ekstensometer

An extensometer, also known as an ekstensometer in some languages, is a measuring instrument used to quantify the deformation of a material specimen under mechanical load. It determines strain by monitoring the relative displacement between two or more points on the specimen, typically over a defined gauge length.

Most common is the mechanical extensometer, which uses two or more pins or jaws attached to the sample ends or to designated points along the gauge length. As the specimen elongates, the distance between sensing points changes, and this displacement is recorded by a dial indicator, a digital sensor, or an electronic transducer. Non-contact variants employ optical methods, such as video extensometry or digital image correlation, to track surface features and measure displacement without touching the specimen.

Extensometers are widely used in tensile testing to determine properties such as Young’s modulus, yield strength, and elongation at break. They are also employed in creep, fatigue, and fracture tests, and in civil engineering or geotechnical monitoring where distributed strain along a length is important. The choice of device depends on factors such as the expected strain, the gauge length, surface condition, temperature, and required measurement accuracy.

Key considerations include alignment to prevent slip or bending, calibration to zero, and temperature compensation. Limitations of mechanical extensometers include a restricted measurable strain range and potential contact damage or surface influence on the specimen. Optical methods mitigate some of these issues but require suitable surface texture and stable lighting conditions. Standards for tensile testing often specify the use of extensometers and definitions for gauge length and measurement methods.