Experimental Studies of Diffuse Ultrasonics and Materials Characterizations

9701142 Weaver将进行一个项目，以进一步了解线性随机波场，即遭受足够的随机散射或反射而失去大部分相干性的波。这些场存在于许多现代非均质材料的超声波应用中。提出的工作主要涉及多晶材料的漫射超声，以期最终应用于微结构的鲁棒超声表征和颗粒噪声中的缺陷检测。主要的焦点将是对多晶体中多次漫射散射的超声辐射传递公式的验证。特别令人感兴趣的是从许多人使用的简单的单一散射极限模型的过渡，经过典型光线散射几次的复杂状态，再到典型光线散射多次的简单扩散极限。对材料表征的广泛工业兴趣，传统的衰减和速度测量是困难的或失败的，因此提议的项目将有应用，包括通过粗糙表面进行晶粒尺寸和纹理表征（与断裂韧性和成形性相关的推论）；检测厚截面有噪声（晶粒）的材料的低孔隙度（即粉末冶金铁中的孔隙度），检测微裂纹并监测使用后微裂纹，检测和监测脆化条件，检测残余应力，以及表征烧结材料或金属泡沫等高度不均匀材料。虽然主要关注和设想的直接应用是在漫射超声，但这类领域也存在于足够长的时间尺度上：地震学、混响室、大型不规则建筑结构的振动、中尺度设备的电子学和浑浊介质中的光学。因此，预计该项目也将对这些其他领域作出贡献。这个计划包括理论、数值和实验。在必要时，将对超声波辐射传递方程进行扩展。它们将应用于实验室中要研究的特定实验配置和样品。由此产生的漫射超声强度的数值预测将与实验室测量和二维非均质弹性介质的直接数值模拟进行比较。广泛的超声波浸泡测试金属样品具有良好控制的多晶微结构，将在各种配置中进行设计，以最佳地说明和测试辐射转移的主要预测。还将进行两次次要但相关的推力。一篇关于具有极强散射微结构的材料中的超声的论文将有助于对具有波数衰减的材料中的波动和输运有一个基本的了解。另一个关于混响超声的研究将在很晚的时间内研究对它们混响的样品的整体特性可能非常敏感的场。所提出的方法有望揭示不容易获得的材料特性。这是一个合作项目，其中理论和数值将主要在伊利诺伊大学进行，实验将主要在密苏里大学进行。

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.