Modeling and Experimental Testing of Strain Gauges in Operational and Failure Modes

Strain gauges are resistive sensors bonded at critical locations on the surface of structural components to detect surface deformation and, thus, measure mechanical stress. However, strain gauges do not always report expected measurements, even under normal operating conditions. The primary goals of this paper were to develop predictive models for strain-gauge behavior and experimentally test them under controlled laboratory settings. A testing station was developed that generated a mechanical motion on a beam, subjecting strain gauges to a sinusoidally varying strain. Predictive models of the testing station were developed and experimentally analyzed. Models were also developed for two particular failure modes, namely, debonding and wire lead termination. For the cases studied, the models overpredict the output of a strain gauge operating under normal conditions, which is a discrepancy that can be explained by the gauge modifying the surface properties of the test component. Models for debonding and loose lead show agreement in terms of reduction in signal amplitude and histogram modification, respectively. Calculated and experimental data are presented that show characteristic signals in terms of time domain and histogram analysis.