What is the material sample being tested for hardness called?

The material sample being tested for hardness is referred to as a specimen. In materials testing, a specimen is specifically prepared to undergo tests that evaluate various properties, including hardness. This term is widely used across different types of material testing and clearly denotes the item from which measurements are drawn.

The other terms provided have distinct meanings that differentiate them from the term "specimen." For example, a substrate typically refers to a surface or layer that supports a material or relates to where a material is applied, especially in fields like electronics or biology. A sample plate might suggest a specific format or configuration for a sample but does not universally apply across all hardness testing scenarios. The term matrix often refers to the environment in which something is embedded or the binding medium for a composite material, which is not applicable in the context of hardness testing.

Recognizing these definitions is essential for understanding proper terminology in material science and testing processes.