The strain gage testing process

Strain gage testing is used to determine material stress due to static and dynamic loads coming from internal and external sources, such as mechanical, thermal, and pressure.

Strain gages can be either bonded or welded to the test surface. The simplest strain gage circuit is a ¼-bridge configuration which uses a solitary gage to measure strain along a single axis. A rosette of three ¼-bridge circuits can be used to determine principal stresses and construct a Mohr's circle of the stress state. Specialized full-bridge circuits are used to measure bending, tension and torsion. For example, when used with telemetry, this testing can identify blade tension due to centrifugal force, bending due to lift, bending due to drag, plus torsion in the drive shaft of an axial flow fan.

The procedure is used for product qualification as well as for vibration troubleshooting and failure analysis purposes.