1. Resistance of a material to deformation, indentation, or penetration by means such as abrasion, drilling, impact, scratching, and/or wear, measured by hardness tests such as Brinell, Knoop, Rockwell, or Vickers. Since there is no standard hardness scale, each test expresses its results in its unique (and arbitrarily defined) measure. For some metals (such as steel) the hardness and tensile strength are empirically related. Hardness of pliable materials such as plastics and rubbers is measured by instruments such as durometer. See also Mohs' hardness scale.
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