A new method for assessing the mean grain size of polycrystalline materials using ultrasonic NDE

We re-analyze published data on ultrasonic inspection of a number of pure metals and alloys involving a range of mean grain sizes (from 0.0125 mm to 0.3 mm). We show that they may be described by one master curve graph consisting mainly of two distinct but parallel linear segments. This means that our presentation clusters the data under study into two distinct groups, each chracterized by its own generalized material constant. The slope of the segments suggests the predominance of scattering other than Rayleigh's, since it is consistent with the second power law rather than the fourth. We argue that the attenuation is likely to be due to multiple scattering, particularly since our generalized material constants seem to be similar to the published stochastic scattering factors. The master curve graph suggests a new fast and simple method for assessing the mean grain size which may be carried out without recourse to standard specimens or measurements other than those routinely carried out during ultrasonic inspection. As the range of materials and grain sizes are in extensive use in industry the simple schedule proposed should prove of substantial use in practical material evaluation and production process control.