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Hardness is dependent on ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity. Common examples of hard matter are ceramics , concrete , certain metals , and superhard materials , which can be contrasted with soft matter .
Fracture toughness: Ability of a material containing a crack to resist fracture (J/m^2) Friction coefficient: The amount of force normal to surface which converts to force resisting relative movement of contacting surfaces between material pairs; Hardness: Ability to withstand surface indentation and scratching (e.g. Brinell hardness number)
Toughness as defined by the area under the stress–strain curve for one unit volume of the material. In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing. [1] Toughness is the strength with which the material opposes rupture.
The Brinell hardness number can be correlated with the ultimate tensile strength (UTS), although the relationship is dependent on the material, and therefore determined empirically. The relationship is based on Meyer's index (n) from Meyer's law. If Meyer's index is less than 2.2 then the ratio of UTS to BHN is 0.36.
An example of undesirable work hardening is during machining when early passes of a cutter inadvertently work-harden the workpiece surface, causing damage to the cutter during the later passes. Certain alloys are more prone to this than others; superalloys such as Inconel require materials science machining strategies that take it into account.
A Rockwell hardness tester. The Rockwell hardness test is a hardness test based on indentation hardness of a material. The Rockwell test measures the depth of penetration of an indenter under a large load (major load) compared to the penetration made by a preload (minor load). [1]
When a material of unknown fracture toughness is tested, a specimen of full material section thickness is tested or the specimen is sized based on a prediction of the fracture toughness. If the fracture toughness value resulting from the test does not satisfy the requirement of the above equation, the test must be repeated using a thicker specimen.
Hence, the hardness and strength (both yield and tensile) critically depend on the ease with which dislocations move. Pinning points , or locations in the crystal that oppose the motion of dislocations, [ 5 ] can be introduced into the lattice to reduce dislocation mobility, thereby increasing mechanical strength.