Experimental Studies of Diffuse Ultrasonics and Materials Characterizations

9701142 Weaver将开展一个项目，以加深我们对线性随机波场的理解，线性随机波场是指遭受了足够的随机散射或反射而失去最大相干性的波。这些领域存在于超声波在许多现代非均质材料中的应用中。建议的工作主要涉及多晶材料的扩散超声波，以期最终应用于颗粒噪声中微结构的稳健超声表征和缺陷检测。主要的焦点将放在多晶体中多次扩散散射的超声辐射传输公式的验证上。特别有趣的是，从许多人使用的简单的单次散射极限模型，过渡到典型射线多次散射的复杂区域，到典型射线多次散射的再次简单的扩散极限。在常规衰减和速度测量困难或失败的情况下，工业上对材料表征的广泛兴趣，因此建议的项目将适用，包括通过粗糙表面的晶粒度和纹理表征(以及关于断裂韧性和成形性的相关推论)，检测具有厚截面的声音(颗粒)噪声材料中的低水平孔隙率(即粉末冶金铁中的孔隙率)，检测微裂纹和监测服役后的微裂纹，检测和监测脆化条件，检测残余应力，以及高度不均匀材料的表征，如烧结材料或金属泡沫。虽然S主要关注并设想立即在扩散超声波中应用，但在地震学、混响室、大型不规则建筑物的振动、中尺度设备的电子学和混浊介质中的光学中，这类场也存在于足够长的时间尺度上。因此，预计该项目也将为这些其他领域做出贡献。所提出的方案包括理论、数值和实验。必要时，将对超声辐射传输方程进行推广。它们将应用于特定的实验配置和待在实验室研究的样本。由此产生的弥散超声强度的数值预测将与实验室测量和二维非均匀弹性介质的直接数值模拟进行比较。对具有良好控制的多晶微结构的金属样品进行广泛的超声波浸没测试，将以各种配置进行，旨在最佳地说明和测试辐射传输的主要预测。还将进行两次但相关的推力。一个关于具有极强散射微结构的材料中的超声波的研究将有助于对具有波数量级衰减的材料中的涨落和输运的基本理解。另一项关于非常晚的混响超声波的研究，将研究对混响样本的全局性质可能非常敏感的领域。所提出的方法有望揭示以其他方式不易获得的材料特性。这是一个合作项目，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州大学进行。

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.