Instrumented indentation testing is a technique widely used in different materials to evaluate the penetration depth in function of the indenter load. Considering Berkovich indenter, this methodology has been used to determine mechanical properties such as hardness, Young modulus and a stress versus strain curve of the elastic-plastic behaviour under compression of the tested materials. However, the implementation of this technique to evaluate mechanical properties and also its results have still brought doubts on research areas. Nowadays, the use of a numerical methodology able to evaluate the stress and strain fields during indentation cycle can lead to a more secure interpretation. The aim of this work was to simulate the Berkovich indentation testing and to propose a methodology to extract the stress-strain curve through experimental and numerical analyses. The obtained numerical results for the load-displacement curve were quite similar to the experimental curve presented in the literature.
This paper describes a numerical simulation and experimental study of the Vickers indentation testing of WC-6Co specimens. The numerical analysis was implemented by a three-dimensional finite element (FE) model using the commercial solver MARC ™ . Hardness values predicted by this model agreed well with those obtained experimentally. It was also observed that the load-displacement curves obtained numerically were quite similar to those presented by the literature for the Vickers testing. The maximum principal stress field was used to locate the most expected areas for crack formation and propagation during the Vickers indentation testing of WC-6Co.
In recent decades, changes in the surface properties of materials have been used to improve their tribology characteristics. However, this improvement depends on the process, treatment time and, essentially, the thickness of this surface film layer. Physical vapor deposition (PVD) has been used to increase the surface hardness of metallic materials. The aim of the present study was to propose a numerical-experimental method to assess the thickness (l) of films deposited by PVD. To reach this objective, Vickers experimental hardness data (H V ) assays were combined with numerical simulation to study the behavior of this property as a function of maximum penetration depth of the indenter (h max ) into the film/substrate conjugate. A strategy was developed to combine the numerical results of the H x h max /l curve with Vickers experimental hardness data (H V ). This methodology was applied to a TiNcoated M2 tool steel conjugate. The mechanical properties of the studied materials were also determined. The thickness results calculated for this conjugate were compatible with their experimental data.
RESUMOO objetivo principal do presente trabalho foi simular através de modelos de elementos finitos o ciclo do ensaio de indentação com penetradores esféricos em um sistema composto de recobrimento superficial fino depositado em um substrato metálico. Recentes trabalhos propõem a utilização dos ensaios de indentação (nanoindentação) como uma ferramenta capaz de avaliar características mecânicas de filmes finos, assim como avaliar possíveis falhas em sistemas que conjugam recobrimentos de alta dureza (recobrimentos tribológicos) com substratos metálicos de aço em serviço, em solicitações tribológicas. Entretanto, a implementação da técnica de indentação para a avaliação do comportamento destes sistemas e os seus resultados obtidos ocasionam dúvidas no meio científico. Em função destas incertezas na análise do ensaio de indentação, o uso de uma metodologia numérica capaz de avaliar os campos de tensões e de deformações durante o ciclo de indentação pode auxiliar em uma interpretação mais segura deste ensaio. Todavia, a utilização da metodologia numérica para avaliar o ensaio de indentação em recobrimentos superficiais finos também tem apresentado problemas principalmente devido à dificuldade na implementação de critérios de falhas, especialmente na avaliação do comportamento da interface entre o recobrimento e o substrato. Finalmente, para estudar os mecanismos de nucleação e crescimento de trincas que ocorrem nestes filmes sob ensaio de indentação utilizou-se um modelo numérico de trinca difusa. Palavras-chaves:Indentação, Elementos Finitos, Fratura, Trinca Difusa. Simulation of indentation testing in thin films using numerical cracking models ABSTRACTThe aim of the present study was simulate the cycle of indentation test with spherical indenters in a system composed of thin surface coating deposited on a metallic substrate through PVD process by finite element models. Recent studies suggest that the indentation technique could be used as a tool to evaluate mechanical properties of thin films, as well as to determinate the fracture process in systems that combine high hardness coatings, like stainless steel substrates, in tribological applications. However, the implementation of this technique to evaluate the behaviour of these systems and their results, have still been doubts in the scientific community. Because of these uncertainties in the analysis of indentation test, the use a numerical methodology capable of evaluating the fields of stresses and deformation during the indentation cycle can help in a more secure interpretation of this testing. Nevertheless, the use of the numerical methodology to evaluate the indentation test in thin surface coatings also has had problems mainly due to the difficulty in implementing failures models, especially in determinating the behaviour for the interface between the coating and the substrate. Finally, it was used a numerical cracking model to study the mechanisms of nucleation and growth of cracks that occur in these films during indentation test.
The need for more components that are more resistant to wear and corrosion has promoted a growing interest in surface engineering. The search for improved tribological properties in materials contributes to the development of processes that extend the useful life of components and their applications in increasingly severe environments. In this respect, thin ceramic coatings have been used to enhance the tribological properties of components that operate under these conditions. However, new experimental assays are needed to assess the behaviour of these films and their surface as substrate. These experimental analyses require the use of sophisticated equipment and specialized personnel. On the other hand, with advances in computational mechanics, the application of numerical analysis to solve numerous technological problems has been increasingly frequent, owing to its low operational costs. This study aims to simulate an indentation assay with spherical penetrator in systems composed of thin ceramic film deposited on metallic substrate using a Finite Element commercial code. The main objective of this study was to evaluate the field behaviour of stresses in the contact region of the indenter with the sample, on the outline of the impression made by the penetrator and, primarily, on the film-substrate interface.
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