hardness


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hardness,

property of matter commonly described as the resistance of a substance to being scratched by another substance. The degree of hardness is relative, different substances being compared with one another. Mohs's scale of hardness (named for Friedrich Mohs), used commonly in mineralogy, lists certain minerals in order of hardness: talc, 1; gypsum, 2; calcite, 3; fluorite, 4; apatite, 5; orthoclase, 6; quartz, 7; topaz, 8; corundum, 9; diamond, 10. The listing indicates merely that gypsum (hardness=2) is harder than—i.e., capable of scratching—talc (hardness=1). The listing does not indicate that gypsum (2) is twice as hard as talc (1). The hardness of many minerals falls between those included in the list. For example, the hardness of barite is 3.3. Hardness may differ with the direction of the scratch made on the substance. Thus the mineral kyanite has a hardness of 5 parallel to the length of its crystals and of 7 at right angles to this direction. There are several other methods based on the resistance to indentation for testing engineering materials. The solid elements have been thus classified: diamond (an allotropic form of carbon) is hardest and listed as 10, with cesium the softest, rated as 0.2, the same degree of hardness as wax (hardness=0.2 at 0°C;). The hardness numeral of the Brinell scale is based upon the indentation produced when pressure is exerted by a sphere on the substance. The value thus obtained has a direct relation to the tensile strength of the substance. The hardness of a material may be modified by the presence of small quantities of another substance, as in metallic alloys, or by impurities in minerals.

hardness

[′härd·nəs]
(chemistry)
The amount of calcium carbonate dissolved in water, usually expressed as parts of calcium carbonate per million parts of water.
(electromagnetism)
That quality which determines the penetrating ability of x-rays; the shorter the wavelength, the harder and more penetrating the rays.
(engineering)
Property of an installation, facility, transmission link, or equipment that will prevent an unacceptable level of damage.
(materials)
Resistance of a metal or other material to indentation, scratching, abrasion, or cutting.

hardness

1. The resistance of wood, rubber, sealant, plastic, or metal to plastic deformation by compression or indentation; in wood, hardness is generally related to density. Common methods of measurement include the Rockwell, Brinell, Scleroscope, and Vickers tests.
2. A property of a paint or varnish film that is a measure of its ability to withstand damage from marring, abrasion, etc.
3. The degree of hardness, applied to water, based on the amount of calcium and magnesium salts in the water, expressed as grains per gallon or parts per million of calcium carbonate.
References in periodicals archive ?
1 shows the trend of color values with respect to hardness of different cations during dyeing process on cotton fabric in range of 0.
Table-2: Hardness of tap water samples from different districts of KPK, in terms of CaCO3, and their pH Values.
12] showed that nanoindentation and microindentation hardness tests have similar load effect and their differences are between 10% and 30%.
After that, the top and bottom surfaces of each specimen were subjected to the Vickers hardness testing machine (Micromet 2100, Buehler, Lake Bluff, IL, USA) (Fig 5).
Conclusion: It can be concluded from this study that micro hardness of imported plates is more than local plates so recommendations should be sent to manufacturers of local industry of Pakistan to improve the hardness of local plates so that they can meet international standards.
Variability: Metal castings are not homogenous, and hardness variations will occur throughout the typical casting, though the variation between locations should not be dramatic.
So, the hardness of water may be one of the characteristics of processing water that should be monitored by poultry processors.
Moreover, as the load force weakens and enters the area of micro-hardness, the Vickers hardness is no more depending on the power of applied load (unlike in macro-hardness that is measured according to geometric similarity of individual dints).
The hardness values (mean values of 10 to 20 times measurements of each processed sample) of different kinds of plant surfaces were measured and results were comparatively analyzed when loaded 50 micronewton.
The measurements of wheel rolling surface hardness (Brinell hardness) are carried out using DinaMIC hardness tester.
After curing, an initial Shore A hardness test was performed on all samples using a digital durometer (Teclock, Osaka, Osaka, Japan) according to ASTM procedures.