Elongations Exceeding 20%

Strain measurements, particularly on materials such as plastic or rubber, sometimes surpass the capability of the EP-Series strain gage. Measurements in this range can be obtained through simple flexure devices designed to reduce the strain level on the gages. These devices, commonly referred to as clip gages, are shown below.

Clip Gage (Half Bridge)

Strain gages are installed on the top and bottom of the clip, and the clip mounted to the specimen by bonding or spot welding, depending on the specimen material. The displacement of the "feet" under strain causes corresponding resistance changes in the strain gages. With the gages wired into either a half or full Wheatstone bridge, their resistance changes are additive, thereby increasing the amount of available signal. Wherever space permits, full bridges are recommended because the effective bridge output is twice the half-bridge signal for the same foot displacement.

Clip Gage (Full Bridge)

Since the clip gage is normally a nonlinear device, the gage output is calibrated against known displacements before installation. The gage "zero" reading is monitored during the calibration, since a permanent zero offset after calibration can usually be traced to localized yielding of the metal strip. If this is indicated, the calibration should be repeated several times to check for reproducibility.

A clip gage is particularly useful in measuring very large specimen strains or actual displacements occurring between two bodies, as with expansion joints or crack openings.

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