity of Missouri.