Vikrant R. Hiwarkar

Damage Assessment of a Cracked Bar: Effect of Material Nonlinearity on Vibro-Impact Response

Structural health monitoring is receiving much attention as a means to prevent catastrophic failure in structures in operating conditions. In most cases fracture is caused by the growth of crack, which cannot be precluded in many engineering structures. Moreover, to have an accurate quantitative estimate of crack tolerance of a structure to prevent fracture of load bearing components, an effective non-destructive evaluation procedure becomes necessary to monitor the structure under working conditions.

Nonlinear Vibro-acoustic Interactions for Crack Detection in Beams

Recent years have shown a growing interest in damage detection methods based on damage-related nonlinearities in structures. In the paper, the numerical simulations of two techniques – classical Higher Harmonic generation and Vibro-Acoustic Modulation - are presented and validated experimentally. Two-dimensional models of beam with non-propagating cracks are investigated. The focus is on bi-linear breathing crack behavior, which was modeled as a contact between crack faces. This phenomenon is known as crack breathing. Numerical simulation results show that nonlinear phenomena investigated are particularly strong in the vicinity of the crack. A number of aluminum beam specimens with different crack lengths and locations are investigated experimentally to validate numerical simulations. Signal responses were measured at several positions using piezoceramic sensors. The results show that nonlinear phenomena investigated depend not only on excitation amplitude – as expected – but also on crack position, sensor location and boundary conditions. doi: 10.12783/SHM2015/181

Vibro-impact response of a cracked bar

The presence of a crack in a structure affects its dynamic behaviour under working conditions. Cracks introduce nonlinearities into the system; the use of such nonlinearit ies for damage detection should be investigated. A model of a one- dimensional cracked cantilever bar subjected to longitudinal harmonic excitation is used to analyse a vibro-impact response as a way to monitor structural health. The effect of contact nonlinearity due to cracks faces interaction is considered . This nonlinear information is obtained based on a combination of the analytical technique and the Matlab-Simulink computation. The procedure uses a numerical approximation for dynamic compliance operators and a nonlinear model of contact faces interaction implemented numerically as a nonlinear feedback. Nonlinear resonant phenomena due to vibro-impact interaction in the cracked bar are obtained and analysed. A distribution of the higher harmonics along the bar length, generated due to the nonlinear response of the crack, is revealed as a function of the distan ce from the crack. Recommendations on structural health monitoring of cracked bars due to contact nonlinearity are presented