Brinell hardness scale

For the structural applications of materials, there is no more useful measurable property than mechanical hardness. It quickly and conveniently probes the strengths of materials at various scales of aggregation. Firstly, it does this at the human scale (Brinell hardness—millimeters to centimeters). Secondly, it does so at a microscopic scale (Vickers microhardness—1 to 100 microns). And thirdly, it does so at a nanoscale (nanoindentation—10 to 1000 nanometers). 

Mohs hardness is a measure of the relative hardness and resistance to scratching between minerals. Other hardness scales rely on the ability to create an indentation into the tested mineral (such as the Rockwell, Vickers, and Brinell hardness - these are used mainly to determine hardness in metals and metal alloys). The scratch hardness is related to the breaking of the chemical bonds in the material, creation of micro fractures on the surface, or displacing atoms in the metals of the mineral. Generally, minerals with covalent bonds are the hardest while minerals with ionic, metallic, or van der Waals bonding are much softer. 

Brinefl Indentation Dla(mm) Brinell Hardness Nunber C-Scale 15-N Scale 30-N Scale 45-N Scale 45-lui Load Shore Scleroscope Hardness Approximate Tensile Strenath (ksi)... 

There are four major indentation hardness tests, which differ from each other in the shape of the indenter (Figure 10.23). The first of these, described in 1900, was the Brinell test, using a 10 mm steel ball indenter (Figure 10.23a), giving the Brinell hardness number, BHN. This was suitable only for metals softer than steel. In 1920 Rockwell developed a number of tests, including the B, E, F and G scales, in which the indenter is steel, and the A, C and D scales, using a conical diamond indenter with a spherical tip (Figures 10.23b and 10.23c). In the Rockwell test the difference in size between the... 

The 136° angle between the opposite faces of the indenter was chosen because of the similarity between the Brinell hardness number (henceforth BHN) and the DPN. Due to this similarity, the DPN is on the same hardness scale as the BHN and their values are about the same up to 300 BHN. Only beyond this BHN value do the two curves shown in Fig. 1.54 deviate one from the other. Significant deviation between these two types of measurement occurs at high hardness values, particularly above 600 BHN, due to the deformation of the indenter. The DPH... 

Hardness -nos n (before 12c) (1) The resistance to local deformation. (2) Ability of a coating film, as distinct from its substrate, to resist cutting, indentation, or penetration by a hard object. An arbitrary scale of hardness is based upon ten selected minerals. For metals the diameter of the indentation made by a hardened steel sphere (Brinnell) or the height of rebound of a small drop hammer (Shore Scleroscope) serve to measure hardness. See Barcol Hardness, Brinell Hardness, Durometer, Indentation Hardness, Knoop Hardness Number,... 

Arbitrary hardness scales have been established that allow some correlation between hardness and yield strength. There are a variety of different methods including Brinell, Rockwell, Vickers, and Knoop, each with its own hardness scale. The reader is referred to ASTM Standards ElO, E18, E92, and E384 for details. The primary value of hardness testing is that it provides a nondestructive method for assessing the strength of a material and is useful for certifying that the actual materials used for specific components in a system meet the required material specifications. 

Other methods of determining the hardness of a material include a variety of "penetration" tests that yield hardness values measured in scales known as the Brinell, Rockwell (B or C), and scleroscope scales. These scales provide reliable hardness values for most materials, including ceramics, glass, metals and alloys, and wood (see Table 21). Unfortunately, as can be seen in the table, the various tests provide somewhat different hardness values for the same materials. 

Comparison of Rockwell hardness HRB with Rockwell (other scales), Brinell and Vickers hardness for soft metals... 

With the rapid advances now observed in hardness test methods (Vickers, Knoop, Grodzinski, Berkovich and Hanneman diamond indenters or Brinell and Rockwell hardness testers, etc.), the 10-degree Mohs scale poses a number of problems owing to the low distinction of hardness... 

The figure given by Copaux may be taken as a fair mean for the rolled metal, and 8-3 for the cast. The hardness of nickel is 3-5 on Mohs scale (Copaux), equivalent to about 80 on the Brinell scale.8 The tensile strength is about 42-4 tons per square inch for wrought, annealed nickel.9 Cast nickel can be rolled into sheets of thickness 0-0008 inch, and drawn into wire of diameter 0-0004 inch. It is thus exceedingly malleable and ductile. 

One of the most popular techniques used for determining the hardness of a material is the Mohs scale that consists of a qualitative but an arbitrary hardness index scheme ranging from extremely soft materials (value of 1 Moh) to very hard materials such as diamond (10 Moh). Other techniques that are often employed for measuring hardness of substances are developed by Rockwell [72], Brinell [72], Knoop, and Vickers [73]. Over the years, more quantitative methods such as nanoindentation [74] have been developed. This technique applies a small and a controllable load on to the substrate with a probe. The depth of penetration along with a known geometry of the probe provides an indirect way to measure the area of contact at full penetration, which is then used to determine the hardness. The hardness is determined by the ratio of the total force to the contact area. Table 7.2 lists the bulk hardness of different materials, metal films, and abrasive particles, in both Moh and microhardness scales [75]. 

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. 

Table 1. Hardness of investigated metals (in Brinell scale)...

Hardness - The resistance of a material to deformation, indentation, or scratching. Hardness is measured on various scales, such as Mohs, Brinell, Knoop, Rockwell, and Vickers. [10]... 

Rockwell s hardness test works in a similar way to Brinell s hardness test, i.e., it uses the depth of penetration. Contrary to Brinell s method, however, it measures the penetration of a sphere while still under a load, and then measures the remaining elastic deformation. For this reason, the Rockwell method always gives lower degrees of hardness than the Brinell method. In addition, the degrees of hardness according to the Rockwell method are not measured in physical units, but in scale numbers of 0-120. Steel balls are used with soft materials, and diamond points with hard ones. The Vicker s hardness test uses a diamond pyramid. A modified Rockwell method is used for plastics. It should be noted that, with the Rockwell hardness thus determined, the plastic deformation contribution increases only gradually, because of creep. With metals, on the other hand, the deformation is always plastic, and therefore, also independent of time. Plastics, therefore, exhibit a relatively high Rockwell hardness compared to metals. 

Figure R.3 compares Rockwell R and M scales to Barcol, Brinell, and Mohs hardness measurements. Also shown for comparison are typical materials.

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