Field-deployable measurement technique for absolute acoustic nonlinearity parameter values.

Over the past two decades, several researchers have demonstrated that changes in the acoustic nonlinearity parameter β can be related to changes in material properties due to mechanical and/or thermal degradation processes. Generally, a piezoelectric sensor-based detection method is used to measure changes in β values because it is operationally simpler than the complex capacitive detection method. However, this method is limited to measuring only relative changes in β values; whereas, the absolute β values of components in service often need to be measured in the field to quantify the degradation level. Accordingly, a novel field-deployable method for measuring absolute β values was developed in this study. Nonlinear ultrasonic experiments were conducted using capacitive detection, conventional piezoelectric sensor-based detection, and proposed detection methods, and the results were compared. The β values of a copper single-crystal sample measured using the new and the capacitive detection methods were 2.49 and 2.1, respectively, and those obtained using the conventional piezoelectric sensor-based detection method ranged between 90 and 130. The test results confirm that the proposed field-deployable measurement method produces more consistent absolute β values without involving the complexity of the capacitive detection method.