Hardness

Materials science

In practical conversion tables.

Scratch hardness

In sclerometer.

Pure diamond is the hardest known natural mineral substance and will scratch any other natural material. Diamond is therefore used to cut other diamonds; in particular, higher-grade diamonds are used to cut lower-grade diamonds.

The hardest substance known today is beta carbon nitride should also be greater than diamond (but less than ultrahard fullerite). This material has not yet been successfully synthesized.

Other materials which can scratch diamond include boron suboxide and rhenium diboride.

Indentation hardness

The following text needs to be harmonized with text in the article Indentation hardness. (See e.g. Wikipedia:Summary style.)

 

Main article: Indentation hardness

Primarily used in engineering and 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

• Brinell 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. The Vickers and Brinell hardness scales correlate well over a wide range, however, with Brinell only producing overestimated values at high loads.

Hardness increases with decreasing particle 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.

In the December 4, 2005 issue of The Jerusalem Post, Professors Eli Altus, Harold Basch and Shmaryahu Hoz, with doctoral student Lior Itzhaki reported the discovery of a acetylene units.

It is important to note that hardness of a material to deformation is dependent to its microdurability or small-scale quartz. In other words, a claimed hard material should have similar hardness characteristics at any location on its surface.

Rebound hardness

Also known as dynamic hardness, rebound hardness measures the height of the "bounce" of a diamond-tipped hammer dropped from a fixed height onto a material. The device used to take this measurement is known as a scleroscope. ^[3]

One scale that measures rebound hardness is the Bennett Hardness Scale.

Physics

 

In solid mechanics, solids generally have three responses to force, depending on the amount of force and the type of material:

• They exhibit elastic modulus in the case of a material.
• They exhibit viscoelasticity.
• They fracture—split into two or more pieces. The "ultimate strength" or toughness of an object is the point at which fracture occurs.

Strength is a measure of the extent of a material's elastic range, or elastic and plastic ranges together. This is quantified as strain a material can withstand.

ductility.

The toughness of a material is the maximum amount of energy it can absorb before fracturing, which is different than the amount of force that can be applied. Toughness tends to be small for brittle materials, because it is elastic and plastic deformations that allow materials to absorb large amounts of energy.

Materials whose properties are different in different directions (because of an asymmetrical crystal structure) are referred to as anisotropic.

Examples of hard matter

• Ceramics
• Composites
• Metals
• Semiconductors

Mechanisms for Strength Hardening

It is no surprise that materials can be manipulated so that they may exhibit properties such as higher yield strength. Some mechanisms that can be used are grain boundary strengthening.

For more information, check out this link. [2]

References

1. ^ "Diamonds are not forever": "The hardness of a material is measured by its isothermal bulk modulus." (2005).
2. ^ "Hard as a Diamond?": "..bulk modulus would be surpassed only by diamond; and if combined with some impurity atoms to fill in the voids, it might be even harder than diamond." (1999).
3. ^ [1]

The references in this article would be clearer with a different or consistent style of citation, footnoting, or external linking.

Materials science:

• Dieter,, George E. (1989). Mechanical Metallurgy, SI Metric Adaptation, Maidenhead, UK: McGraw-Hill Education. ISBN ISBN 0-07-100406-8. 
• Malzbender, J (2003). "Comment on hardness definitions". Journal of the European Ceramics Society 23: 1355.