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Hardness is a measure of plastic deformation and is defined as the force per unit area of indentation or penetration. Hardness is one of the most important parameters for comparing properties of materials. It is used for finding the suitability of the clinical use of biomaterials. Biomaterial hardness is desirable as equal to bone hardness.
Toughness is the strength with which the material opposes rupture. One definition of material toughness is the amount of energy per unit volume that a material can absorb before rupturing. This measure of toughness is different from that used for fracture toughness, which describes the capacity of materials to resist fracture. [2]
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.
Toughness often increases as strength decreases, because a material that bends is less likely to break. Hardness – A surface's resistance to scratching, abrasion, or indentation. In conventional metal alloys, there is a linear relation between indentation hardness and tensile strength, which eases the measurement of the latter. [7]
In bone for example, the organic layer is the protein collagen. [3] The degree of mineral in mineralized tissues varies and the organic component occupies a smaller volume as tissue hardness increases. [1] [18] However, without this organic portion, the biological material would be brittle and break easily.
At such low load, the hardness values are also overestimated for other materials, for example it exceeds 100 GPa for c-BN. [4] Other researchers, while having reproduced the high ReB 2 hardness at low load, reported much lower values of 19–17 GPa at a more conventional load of 3–49 N, that makes ReB 2 a hard, but not a superhard material ...
The strength of materials is determined using various methods of calculating the stresses and strains in structural members, such as beams, columns, and shafts. The methods employed to predict the response of a structure under loading and its susceptibility to various failure modes takes into account the properties of the materials such as its yield strength, ultimate strength, Young's modulus ...
Fracture toughness varies by approximately 4 orders of magnitude across materials. Metals hold the highest values of fracture toughness. Cracks cannot easily propagate in tough materials, making metals highly resistant to cracking under stress and gives their stress–strain curve a large zone of plastic flow.