| Acoustic Emission (AE) has become a prominent Nondestructive Testing (NDT) technique with capabilities to be used for Structural Health Monitoring (SHM) applications that entail in-service monitoring, detecting damage-prone areas, and establishing damage prognostics of structures. The next generation of acoustics-based techniques for SHM will rely upon the reliable and quantitative characterization of AE signals related to dominant damage mechanisms. In this context, the forward problem of simulating AE activity is addressed herein by proposing advanced finite element models for damage-induced stress wave generation and propagation. Acoustic emission for this purpose is viewed as part of the dynamic process of energy release caused by damage initiation. To form the computational approach, full field experimental information obtained from monitoring the damage initiation process using digital image correlation is used to construct constitutive laws, e.g. traction-separation law, and to define other damage related parameters. Subsequently, 3D FE simulations based on such experimental data are implemented using cohesive zone modeling and extended finite element method to create an initial failure. Numerically simulated AE signals from the dynamic response due to the onset of damage are evaluated in the context of the inverse problem of source identification and localization. The results successfully demonstrate material and geometry effects of the propagating source and describe completely the AE process from crack-induced isolated source to transient and steady-state dynamic response. Furthermore, the computational model is used to provide quantified measures of the energy release associated with crack. In addition, the effect of plasticity on simulated traveling waves ahead of the crack tip was investigated and revealed nonlinear interactions that had been postulated to exist. Ultimately, the forward AE methodology is applied to an aerospace structural component to recreate the debonding process and associated stress release propagation. All damage-induced wave propagation simulations presented in this dissertation create a pathway for the quantitative comparison between experimental and theoretical predictions of AE. |
