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This work investigates the mechanical behavior under out-of-plane compression of the Al core and honeycomb sandwich at increasing temperatures of up to 300 °C. After the first introductive theoretical modeling on room-temperature compressive behavior, the experimental results at increasing temperatures up to 300 °C are presented and discussed. The analysis of the results shows that peak stress, plateau stress, and specific absorbed energy gradually decrease as the temperature increases. The final densification occurs always at the same strain level (around 75%). Sandwich honeycomb test temperatures have been limited to 200 °C for bonding problems of the skin to the sandwich due to the glue. The experimental and modeling results agree well at room temperature as well at increasing temperatures. The results can provide useful information to choose base materials for greater energy absorption at increasing temperatures. [ABSTRACT FROM AUTHOR]

A flexible and versatile method for manufacturing open-cell metal foams, called lost-PLA, is presented in this work. With a double extruder 3D printer (FDM, Ultimaker S3, Utrecht, The Netherlands), it is possible to make polymer-based samples of the lost model. Through CAD modeling, different geometries were replicated so as to get black PLA samples. This method combines the advantages of rapid prototyping with the possibility of manufacturing Al-alloy specimens with low time to market. The production process is articulated in many steps: PLA foams are inserted into an ultra-resistant plaster mix, after which the polymer is thermally degraded. The next step consists of the gravity casting of the EN-6082 alloy in the plaster form, obtaining metal foams that are interesting from a technological point of view as well as with respect to their mechanical properties. These foam prototypes can find application in the automotive, civil and aeronautical fields due to their high surface/weight ratio, making them optimal for heat exchange and for the ability to absorb energy during compression. The main aspects on which we focus are the set-up of the process parameters and the characterization of the mechanical properties of the manufactured samples. The main production steps are examined at first. After that, the results obtained for mechanical performance during static compression tests with different geometry porosities are compared and discussed. The foam with truncated octahedron cells was found to show the highest absorbed energy/relative density ratio. [ABSTRACT FROM AUTHOR]

Microstructural stability is one of the utmost important requirements for metallic materials in engineering applications, particularly at high temperatures. The paper shows how Mechanical Spectroscopy (MS) (i.e., damping and dynamic modulus measurements) permits the monitoring of the evolution of lattice defects, porosity, and cracks which strongly affect the mechanical behavior of metals and sometimes lead to permanent damage. For this purpose, some applications of the technique to different metals and alloys (AISI 304 stainless steel, PWA 1483 single crystal superalloy, nanostructured FeMo prepared via SPS sintering and tungsten) of engineering interest are presented. These experiments have been carried out in lab conditions using bar-shaped samples at constant or increasing temperatures. The results can be used to orient the interpretation of frequency and damping changes observed through other instruments in components of complex shape during their in-service life. [ABSTRACT FROM AUTHOR]

Aluminum foam sandwiches (AFS) with AlSi10 foam cores and AISI 316L steel skins are manufactured by an in-situ bonding process. The precursor of the core foam was made with the powder compacted method. The precursor and skins, coupled together, were then heated up to the melting point of the Al alloy. The gas released by the blowing agent formed hydrogen bubbles in the melt. producing the foam. Such a porous structure was kept frozen at room temperature via cooling in cold water. To optimize the process conditions, some foaming experiments have been conducted with different holding times and temperatures. Such manufactured AFS were cut, chemically etched and studied with an optical microscope associated with image analysis software to get information about pores morphology in terms of circularity and equivalent diameter. The interface AlSi10-AISI316L has been characterized by SEM and EDX to investigate the bonding conditions between cores and skins. Finally, the AFS have been polished and etched to analyze the microstructure. Quasi-static compressive tests have been performed on the AFS. Obtained results showed that the interface formed during the foaming can be characterized by the inter-diffusion of alloying elements, as confirmed by the good quality of metallurgical joints. [ABSTRACT FROM AUTHOR]

In the last decades, great attention has been focused on the characterization of cellular foams, because of their morphological peculiarities that allow for obtaining effective combinations of structural properties. A predictive analytical model for the compressive behavior of closed-cell Al foams, based on the correlation between the morphology of the cellular structure and its mechanical response, was developed. The cells' morphology of cylindrical specimens was investigated at different steps of compression by X-ray computed tomography, in order to detect the collapse evolution. The structure, typically inhomogeneous at local level, was represented by developing a global virtual model consisting of homogeneous cells ordered in space, that was fitted on the experimentally detected structure at each deformation step. As a result, the main parameters characterizing the two-dimensional cells morphology (equivalent diameter, circularity), processed by the model, allowed to simulate the whole compression stress–strain curve by enveloping those obtained for each step. The model, fitted on the previous foam, was validated by comparing the simulated stress–strain curve and the corresponding experimental one, detected for similar foams obtained by different powder compositions. The effectiveness in terms of an accurate prediction of the compression response up to the final densification regime has been confirmed. [ABSTRACT FROM AUTHOR]