Detecting Crack Initiation through Mapping Nonlinear Parametric Models

摘要

The detection of crack initiation and growth in an externally excited cantilevered beam is investigated. The method of nondestructive testing is based on mapping variations in the beam's nonlinear parametric model as identified through the system's excitation and nonlinear response. The studied system is a slender cantilever beam harmonically excited around its second natural frequency. Of the known significant nonlinear parameters for this system, including quadratic damping and terms due to bending and inertia, only the nonlinear bending term was included. This study uses the Continuous Time based nonlinear system identification technique. While harmonic in this application, the identification technique is readily translated into non harmonic and time varying excitations, thereby making it robust in its applicability. The method used here has advantages over mappings of the system's linear parameters, such as natural frequency whose value changes as the amplitude of excitation is increased for physical systems behaving nonlinearly. Results indicate that this method can identify changes in the system's behavior well before the failure of the system being studied, suggesting the method may lead users to avoid catastrophic failure in practice.