Department of Mechanical Engineering, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom.
Department of Mechanical Engineering, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom.
Ultrasonics. 2021 Aug;115:106441. doi: 10.1016/j.ultras.2021.106441. Epub 2021 Apr 15.
Industrial inspection protocols are qualified using mock-ups manufactured according to the same procedure as the plant part. For coarse-grained castings, known for their low inspectability, relying on mock-ups becomes particularly challenging owing to the variability of grain properties among components. Consequently, there is a keen interest in the capability to verify whether the grain size of the component under test matches the qualification specification in-situ. This paper investigates the potential of an attenuation measurement for assessing the ultrasonic inspectability of coarse-grained components using qualified procedures in a practical setting. The experimental part of the study focuses on an industrial Inconel 600 mock-up with spatially varying attenuation, measured across the entire sample in an immersion tank. Three zones with distinctly different attenuations were examined using metallography, which allowed for calculating classical grain size histograms and two-point correlation functions. For one of the zones, we synthesised the microstructure with the same statistical properties numerically and simulated the propagation of ultrasound using a grain-scale finite element model. The results showed good agreement with the experiment, and lead to several suggestions for the reasons for the discrepancy, the varying grain size statistics being the most likely. A parametric study, which followed, depicted the effect of the mean and standard deviation-to-mean ratio of the log-normal grain size distribution on the attenuation of ultrasound and its frequency dependence. Most notably, we demonstrated the known non-uniqueness of the relationship between the log-normal grain size distribution parameters and the attenuation. We suggested that the correlation length calculated from a single exponential fit to the two-point correlation function is a more robust metric describing grain statistics for this context, which can be obtained from attenuation. The correlation lengths estimated from measured attenuation using the second-order approximation model for the three zones of the studied mock-up yielded results of acceptable accuracy. We concluded that this metric could replace the average grain size in practical settings, as it retains more statistical information than the mean grain size and allows for linking measurements to the established theoretical attenuation models which this paper demonstrates.
工业检测规程是通过按照与工厂部件相同的程序制造的模拟件来进行合格性评估的。对于晶粒较粗的铸件，由于其可检测性较低，因此依赖模拟件尤其具有挑战性，这是因为组件之间的晶粒特性存在差异。因此，人们非常关注是否能够在现场验证被测部件的晶粒尺寸是否符合资格规范。本文研究了在实际环境中使用合格程序评估晶粒较粗部件的超声可检测性的衰减测量的潜力。研究的实验部分侧重于一个具有空间变化衰减的工业 Inconel 600 模拟件，该模拟件在浸入式罐中跨整个样本进行测量。使用金相学检查了三个具有明显不同衰减的区域，这允许计算经典的晶粒尺寸直方图和两点相关函数。对于其中一个区域，我们使用数值方法合成了具有相同统计特性的微观结构，并使用晶粒级有限元模型模拟了超声波的传播。结果与实验吻合较好，并导致对差异原因的一些建议，其中变化的晶粒尺寸统计是最有可能的。随后进行的参数研究描绘了对数正态晶粒尺寸分布的平均值和标准差与平均值之比对超声波衰减及其频率依赖性的影响。值得注意的是，我们证明了对数正态晶粒尺寸分布参数与衰减之间关系的非唯一性。我们建议，从两点相关函数的单个指数拟合中计算出的相关长度是一种更稳健的度量标准，用于描述该背景下的晶粒统计信息，并且可以从衰减中获得。使用研究模拟件的三个区域的二阶近似模型测量衰减后，估计出的相关长度结果具有可接受的准确性。我们得出结论，该度量标准可以替代实际环境中的平均晶粒尺寸，因为它保留了比平均晶粒尺寸更多的统计信息，并允许将测量结果与本文所展示的已建立的理论衰减模型联系起来。
