When a bolt stretches under a load, the ratio of the amount it stretches to its original length is called what?

The term that describes the ratio of the amount a bolt stretches under a load to its original length is known as linear strain. Strain is a dimensionless quantity that measures the deformation of a material due to applied stress. It is defined as the change in length (the amount of stretching or deformation) divided by the original length of the material. Linear strain is crucial in the analysis of materials under load because it provides insight into how much a material will deform, which is vital for ensuring the integrity and safety of structural components.

Other terms mentioned, such as linear stress, compressive stress, and axial stress, relate more to the forces applied or the internal reaction of a material to those forces rather than the ratio of deformation to original length. Linear stress refers to the applied force per unit area, compressive stress deals with forces that push material together, and axial stress is related to forces applied along the axis of a component. While these concepts are important in material mechanics, they do not define the behavior of a material in terms of its deformation ratio, which is specifically described by linear strain. Thus, the correct answer effectively identifies the specific relationship of stretch to original length that is a key aspect of material deformation.