CMMI-EPSRC: Quantitative Characterization of Mission Critical Microstructures of Engineering Metals with Diffusive Ultrasound

部件（例如航空发动机）的灾难性故障残酷地暴露了现有工业能力的局限性，以定量表征关键任务工程金属。这些金属是多晶的，其微晶的物理和结构特性通常是各向异性的;因此，成品部件的许多重要特性，包括强度、疲劳寿命、抗蠕变性和耐腐蚀性，强烈地依赖于体积晶粒微观结构，例如晶粒尺寸、形状和簇。然而，这些细节很难衡量。目前的标准实践仅限于牺牲样品的破坏性二维切片，这仍然是费力的、昂贵的和不准确的。超声波提供了一种可访问和非破坏性的方式来评估整个体积中组件的适用性。然而，它受到复杂的影响，从样品的几何形状，微观结构和优选的晶体取向（纹理），尽管几十年的研究，缺乏模型支持的定量联系，可靠地从超声波提取的微观结构特征，本建议旨在建立超声扩散波场（XDD）的方法，以满足这种体积表征的需要。从根本上说，微结构的最终结果是由波能在晶粒不均匀性边界处的多次散射产生的。最重要的物理特征是，在两个任意点处记录的信号的互相关提供平均绿色函数，其等效于点之间的脉冲响应，并且本质上携带散射历史和临界微结构的信息。重要的是，该方法对这些微结构的灵敏度不受复杂样品几何形状的限制;因此，它可以充分利用最先进的设备，（例如激光超声或相控阵），用于更灵活的模式，例如在高温下以及在从原材料到成品部件的制造阶段进行无物理接触测量。为了实现这些潜力，皮兰将开发实验手段来测量弹性动力学绿色张量从局部检查的岩石。输出将利用最近的颠覆性科学进展来测量超声波速度的体积纹理，这使得纹理对超声波的影响与微观结构解耦。与此同时，PI Kube将开发理论模型，以揭示与现代金属合金中微观结构异质性相关的DWFs的新物理理解。这将发展最近的重大进展的多次散射和辐射传输理论的张量弹性动力学形式。PI还将联合力量在非相干扩散场的动态演变的计算建模，利用领先的模拟能力在帝国。这些方面的研究将相互作用，相互促进，并将结合在一个定量方法的发展，逆微观结构表征。先进的实验能力，基本的物理理解和定量反演，这是我们的项目的目标，将允许的反渗透方法过渡到生产线和常规的在役无损检测协议。原材料和真实的组件可以在整个生产和服务阶段进行连续和非破坏性的表征，以减少破坏性测试，降低制造浪费，最重要的是，确保性能和安全性。与材料设计、材料基因组和工艺-结构-性能-性能的潜在联系尤其令人兴奋。该提案是作为英国无损检测研究中心（RCNDE）的一个联合项目提交的。

Catastrophic failures of components (e.g. in aero engines) brutally expose the limitations of the existing industrial capability to quantitatively characterize mission-critical engineering metals. These metals are polycrystalline, with physical and structural properties of the crystallites typically anisotropic; thus, many vital properties of the finished components, including strength, fatigue life, and creep and corrosion resistance, are strongly dependent on the volumetric grain microstructures, such as the grain size, shape and clusters. Yet these details are very difficult to measure. Current standard practice is restricted to destructive, two-dimensional sections of sacrificial samples, which remains laborious, costly and inaccurate. Ultrasound provides an accessible and non-destructive way to evaluate the fitness-for-service of components throughout the volume. However, it is subject to convoluted effects from sample geometries, microstructures and preferred crystallographic orientations (texture) and, despite decades of research, there lacks model-supported quantitative linkages to extract the microstructural characteristics reliably from ultrasound.This proposal seeks to establish the ultrasonic diffuse wave field (DWF) method to fulfil the need for such volumetric characterization. The DWF is fundamentally an end-result of the microstructures, created by multiple scattering of wave energy at the boundaries of grain inhomogeneities. The most important physical feature of the DWF is that a cross-correlation of the signals recorded at two arbitrary points delivers the mean Green's function, which is equivalent to the impulse response between the points, and intrinsically carries information of the scattering history and the critical microstructures. Importantly, the DWF method's sensitivity to these microstructures is not limited by complex sample geometries; therefore, it could take full advantages of state-of-the-art equipment (e.g. laser ultrasound or phased arrays) for more flexible modalities, e.g. measuring without physical contact, at elevated temperatures, and at manufacturing stages from raw material to finished components.To realise these potentials, PI Lan will develop the experimental means to measure the elastodynamic Green's tensor from localised inspections of the DWF. The output will capitalise on a recent disruptive scientific progress to measure volumetric texture from ultrasonic wave speeds, which enables the effects of texture on ultrasound to be de-coupled from microstructures. Meanwhile, PI Kube will develop theoretical models to uncover new physical understanding of the DWFs in relation to microstructural heterogeneities seen in modern metallic alloys. This will develop recent major advances on multiple scattering and radiative transfer theories for the tensorial elastodynamic form. The PIs will also join forces in computational modelling of the dynamic evolution of the incoherent diffuse field, utilising the leading simulation capabilities at Imperial. These aspects of research will interact with and facilitate each other, and will all be combined in the development of a quantitative methodology for inverse microstructure characterization. The advanced experimental capability, fundamental physical understanding, and quantitative inversion, which are targeted by our project, will allow the DWF method to transit into manufacturing lines and routine in-service non-destructive testing protocols. Raw materials and real components could be continuously and non-destructively characterized throughout the production and service stages, to reduce destructive testing, lower manufacturing waste, and, most importantly, to assure performance and safety. The prospective connections to materials-by-design, materials genome, and process-structure-property-performance are especially exciting. The proposal is submitted as an Aligned Project of of the UK Research Centre in NDE (RCNDE).