The present research investigates the complex phenomena of wave scattering in bolted joint. The goal is to develop an understanding of the attenuation behavior of propagating waves, through the structure, as the bolt is subjected to different torques. This is a first step towards developing a structural health monitoring technique for detecting torque loss at a bolted joint. To simulate the local effects of the bolt, a micromechanics based model has been developed to model the scattering and attenuation behavior due to a single fiber in a matrix with a circumferential interface crack. A slicing approach is used to account for the effect of multiple interfacial cracks at different orientations through the depth
of the structure, to simulate the global effects of the bolt. The change in wave attenuation as a function of bolt location, at different depths in a plate, is studied. Next, the variation in wave scattering as the bolt, which is now fully embedded in the plate, is subjected to different torque is investigated. The local stress fields that develop in the plate due to the torque are treated as a pre-stress condition and their effect on the resultant wave scattering is investigated using the developed model. The resultant attenuation accounts for the combined effect of the geometrical attenuation and the attenuation due to the pre-stress. Numerical results obtained show small but steady increase in the attenuation with the applied torque. Experiments conducted to validate the developed model show similar trends.
In structural health monitoring, energy dissipation of wave propagation is a key factor to determine optimal placement of sensors and quantify damage. This paper focuses on the study of wave scattering and attenuation in fiber-reinforced composite laminates with damage. In order to obtain the overall attenuation coefficient, the propagation of elastic shear wave in fiber-matrix medium is investigated starting from the Helmholtz equation. The wave attenuation due to interfacial damage is considered. The attenuation due to cracks of varying sizes and the effect of frequency on the attenuation value has been examined. It can be shown that a critical frequency exists at a given crack size for which the attenuation in the composite medium is at its highest value. Furthermore, the wave attenuation in composite laminates is investigated by incorporating energy transfer in layerwise medium. The overall attenuation coefficient for the laminate is obtained. Experiments are also conducted to evaluate some of the observations obtained from the model.