Morrell, R; Gant, A J; Jennett, N M (2006) Characterising surface damage in advanced technical ceramics. NPL Report. DEPC-MPE 027

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Abstract

Two aspects of characterising the surface of advanced technical ceramics have been evaluated in this work: Hertzian indentation ring-cracking and surface acoustic wave (SAW) propagation. The purpose was determine the applicability of these techniques to technical surfaces, as opposed to highly polished ones.
Hertzian ring-cracking was performed using acoustic emission to detect the development of the surface ring crack. Several problems of consistency were obtained due, it is thought, to several factors including material inhomogeneity and tendency of coarser-grained materials to microcrack. Indentation force distributions have been examined and evaluated according to the technique of Warren which allows the apparent fracture toughness to be determined. Values of toughness obtained were of the correct order, but different (possibly appropriately) to expectations for larger planar cracks.
Surface acoustic wave (SAW) propagation was used to investigate the potential for characterising the depth of damage produced by machining processes, as well as the ability to detect additional damage, such as surface cracks produced by indentation. Appropriate values for the velocity of sound and hence elastic modulus could be obtained, but pulse transmission was not as good as in polished metals, and the frequency dispersion used as a measure of surface modulus was not consistent. Additional damage produced considerable scattering, restrictions of determinable frequency range, and difficulties with interpretation.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	DEPC-MPE 027
Subjects:	Advanced Materials Advanced Materials > Powder Route Materials
Last Modified:	02 Feb 2018 13:15
URI:	http://eprintspublications.npl.co.uk/id/eprint/3453

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