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Advanced manufacturing techniques, aimed at implants with high dependability, flexibility, and low manufacturing costs, are crucial in meeting the growing demand for high-quality products like biomedical implants. Incremental sheet forming is a promising flexible manufacturing approach for rapidly prototyping sheet metal components using low-cost tools. Titanium and its alloys are used to shape most biomedical implants because of its superior mechanical qualities, biocompatibility, low weight, and great structural strength. The poor formability of titanium sheets at room temperature, however, limits their widespread use. The goal of this research is to show that gradual sheet formation of a titanium biomedical implant is possible. The possibility of creative and cost-effective concepts for the manufacturing of such complicated shapes with significant wall angles is explored in this study. A numerical simulation based on finite element modeling as well as a design process tailored to metal forming is used to complete the development. The mean of uniaxial tensile tests with a constant strain rate was used to study the flow behavior of the studied material. To forecast the crack, the obtained flow behavior was modeled using the behavior model and failure model.

Advanced manufacturing techniques aimed at implants with high dependability, flexibility, and low manufacturing costs are crucial in meeting the growing demand for high-quality products such as biomedical implants. Incremental sheet forming is a promising flexible manufacturing approach for rapidly prototyping sheet metal components using low-cost tools. Titanium and its alloys are used to shape most biomedical implants because of their superior mechanical qualities, biocompatibility, low weight, and great structural strength. The poor formability of titanium sheets at room temperature, however, limits their widespread use. The goal of this research is to show that the gradual sheet formation of a titanium biomedical implant is possible. The possibility of creative and cost-effective concepts for the manufacture of such complicated shapes with significant wall angles is explored. A numerical simulation based on finite element modeling and a design process tailored for metal forming are used to complete the development. The mean of uniaxial tensile tests with a constant strain rate was used to study the flow behavior of the studied material. To forecast cracks, the obtained flow behavior was modeled using the behavior and failure models.

Flow and heat or mass transfer in channels provided with woven spacers made up of mutually orthogonal filaments were studied by Computational Fluid Dynamics. The problem addressed was the combined effect of the parameters that characterize the process: pitch to height ratio P/H (2, 3 and 4), flow attack angle θ (0, 7, 15, 20, 30, 40 and 45°) and Reynolds number Re (from ~1 to ~4000). The Prandtl number was 4.33, representative of water at ~40°C, while the Schmidt number was 600, representative of NaCl solutions. Simulations were performed by the finite volume code Ansys CFX™ 18.1 using very fine grids of ~6 to ~14 million volumes. For Re > ~400, the SST turbulence model was used to predict flow and heat transfer; no simulations of mass transfer were performed in the turbulent regime because the resolution of the diffusive sublayer would have required a prohibitive number of grid points. Results were validated against experimental data, including results obtained by Liquid Crystal Thermography and Digital Image Processing. The flow attack angle θ = 45° was the most effective for mixing (higher Nusselt number, Nu, and Sherwood number, Sh) and caused lower values of friction coefficient (f). In the range investigated, increasing the pitch to height ratio P/H caused Nu, Sh and f all to decrease. Therefore, the highest values of Sh and Nu were provided by the configuration P/H = 2, θ = 45°. Compared with non-woven spacers, woven spacers provided a better mixing, especially at intermediate values of Re, but at the expenses of higher pressure drops.

International audience; In this paper, hexagonal closed packed (HCP) sheet metal ductility for a viscoplastic material is analyzed by using a linear perturbation technique. It can be used for the analysis of local-ized necking. This technique is used to perturbate the material behavior in a rate dependent formulation by superimposing a perturbation to the basic flow which its stability or instability is characterized by the increasing or decreasing of the perturbation. Hardening and initial ani-sotropic parameters are fitted by experimental results from the literature. In this investigation, Cazacu yield function is used to predict the forming limit diagrams (FLDs) of HCP sheet metals. The coupling between analytic perturbation method and the behavior modelling is provided by an efficient implicit algorithm to solve the constitutive equations. After verifica-tions and validations of the numerical simulations from the literature, the ductility limit of a particular HCP magnesium alloy is numerically predicted. A parametric study is presented to analyze the effect of instability and mechanical parameters, viscosity and distortion on the FLDs. Moreover, a comparative study between Marciniak and Kuckzynski ductility approach and linear perturbation technique is done in this contribution.

The thermo-fluid dynamic behavior of spacer-filled channels for membrane distillation was investigated experimentally. Several different geometry were investigated thanks to customized reference spacers manufactured using a 3D printer. In particular, two sets of experiments were conducted: in the first set, cylindrical filaments were orthogonally arranged and the flow attack angle was made to vary from 0o to 90o; in the second set, the flow attack angle was kept symmetrical and the filament angle was made to vary from 30° to 150°. Each spacer was tested for Reynolds numbers between 200 and 900 in the hot channel, while maintaining a constant temperature difference of 13 °C between the hot and the cold channels. Thermochromic Liquid Crystal (TLC) sheets were used for surface temperature measurements. Results showed that, for all spacers, the heat transfer coefficient increases with hot feed flow rate and that the combination of attack angle 45° and filament angle 90° gave the highest heat transfer. Pressure drop measurements showed that spacers could be categorized into two groups relevant to the values of the Darcy friction coefficients (f). One group, associated with spacer designs with filament angles greater than 90°, led to high f values, while the other, associated with filament angles less than 90°, led to moderate f values.

Forward osmosis (FO) is a membrane technology which has attracted attention for water treatment and desalination. However, selecting an appropriate draw solute is vital to optimize its performance. This study seeks the efficiency of aluminum sulfate as an alternative draw solute in FO desalination with a cellulose triacetate (CTA) membrane. The effects of operating parameters on the performance of the FO were studied such as feed and draw temperatures, concentrations and flow. The experiments revealed that the permeate flux was improved by monitoring draw temperature, with a maximum of 2.5 L/m2 h was obtained at 53 °C. Also, the permeate flux was found to decrease with feed concentration. A maximum permeate flux of 2 L/m2 h was obtained at a draw flow rate of 35 L/h and draw concentration of 1 mol/L. On the other hand, using deionized water as feed solution yielded a reverse aluminum sulfate flux of 1.46 g/m2 h. The plots of the experimental and the modeling water flux displayed analogous trends in all tests, but the results showed a large deviation which was attributed to reverse solute flux, internal polarization concentration (ICP), external polarization concentration (ECP) and membrane fouling. Precipitation reaction using calcium hydroxide served to recover product water from the diluted draw solution. This operation was carried out via a precipitation reaction of aluminum sulfate with calcium hydroxide to eliminate the soluble chemicals like insoluble aluminum hydroxide and calcium sulfate. Eventually, aluminum sulfate draw solution was recovered by the reaction of aluminum hydroxide with sulfuric acid.

Background We applied a previously established and validated numerical model to a novel short-stemmed implant for a ‘pre-launch’ investigation. Methods The implant system consists of two different implant geometries for valgus/varus-positioned proximal femurs with differences in volume distribution, head/neck angle, and calcar alignment. The aim of the design was to achieve a better adaption to the anatomic conditions, resulting in a favourable load transfer. The implant type G showed the best fit to our model, but both stem geometries were implanted; the implant type B was used to compute an ‘imperfection scenario’. Findings Apparent bone density decreased by 4.3% in the entire femur with the implant type G, and by 12.3% with the implant type B. Bone mass loss was pronounced in the proximal calcar region. Apparent bone density increased at the lateral cortical ring and in the minor trochanter. The apparent bone density in the imperfection scenario was very similar to that of a straight stem, indicating a distal load transfer. Interpretation No adverse effects of the A2 short-stemmed implant system on bone remodeling could be detected. The overall bone density reduction was acceptable, and wedge fixation was not observed, indicating that there was no distal load transfer. The simulation of an incongruous implant indicates the sensitivity of our model in response to modifications of implant positioning. Correct implant selection and positioning is crucial when using the A2 system.

Incremental sheet metal forming is a flexible manufacturing technology that allows to form of various components on the same milling machine, without expensive tools. A hemispherical tool moves along a CNC-controlled tool path and deforms the sheet into the desired shape. The tool path has a significant role in the geometric accuracy of the final part. There has been very little research on the problem of the forming of sophisticated parts with asymmetric wall angles. This paper presents a new approach to generating optimized tool paths for single-point incremental sheet forming (SPIF). At first, a strategy is proposed for the automatic generation of a 3D tool path during forming in a single-step operation. Then, a systematic technique of creating intermediate shapes is investigated by defining tool paths interpolated from the final part shape. The proposed methodology is applied to form a hip cup prosthesis. This part has a complex asymmetric geometry with important angles, a multi-step approach is used. The proposed methodology to define the different tool paths was implemented in Matlab. A numerical simulation of the incremental forming process is performed to predict the final geometry of the aluminum sheet. A comparison of desired and predicted geometries shows the reliability of the proposed method.

We are witnessing a great increase in the use of auxetic structure in comparison to their conventional counterparts in these recent years. They have exhibited numerous advantages such as a high strength, stiffness and energy absorption. On the other side, we are also witnessing the emergence of eco-composite materials that significantly have the upper hand when compared to synthetic alternatives. This paper describes the static and fatigue bending behaviour of a bio-based sandwich structure with conventional and auxetic honeycomb core. The eco-composite used is a tape of polylactic acid reinforced with flax fibers. Additive manufacturing technology is used to produce these structures. The quasi-static bending tests were performed to identify the mechanical properties of sandwich composites and the ultimate loading. The fatigue tests were conducted with displacement-controlled technique in order to study the effect of the core configuration on the stiffness, hysteresis loops, energy absorption and damping ratio of the sandwich composite. The interesting part is that we observed a great increase in the capacity of energy absorption for the auxetic structure when compared to the conventional ones, which results higher loss factors. This work is used to determine the static and fatigue properties and to give an opinion on the damage mechanisms of these composites during its lifetime.

In this paper, an anisotropic plasticity model is coupled with Marciniak and Kuczynski localized necking criterion to predict the ductility limit of hexagonal closed packed (HCP) crystal structure sheet metals submitted to uniaxial and biaxial stretching. The anisotropic plastic evolution at room temperature is in fact described by the constitutive model using the non-associated flow rule (non AFR). In the current investigation, the plastic potential and the yield function are independently defined by taking into account the quadratic anisotropic yield criterion Hill48 which leads to the accurate prediction of the progressive plastic anisotropy as well as the material behavior using a minimal set of material parameters. To predict forming limit diagrams (FLDs), An efficient implicit algorithm is developed to solve the necessary constitutive equations to provide the coupling between Marciniak and Kuczynski instability approach and the anisotropic plasticity model with non-AFR. The numerical simulations are compared with several reference results from the literature to validate the mechanical behavior of the particular HCP magnesium alloy AZ31. Then, the ductility limit of this particular HCP magnesium alloy is numerically predicted and compared with analytical results of forming limit diagrams from the literature based on the associated and non-associated flow rule.

This study aims to prove the recyclability of an innovative thermoplastic called Elium resin. It’s the first liquid thermoplastic resin that provides the production of composite materials with an interesting mechanical behavior. Until now, its recyclable character is unjustified. It appeared on the resin market in 2014. But until now, no studies were available concerning how it can be recycled and reused. For this study, a thermocompression recycling process was investigated and applied to Elium resin. Three levels of recycling were carried out on the initial material. The recycled specimens were investigated and tested by means of tensile tests. Also, the acoustic emission (AE) technique was used to characterize microstructural damage events leading to overall failure of the recycled Elium. This study has been further supported by scanning electron microscopy (SEM) micrographs of the fractured face. The results obtained show that the failure tensile properties of Elium resin as well as flax fiber reinforced composites decrease during recycling operations. Conversely, recycling induces a rise in the elastic modulus. Also, the acoustic emission technique associated with SEM observation showed two classes of damage mechanisms. A first “class A” related to “matrix cracking” and a second “class B” associated to matrix/matrix friction.

This work presents computational fluid dynamics simulations aimed at characterizing flow and mass/heat transport mechanisms in spacer-filled channels for membrane processes, with particular reference to (reverse) electrodyalisis and membrane distillation.

In this research contribution, the static behavior and failure mechanisms are developed for a three-dimensional (3D) printed dogbone, auxetic structure and sandwich composite using acoustic emissions (AEs). The skins, core and whole sandwich are manufactured using the same bio-based material which is polylactic acid reinforced with micro-flax fibers. Tensile tests are conducted on the skins and the core while bending tests are conducted on the sandwich composite. Those tests are carried out on four different auxetic densities in order to investigate their effect on the mechanical and damage properties of the materials. To monitor the invisible damage and damage propagation, a highly sensitive AE testing method is used. It is found that the sandwich with high core density displays advanced mechanical properties in terms of bending stiffness, shear stiffness, facing bending stress and core shear stress. In addition, the AE data points during testing present an amplitude range of 40–85[Formula: see text]dB that characterizes visible and invisible damage up to failure.

International audience; Auxetic structure became the center of attention in the recent years because of their abnormal properties such as negative Poisson’s ratios. These materials exhibited many benefits like strength, higher stiffness and energy absorption, in comparison with conventional ones. This article presents the mechanical characterization of a bio-based sandwich structure with an auxetic core. The structure has been manufactured using additive manufacturing (3D printing technology). The core and the skins are made from the same biological material which is the polylactic acid. Thus, the sandwich structure is 100% bio based which makes it recyclable. Different density of the auxetic structure was studied in order to evaluate their influence on the mechanical properties of the sandwich. Uniaxial loading was performed on the skins in order to obtain the mechanical properties of the materials and on the core to obtain the Poisson’s ratios. Then, the sandwiches were tested in three points bending. The flexural and shear rigidity were measured for each beam. The results obtained showed that the auxetic core density plays a major role on the mechanical characteristic of the sandwich structure.

International audience; In the present contribution, a two-surface plasticity model is coupled with several diffuse and localized necking criteria to predict the ductility limits of hexagonal closed packed sheet metals. The plastic strain is considered, in this two-surface constitutive framework, as the result of both slip and twinning deformation modes. This leads to a description of the plastic anisotropy by two separate yield functions: the Barlat yield function to model plastic anisotropy due to slip deformation modes, and the Cazacu yield function to model plastic anisotropy due to twinning deformation modes. Actually, the proposed two-surface model offers an accurate prediction of the plastic anisotropy as well as the tension–compression yield asymmetry for the material response. Furthermore, the current model allows incorporating the effect of distortional hardening resulting from the evolution of plastic anisotropy and tension–compression yield asymmetry. Diffuse necking is predicted by the general bifurcation criterion. As to localized necking, it is determined by the Rice bifurcation criterion as well as by the Marciniak & Kuczynski imperfection approach. To apply both bifurcation criteria, the expression of the continuum tangent modulus associated with this constitutive framework is analytically derived. The set of equations resulting from the coupling between the Marciniak & Kuczynski approach and the constitutive relations is solved by developing an efficient implicit algorithm. The numerical implementation of the two-surface model is assessed and validated through a comparative study between our numerical predictions and several experimental results from the literature. A sensitivity study is presented to analyze the effect of some mechanical parameters on the prediction of diffuse and localized necking in thin sheet metals made of HCP materials. The effect of distortional hardening on the onset of plastic instability is also investigated.

Sintering technology is becoming increasingly important in metal industry as they offer numerous advantages comparing to other manufacturing processes. So that, the powder metal (PM) technology is currently well-established for the manufacturing of near-net-shape thin-walled sintered components with strong cross-sectional transitions, especially in the automotive industry. The density gradients in the green bodies caused during the powder compacting process lead to the sintering distortion which is a relevant problem in this industry. The numerical simulation based on the finite element method (FEM) can provide a significant contribution in the design and optimization of powder compacting processes to reliably reduce such problems. Here, the material modeling required for the FE calculation is of crucial importance. In this presented work, the DRUCKER-PRAGER-Cap model was chosen for the numerical description of the compressible behavior of magnesium powder. Here, in the first step, the material-dependent failure line was determined on the basis of diametrical and uniaxial compression tests. In the second step, the elliptical caps depending on the relative density were specified by means of a simple axial compression test combined with the assumption of associated flow. This material modeling is then used to study the influence of the powder compacting strategy on the homogeneity in the distribution of the relative density is shown for the rotationally symmetric L-shape.

The aim of this study is to investigate the effects of recycling on the mechanical properties of Elium resin reinforced by flax fibers. A thermocompression recycling process is investigated and applied to production waste of thermoplastic composites. Five recycling operations are carried out on the initial material. Specimens are tested under static and fatigue tensile tests. In addition, the acoustic emission technique is used to identify damage mechanisms evolution during mechanical tests. Recorded events are post processed by the k-means unsupervised pattern recognition algorithm. The classes of acoustic emissions obtained are correlated with scanning electron microscopy observations to justify the existence of damage mechanisms detected. Results of static tests show that the ultimate tensile properties of the composites studied decrease with recycling operations. However, an increase in the elastic modulus is reported. In the fatigue tests, results show that stiffness, hysteresis loop and loss factor are affected by recycling operations. Also, a decrease in the life time with reprocessing conditions is observed. In acoustic tests, depending on the recycling operations, two or three classes of events are detected. The acoustic characteristics of these classes are compared. Then, a correlation between these AE classes of events and damage mechanisms observed is proposed.

Warmumformwerkzeuge unterliegen wahrend des Betriebes komplexen thermischen und mechanischen Beanspruchungen. In kritischen Bereichen konnen dadurch lokal Spannungen entstehen, die die Fliesgrenze uberschreiten. Bei der Serienproduktion fuhrt dies zu zyklischen plastischen Verformungen und zur thermomechanischen Ermudung, welche die Lebensdauer der Warmumformwerkzeuge masgeblich bestimmen kann. Zur Bewertung der thermomechanischen Ermudung der Warmumformwerkzeuge gibt es jedoch heute keine etablierten Konzepte, da dieser Aspekt erst durch die Notwendigkeit einer hoheren Ressourcen- und Energieeffizienz und optimierter Produktionsprozesse (beispielsweise im Rahmen von Industrie 4.0) eine hohere Aufmerksamkeit erreicht. In dieser Arbeit wird zum einen die aktuell industriell angewandte Vorgehensweise zur Auslegung von Warmumformwerkzeugen hinsichtlich der Lebensdauer erlautert. Des Weiteren wird ein Uberblick uber existierende Plastizitatsmodelle und Lebensdauermodelle gegeben. Dabei wird zwischen rein phanomenologischen und mechanismenbasierten Modellen unterschieden. Aus der betriebenen Recherche wird ersichtlich, dass weiterer Forschungsbedarf auf diesem Gebiet notwendig ist.