The influence of enhanced closed-loop sensitivity towards breathing-type structural damage

This paper investigates the performance of a nonlinear damage detection method using sensitivity enhancing control (SEC). Damage nonlinearity due to the cyclic behavior of crack breathing could provide valuable evidence of structural damage without information of the structure's original healthy condition. Not having such information is considered a major challenge in vibration-based damage detection. In this study, two different categories of damage detection methods are investigated: frequency and time-domain techniques focusing on the benefit of SEC for breathing-type nonlinear damage in a structure. Numerical simulations using a cantilevered beam and spring-mass-damper system demonstrated that the level of nonlinear dynamic behavior heavily depends on the closed-loop pole placement through feedback control. According to SEC theory, the characteristic of the feedback gain defines the sensitivity of modal frequency to the change of stiffness or mass of the system. The sensitivity enhancement by properly designed closedloop pole location more visually clarifies the evidence of crack nonlinearity than the open-loop case where no sensitivity is enhanced. A damage detection filter that uses time series data could directly benefit from implementing SEC. The amplitude of damage-evident error signal of the closed-loop case significantly increases more than that of the open-loop case if feedback control or SEC properly modifies the dynamics of the system.