Which property allows a material to absorb energy when elastically deformed and release it upon unloading?

The property that allows a material to absorb energy when elastically deformed and then release that energy upon unloading is resilience. Resilience is specifically related to the ability of a material to store elastic energy. When a material is subjected to stress, it deforms elastically within its limit; this deformation stores energy. Upon removal of the load, the material returns to its original shape and releases that stored energy.

Understanding resilience is crucial in design applications where materials need to withstand repetitive loading and unloading cycles, such as in springs or structural components subject to vibrations. In contrast, toughness refers to a material's ability to absorb energy and plastically deform without fracturing; elasticity relates to the material's ability to return to its original shape after deformation, but does not necessarily imply energy absorption as part of a cycle; and ductility is a measure of how much a material can deform plastically before breaking. Each of these properties plays a unique role in material behavior but resilience is the specific aspect dealing with elastic energy storage and release.