Strain Gages

These are sometimes called piezoresistive elements because their resistance changes in response to applied pressure or strain.

This is a grid-type, bonded-wire strain gauge. It is mounted to a thin piece of paper, and the entire assembly is then bonded to the test surface. When the gauge is bonded tightly to some material that experiences strain, the wire undergoes a change in length.

The area of the wire also changes according to Poisson's ratio, and that causes the gauge to show a change in resistance.

We can, therefore, determine the load applied as a function of the change in resistance.

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