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

部件的灾难性故障（例如在航空发动机中）残酷地暴露了现有工业能力在定量表征关键任务工程金属方面的局限性。这些金属是多晶的，具有典型的各向异性的物理和结构性质；因此，成品部件的许多重要性能，包括强度、疲劳寿命、抗蠕变和耐腐蚀性，都强烈依赖于体积晶粒微观结构，如晶粒尺寸、形状和团簇。然而，这些细节很难衡量。目前的标准做法仅限于破坏性的，牺牲样品的二维截面，这仍然是费力的，昂贵的和不准确的。超声提供了一种方便和非破坏性的方法来评估整个体积的组件的适用性。然而，它受到样品几何形状，微观结构和首选晶体取向（纹理）的复杂影响，尽管几十年的研究，缺乏模型支持的定量联系，以可靠地从超声波中提取微观结构特征。本提案旨在建立超声漫射波场（DWF）方法，以满足这种体积表征的需要。DWF基本上是微观结构的最终结果，是由波能在晶粒不均匀性边界的多次散射产生的。DWF最重要的物理特征是，在任意两个点记录的信号的相互关联提供了平均格林函数，它相当于点之间的脉冲响应，本质上携带了散射历史和关键微观结构的信息。重要的是，DWF方法对这些微观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（例如激光超声波或相控阵）来实现更灵活的模式，例如在没有物理接触的情况下进行测量，在高温下进行测量，以及在从原材料到成品部件的制造阶段进行测量。为了实现这些潜力，皮兰将开发实验手段，通过对DWF的局部检查来测量弹性动力学格林张量。该输出将利用最近一项突破性的科学进展，通过超声波速度测量体积纹理，从而使纹理对超声波的影响与微观结构分离。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非均质性相关的dwf的新物理理解。这将发展张拉弹性动力形式的多重散射和辐射传递理论的最新重大进展。pi还将联手利用帝国理工学院领先的模拟能力，对非相干漫射场的动态演化进行计算建模。这些方面的研究将相互作用，相互促进，并将在开发一种定量方法中结合起来，用于逆微观结构表征。先进的实验能力、基本的物理理解和定量反演是我们项目的目标，将使DWF方法过渡到生产线和常规的现役无损检测方案。在整个生产和服务阶段，原材料和实际部件可以连续和非破坏性地进行表征，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。材料设计、材料基因组和工艺结构-性能-性能之间的前景联系尤其令人兴奋。该提案是作为英国NDE研究中心（RCNDE）的联合项目提交的。

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).