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 behavior 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.

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Triply periodic minimal surface structures (TPMS) can create tailored complex structures that could be a substitute for polymeric foams in certain applications, owing to the advantages of additive manufacturing processes. The main application is the absorption of energy under compression loads. Consequently, it is necessary to study the different types of TPMS structures (Neovious, gyroid, Schwarz-P, Lidinoid, split-P, and diamond) to analyze them in terms of their energy-absorbing capability, mechanical properties, effectivity, ideality, etc. Additionally, it is necessary to compare them in terms of volume and in terms of weight using the specific properties.

Mechanical properties and energy-absorption capabilities of thermoplastic sheet gyroid structuresThe 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 and 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 stressstrain 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, the area under the curves were. Hence, for most materials, specific energy absorption was larger for higher volume fractions and smaller cells. 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.

Author Comments:The authors after the review have prepared all the images to be published in black and white. Fig1 has been generated using PPT, fig 2 is a photo, fig 3 to 11 have been generated using excel and they have been introduced in a word or a power point. All the tables are generated using word.

Comparative analysis of mechanical properties and energy absorption capabilities of functionally graded and non-graded thermoplastic sheet gyroid structuresAdditive manufacturing allows the tailoring of the structure of energyabsorbing 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 nongraded structures.

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The interlaminar tensile strength of carbon/epoxy laminated curved beams with variable thickness and through-the-thickness tufted reinforcement is studied experimentally by means of a four-point-bending test in accordance with ASTM D6415. These tests are monitored by means of the Acoustic Emission (AE) technique in order to gain deeper knowledge of the delamination onset and post-failure behavior. The results show that AE technique has proven to perform well when identifying delamination initiation and evolution after failure. In addition to this, AE has proven to be an appropriate tool to assess the manufacturing quality of the curved-beam, once a previous pattern has been established.