hardness? what is hardness?

Question

how can hardness be measured?

Answer 1

The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German mineralogist Friedrich Mohs and is one of several definitions of hardness in materials science.

Mohs based the scale on ten minerals that are all readily available. As the hardest known naturally occurring substance, diamond is at the top of the scale. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, and/or the softest material that can scratch the given material. For example, if some material is scratched by apatite but not by fluorite, its hardness on the Mohs scale is 4.5.

Other hardness include

Scratch hardness (the formentioned Mohs scale)
Indentation hardness
Rebound, dynamic or absolute hardness.

Primarily used in engineering and metallurgy, indentation hardness seeks to characterise a material's hardness; i.e. its resistance to permanent, and in particular plastic, deformation. It is usually measured by loading an indenter of specified geometry onto the material and measuring the dimensions of the resulting indentation.

There are several alternative definitions of indentation hardness, the most common of which are:


A Vickers hardness testerBrinell hardness test (HB);
Janka Wood Hardness Rating;
Knoop hardness test (HK) or microhardness test, for measurement over small areas;
Meyer hardness test;
Rockwell hardness test (HR), principally used in the USA;
Shore durometer hardness, used for polymers;
Vickers hardness test (HV), has one of the widest scales;
Barcol hardness test, for composite materials, scale from 0 to 100.
There is, in general, no simple relationship between the results of different hardness tests. Though there are practical conversion tables for hard steels, for example, some materials show qualitatively different behaviours under the various measurement methods.

Hardness increases with decreasing grain size. This is known as the Hall-Petch effect. However, below a critical grain-size, hardness decreases with decreasing grain size. This is known as the inverse Hall-Petch effect.

For measuring hardness of nanograined materials, nanoindentation is used.

Also known as dynamic or absolute hardness, rebound hardness measures the height of rebound of an indenter dropped onto a material using an instrument known as a scleroscope. One scale that measures rebound hardness is the Bennett Hardness Scale.

Answer 2

It depends in what context - but hardness is a measure of how compact molecules of the specific material are packed together.
There is specifically a measure of hardness of steel for example, called the Brinell measurement.

Answer 3

The Metals Handbook defines hardness as "Resistance of metal to plastic deformation, usually by indentation. However, the term may also refer to stiffness or temper, or to resistance to scratching, abrasion, or cutting. It is the property of a metal, which gives it the ability to resist being permanently, deformed (bent, broken, or have its shape changed), when a load is applied. The greater the hardness of the metal, the greater resistance it has to deformation

Answer 4

Hardness in water is caused by the presence of Ca2+ (or Mg2+) ions. The hardness of the water can be estimated by carrying out a soap titration. Hardness makes it difficult for soap to form a lather.

Answer 5

by the ammount of calcium carbonate if your refering to water.

it is measured usually in degrees or ppm, there is also carbonate hardness which is measured in kh and is the ammount of (CO32-) and (HCO3-)

Answer 6

By the degree and rigidity of electrostatic bonding.

Answer 7

how much pressure somemthing can handle?