The Use of Acoustic Emission to Characterize Fracture Behavior During Vickers Indentation of HVOF Thermally Sprayed WC-Co Coatings |
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Authors: | N H Faisal J A Steel R Ahmed R L Reuben |
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Affiliation: | (1) Department Mechanical Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK; |
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Abstract: | This paper describes how acoustic emission (AE) measurements can be used to supplement the mechanical information available
from an indentation test. It examines the extent to which AE data can be used to replace time-consuming surface crack measurement
data for the assessment of fracture toughness of brittle materials. AE is known to be sensitive to fracture events and so
it was expected that features derived from the AE data may provide information on the processes (microscale and macroscale
fracture events and densification) occurring during indentation. AE data were acquired during indentation tests on samples
of a WC-12%Co coating of nominal thickness 300 μm at a variety of indentation loads. The raw AE signals were reduced to three
stages and three features per stage, giving nine possible indicators per indentation. Each indicator was compared with the
crack profile, measured both conventionally and using a profiling method which gives the total surface crack length around
the indent. A selection of the indents was also sectioned in order to make some observations on the subsurface damage. It
has been found that reproducible AE signals are generated during indentation involving three distinct stages, associated,
respectively, with nonradial cracking, commencement of radial cracking, and continued descent of the indenter. It has been
shown that AE can give at least as good a measure of cracking processes during indentation as is possible using crack measurement
after indentation. |
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