Testing Metals using a Clip-On Extensometer
A laboratory that rarely tests metals tends to favor a cost-effective solution. Nevertheless, the typical values of the metal standard specimens (L0 50/80 mm or 2.0/3.0 inches) are to be determined reliably, without compromising accuracy—even under temperature conditions. The clip-on extensometers 5025-1 and 8040-1 are developed by ZwickRoell for this specific type of situation.
Determination of uniform elongation Ag / Elu’ with a Clip-On—made possible by the wide measurement range
A wide measurement range was therefore a requirement in the development of the Clip-on extensometers 5025-1 / 8040-1, which cover an elongation of up to 50% of the initial gauge length. In metals testing, this feature is used to determine every typical value that occurs before fracture, from the slope of the elastic section to uniform elongation Ag / Elu’:
- mE – slope of the elastic range
- Rp 0.1, Rp 0.2 – elongation at 0.1/0.2 % plastic deformation
- ReH/ReL, UYS/LYS – upper / lower yield strength
- Ag, Elu’ – uniform elongation / plastic extensometer strain at maximum force
High extensometer accuracy in many areas
Other than based on its classification, the accuracy of an extensometer can be established by its capability to be used for strain rate control, among other features:
- Accuracy class 0.5 (ISO 9513 ) / B1 (ASTM E83).
- Can be used for closed loop strain rate control on metals to ISO 6892-1 Method A(1) and to ASTM E8 Method B.
- Extremely high accuracy in a temperature chamber: temperature-related deviations are recorded on a compensation curve. When testing under temperature conditions, accuracy deviations are compensated and high accuracy is guaranteed.
- Precise initial gauge length: Reproducible results through exact and lockable setting of the initial gauge length (no operator influence).
- Low influence on the specimen during the measurement due to its lightweight construction.
Special circumstances presented by round specimens: the Clip-on grasps the challenge
Round specimens make the attachment of clip-on extensometers difficult: however, these clip-ons feature a special gripping adaptation. Typical gripping of round specimens is achieved through fragile 2-point contact. Our Clip-on extensometer achieves a clean grip with special prismatic counter rollers. This turns attachment into child’s play and the test runs smoothly.
