extensometrie

Extensometrie, or extensometry, is the branch of measurement focused on quantifying strain—the relative change in dimension—of materials or structures under mechanical load. It is essential for characterizing mechanical properties such as stiffness, yield behavior, ductility, and fatigue performance. Extensometry can be performed on a specimen during tensile, compression, bending, or cyclic tests, typically using devices that track length change with high precision.

Types of extensometers include mechanical contact devices that attach to the specimen and measure extension over a defined gauge length using pins, jaws, or hooks; clip-on or screw-in variants are common. Non-contact optical methods, such as digital image correlation (DIC) or laser-extensometry, derive strain from images of the specimen surface. Strain gauges are sometimes used to infer local strain and can be integrated in extensometer configurations. Universal testing machines often provide integrated extensometers and data acquisition interfaces.

Principles and considerations: strain is usually expressed as epsilon = ΔL/L0, where L0 is the initial gauge length and ΔL is the change in length. Measurements require careful alignment, temperature control, and an appropriate gauge length to balance resolution and representativeness. Calibration, drift correction, and compensation for thermal expansion are important, especially for high-temperature tests.

Applications and standards: extensometry is used across metals, polymers, composites, ceramics, and biomaterials to determine modulus, yield strength, ultimate tensile strength, and creep or fatigue behavior. Standards from ISO, ASTM, and other bodies prescribe measurement procedures, tolerances, and data interpretation for accuracy and comparability. Advances include full-field optical methods (DIC) and multi-axial or high-temperature extensometry.