What term describes the change of volume per unit volume?

The term that describes the change of volume per unit volume is dilatation. In the context of materials science and civil engineering, dilatation refers specifically to the volumetric changes that occur in a material as a response to changes in temperature, pressure, or other environmental factors. It quantifies how much a material expands or contracts relative to its initial volume.

This definition is crucial when analyzing how materials behave under different load conditions or environmental changes, especially in surveying and construction, where understanding material properties can impact design and stability.

In contrast, deformation is a broader term that encompasses all types of shape changes—both volume and shape alterations—due to applied forces, not just changes in volume. Compression typically refers to forces that reduce volume, and tensile strength relates to the ability of a material to withstand tension before it fails, neither of which directly conveys the concept of volume change per unit volume. Thus, dilatation is the most accurate term for describing this specific phenomenon.