Vickers hardness tests

Vickers hardness test Vickers hardness tests Vicor Vicryl... 

The Vickers hardness test is a macrohardness test in which loads are commonly varied from 9.8 to 1180 N (1 to 120 kgf). Vickers hardness numbers are invariant with load within the stated limits. 

The Vickers hardness test is commonly made on a flat specimen on which the indenter is hydrauhcaHy loaded. When the desired number of indentations have been made, the specimen is removed and both diagonals of the indentations, measured using a caUbrated microscope, are then averaged. The Vickers hardness number may be calculated, or for standard loads taken from a precalculated table of indentation size vs VHN. The preferred procedures are described in ASTM E92 (2). 

The Vickers hardness test, developed in the United Kingdom, is more popular there than in the United States. VHN (Vickers hardness number) and DPH (diamond pyramid hardness) are synonymous terms. 

Hardness is determined by measuring the penetration (depth or area) when a harder material, such as diamond, is pushed into the surface of the material of interest under a specified load. Tme hardness is defined as the force divided by the projected area. Vickers hardness tests, which employ a pyramid-shaped indentor, are frequently used to characterize ceramics however, Vickers hardness calculations normally employ total surface area rather than projected area (43). Measurements are made on the diamond impression shown in Figure 6. Vickers hardness is calculated using... 

The influence of atmospheric air on the properties of mineral materials manufactured in thermal processes is generally known. An example of the nature of this phenomenon as regards hardness, is a series of Vickers hardness tests of a material made of sintered corundum modified with 0.6% MgO sintered at 1950-2050 K in various environments. The sintering process is accelerated in the presence of hydrogen and is slowest in air thus allowing a material with optimum parameters to be obtained at a significantly lower temperature. The results, specified in Table 6.2.4, show the gases used as... 

A Recommended Programme for Complete Mechanical Specification of a Mineral from Vickers Hardness Tests... 

In 1951, after making a series of Vickers hardness tests on silicate glasses, Derter proposed the following formula to determine their brittleness ... 

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. 

Another criterion is used with the Vickers hardness test after penetration of a pyramid-shaped diamond under stress, the diameter of the indent is measured after removal of the diamond. The hardness is defined as the applied force divided by the area of the indent. This is again a measure of the permanent deformation, or, possibly, of the yield stress. 

The hardness number is usually combined with the name of the method used, to indicate how the value was obtained. The commonly used tests are the Brinell, Rockwell, and Vickers hardness tests. The results of these tests are presented as the HB or Brinell hardness number, or the HV, and so on. 

VanKrevelen-Hoftijzer viscosity-temperature relationship, 539 Van t Hoff equation, 751 Velocities of sound waves, 390 Velocity gradient, 526 Vertical Burning Test, 854 Vicat softening temperature, 849 Vickers hardness test, 837 Viscoelasticity, 405... 

The Vickers Hardness test uses a square-based diamond pyramid as the indenter. The Vickers Hardness, Hv, is calculated by... 

Figure 8.1. Vickers hardness test shown schematically...

BS 427, Method for Vickers hardness test and for verification of Vickers hardness testing machines, 1990. 

The Vickers hardness test differs from the Brinell test in that the indentor is a diamond (square-based) pyramid (Figure 3.42) having an apex angle of 136°. If the average diagonal of the indent is d, the hardness number is calculated from... 

Other common hardness tests involve the use of diamond pyramids. In the Vickers hardness test, a square pyramid is used and in the Knoop hardness test, the pyramid is elongated. The area term in the former test is the actual indentation area and in the latter, the projected area. From the impression geometries, shown in Fig. 6.30, the Vickers Hardness Number (VHN) and Knoop Hardness Number (KHN) can be shown to be VHN=1.854F/a and KHN=14.2F/L, respectively. A common hardness test in the USA is the RockweO hardness test, which uses various indenter types and loads. The result of these tests is a dimensionless number and leads to the use of various hardness scales (e.g., Rockwell B, Rockwell C). 

Figure 1. The Vickers hardness (testing load 1 kg) of fine-grained sintered alumina ceramics prepared by a sol/gel approach starting with boehmite (7-seeding).

Boe] Vickers hardness tests Hardness, breaking strengfli, electrical conductivity, residual voltage... 

Fujl] Vickers hardness tests, electrical resistivity measurements Hardness, electrical resistivity... 

Metallic materials - Vickers hardness test - Part 1 Test method... 

The strengths of the Pb-Ag-Ca alloys were experimentally examined using tensile and Vickers hardness tests. The results were compared to the data for a conventional Pb-Ag alloy used as anode material for zinc electrowinning. 

Figure 15 shows the Vickers hardness test results for various alloys. The increase in the Ca content of the Pb-0.5 wt% Ag - Ca alloy was considered to increase the Vickers hardness of the alloy. The rolling rate increased the hardness of the Pb-0.5 wt% Ag - Ca alloy, but after annealing, the hardness decreased. Because the Vickers hardness shows a constant value after annealing at 200 C for 48 h, it was considered that the strain in the anode material could be removed by annealing at 200 C for 48 h. The Pb-0.5 wt% Ag - Ca alloy annealed at 200 C for 48 h after rolling showed the same or better mechanical properties relative to the conventional Pb-1.0 wt% Ag alloy. 

The Vickers hardness test is one of the most common techniques for hardness measmements [50,57,64,67,82,88]. In this method the hardness values are obtained by dividing the indentation force by the residual area after the indentation [67]. Hardness measurements of oxidized NDs/epoxy nanocomposites increased sharply by increasing the filler content to 0.4 wt%, showing a 86% enhancement of this property compared to that of the pure epoxy. Furthermore, Figure 10.18 shows that a higher increase of oxidized NDs improved the hardness to a lower extent [50]. The distortion... 

The Vickers Hardness Test is similar to the BrineU method, with a square based pjrramid used as the indentor. As in the BrineU test, the Vickers number is the ratio of the load to the surface area of the indentation in kUograms per square miUimeter. An advantage of the Vickers test is the increased accuracy in determining the diagonal of a square as opposed to the diameter of a circle. 

Hardness is the resistance that a body offers to penetration by a harder body. Polished sections of ceramic materials are primarily tested by the Vickers or Knoop methods, both of which can be described as indentation hardness testing methods (Fig. 143). The indenter used in Vickers hardness testing is a four-sided diamond pyramid with an included apical angle of 136°. The diamond indenter used in the Knoop method is also a four-sided pyramid, but this indenter has two different included apical angles, measuring 130° and 172°30. This causes an elongated indentation in the material being tested. 

Figure 144. Vickers hardness testing indentation in SiSiC containing 20% Si by volume. Load 100 N. The indentation has caused severe spalling.

Figure 145. Vickers hardness testing indentations in a sintered SiC ceramic. Loads (from left to right) 0.2, 0.3, 0.5, 1 kgf...

---