What does "hardness testing" measure in materials during non-destructive testing (NDT)?

Hardness testing measures a material's resistance to deformation, particularly in the context of indentation, scratching, or abrasion. This property is critical in evaluating how well a material can withstand mechanical forces and wear without permanent shape changes. The results of hardness tests can inform decisions about material selection for specific applications, where durability and resistance to wear are essential.

This assessment is accomplished through various methods, such as the Rockwell, Brinell, and Vickers tests, which apply a specific load via an indenter to the material's surface. The depth or size of the resulting indentation is then measured to determine hardness.

The other options refer to properties that, while important in material science and engineering, do not pertain specifically to hardness testing. The ability to conduct electricity relates to electrical conductivity rather than hardness, density under stress involves physical mass considerations rather than deformation, and temperature resistance pertains to thermal properties. Each of these attributes can influence material behavior but relies on different types of evaluations and measurements unrelated to hardness.