Analysis of Indentation Size Effect of Vickers Hardness Tests of Steels

Abstract

In this work, the indentation size effect (ISE) in Vickers hardness tests of steel with selected heat treatments (annealed or tempered) has been investigated and analysed. Systematical hardness tests were performed within a commonly used micro-load range. The experimental data was analysed according to the Meyer power-law and the proportional specimen resistance (PSR) models and the link between ISE and material properties was discussed. The results showed that the experimental data fitted well with the Mayers power-law (P = A.dn) and the PSR (P/d = al + a2d) models. The ISE index (n) showed a good correlation with the hardness-elastic modulus ratio (H/E), which potentially could be used to predict the relative contributions of the elastic and plastic deformation contact area under indentation load and to normalize the hardness values for inverse material properties .

Indentation size effects in pack carbo-nitrided AISI 8620 steels

“…Unlike prior work in which micro-indentation techniques were used to characterize the indentation size effects in steels [16][17][18][19][20], the current work using nano-indentation techniques to characterize the indentation size effects in an AISI 8620 steel in which the variations in carbon and nitrogen content are not very significant over the range of indentation depths. Hence, the measured changes in hardness are attributed to effects of strain gradients that give rise to the formation of geometrically necessary dislocations that are the causes of the ISE [22].…”

“…However, to the best of our knowledge, there have been relatively few studies of ISEs in body centered cubic (b.c.c.) polycrystalline materials, such as steels [16][17][18][19][20]. There is also the potential to extend the studies of ISE to surface-modified steels [19], such as those produced by bio-carbo-nitriding processes.…”

“…The hardness of steels [20] has been shown to exhibit ISE. This makes it difficult to obtain a unique hardness data of multi-phase steel for design and application purposes.…”

Determining Plastic Properties of Material Through Instrumented Indentation Approach

“…The Vickers hardness test was carried out using the Duramin-1 Struers Vickers hardness testing machine using the direct loading method with various loads from 19.61 N to 490.3 mN. The indenter used has the right pyramid shape with a square base and 136 o angles facing opposite sides [18], [20] while the shear test is applied to a welding joint of better sheet metal using a Lloyd LR 30K Universal fuel engine with maximum capacity 30 KN with accurate readings of up to 0.5% of strength. This machine is connected to a microcomputer which allows graphical output of the results and data obtained and stored.…”

“…Another active area of research is research related to instrumentation indentation of complex structures [16]. Previous studies have shown that the hardness value is closely related to the correspondence between the representative stress (σr) and the representative strain (εr) which is the average value of the plastic strain produced in the indentation process [18], [19]. Analysis of representative strain and stress systems based on indentation Instrumentation with sharp indenter (Vickers) using a fixed indenter angle, through a numerical approach finite element model has been developed.…”