Abstract
Material grain size is related to metallic material properties and its elastic behaviour. Measuring and monitoring material grain size in material manufacturing and service is an important topic in measurement field. In this paper, three materials, i.e., aluminium 2014 T6, steel BS970 and copper EN1652, were chosen to represent materials with small, medium and large grain size, respectively. Various techniques of measuring material grain size were demonstrated and compared. These techniques include the measurements from material microstructure images, backscattered ultrasonic grain noise using a conventional transducer, longitudinal wave attenuation using ultrasonic arrays and shear wave attenuation using a lead zirconate titanate (PZT) plate. It is shown that the backscattered ultrasonic noise measurement and material attenuation measurement are complementary. The former is pretty good for weak scattering materials, e.g., aluminium, while the latter for materials with large grains, e.g., steel and copper. Consistent measured grain size from longitudinal and shear wave attenuations in steel and copper suggests that shear wave attenuation can be calculated from the measured longitudinal wave attenuation integrated with Stanke–Kino’s model or Weaver’s model, if there is a difficulty to either excite or capture shear waves in practice. The outcome of the paper expects to provide a further step towards the industrial uptake of these techniques.
Highlights
Material grain size has significant effect on metallic material properties and its elastic behaviour
The motivation of this paper is to demonstrate the various techniques of measuring material grain size and expect to provide a further step towards the industrial uptake of these techniques
The variability of material grain size measurement demonstrates an acceptable measurement accuracy compared with the measurements from material microstructure images
Summary
Material grain size has significant effect on metallic material properties and its elastic behaviour. Measuring and monitoring material grain size in material manufacturing and service is an important topic in measurement. Compared with the grain size measurement from either ultrasound dispersion or attenuation, that from backscatter grain noise has no requirement of parallel front-wall and back-wall surfaces and known wall thickness of a specimen. Margetan et al [10] measured the root-mean-square (RMS) of noise amplitude as a function of material microstructure, termed as the figure of merit (FOM). Ghoshal et al [13] developed a general backscattered grain noise model under multiplescattering assumption and simplified to the case for singly scattered response (SSR) [14] which is in agreement with the Margetan’s model [10].
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