Acoustic testing on engineering materials

Dong, Yishan (2023). Acoustic testing on engineering materials. PhD thesis The Open University.



This thesis provides the findings from a project to investigate if a mechanical property of a material can be defined through an acoustic recording method which would be conducted in a non-destructive testing manner.

This project has found two successful acoustic recording methods to define viscosity in a fluid mixture, and surface roughness in a solid substrate.

The dynamic viscosity of a fluid mixture is found to be defined by a steady-state sound recording when the fluid is contained within a conical flask and is stirred by a ferrous stirring device inside the fluid mixture which is induced to spin at a set rate. The sound is processed into the Frequency Domain for assessment and resonant frequencies are observed to change in amplitude for different fluid mixtures up to a ceiling viscosity threshold, thereby enabling the classification of fluid mixture by viscosity.

The surface roughness of a solid substrate is classified through an impact sound recording when a solid nylon sphere contacts the substrate. The impact sound is processed using analysis of the decay constant which is the reduction of sound pressure level over time. It has been found that the decay constant varies in a predictable manner for aluminium substrates from 1 mm to 5 mm thickness when surface roughness is between 0.8 µm to 1.6 µm, thus facilitating material property definition through acoustic recording.

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