The development of additive manufacturing and lattice structures has created opportunities for the development of lightweight impact–absorption structures that can overcome most constraints of previously used materials such as expanded polystyrene foams. However, for the successful application of such structures, the effects of their variables in their mechanical performance must be established. In this study, the mechanical properties and energy absorption of thermoplastic sheet gyroid structures were investigated and compared with the performance of current materials. Consequently, the specimens were tested after changing the main variables, i.e., cell size and volume fraction, of various thermoplastic materials such as acrylonitrile butadiene styrene, polylactic acid, thermoplastic polyurethane, and polyamide 12. Finally, they were tested in a quasi-static compression test and their deformation stages were photographed. The stress–strain curves of all materials changed after adopting the sheet gyroid structure, exhibiting three distinct regions: linear elastic, long collapse plateau, and densification that made them particularly applicable for energy absorption. Volume fraction affected the layer collapse. The elastic geometrical stiffness increased for higher volume fractions and smaller cells. In addition, the peak and plateau stresses increased at higher volume fractions, and while smaller cells were not directly affected. Additionally, the area under the curves increase with the volume fraction; hence, for most materials, specific energy absorption was larger for higher volume fractions. The constituent material properties contributed significantly to the structural behavior, exhibiting three primary deformation mechanisms, i.e., elastomeric, elastic–plastic, and elastic–brittle, resulting in a wide spectrum of properties for each application requirement. The comparison of the optimal properties with the expanded polystyrene demonstrated the ability of sheet gyroid structures to overcome most of its challenges, exhibiting a superior specific energy absorption, ability to withstand various impacts, letting air flow in its all axes, and being recyclable. Thus, sheet gyroid structures can be considered promising alternatives.

Triply periodic minimal surface (TPMS) structures can produce tailored complex structures for various applications and serve as substitutes for polymeric foams. In this study, six different types of TPMS structures (Neovious, gyroid, Schwarz P, Lidinoid, split P, and diamond) were examined under quasi-static compression in terms of their energy absorption capabilities, mechanical properties, and weights, which were compared with those of expanded polystyrene foam and the original printing material Z-Ultra. It was found that the Neovious, diamond, and Lidinoid structures were most suitable for substituting expanded polystyrene foam, especially in safety helmets requiring high specific energy absorption capabilities.

The interlaminar tensile strength of carbon/epoxy laminated curved beams with variable thicknesses is experimentally studied by means of a four-point-bending test. Firstly, the relationships between the used formulae and the results obtained are analyzed on the curved beams with different thicknesses and tested in compliance with ASTM D6415 standard. Secondly, both the interlaminar tensile stresses and the post-failure behaviour are determined. Finally, the critical area, where delamination begins, is reinforced through-the-thickness by means of tufting technology with different densities. The influence on the maximum interlaminar tensile stress as well as delamination evolution of the carbon/epoxy laminated curved beams are analyzed. These results play an important role in the prediction of interlaminar tensile strength and post failure behaviour of laminated curved beams.Peer Reviewe

Additive manufacturing allows the tailoring of the structure of energy-absorbing materials. It is thus feasible now to use light, printed structures instead of other materials such as foams and honeycombs, signifying greater possibilities for customization. Some of these structures are triply periodic minimal-surface structures that is a family of different structures like the gyroid one. Another benefit of additively manufactured graded structures, which foams or honeycombs lack, is the flexibility to vary the internal parameters along one or more directions. This study focuses on the comparative analysis of graded and non-graded gyroid structures for four common thermoplastic materials used in additive manufacturing. These structures are compared with each other under quasi-static compression testing, as well as with expanded polystyrene foam and solid samples of the thermoplastic materials. The analysis includes investigation of the stress–strain and specific stress–strain curves, capability of absorbing energy per unit weight and per unit volume, ideality, total efficiency, and normalized energy vs. normalized stress characteristics. We also analyze the internal fracture mechanism of the structures. The objective is to obtain more extensive knowledge of the behavior of non-graded structures.

This paper proposes an enhanced Cohesive Zone Model (CZM) for the prediction of delamination in curved beams of epoxy carbon laminates. This model improves the conventional CZM, taking into account the fiber-bridging phenomenon and the variation of the element size among the thickness in the curved zone. The advantages of the enhanced model are underlined when results obtained from the numerical simulations of a four-point-bending test in compliance with ASTM D6415 standard are compared with the corresponding experimental results. The prediction of the post-failure behavior obtained with this model is closer to that obtained experimentally than with the conventional model.