Amy N. Robertson

Piezoelectric Active Sensor Self-Diagnostics using Electrical Admittance Measurements

This paper presents a piezoelectric sensor self-diagnostic procedure that performs in situ monitoring of the operational status of piezoelectric materials used for sensors and actuators in structural health monitoring (SHM) applications. The sensor/actuator self-diagnostic procedure, where the sensors/actuators are confirmed to be functioning properly during operation, is a critical component to successfully complete the SHM process with large numbers of active sensors typically installed in a structure. The premise of this procedure is to track the changes in the capacitive value of piezoelectric materials resulting from the degradation of the mechanical/electrical properties and its attachment to a host structure, which is manifested in the imaginary part of the measured electrical admittances. This paper concludes with an experimental example to demonstrate the feasibility of the proposed procedure.

Singularity detection for structural health monitoring using Holder exponents

The majority of structural health monitoring studies reported in the technical literature focus on identifying damage sensitive features that can be extracted from dynamic response data. However, many of these studies assume the structure can be modeled as a linear system before and after damage and use parameters of these models as the damage sensitive features. The study summarized in this paper proposes a damage sensitive feature that takes advantage of the nonlinearities associated with discontinuities introduced into the dynamic response data as a result of certain types of damage. Specifically, the Holder exponent, a measure of the degree to which a signal is differentiable, is the feature that is used to detect the presence of damage and when that damage occurred. A procedure for capturing the time varying nature of the Holder exponent based on wavelet transforms is demonstrated through applications to non-stationary random signals with underlying discontinuities and then to a harmonically excited mechanical system that contains a loose part. Also, a classification procedure is developed to quantify when changes in the Holder exponent are significant. The results presented herein show the Holder exponent to be an effective feature for identifying damage that introduces discontinuities into the measured dynamic response data.

A Coupled Approach to Developing Damage Prognosis Solutions

Funding for the Los Alamos Damage Prognosis Initiative is being provided by the Department of Energy through Laboratory Directed Research Development. In addition to the authors, the Damage Prognosis research team includes Los Alamos staff members Matt Bement, Irene Beyerlein, Norm Hunter, Cheng Liu, Brett Nadler, and Jeni Wait. Los Alamos graduate research assistants Tim Fasel, Jan Goethals and Trevor Tippetts, and. Professor Dan Inman and graduate student David Allen at Virginia Tech.