Elongamenti

Elongamenti, or elongation, is the increase in length that a body experiences when subjected to a force along its length. It is typically defined as the difference between the final length and the original length, ΔL = L − L0, where L0 is the original length. The relative elongation or strain is the ratio ΔL/L0 and is dimensionless.

In uniaxial tension, the elongation depends on the applied force F, the original length L0, the cross-sectional area A, and the material’s stiffness, characterized by Young’s modulus E. For small deformations within the elastic range, the elongation is given by ΔL = (F L0) / (A E). This relation is a simplification that assumes uniform stress distribution and linear elastic behavior.

Elongation has two components: elastic elongation, which is reversible when the load is removed, and plastic elongation, which remains as permanent deformation after yielding. The total elongation can be expressed as ΔL = ΔLelastic + ΔLplastic. The percentage elongation is (ΔL/L0) × 100%, and the percent elongation at break is a common measure reported in tensile tests.

Measurement of elongation uses devices such as extensometers, optical methods, or direct length measurements. In engineering, elongation informs design for serviceability and safety, affecting deflection, stability, and failure modes. Material behavior varies: metals may exhibit substantial plastic elongation before fracture, ceramics are typically brittle with limited elongation, and polymers show a wide range of elongation depending on temperature and rate of loading.