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Axial Loading
When measuring the maximum principal strain in a known uniaxial stress state, a simple means for assuring effective temperature compensation is to mount a second gage adjacent and perpendicular to the primary gage, and connect the two gages in a half-bridge circuit as shown below. Such an arrangement is said to have active gages, since the bridge output is increased by that factor. The circuit behavior is nonlinear, however, because the resistance changes in the two active gages are not equal and opposite.

Uniform uniaxial stress : = 1+

It is assumed in the following that in the circuit above represents the primary gage, and that the object is to scale the instrument to register the test-surface strain under that gage. Whether shunting , to simulate compression in the primary gage, or shunting to simulate tension, the nonlinearity during scaling is different from that during actual strain measurement. Thus, two different shunt-calibration relationships are required for precise strain simulation, as in the case of the quarter-bridge circuit. These relationships are developed in the same manner as before; that is, by enforcing the condition that the bridge output voltage be identical, whether scaling to a simulated strain level or measuring the same surface strain with the primary gage.

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