Hardness Vickers number

Vickers hardness numbers are calculated from measurement of the indentation diagonals as follows, where HV = Vickers hardness,... 

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. 

Brinell hardness number Vickers hardness number hour... 

Vickers hardness number (kg./sq.mm.) jjj Vickers hardness number (kg./sq.mm.)... 

Figure 9.10 Vickers hardness numbers as a function of the molecular volumes of the alkaline earth sulfides.

The influence of fillers has been studied mostly at hl volume fractions (40-42). However, in addition, it is instructive to study low volume fractions in order to test conformity with theoretical predictions that certain mechanical properties should increase monotonlcally as the volume fraction of filler is Increased (43). For example, Einstein s treatment of fluids predicts a linear increase in viscosity with an increasing volume fraction of rigid spheres. For glassy materials related comparisons can be made by reference to properties which depend mainly on plastic deformation, such as yield stress or, more conveniently, indentation hardness. Measurements of Vickers hardness number were made after photopolymerization of the BIS-GMA recipe, detailed above, containing varying amounts of a sllanted silicate filler with particles of tens of microns. Contrary to expectation, a minimum value was obtained (44.45). for a volume fraction of 0.03-0.05 (Fig. 4). Subsequently, similar results (46) were obtained with all 5 other fillers tested (Table 1). 

Table 1. Influence of fillers on Vickers Hardness Number...

Fig. 4 Influence of volume fraction of rigid filler particles on Vickers hardness number of a BIS-GMA conolymer.

Fig. 6 Influence of Y-irradiation on Vickers hardness number of BIS-GMA copolymers, with and without fillers.

VHN Vickers hardness number VT vacuum tube(radio)... 

Vickers hardness number corrected for microbrittleness —scratch depth, indent depth, height of cylinder —thickness of material —corrected height of cylinder —ionization potential —dimensionless constants —temperature in Kelvin... 

Minerals Arranged in Order of Increasing Vickers Hardness Numbers 75 Ed. 

Molybdenum specimen in contact with sodium in a nickel container. Great hardness of transfer layer indicated by Vickers hardness numbers. Etched with oxalic acid... 

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). 

The alternative approach used in published studies has been to determine the micro-hardness at varying depths [18,19], an approach that assumes the existence of a correlation between micro-hardness and degree of conversion (DC) of monomer to polymer. Studies using this approach have shown that depth of cure does not correlate well with measurements made using a proper hardness measurement technique, in this case Vicker s hardness [20], In particular, for the so-called bulk fiU materials the ISO 4049 method, which involves scarping away unset material from the base of a cylinder of composite that has been exposed to light from the top, was found to overestimate the depth of cure compared to that determined from Vickers hardness number. 

Vickers Square pyramid Vickers hardness number (VHN) using contact area VHN using projected area VHN = 1.854F/a VHN = 2.000F/a The ceramics community uses mainly the number calculated using the projected area need to be careful when comparing data from different sources... 

The hardness of metals is generally expressed in terms of their resistance to indentation. A hard indenter is pressed into the surface under the influence of a known load and the size of the resulting indentation is measured. A widely used instrument is the Vickers indenter, which gives a pyramidal indentation, and the results are expressed as a Vickers hardness number (kgf mm ). Other... 

Mohs hardness number M Reference substance Formula Vickers hardness number V... 

---