What defines a change of length per unit of length?

Normal strain is defined as the change in length per unit of original length of a material when it is subjected to axial loads. This measurement is foundational in understanding how materials deform under tension or compression. Normal strain represents how much a material stretches or contracts relative to its original size, which is crucial in structural analysis and material science.

When a load is applied to a structural element, it experiences deformation, and normal strain quantifies this change in length. It is expressed mathematically as the change in length divided by the original length, typically denoted as ε (epsilon). This concept is pivotal for engineers to predict how structures will serve under applied loads and ensure safety and integrity.

In contrast, the other types of strain mentioned—shear strain, elastic strain, and plastic strain—refer to different aspects of material deformation. Shear strain involves angular changes and is related to shear stress rather than direct length changes. Elastic strain describes the reversible deformation of materials returning to their original shape after the removal of loads, while plastic strain refers to permanent deformation that occurs after yielding. Understanding these distinctions is important, but for the specific definition of "change of length per unit of length," normal strain is the accurate choice.