Axial stress monitoring strategy in arbitrary cross-section based on acoustoelastic guided waves using PZT sensors

Axial stress monitoring in arbitrary cross sections is a challenging task. Stringers are the main axial load carrying components of aircraft skin structures and have typical complex cross sections. This paper investigates the strategy of axial stress monitoring in an arbitrary cross section based on acoustoelastic guided waves using piezoelectric lead zirconate titanate (PZT) sensors. To select appropriate guided wave frequencies and modes sensitive for axial stress monitoring in an arbitrary cross section, the feature guided waves are investigated using acoustoelastic theory combined with the semianalytical finite element method. The mode shapes are derived, which show that these longitudinal-like modes are more sensitive to axial stress. A PZT transducer array is also considered to maximize desired modes. Piezoelectric sensors are used to excite and detect the guided waves in the experiments. Results from acoustoelastic measurements on a T-type stringer are presented, showing the feasibility of this method for axial stress monitoring.