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A novel structural health monitoring approach consisting of guided ultrasonic waves, acoustic emission, and digital image correlation, as well as real-time and postmortem analyses, was implemented to monitor and quantify crack growth in Al 2024 compact tension specimens, designed, and precracked according to ASTM E647-08. Tensile loads were applied according to ASTM E1290-08. Guided ultrasonic waves were generated with pulses centered at three different frequencies and were recorded using piezoelectric transducers. Guided ultrasonic waves were also modeled using finite element wave propagation models. The same transducers were further used for online acoustic emission monitoring. A digital image correlation system continuously monitored the crack growth and provided full-field surface strains. The application of this integrated structural health monitoring approach resulted in reliable damage detection and quantified crack growth measurements. In addition, a novelty detector based on the Mahalanobis distance was implemented in a data fusion scheme to assess the extent of damage. The reported results constitute a proof-of-concept investigation of a novel structural health monitoring approach based on the combination of real-time optical and acoustic nondestructive testing.

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A novel experimental mechanics technique using Scanning Electron Microscopy (SEM) in conjunction with Acoustic Emission (AE) monitoring is discussed to investigate microstructure-sensitive mechanical behavior and damage of metals and to validate AE related information. Validation for the use of AE method was obtained by using aluminum alloy sharp notch specimens with different geometries tested inside the microscope and compared to results obtained outside the microscope, as well as to previously published data on similar investigations at the laboratory specimen scale. Additionally, load data were correlated with both AE information and microscopic observations of microcracks around grain boundaries as well as secondary cracks, voids, and slip bands. The reported AE results are in excellent agreement with similar findings at the mesoscale, while they are further correlated with in situ and post mortem observations of microstructural damage processes.