It also allows for proper measurement of the elongation, as it occurs along the sample’s whole length where appropriately gripped.
Using a wire instead of the coil spring provides an additional advantage. In environments where high precision is required, an elongation measuring tool called an extensometer can be used. These devices are designed to grip the samples at fixed points, and measure the change in distance between two points as the sample stretches. For example, if an extensometer has grips with an initial separation of one inch, and the sample stretches to further separate them by an additional half inch, the recording of the test will note a fifty percent increase of sample length, or elongation. The design of the extensometer often takes into account the intended sample material, and are constructed with physical limits to their maximum travel distance. Depending on the extensometer, these travel limits might be shorter than the full length of a test stand, but well within the expected limits of elongation based on material ductility. Integrated extensometer units have the advantage of being able to operate with the test system’s software, while independent units can be specifically configured for the material type. For example, longer elongation devices may be used for highly ductile samples, and more durable models are appropriate for less ductile samples so that they can stay on the sample through its break.
Author: Jacob Morales, Technical Support – Starrett Force Equipment
The L.S. Starrett Company - (978) 249-3551 - www.starrettmetrology.com/force
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