Axial stress determination using highly nonlinear solitary waves.

This article presents a nondestructive evaluation (NDE) method to infer the neutral temperature and the axial stress in thick beams. The method relies on the propagation of highly nonlinear solitary waves generated at one end of a chain of spherical particles in a dry point contact with the beam to be evaluated. The waves are reflected back to the chain and the research hypothesis is that the axial stress, which influences the beam's stiffness, affects the amplitude and speed of the reflected waves. To verify this hypothesis a general finite element model of thermally stressed beams was developed and coupled to a discrete particle model able to predict the propagation of the waves along an L-shaped granular medium. The models were validated experimentally to quantify the repeatability of the setup, the sensitivity of the wave features on the thermal stress, and the independence of the wave features on the neutral temperature of the beam. The hypothesis was proven valid by both the numerical and the experimental results. In the future, these findings may be used to refine a NDE method to assess stress in columns, to infer the neutral temperature of continuous welded rails, and to prevent thermal buckling of critical structures.