Monitoring applied and residual stress in materials and structures by non-destructive acoustoelastic techniques

We present an innovative non-destructive approach based on the analysis of acoustoelastic effect for monitoring applied and residual stress in materials and structures. The proposed approach can be considered as base for a structures monitoring system. The analysis of the acoustoelastic effect for solid bodies, i.e., the correlation between the acoustic properties and the stress state, may be suitably exploited for experimental purposes. To this aim, relevant modeling and experimental issues should be overcome. Indeed, the usual theoretical framework of the acoustoelastic measurements is the so-called third-order elasticity, based on the use of the acoustoelastic coefficients, and requiring relatively simple experimental measurements. Here, by adopting an innovative ultrasonic setup, we investigate the capability of a theoretical model developed within the linearized elasticity, and used for describing the propagation of small amplitude waves in prestressed elastic materials. The results of the ultrasonic tests show that this approach in capable of accurate in situ stress measurements. The proposed experimental setup could be further investigated for monitoring applications of stress states in structures during their service life.