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Title: Computational modelling of hardness and soft impresser testing of materials
Author: Hu, Jinhua
ISNI:       0000 0001 3583 0889
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2005
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Hardness testing is a traditional, widely used experimental method to evaluate material properties. Reeent 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 phenomenologieally 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 fuifher 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 fiat 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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available