þrengsl

Þrengsl is the Icelandic term for the internal forces per unit area that arise within a material when external loads are applied. In physics and engineering contexts it corresponds to the English word stress. It is distinct from strain, which is the deformation that results from stress; stress is the cause, while strain is the effect.

Types of þrengsl include tensile stress, which pulls material fibers apart and tends to elongate the object; compressive stress, which squeezes and tends to shorten it; and shear stress, which acts parallel to a plane and can cause layers to slide past one another. The same object can experience different types of stress in different regions, especially under complex loading.

Measurement and magnitude are typically given in pascals (Pa), with larger structures described in megapascals (MPa) or gigapascals (GPa). For simple axial loading, normal stress is approximated by σ = F/A, where F is the applied force and A the cross-sectional area. In bending and real components, the stress distribution varies with position and direction. In advanced analysis, stress is represented by a second-order tensor, with concepts such as principal stresses, shear stresses, and yield criteria (for example, the von Mises criterion) guiding material design and failure prediction. The relationship between stress and deformation in the elastic region is governed by constitutive laws such as Hooke’s law, σ = Eε, where E is Young’s modulus and ε is strain.

Applications of þrengsl knowledge include the design and safety assessment of structures, machinery, and consumer products, as well as failure analysis and material selection. Understanding nægilegur stress states helps engineers predict performance and prevent collapse or fatigue.