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Purpose The purpose of this paper is the design and experimental investigation of compact hybrid sound-absorbing materials presenting low-frequency and broadband sound absorption. Design/methodology/approach The hybrid materials combine microchannels and helical tubes. Microchannels provide broadband sound absorption in the middle frequency range. Helical tubes provide low-frequency absorption. Optimal configurations of microchannels are used and analytical equations are developed to guide the design of the helical tubes. Nine hybrid materials with 30 mm thickness are produced via additive manufacturing. They are combinations of one-, two- and four-layer microchannels and helical tubes with 110, 151 and 250 mm length. The sound absorption coefficient of the hybrid materials is measured using an impedance tube. Findings The type of microchannels (i.e. one, two or four layers), the number of rotations and the number of tubes are key parameters affecting the acoustic performance. For instance, in the 500 Hz octave band (α500), sound absorption of a 30 mm thick hybrid material can reach 0.52 which is 5.7 times higher than the α500 of a typical periodic porous material with the same thickness. Moreover, the broadband sound absorption for mid-frequencies is reasonably high with and α1000 > 0.7. The ratio of first absorption peak wavelength to structure thickness λ/T can reach 17, which is characteristic of deep-subwavelength behaviour. Originality/value The concept and experimental validation of a compact hybrid material combining a periodic porous structure such as microchannels and long helical tubes are original. The ability to increase low-frequency sound absorption at constant depth is an asset for applications where volume and weight are constraints.

2 V has been generated from four FFF printed “piezo leaves” through 3 min of fan blowing.

Additive manufacturing (AM) technologies have transformed manufacturing, by providing greater control over material deposition and consumption. Thanks to greater customization and their high strength-to-mass ratio, AM with composite materials has grown significantly over the past few years. Main focus in research area are on improving printing precision and higher production rates. However there is a lack of thorough analysis on the energy consumption of Fused Filament Fabrication (FFF) machines for composite manufacturing. We designed an experimental method, based on flow analysis for measuring the impact of temperature parameters on total cost, energy consumption, and tensile resistance of composite parts made by FFF. As the user should be able to improve FFF efficiency regarding economic, energy and technical aspects and obtain recommendations for setting up and using the machine. This study confirms that combining traditional economic and technical indicators (total cost and tensile resistance) to emerging energy indicators (specific energy consumption) can be successfully applied to additive manufacturing to provide an overview of those impacts. Results are yielding information to support optimization investigations depending on the need and goal. For example, two tested parameter combinations that offer similar tensile properties (4% reduction in tensile resistance compared to best combination) show a 20% difference in energy consumption.

Single layer optimized microchannels (268µm channels size) present high absorption at the quarter-wave resonance frequency (2460Hz for 30mm-thick treatment) but cannot provide significant absorption at lower frequencies. In this work, the absorption coefficient of multilayer treatments with 2, 5, 10- and 30-layers of channels with size varying from 50µm to 15mm was numerically optimized. The equivalent fluid wave number and characteristic impedance of each layer were predicted using the JCAL model. The Double-scale Asymptotic Method (DAM) was used to obtain the JCAL parameters. The multilayer treatment absorption was modelled with the Transfer Matrix Method (TMM). It was shown that multilayer treatments present superior absorption than single layer. For instance, bilayer treatment made of a 1mm-thick top layer (facing incident wave) of channels of 58µm and a 29mm-thick bottom layer of channels with 8.1mm provides perfect absorption around 1200Hz (i.e. 1260Hz below the quarter-wave resonance frequency of 30mm-thick single layer treatment). Alternatively, a 30-layer treatment with channels size varying from 100µm to 9.6mm provides absorption higher than 0.8 between 1350 and 6270Hz (i.e. 54% higher than single layer treatment with same thickness). These results pave the way to the fabrication of new multilayer treatments with interesting subwavelength and broadband absorption capabilities.

This paper presents a simple and computationally efficient multi-scale procedure to predict the macroscopic temperature dependent coefficient of thermal expansion (CTE) of any linearly thermoelastic material from isothermal mechanical simulations only. The approach relies on Levin’s demonstration that, in analytical homogenization, the effective coefficient of thermal expansion is related to the local coefficient of thermal expansion and the stress concentration tensor. For demonstration purposes, this procedure was applied to a 3D woven composite material. The proposed approach was successfully validated with full thermal simulations.

Advances in binder jet printing (BJP) require the development of new binder-powder systems, for example, to increase compatibility with better performance metal alloys or to increase the strength of parts using stronger binders. The dynamics of binder absorption are principally understood through capillary models. However, validation of these models in BJP has focused on variation of powder properties. Using a design-of-experiments approach and an optical observation method to track absorption of droplets, this study tests the influence of fluid properties on absorption time against the predictions of capillary models. Properties specific to polymeric binders, such as molecular weight and entanglement state, are also considered. Capillary models are found to be generally accurate in predicting absorption time in dilute systems; however, these predictions are not accurate for highly concentrated binder solutions. The effect of polymer entanglement becomes prevalent as the solution concentration increases, which can also potentially occur as a result of increased evaporation due to powder bed heating. Specifically, concentrated solutions close to the onset of entanglement will absorb much more slowly than predicted. Future models of BJP systems must account for the possibility of polymer entanglement throughout the absorption process. Improved models will provide a more accurate understanding of the flow and solidification of the binder in the powder, allowing faster development of new binders for improved performance in printing.

International audience; Micromechanics damage models applied to composites predict stresses and strains in the matrix and fibers as a function of the microstructure, constituting phases mechanical properties and load histories. Material parameters, like interface properties, are identified through inverse methods based on macroscopic stress-strain curves. Predictions are also benchmarked against macroscopic measurements. This situation does not capture local phenomena and hinders the robustness of the indentification/validation process. The purpose of this work is to provide full displacement and strain fields at the scale of a single fibre embedded into a matrix to allow the modelling community to either develop and identify micromechanics damage models or to benchmark their own predictions. Such data is critically lacking in the community. To that end, we have investigated three single fibers having radically different bonding strength with epoxy in addition to a bundle of about a hundred carbon fibers that were used as reinforcements of standard “dogbone” epoxy specimens. A laser scanning confocal microscope (LSCM) is used for micro digital image correlation (μDIC) during in-situ quasi-static tests of single-reinforcement dogbone specimens. For all specimens, damage initiated with fiber debonding at the free surface along the tensile direction. The crack then propagates around the interface while slightly growing along the fiber. The interfacial crack is shown to grow faster for couples with weak interfacial bonding. Strong fiber / matrix bonding is shown to stop Mode II transverse interfacial debonding which significantly delays specimen failure. Analysis of the LSCM micrographs with μDIC is used to provide measurements of displacements, strains, and measure depth during each test. The importance of out of plane displacements in interfacial debonding is highlighted. Out of plane displacement is shown to play a role in interfacial crack opening and growth and ought to be considered when studying or modeling damage in FRCs. μDIC is shown to be a promising technique to provide a better understanding of the damage mechanisms at the fiber or bundle scales and to determine interfacial toughness of a specific fibre / matrix couple in order to perform accurate damage modeling in FRCs. Displacement, strain, and confidence field results for each pixel from each experiment and at each time step are also provided in an extensive data package for detailed comparison with simulation results.

Periodic architected cellular metamaterials, as a novel class of low-density materials, possess unprecedented multifunctional properties mainly due to their underlying microarchitecture. In this paper, we study the thermal conductivity of cellular metamaterials and evaluate their performance for thermal management applications. To understand the relations between the microarchitecture and the thermal response, we analyze the thermal conductivity of a wide range of cellular metamaterials with strategically developed microarchitectures from two-dimensional (2D) cells with Supershape pores to three-dimensional (3D) thin-walled open lattices and shellular materials. We implement standard mechanics homogenization on the periodic representative volume elements (RVEs) of these cellular metamaterials to examine the effect of pore architecture (relative density, pore shape, pore orientation, and pore elongation) on their effective thermal conductivity. The numerical results show how the thermal conductivity of an isotropic material can be modified by pore introduction and how the pore architecture could lead to an anisotropic effective thermal conductivity tensor. To examine the impact of having 2D Supershape cuts on 3D RVEs, thin-walled open lattices are designed as an assembly of thickened 2D RVEs with Supershape pores. A mathematical model is derived based on the effective thermal properties of the constituent 2D RVEs to predict the effective thermal properties of these lightweight cellular materials. Effective thermal conductivity of shellular materials based on triply periodic minimal surfaces is also compared with those of the previously introduced architectures. Unlike the shellular materials, which only cover a narrow region of thermal conductivity versus relative density chart, cellular materials with a wide range of anisotropic effective thermal conductivities can be engineered by using 2D Supershape pores on 2D or 3D thin-walled cells. Finally, we show how the concept of architected functionally graded cellular materials can be used to tune the heat flow within cellular media to guide it in a specific direction to control the temperature inside advanced 3D printed materials. As a case study, the optimum spatial distribution of pore rotation angle is found to maximize or minimize the heat flow passing through different sides of a square-shaped porous slab. This paper opens an avenue for developing thermal metamaterials with programmable anisotropic thermal properties.

Direct ink writing (DIW) combined with post-deposition thermal treatments is a safe, cheap, and accessible additive manufacturing (AM) method for the creation of metallic structures. Single-material DIW enables the creation of complex metallic 3D structures featuring overhangs, lengthy bridges, or enclosed hollows, but requires the printing supporting structures. However, the support printed from the same material becomes inseparable from the building structure after the thermal treatment. Here, a multi-material DIW method is developed to fabricate complex three-dimensional (3D) steel structures by creating a removable support printed from a lower melting temperature metal (i.e., copper) or a ceramic (i.e., alumina). The lower melting temperature metal completely infiltrates the porous steel structures for a hybrid configuration, while the ceramic offers a brittle support that can be easily removed. The influence of the support materials on the steel structure properties is investigated by characterizing the dimensional shrinkage, surface roughness, filament porosity, electrical conductivity, and tensile properties. The hybrid configuration (i.e., copper infiltrated steel structures) improves the electrical conductivity of the fabricated steel structure by 400% and the mechanical stiffness by 34%. The alumina support is physically and chemically stable during the thermal treatment, bringing no significant contamination to the steel structure.

Uniform foams (UF) and density graded foams (DGF) were produced by using similar or different temperatures on both sides of a compression molding system. The samples were produced using linear low density polyethylene as the matrix and activated azodicarbonamide as the chemical blowing agent. Morphological properties of the produced samples were analyzed via scanning electron microscopy to relate them to their mechanical properties. In particular, flexural and impact properties are reported for samples produced under a range of temperatures (140–200°C) and blowing agent concentration (0.7–1.0 wt%). The experimental results showed that a significant difference can be obtained in flexural modulus (up to 17%) and impact strength (up to 48%) depending on the side the stress is applied on. In all cases, the DGF showed better mechanical responses than UF of similar relative density for the range of conditions tested.

Soft materials capable of large inelastic deformation play an essential role in high-performance nacre-inspired architectured materials with a combination of stiffness, strength and toughness. The rigid "building blocks" made from glass or ceramic in these architectured materials lack inelastic deformation capabilities and thus rely on the soft interface material that bonds together these building blocks to achieve large deformation and high toughness. Here, we demonstrate the concept of achieving large inelastic deformation and high energy dissipation in soft materials by embedding microstructured thermoplastic fibers with sacrificial bonds and hidden lengths in a widely used elastomer. The microstructured fibers are fabricated by harnessing the fluid-mechanical instability of a molten polycarbonate (PC) thread on a commercial 3D printer. Polydimethylsiloxane (PDMS) resin is infiltrated around the fibers, creating a soft composite after curing. The failure mechanism and damage tolerance of the composite are analyzed through fracture tests. The high energy dissipation is found to be related to the multiple fracture events of both the sacrificial bonds and elastomer matrix. Combining the microstructured fibers and straight fibers in the elastomer composite results in a ~ 17 times increase in stiffness and a ~ 7 times increase in total energy to failure compared to the neat elastomer. Our findings in applying the sacrificial bonds and hidden lengths toughening mechanism in soft materials at the microscopic scale will facilitate the development of novel bioinspired laminated composite materials with high mechanical performance.

The ability to precisely control the properties of natural polymers and fabricate three-dimensional (3D) structures is critical for biomedical applications. In this work, we report the printing of complex 3D structures made of soft polysaccharide (chitosan) inks directly in air and at room temperature. We perform a comprehensive characterization of the 3D printing process by analyzing the effect of ink properties (i.e., rheological properties and solvent evaporation) and process-related printing parameters (i.e., nozzle diameter, robot velocity, and applied pressure). The effects of the neutralization step on the hydrogel formation and their mechanical properties are also investigated. Solvent evaporation tests show that the chitosan ink prepared using an acidic mixture contains residual acids after printing, helping reducing shrink-induced shape deformation. A processing map presents the appropriate ranges of process-related parameters for different structures including filaments, 30-layer scaffolds, starfish, leaf, and spider shapes, showing the versatility of the fabrication approaches. After neutralization, 3D scaffolds still maintain their shape while neutralized filaments show high tensile properties such as a maximum tensile strength of ∼97 MPa in the dry state and high strain at break ∼360% in the wet state. Our fabrication approach provides guidelines to optimize the design and fabrication of aqueous-based inks and opens a new door for fabricating complex structures from natural polymers and achieving tunable material properties for biomedical applications such as tissue engineering and drug delivery.

Variational phase-field methods have been shown powerful for the modeling of complex crack propagation without a priori knowledge of the crack path or ad hoc criteria. However, phase-field models suffer from their energy functional being non-linear and non-convex, while requiring a very fine mesh to capture the damage gradient. This implies a high computational cost, limiting concrete engineering applications of the method. In this work, we propose an efficient and robust fully monolithic solver for phase-field fracture using a modified Newton method with inertia correction and an energy line-search. To illustrate the gains in efficiency obtained with our approach, we compare it to two popular methods for phase-field fracture, namely the alternating minimization and the quasi-monolithic schemes. To facilitate the evaluation of the time step dependent quasi-monolithic scheme, we couple the latter with an extrapolation correction loop controlled by a damage-based criteria. Finally, we show through four benchmark tests that the modified Newton method we propose is straightforward, robust, and leads to identical solutions, while offering a reduction in computation time by factors of up to 12 and 6 when compared to the alternating minimization and quasi-monolithic schemes., Comment: Accepted manuscript: Added references, added Armijo algorithm, more details on modified Newton algorithm, added mesh sensitivity analysis, comparison with original extrapolated scheme in Annex