An improved measurement of Vickers indentation behaviour through enhanced instrumentation

Abstract

This work presents an enhanced instrumented Vickers indentation technique capable of recording force, displacement and acoustic emission (AE) during loading condition. Four materials were chosen for examination; copper, aluminium, steel and as-sprayed HVOF WC-12%Co coating. Results indicate that force-displacement (P-h) profiles are essentially bilinear with two characteristic slopes separated by a distinct displacement arrest for all loads above 98 N. The P-h curve indicates three distinct loading stages (I, II and III) and the stage III mechanical energy increases with loads. About 66% of the hardened steel indentations but only about 18% of the as-sprayed HVOF WC-12%Co coating indentations exhibited an AE record that could be separated into three distinct zones (A, B and C). Where zoning was possible the AE corresponding to a zone correlated well with the AE associated with a loading stage. It is concluded that plastic deformation in soft metals produced little AE, whereas brittle fracture in hardened steel and as-sprayed HVOF WC-12%Co coating produced significant AE. AE may or may not be focused onto particular stages of the indentation and a full measure of crack prevalence would require fractal dimension analysis, which is time consuming, offering a motivation for AE-based indentation testing.

An improved Vickers indentation fracture toughness model to assess the quality of thermally sprayed coatings

“…In the coating materials investigated, accommodation is by crumbling of the surface to the extent that cracking cannot be entirely identified by metallographic means [8][9][10][11][12]27]. As expected in brittle thermally sprayed coating materials [8][9][10][11][12]27], material accommodation such as 'sinking-in' can be identified for all coatings.…”

“…in cermets (all three WC-Co coatings), to fracture with little or no plastic deformation in ceramics (both Al 2 O 3 coatings). In preparation for the indentation tests, specimens surface were ground and polished using diamond paste to avoid any effect of polishing which was expected to be broadly similar for all coated specimens [8][9][10][11][12][27][28][29].…”

“…The empirical models tend to be based on an idealised cracking pattern and do not account for other cracks around indentations. Previously, authors investigated an acoustic emission (AE) based non-destructive technique of characterising the indentation fracture pattern in thermally sprayed coatings with a view to quantitatively evaluate WC-Co coatings [8] and Al 2 O 3 coatings [9][10] quality, indentation loading stages based on the AE criteria [11], and AE based analysis of fracture toughness of various cermet and ceramic coatings [12]. However, in this paper the work has been to establish a non-AE based working mathematical (empirical) model, which is based on measurable total surface crack and total surface crack length but excluding total radial cracks (i.e.…”

Stress analysis at the interface of metal-to-metal adhesively bonded joints subjected to 4-point bending: Finite element method

“…in deflection based flexural investigation). These stress analysis findings can be incorporated in manufacturing adhesive joint specimens with desired properties and developing experimental framework under fully instrumented mechanical testing procedures [21][22] (e.g. acoustic emission, displacement and force transducer based 4-point bending, indentation or impact testing).…”

Influence of test methodology and probe geometry on nanoscale fatigue failure of diamond-like carbon film

“…shows the corresponding post-test AFM images and topography mapping of these impacts. In general, the characterization of the material was done by the size of the impression and/or by the cracking pattern left on the surface upon retraction [33][34].…”