Non-linear SHM Based Damage Detection in Doubly-Curved-Shells

Abstract

Doubly curved shells are used as structural members in space launch vehicles as part of propellant tanks, pressure bulkheads in aircrafts, submarine-hull, etc. SHM techniques for these structures are limited in the literature. The present study is based on the fact that higher harmonics will be generated in guided wave propagation in presence of Contact Acoustic Nonlinearity (CAN) type defects such as fatigue crack and de-lamination. The higher harmonics are generated due to non-linear interaction of the crack surfaces when the incident wave passes through these surfaces. Also, the study explores capability of non-linear Vibro-Acoustic Modulation (VAM) technique on doubly curved shell structures for the detection of CAN type defects. VAM is based on the response of the system where effects of modulation of low-frequency vibration (pumping vibration) on high frequency guided wave propagation (probing wave) are studied. In the presence of damage, the frequency spectrum of the response shows sidebands with respect to the frequency of the guided wave excitation. These non-linearity features of guided wave propagation are numerically and experimentally investigated on a doubly-curved-shell structure which has a CAN type defect of partially bonded attachment.