Determinação da flexibilidade elástica de equipamentos de indentação instrumentada

Abstract

Currently, instrumented indentation tests are becoming increasingly important, as they represent a promising measurement method that allows a variety of mechanical properties to be measured using small volumes of material. Unlike traditional hardness measurement methods, which only analyze the plastic response of the material, the instrumented indentation test records in real time both the force applied and the displacement resulting from the action of the penetrator on the specimen. This makes it possible to evaluate the elastic and plastic responses of the material during the indentation process, allowing the calculation of various static properties on small material samples. A significant advantage of this approach is that it saves time, especially in preparing the specimen. However, the analysis of the data and, consequently, the results can be influenced by various factors. These include the quality of the specimen surface, the wear of the indenter tip, its geometry and material, as well as the compliance of the testing machine frame. When the structure of the testing machine has non-zero compliance, displacements occur not only in the indenter, but also in the structure itself, especially when high indentation forces are applied, a phenomenon which has a negative impact on the measurement results. Therefore, this study evaluated the compliance of two instrumented indentation machines - the PropinSitu II and the Stress-Strain Microprobe® (SSM-M1000™) - based on the linear regression method of the C_t vs. F^(-0,5), function proposed by Ullner et al. (2010). Thus, the compliance values obtained for the PropinSitu II and SSM-M1000™ machine were C_m~ 6,6 nm/N and C_m~ 4,1 nm/N, respectively. When analyzing these results, two main conclusions can be noted: the SSM-M1000™ machine exhibits superior stiffness compared to the PropinSitu II, and the low elastic flexibility values suggest that there is no significant compromise on the indentation tests carried out on the machine evaluated.