The increase in accessibility of fused filament fabrication (FFF) machines has inspired the scientific community to work towards the understanding of the structural performance of components fabricated with this technology. Numerous attempts to characterize and to estimate the mechanical properties of structures fabricated with FFF have been reported in the literature. Experimental characterization of printed components has been reported extensively. However, few attempts have been made to predict properties of printed structures with computational models, and a lot less work with analytical approximations. As a result, a thorough review of reported experimental characterization and predictive models is presented with the aim of summarizing applicability and limitations of those approaches. Finally, recommendations on practices for characterizing printed materials are given and areas that deserve further research are proposed.

Development of Autonomous Underwater Vehicles (AUVs) has permitted the automatization of many tasks originally achieved with manned vehicles in underwater environments. Teams of AUVs designed to work within a common mission are opening the possibilities for new and more complex applications. In underwater environments, communication, localization, and navigation of AUVs are considered challenges due to the impossibility of relying on radio communications and global positioning systems. For a long time, acoustic systems have been the main approach for solving these challenges. However, they present their own shortcomings, which are more relevant for AUV teams. As a result, researchers have explored different alternatives. To summarize and analyze these alternatives, a review of the literature is presented in this paper. Finally, a summary of collaborative AUV teams and missions is also included, with the aim of analyzing their applicability, advantages, and limitations.

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Flexure of slender structures, composed of filaments in a woodpile arrangement, is theoretically studied. Expressions for the apparent bending stiffness are derived. The model is validated experimentally using three-point bending. Computer simulations show that bending is accompanied by lattice shear for increased porosity. A shear-inclusive micromechanical model for two different stacking arrangements is developed. This is further refined by including shear deformation within the filaments, which is supported by numerical simulations for relatively short filament overhang. The apparent flexure and shear of lattice beams are attributed primarily to stretch and flexure of the filaments, respectively. Asymptotic formulas for the effective bending stiffness in terms of the relative density are presented. The apparent bending stiffness scales linearly with the volume fraction, whereas the apparent shear stiffness scales with the cube of the volume fraction. Exclusion of lattice shear leads to errors for by over an order of magnitude in the extreme, unlike void-free solid beams where shear is a higher order effect. Excellent quantitative agreement with numerical results is obtained for a wide range of porosity and external aspect ratio, when lattice shear is included in the model.