What property of a material describes its ability to deform under stress?

The property of a material that describes its ability to deform under stress is ductility. Ductility refers to the capacity of a material to undergo significant plastic deformation before rupture or fracture. This means that ductile materials can be stretched into wires or deformed under tensile stress without breaking.

Ductility is particularly important in applications where materials need to be reshaped or when they encounter stresses that could lead to permanent deformation. For example, metals like copper and aluminum are known for their high ductility, allowing them to be easily formed into various shapes in manufacturing processes.

In contrast, other properties such as brittleness describe a material's tendency to fracture without significant deformation, and strength represents the ability of a material to withstand an applied load without failure. Toughness combines both strength and ductility, representing a material's ability to absorb energy and plastically deform without breaking; however, it is not solely focused on the ability to deform. Thus, the most accurate descriptor for the ability to deform under stress is ductility.