In materials science, how is stress defined?

Stress in materials science is defined as the force applied per unit area of a material. This definition is derived from the fundamental relationship that describes how external loads interact with materials. When a force is applied to a material, it tends to deform or change shape. Stress quantifies this interaction by measuring how much force is exerted over a specific area, typically expressed in units such as pascals (Pa) or pounds per square inch (psi).

Understanding stress is crucial in engineering and materials science, as it helps predict how materials will behave under various loading conditions. For instance, if a material is subjected to a high level of stress, it may yield or even fracture, while lower stress levels might allow materials to return to their original shape once the load is removed.

While the other options touch upon relevant concepts in materials science, they do not accurately define stress itself. Energy stored in a material refers to strain or potential energy, deformation describes the mechanical change resulting from applied stress, and resistance to deformation relates more closely to material properties like stiffness or elasticity, but does not define stress directly. Thus, the definition focusing on force per unit area encapsulates the core of what stress represents in the context of materials under load.