Multi-materials of metal-polymer and metal-composite hybrid structures (MMHSs) are highly demanded in several fields including land, air and sea transportation, infrastructure construction, and healthcare. The adoption of MMHSs in transportation industries represents a pivotal opportunity to reduce the product’s weight without compromising structural performance. This enables a dramatic reduction in fuel consumption for vehicles driven by internal combustion engines as well as an increase in fuel efficiency for electric vehicles. The main challenge for manufacturing MMHSs lies in the lack of robust joining solutions. Conventional joining processes, e.g., mechanical fastening and adhesive bonding involve several issues. Several emerging technologies have been developed for MMHSs’ manufacturing. Different from recently published review articles where the focus is only on specific categories of joining processes, this review is aimed at providing a broader and systematic view of the emerging opportunities for hybrid thin-walled structure manufacturing. The present review paper discusses the main limitations of conventional joining processes and describes the joining mechanisms, the main differences, advantages, and limitations of new joining processes. Three reference clusters were identified: fast mechanical joining processes, thermomechanical interlocking processes, and thermomechanical joining processes. This new classification is aimed at providing a compass to better orient within the broad horizon of new joining processes for MMHSs with an outlook for future trends.
The present study is aimed at determining the local density of components made by fused deposition modeling (FDM) through non-destructive indentation tests. An experimental campaign was performed to assess such a relationship. Specimens were made varying the amount of material flow and the direction of deposition. The specimen’s dimension and weight were measured to determine the average density. The internal porosity due to uncomplete filling produced due to the deposition process was also assessed through cross-sectioning. Instrumented indentation tests were conducted on the samples to determine a relationship between the density and the slopes during the loading and unloading phases. The tests were performed using flat cylindrical indenters of different diameters. The results indicated that the density of the specimens was strongly influenced by the adopted material flow and the orientation during deposition. An empirical relationship was determined between the slopes measured during indentation tests and the density. Such a relationship is independent of the deposition orientation. The optimized procedure represents a valuable tool to determine the local density of components made by fused deposition modeling through non-destructive indentation tests.
Evaluating local mechanical properties of parts made by additive manufacturing processes can improve the deposition conditions. This study proposes a non-destructive characterization test to determine the mechanical behavior of fused deposition modeling (FDM) components. Indentation and compression tests were conducted on samples produced by the FDM process, which were created by varying the material flow during the deposition. An empirical relationship was determined between yield strength determined through compression and indentation tests. R2 = 0.92 characterized the correlation between the compression and indentation test. The results indicated that both the yield strength measured through compression tests and that measured by the indentation tests increased linearly with the density of the components. Indentation tests provided more insights concerning the tested surface’s local characteristics than the compression test.
Evaluating local mechanical properties of parts made by Additive Manufacturing processes can improve the deposition conditions. This study proposes a non-destructive characterization test to determine the mechanical behavior of fused deposition modeling (FDM) components. Indentation and compression tests were conducted on samples produced by the FDM process, which were produced by varying the material flow during the deposition. An empirical relationship was determined between yield strength determined through compression and indentation tests. R2 = 0.92 characterized the correlation between the compression and indentation test. The results indicated that both the yield strength measured through compression tests and that measured by the indentation tests increased linearly with the density of the components. Indentation tests provided more insights concerning the tested surface's local characteristics than the compression test.
The present study investigates the compression behavior of components made by material extrusion, also known as fused filament fabrication (FFF) or fused deposition modeling (FDM). An experimental plan was conducted by adopting a high-density fulfillment and varying the material flow. Additional tests were performed by thermomechanical compaction to produce full-density samples. Compression tests were performed at various strain rates ranging between 5 10− 4 to 5 10− 1 s− 1. Yielding and post-yielding behaviors were analyzed. Morphological analysis was carried out to determine the mesostructural features (interlayer neck and void sizes) and how they behave during the compression test. The results indicated that the principal dimension of the voids ranged between 65 µm and 170 µm depending on the adopted value of the extrusion multiplier. On the other hand, thermomechanical compaction enabled the restriction of the voids of printed samples to 10 µm. The cross-sectioning of samples at different strains indicated the formation of shear banding strain localization. In addition, printed samples behaved like porous media during the compression tests and showed different characteristic regions with different voids dimensions. The samples printed at the higher material extrusion showed similar behavior to compacted samples. Post-yielding analysis indicated that strain softening observed on compacted samples was more severe as compared to that observed on printed samples. this behavior is dramatically reduced by decreasing the extrusion multiplier.
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