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Additive manufacturing is a novel way of processing metallic cellular structures from a powder bed. However, differences in geometry have been observed between the CAD and the produced structures. Struts geometry has been analysed using X-ray microtomography. From the 3D images, a criterion of ‘mechanically efficient volume’ is defined for stiffness prediction. The variation of this criterion with process parameters, strut size and orientation has been studied. The effective stiffness of struts is computed by finite element analysis on the images obtained by X-ray tomography. Comparison between the predicted stiffness and the effective one tends to show that the efficient volume ratio leads to a slight underestimation of the stiffness. Finally, the effective stiffness is used at the scale of a unit cell. This can help define the build orientation and loading direction that lead to the highest stiffness.

. Building new entities from existing titanium part by electron beam melting: microstructures and mechanical properties.

International audienceThis paper aims at presenting the main processing routes that are used to produce foams in their general definition and the typical structure that can be obtained according to the process. We first describe the main classification of the foam according to the level of porosity (open cells, closed cells, partially open cells and mixed cells). We present briefly the main processes to obtain such structures (non-removable space holder stacking and impregnation, removable space holder, foaming from gas or from precursor and shortly additive manufacturing) with a specific focus on the metal foam processing. We finally indicate the main structure that can be obtained with these types of processes and the main characteristics that are necessary to quantify at the various scale of the structure

Selective laser melting (SLM) is of great interest for manufacturing lightweight structures such as lattices. It allows a broad range of lattice topologies to be created. However, when manufacturing small struts, roughness, lack of dimensional accuracy, and porosity level can decrease their mechanical properties and thus affect the mechanical response of the entire structure. This study focuses on the high‐resolution characterization of alloy 718 (UNS N07718) single struts (constitutive elements of the lattice) manufactured by SLM. Process parameters, strategy, and post‐treatments remain constant while varying strut positions on the build plate and orientations. A methodology for the systematic characterization of 19 struts with high‐resolution X‐ray tomography has been developed. Different features related to the strut size, shape, waviness, roughness, and porosity are extracted. The analysis of those features when varying strut positions and orientations highlights the influence of each parameter. The build orientation is a first‐order parameter influencing strut morphology as already referenced in the literature. This systematic study reveals also the influence of the in‐plane orientation for inclined struts that alters their roughness, shape, and size.

Corrugated struts as part of lattice structures can lead to novel mechanical behavior by a combination of material and geometrical hardening. The unfolding behavior of such struts offers a potential of large macroscopic straining. However, their ability to be unfolded is impacted by the surface characteristics inherited from the additive manufacturing process. This study evaluates the unfolding sensitivity to these surface characteristics. Corrugated struts with varying surface roughness have been produced using a combination of Electron Beam Powder-Bed Fusion to produce corrugated samples with different nominal diameters, and chemical etching assisted by micro-CT to achieve a given final diameter. In-situ micro-CT tensile tests have been carried out to track the evolution of the struts morphology under loading. Surface defects play a significant role in the unfolding ability of such struts. They are characterized either by a global roughness or by a local notch depth. A quite broad unfolding dispersion remains for samples with the same level of roughness. A finer description of notch depth and location within the gauge length allows a more accurate prediction of the unfolding ability. A model for predicting the probability of failure during unfolding is presented.

A pragmatic design strategy to achieve unusual mechanical responses in metal lattice structures is deployed. This strategy, referred to as behavior by design, is illustrated with an architectured material fabricated to provide a "whistle-blower" mechanical response under tensile loading. Struts with unusual geometries, e.g. dog-bone struts and corrugated struts, are assembled in parallel in a standard lattice unit-cell to obtain the targeted elasto-plastic behavior, here a "whistle-blower" behaviour. The design strategy benefits from the freedom provided by additive manufacturing.