Vickers indentation method

Vickers indentation method will be pursued here (in both its micro- and nanomanifestations). 

The phase composition from the surface to the interior of the samples was determined by X-ray diffractometry (XRD) through successive grinding of the surface at 100 pm intervals. The microstructural characterization of the sintered specimens was achieved by scanning electron microscopy (SEM) in backscattered mode. The hardness change from the surface to the interior of the sample was measured by the Vickers indentation method at 19.6 N load. 

In this work, DC electric field-assisted ion exchange was carried out to enhance the sodium-potassium inter-diffusion and improve the mechanical performance of borosilicafe glass. Elecfric fields with intensity varying between 100 V cm and 3000 V cm were applied in both direct and inverted polarizations. Four point bending test and the Vickers indentation method were used to characterize the mechanical properties. Energy dispersion x-ray spectroscopy was carried out to determine the potassium concentration within the surface layers of the samples. 

The presence of residual stresses on the surface layers was estimated by Vickers indentation method. The residual stress, o, approximated as constant on the surface layers can be calculated as [23]... 

A recent comprehensive review on the Vickers indentation method [76] for fracture... 

In particular, the Vickers indentation method seems favourable to compare the response of inorganic matrix composites containing CNTs to contact loads due to its simplicity and easy sample preparation and test operation. It should be noted that the fracture toughness values shown in Table 1 were all determined by the Vickers indentation method as this has been the accepted practice in the field in the last years and in most cases the fracture toughness of CNT/ceramic composites has been obtained by this method. 

Mechanical properties were determined before and after oxidation. Fracture torrghness was determined by means of Vickers indentation method with indentation load in the range 49-196N, whereas thermal shock resistance was determined by water qirenching method in accordance with the standard EN 820-3. Finally, flexiual strength was determined by four-point bend tests at room temperature. Nine samples as bars of 3 x 4 x 45 mm were prepared and tested in accordance with the standard ENV 843-1 (crosshead speed 0.5 mm/min). 

Microhardness (Hv) and fracture toughness (Kic) of the ceramics was determined by Vickers indentation method at 2 and 7 N load correspondingly (Micro Materials Ltd Nanotest 600). 

Figure 9 X-Ray diffraction patterns of SPS sintered samples and base powders Hardness and Fracture Toughness by the Vickers Indentation Method...

There are two main techniques used to measure the fracture toughness of ceramics fracture stress and hardness indentation. The former measures the load to fracture of a pre-cracked specimen using a single edge notched beam (SENB) or a chevron notched beam (CNB) sample. The main drawback of this technique is ensuring that the crack tip is atomically sharp. The second method uses the crack formed at the corners of the indentation produced during a Vickers indentation hardness test. This technique is rapid and relatively inexpensive. However, the toughness values measured are those of the surface, unlike the values obtained by fracture of the pre-cracked beams which are a measure of the bulk material properties. 

The bulk densities of all the materials were determined using Archimedes method (AS 1774.5, 1979). The Vickers indentation technique was used to measure the hardness in each case. The applied load in the Vickers hardness tests was 10 kg for silicon nitrides and sialons. However, using the same load produced severe lateral cracking in silicon carbides around indents, which prevented the accurate measurement of the diagonals of indents. Therefore the load was reduced to 0.3 kg for silicon carbide samples. 

Tests such as Vickers, Knoop, and Brinell use an indentation technique that impinges a hard tip (e.g., diamond) into the sample with a known load (Figure 2.35a). After a designated period of time, the load is removed, and the indentation area is measured. The hardness, H, is defined as the maximum load, L, divided by the residual indentation area, (Eq. 11). The coefficient, F, varies depending on which indentation method is used. This value (14.229 for Knoop and 1.854 for Vickers)... 

Vicker s hardness number (VHN). Hardness on Rockwell and Brinell scales are also reported for metals and alloys. In both KHN and VHN measurements, the approach is to make an indentation on the surface of the sample using a diamond micro-indenter. In the Vicker s method the indenter has the shape of a square pyramid, while in the Knoop s method it has the shape of an elongated pyramid. The indentation is generally of the order of few microns and a load of 5 to 1000 gm are used (in order to determine fracture toughness, it becomes necessary to use higher values of load (due to the necessity of initiating cracks)), VHN is given by. 

Cracks were observed on the top surface and the section surface of the disk with an optical microscope. The microstructure was observed by SEM. The surfaces were polished with diamond paste. The Vickers indentation technique was used to evaluate the direction of residual stress. The residual stresses were calculated by an analytical technique on the assumption of elastic condition [2]. For electrical measurement, Pt electrode was formed on the disk surfaces with Pt paste. The electrical resistivity was measured by two-probe method. 

Indentation strength in bending was widely used to characterize the crack propagation resistance with increasing crack length. In this method a controlled crack is formed by Vickers indenter and... 

C1327-97 Test Method for Vickers Indentation Hardness of Advanced Ceramics... 

Indenting methods (Vickers, Knoop, Brinell, Rockwell, Shore). 

ASTM C 1327, Test method for Vickers indentation hardness of advanced ceramics, Annual Book of ASTM Standards, Vol. 15.01, American Society for Testing and Materials, West Conshohocken, PA (2001). 

The loading of a diamond-tipped Vickers indenter into most ceramic and glass materials results in the formation of cracks from the corners of the indentation (Figure 14.22). Anstis et al. [22] developed a method to correlate the length of these cracks with the fracture toughness of the material ... 

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