Computational modelling of hardness and soft impresser testing of materials.

Hu, J, 2005. Computational modelling of hardness and soft impresser testing of materials. PhD, Nottingham Trent University.

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Abstract

Hardness testing is a traditional, widely used experimental method to evaluate material properties. Recent years have seen significant improvements in indentation equipment and a growing need to measure the mechanical properties of materials at small scales. Much research work has been carried out in this area using experimental methods. Until recently, it has not been possible to model in detail the deformation behaviour around an indentation, and phenomenologically based simplified models have been used. These have been very successful in some respects, but have distinct limitations. Commercial Finite Element software packages, and hardware technology, have been developed within the last several years to now be able to model the indentation process, which combines non-linear geometric behaviour and non-linear material models with contact analysis, in a reasonable time. Since it is a very complicated modelling problem, there are a number of issues that remain unresolved and which require further investigation. In the present study, the initial research concentrated upon evaluating different commercially available FE software programs to determine their suitability with regard to modelling indentation. ABAQUS was identified as the most appropriate software. Thereafter, the geometry, mesh, contact and loading conditions were investigated to establish the appropriate parameters to enable reliable results to be obtained. It was found that the hardness values were relatively robust with regard to the details of the FE model, particularly mesh and contact conditions, but the detailed parameters, such as local deformations and stresses could be very sensitive. The established parameters were then used in the modelling of indentation in a ceramic (single crystal MgO), in a multilayered coating system (A1 and TiB2 on a steel substrate), and indentation creep in a Yttria stabilized cubic Zirconia and MgO.

The soft impresser test involves placing a 'sharp' cone in contact with a flat substrate and applying a load sufficient to cause the cone to plastically deform to conform to the surface of the substrate. Its main advantage with regard to the diamond pyramid indentation test is that it induces far less plastic deformation into the substrate, which renders the analysis less problematical, and it can be used to apply repeated loads at one position. A parallel study was thus undertaken to model soft impresser testing by establishing the appropriate parameters and applying the results to analyse soft impresser testing of Ceria stabilised Zirconia, including repeated loading (fatigue) and sliding.

Item Type:	Thesis
Creators:	Hu, J.
Date:	2005
ISBN:	9781369316438
Identifiers:	Number Type PQ10183442 Other
Divisions:	Schools > School of Architecture, Design and the Built Environment
Record created by:	Jeremy Silvester
Date Added:	25 Sep 2020 14:24
Last Modified:	08 Sep 2023 12:47
URI:	https://irep.ntu.ac.uk/id/eprint/40952

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