Engineeringjännitys

Engineeringjännitys, commonly known in English as engineering stress, is the axial stress in a material calculated from the applied force divided by the original cross-sectional area of the specimen. It is defined as σe = F / A0, where F is the axial force and A0 is the initial cross-sectional area before deformation. Units are pascals (Pa) or megapascals (MPa). This quantity assumes the cross section remains constant during loading, which simplifies many engineering calculations and design tasks.

A related concept is true stress, σt = F / A, where A is the instantaneous cross-sectional area. Since necking reduces A during deformation, true stress can continue to rise after yielding even as engineering stress may peak or decrease. The two are related by σt = σe · (A0 / A). For small strains, σe and σt are similar; for large strains they diverge.

Engineering stress is widely used in standard tensile tests and in design codes because it relies on original geometry. On a typical engineering stress–strain curve, yield strength, ultimate tensile strength, and ductility are defined using σe. It remains a practical measure for many metals, polymers, and composites in early-stage deformation and design calculations.

Limitations include its decreasing representativeness at large strains, where necking occurs and the actual local stresses diverge from σe. In such regimes, true stress and related measures provide more accurate descriptions of material behavior.