Since mechanical stress in structures affects issues such as strength, expected operational life and dimensional stability, a continuous stress monitoring scheme is necessary for a complete integrity assessment. Consequently, this paper proposes a stress monitoring scheme for cylindrical specimens, which are widely used in structures such as pipelines, wind turbines or bridges. The approach consists of tracking guided wave variations due to load changes, by comparing wave statistical patterns via Principal Component Analysis (PCA). Each load scenario is projected to the PCA space by means of a baseline model and represented using the Q-statistical indices. Experimental validation of the proposed methodology is conducted on two specimens: (i) a 12.7 mm (1/2″) diameter, 0.4 m length, AISI 1020 steel rod, and (ii) a 25.4 mm (1″) diameter, 6m length, schedule 40, A-106, hollow cylinder. Specimen 1 was subjected to axial loads, meanwhile specimen 2 to flexion. In both cases, simultaneous longitudinal and flexural guided waves were generated via piezoelectric devices (PZTs) in a pitch-catch configuration. Experimental results show the feasibility of the approach and its potential use as in-situ continuous stress monitoring application.

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Lattice structures are employed as lightweight sandwich cores, supports, or infill patterns of additive manufacturing (AM) components. As infill structures, the mechanical properties of AM parts are influenced by the infill pattern. In this work, we present the mechanical characterization of three commonly used infill patterns in AM, triangular, square, and hexagonal, and compare them with analytical and numerical models. Fused filament fabrication of polylactic acid (PLA) thermoplastic is used as the printing material for the compressive and tensile tests. First, a parametric analysis is performed by changing the infill density to obtain numerically and analytically the mechanical properties of the studied samples. Next, we compare the experimental results with numerical and analytical models and propose numerical correlations for high-density honeycombs. The stiffest infill pattern was the square, and the explanation is provided in detail. Also, there is a nonlinear correlation between density and the mechanical properties; however, the strongest part was not possible to determine with a significant statistical value. Finally, we propose simplified models for predicting the compressive and tensile response of AM PLA structures by considering the infill regions as homogenized structures.

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