This paper presents the results of a comparative evaluation of the tensile strength behaviors of parts obtained by additive manufacturing using fused filament fabrication (FFF) technology. The study investigated the influences of the deposition printing parameters for both polymers and fiber-reinforced polymers. Polymeric materials that are widely used in FFF were selected, including acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and nylon. Carbon and glass continuous fibers were used to reinforce the nylon matrix in composite materials. The study utilized two manufacturing methods. Polymers were manufactured using an Ultimaker 2 Extended+ device and the fiber-reinforced polymer specimens were obtained using a Markforged Mark Two printer. The entire set of specimens was eventually subjected to destructive monoaxial tensile tests to measure their responses. The main goal of this study was to estimate the effect of the different infill patterns applied (zig-zag, concentric, and four different orientations lines) on the mechanical properties of pure thermoplastic materials and reinforced polymers. Results show a spectacular increase in the tensile stress at break, which for polymers reaches an average value of 27.53 MPa compared to 94.51 MPa in the case of composites (increase of 70.87%). A similar increase occurs in the case of tensile stress at yield with values of 31.87 MPa and 105.98 MPa, respectively, which represents an increase of 69.93%. The influence of the infill of the fiber is decisive, reaching, in the 0-0 arrangement, mean values of 220.18 MPa for tensile stress at break and 198.26 MPa for tensile stress at yield.

The aim of this work was to conduct a dimensional study, in terms of microgeometry, using parts from an additive manufacturing process with fused filament fabrication (FFF) technology. As in most cases of additive manufacturing processes, curved surfaces were obtained via approximation of planes with different inclinations. The focus of this experimental study was to analyze the surface roughness of curve geometry from surface-roughness measurements of the plane surfaces that generate it. Three relevant manufacturing parameters were considered: layer height, nozzle diameter and material. Taguchi’s experimental design based on the Latin square was applied to optimize the set of specimens used. For the manufactured samples, the surface-roughness parameters Ra (roughness average), Rq (root mean square roughness) and Rz (maximum height) were obtained in eight planes of different inclinations (0° to 90°). The results were analyzed using both a graphical model and an analysis of variance study (ANOVA), demonstrating the dependency relationships among the parameters considered and surface finish. The best surface roughness was reached at 85°, with a global average Ra value of 8.66 µm, increasing the average Ra value from 6.39 µm to 11.57 µm according to the layer height increase or decreasing it slightly, from 8.91 µm to 8.41 µm, in relation to the nozzle diameter increase. On the contrary, the worst surface roughness occurred at 20°, with a global average Ra value of 19.05 µm. Additionally, the theoretical profiles and those from the surface-roughness measurement were found to coincide greatly. Eventually, the eight regression curves from the ANOVA allowed prediction of outputs from future specimens tested under different conditions.

The paper describes an experimental study developed on the AA7075 T651, which is an aluminum alloy extensively used in the aeronautical industry. This work presents a double approach of investigation where there is no literature about previous research. This includes the analysis of the results obtained by the combination of mechanical and chemical actions on the mechanical properties of this material. On the one hand, the combinations of relevant milling parameters (feed rate, cutting speed) on flat samples (flat specimens have been selected by attempting to reproduce with the most accurate way the geometry and the type of machining process known as face milling is usually used in this manufacturing field). On the other hand, the stimulating effect of the corrosion by salt spray on selected batches of specimens was machined in the previous stage. Results from tensile tests performed on the whole of specimens allowed us to evaluate how the main mechanical properties (yield strength, tensile strength, and elongation at break) have been affected by the processes applied. Elongation at the break presents a reduction in an inverse order to feed a rate increase (up to 24.5%) and this reduction is extended (additional 19.17%) in specimens under corrosion conditions, which results in a greater fragility of the material.

Nowadays, thanks to the new manufacturing processes, indentation is becoming an essential part of the new arising processes such as the Incremental Forming Processes. This work presents the experimental validation of the analytical model developed for an indentation-based process. The analytical model is originated from the Upper Bound Theorem application by means of its new modular distribution. The modules considered are composed of two Triangular Rigid Zones each. The experimental validation is performed through a series of indentation tests with work-pieces of annealed aluminium EN AW-2030 and punches of steel AISI 304, under plane strain conditions. The results are compared with the ones obtained from the application of this new modular distribution of the Upper Bound Theorem, showing a good approximation and suitability of the model developed for an indentation-based process.

The work developed presents, for the first time, a tool to analyze all the thermodynamic models used in the study and development of Stirling engines: isothermal, ideal adiabatic and adiabatic with losses, combined adiabatic thermodynamic with finite speed (CAFS), thermodynamic with finite speed (FST), ideal polytropic and polytropic with losses (PSVL), allowing a comparative study of them.