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Objectives To assess the super-elasticity of CuNiTi wires (Ormco, Glendora, Calif) according to their Austenite finish temperature (Af) and to the imposed displacement. The secondary objective was to compare the wire dimensions with the stated measurements and to study interbatch variability. Materials and Methods 10 types of CuNiTi wires (Ormco, Glendora, Calif) (n = 350) were investigated at 36 ± 1°C, with conventional brackets (Victory Series, 3M Unitek, Monrovia, Calif). Tensile test with coronoapical displacement ranging from 1 to 5 mm of the canine bracket was imposed. The wire dimensions were initially measured from two batches (n = 10). Results Dimensional heterogeneity varied by ± 2.00% compared to the manufacturer's data, and even up to 5.54% for 0.014-inch CuNiTi (P = .00069). However, all unloading forces were reproducible. In decreasing order, the forces delivered by a CuNiTi 27 were greater than those with CuNiTi 35 and 40. The super-elasticity was expressed only for displacements of 1 to 2 mm, at best up to 3 mm for 0.014-inch CuNiTi 27. Conclusions The value of Af as well as the amount of imposed displacement seem to influence the expression of the super-elasticity of CuNiTi wires and the amount of corrected malocclusion. Among the tested wires, under these experimental conditions, 0.014-inch wire could be suitable as a first archwire. CuNiTi 35, therefore, seems to offer the best compromise among the force level, the expression of super-elasticity and the amount of malocclusion correction.

Ti-Nb alloys are high-profile candidates for the biomedical applications. However, because of poor surface integrity (i.e. residual stress and surface roughness), Ti-Nb implantable medical devices need to be machined in order to obtain functional surfaces finish. In this work, experimentaland numerical investigations are conducted to study the micro-cutting response of Ti42Nb titanium alloy produced by laser-based powder bed fusion. Experimental micro-cutting tests are carried out using precision turning lathe. Trials are performed with two cutting velocities of 60 m/min and 120 m/min and different feed rates, varying from 5 to 40μm/rev. For the numerical study, a porous crystal plasticity-based model is proposed to address the impact of anisotropy and microstructure heterogeneities of the polycrystalline material. The crystal plasticity-basedmodel is identified using strain–stress curves obtained from compression tests performed under two strain rates and a wide range of temperatures. Numerical micro-cutting simulations are performed in order to gain insight into the impact of microstructural features (i.e. crystallographic orientation and grain size) on the machinability of the alloy.According to the results, the effect of the strain rates and the temperature on the thermomechanical behavior of the Ti42Nb titanium alloy produced by laser-based powder bed fusion is correctly depicted. The model captured the strain localization on adiabatic shear band during compression tests. According to the micro-cutting simulations, the local variables such as temperature, damage and plastic deformation are strongly impacted by the crystallographic orientations and the grain size.In addition, depending on the crystallographic orientations, the chip morphology changes form continues, slightly segmented to largely segmented.

Summary Introduction The mechanical properties of orthodontic archwires can be defined using experimental setups incorporating brackets that provide conditions closer to those encountered in vivo. We aimed to compare a methodology based on computer-aided design with the gold standard protocol, performed when brackets are engaged to a full-size archwire to test the behaviour of wires in this condition. Methods Three models simulating a dental arch with an orthodontic fixed appliance (0.018-inch aesthetic conventional brackets) were designed. The brackets were positioned with a stainless-steel full-size wire on the first two models, with different interbracket distances. The setup 3, based on a computer-assisted design, allowed individualized placement of each bracket. Mean forces recorded and standard deviation were compared for a 0.016 × 0.022–inch copper-nickel-titanium wire deflected until 2 mm. Results The inter-bracelet distances do not cause a statistical difference in the average maximum force recorded (12.6 N and 11.4 N; P = 0.081) whereas the behaviour of the wires is affected. With setup 3, the recorded efforts (mean value: 8 N) are statistically lower than with setup 1 and 2 respectively (P = 0.018; P = 0.012). Conclusion An individualization of the housings by CAD-CAM dedicated to each bracket optimizes their placement. In our test conditions, the mechanical behaviour of the wires is more influenced by the positioning methods of the brackets than by the value of the interbracket distance. In perspective, our innovative methodology can be extended to other types of brackets.

Finishing operations of parts produced by additive manufacturing are nowadays an important challenge in this field. To obtain a functional part, certain surfaces require post-processing by machining operations. In this study, an innovative approach is developed using the manufacturing supports as a clamping device for the milling operation. This approach saves time and operations in the overall value chain to obtain a finished part. To achieve this goal, the effects on the machining operation of the heterogeneous flexibility of the assembly composed of the part and its supports have to be analyzed. The present study aims to propose a model combining an analytical approach to determine the cutting forces with a finite element model (FEM) to predict the dynamical response of the workpiece-supports system. The effect of the workpiece displacements on the material removal by the tool is taken into account. The mechanical loading on the workpiece, due to the cutting forces, is introduced in the FEM through a user subroutine provided by ABAQUS/standard. To reduce the calculation time, a homogenization procedure is used by replacing the complex structure of the supports with a simplified geometry with equivalent stiffness and mechanical properties. To validate the proposed approach, end milling tests were performed on Ti6Al4V parts produced by SLM additive manufacturing. In general, the comparison between the experiment and the model shows a match of the cutting force signals for the rigid and flexible samples. From this study, it appears that the present approach can be used to validate the design of additive manufacturing supports as a machining device and to optimize cutting conditions to reduce machining vibrations.

International audience; The supports in additive manufacturing can be used in an innovative way by being considered as supports for machining operation. This innovative use of manufacturing supports can facilitate the finishing of functional thin structures. But the flexible global workpiece-supports system can potentially cause vibrations during the machining operation. This can cause irregular surfaces with bad quality. This study highlights the importance of additively manufactured support structures on the stability of Ti-6Al-4V parts milling by using supports as a machining fixture. Nowadays, the control of the support stiffness and mechanical properties is not proposed by specific AM software. A way to develop a numerical method to optimize the post-processing of additive manufacturing parts is to use specific lattice structures as supports. Indeed, by adjusting the topology and the beam diameter of lattices, the relative stiffness and the relative density of the global structure can be controlled. The objective of this study is to show that the stiffness of the manufacturing supports is crucial for the machining operation. To validate this concept, milling tests are proceeded on thin-walled plates produced by Selective Laser Melting (SLM) using defined finish milling cutting conditions. Three types of results are obtained: cutting forces signals, displacements and surface qualities by confocal microscopy. The study reveals that milling can induces chatters. Also, surface qualities and dimensional deviations depend on the support choice. The control of mechanical properties of support structures appears to be a good way to favor machining operation of flexible and thin-walled structures. Topology and dimensional parameters of supports have to be considered in preliminary design steps of the additive manufacturing digital chain.

In this work, a microstructural-related model was developed to simulate micromachining of FCC polycrystalline copper. Indeed, a crystal plasticity framework was adopted to describe the anisotropy of the mechanical behavior. Some material microstructure characteristics (such as grain size, grain misorientation and crystallographic orientation) are explicitly considered through the constitutive model. For describing the material removal during chip formation, a modified thermodynamically consistent formulation of the Johnson-Cook damage model was used. The model was implemented in the ABAQUS/Explicit finite element solver with a user-defined subroutine, and the experimental validation was performed using data on the cutting forces available in the literature. Finally, the model was used to investigate the effect of the microstructure on the micro-machining cutting forces and chip formation process. According to the results, the proposed model allows capturing the cutting forces trends due to the crystallographic anisotropy.

The success of biomedical implantation is linked to osseointegration, depending on the mechanical loading of the bone interface. The large difference in stiffness between the host bone (30 GPa) and the usual implant material (over 100 GPa), as well as the absence of mechanical stress at the surrounding bone, induce a stress shielding effect, which leads to bone atrophy and implant loss. A recent work has shown the possibility to produce so-called second-generation titanium alloys. β-type Ti alloys have been studied for biomedical applications, due to the composition of non-cytotoxic elements. Some TiNb alloys can reach after heat treatment a Young’s modulus close to 35 GPa, which is really close to bone’s one. Unfortunately, titanium and its alloys are well known for their poor machinability due to the hardness and low thermal conductivity. Machined surfaces of titanium alloys are also easily damaged (micro cracks, build-up edge, plastic deformation, heat-affected zones, and tension residual stresses) during the process. Studying process parameters is important to avoid these phenomena. The machinability of TiNb (turning, milling) has not been studied to date. Therefore, in this study, we examined the behavior of the TiNb titanium alloy for applications as a biomaterial in micro-cutting. Orthogonal cutting tests were performed on austenite and martensite states TiNb alloys and compared with Ti40 pure titanium. The aim was to evaluate the influence of the alloys and the cutting parameters on the evolution of the cutting forces, specific cutting energy, friction coefficient which are good indicators of machinability.

In order to simulate micromachining of Ti-Nb medical devices produced in situ by selective laser melting, it is necessary to use constitutive models that allow one to reproduce accurately the material behavior under extreme loading conditions. The identification of these models is often performed using experimental tension or compression data. In this work, compression tests are conducted to investigate the impact of the loading conditions and the laser-based powder bed fusion (LB-PBF) building directions on the mechanical behavior of β-Ti42Nb alloy. Compression tests are performed under two strain rates (1 s−1 and 10 s−1) and four temperatures (298 K, 673 K, 873 K and 1073 K). Two LB-PBF building directions are used for manufacturing the compression specimens. Therefore, different metallographic analyses (i.e., optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), electron backscatter diffraction (EBSD) and X-ray diffraction) have been carried out on the deformed specimens to gain insight into the impact of the loading conditions on microstucture alterations. According to the results, whatever the loading conditions are, specimens manufactured with a building direction of 45∘ exhibit higher flow stress than those produced with a building direction of 90∘, highlighting the anisotropy of the as-LB-PBFed alloy. Additionally, the deformed alloy exhibits at room temperature a yielding strength of 1180 ± 40 MPa and a micro-hardness of 310 ± 7 HV0.1. Experimental observations demonstrated two strain localization modes: a highly deformed region corresponding to the localization of the plastic deformation in the central region of specimens and perpendicular to the compression direction and an adiabatic shear band oriented with an angle of ±45 with respect to same direction.

Orthodontic fixed appliances are used to correct dental malocclusions by optimizing tooth movement and associated bone remodelling. Currently, orthodontic archwires made of shape memory alloys (SMAs) are widely used to initiate these treatments. We conduct experiments on SMA wires in pseudo in-vivo conditions, complementary to ISO standards, to assess the influence of temperature and humidity and to highlight their expected mechanical behaviour for clinical use. For this, an in-house built measurement device was developed to carry out experiments at controlled temperatures (21°C and 35°C) and in dry or wet conditions (artificial saliva). The dental arch was reproduced by 3D printing. The results show that the temperature has a major influence on the delivered forces whereas wet or dry conditions seem to have less impact. Also, we emphasize that at 35°C (in mouth conditions), in wet or dry conditions, SMAs superelasticity is only effective for displacements up to about 3 mm when an entire dental arch is considered.

Additive manufacturing (AM) is recently imposing as a fast, reliable, and highly flexible solution to process various materials, that range from metals to polymers, to achieve a broad variety of customized end-goods without involving the injection molding process. The employment of biomaterials is of utmost relevance as the environmental footprint of the process and, consequently, of the end-goods is significantly decreased. Additive manufacturing can provide, in particular, an all-in-one platform to fabricate complex-shaped biobased items such as bone implants or biomedical devices, that would be, otherwise, extremely troublesome and costly to achieve. Polyhydroxyalkanoates (PHAs) is an emerging class of biobased and biodegradable polymeric materials achievable by fermentation from bacteria. There are some promising scientific and technical reports on the manufacturing of several commodities in PHAs by additive manufacturing. However, many challenges must still be faced in order to expand further the use of PHAs. In this framework, the present work reviews and classifies the relevant papers focused on the design and development of PHAs for different 3D printing techniques and overviews the most recent applications of this approach.

International audience; Five high entropy alloys with shape memory effect or superelastic effect were prepared by cold crucible melting to understand the effect of their chemical composition on the transformation temperatures. The microstructure and phases of the alloys at room temperature were investigated by optical and scanning electron microscopy. The calorimetric study of these alloys is employed to analyze the reversible transformation from austenite to martensite and to determine the transformation temperatures of the five alloys. The paper presents the results of several published works relating the transformation temperatures of high entropy shape memory alloys (HE-SMA). An experimental database has been built up to understand the influence of the different alloying elements and their related concentrations on the transformation temperature Ms (Martensite Start) of the HE-SMAs. An equation is identified using the database to predict the transformation temperature Ms of a high entropy shape memory alloy as a function of its weighted chemical composition, which exhibits a metallurgical Solutioned Treatment (ST) state and a specific mixing entropy (ΔSmix/R) range.

In this work, the effect of the crystallographic anisotropy on machining forces is studied through a thermomechanical approach based on rate sensitive plasticity based model. A crystal plasticity f...

International audience; Transparency is a crucial factor in developing functional and decorative thin films and coatings, but incorporation of nanoparticles into organic resins for improving their properties quite often makes them opaque. In this work, photophysical properties of epoxy/layered double hydroxide (LDH) nanocomposite coatings were correlated with the dispersion state of LDH in the epoxy resin. The quality of solid epoxy network was assessed in terms of the Cure Index (CI) in relation to the transparency of the films containing 0.1, 0.5, 0.7, 1.0, and 3.0 wt% Mg–Al–LDH and Zn–Al–LDHs. At high loadings, direct transmittance (YDirect) decreased, while the light scattering in the coatings improved with respect to the neat epoxy. The highest Zn–Al–LDH loading (3.0 wt%) slightly deteriorated the transparency (YDirect = 93.3), but it was still higher than that of epoxy nanocomposite containing 0.5 wt% Mg–Al–LDH (YDirect = 89.8). A Good label was assigned to the epoxy nanocomposites containing up to 1.0 wt% Zn–Al–LDH, while epoxy/Mg–Al–LDH nanocomposites were Poor in terms of the CI labeling when Mg–Al–LDH content was more than 0.1 wt%. An increase of about 28 °C in the Tg value after the addition of 0.1 wt% Zn–Al–LDH indicated that Zn–Al–LDH can make strong the interaction between the epoxy matrix and nanoplatelets. However, decrease in the Tg of the epoxy/Mg–Al–LDH nanocomposites was a signature of the weak interactions between the Mg–Al–LDH nanoplatelets ‎and epoxy matrix due to inappropriate dispersion. In general, it was revealed for the first time that the CI enables correlating the chemical crosslinking with the photophysical properties of the epoxy/LDH nanocomposites.

International audience; This work is focused on the effect of natural defect on the fatigue resistance of a laser powder bed fusion additively manufactured Ti-6Al-4V titanium. To reveal the fatigue strength variability and its sensitivity to the defect size, push-pull fatigue tests have been undertaken on specimens with different sizes of highly loaded volume of material. In order to easily vary the size of the highly loaded volume, specimens containing different numbers of surface hemispherical shape holes of 600 μm in diameter have been tested. This method also allowed to test small volume which triggered crack initiation from microstructural features.The fatigue damage mechanisms observed and the average natural defect size measured on the failure surfaces depend on the size of the highly stressed region. A higher fatigue strength is observed for smaller stressed volumes and defect free regions. To reduce the impact lack-of-fusion on fatigue and increase the probability of triggering crack initiation from a microstructural feature, the specimens were built in the horizontal direction. For specimens where fatigue cracks initiated at natural discontinuities, the results reported in a Kitagawa-Takahashi diagram revealed a critical defect size (√area ) in the range of 30 μm. In addition, a probabilistic approach based on the weakest link theory is proposed. The model describes a probabilistic Kitagawa-Takahashi diagram accounting for the size of both the highly stressed volume and the natural defect.

International audience; In this work, a (TiHfZr)(NbTa) 26 (%at) high-entropy quinary alloy has been developed especially for high-temperature superelastic applications and studied over a large range of temperatures. The mechanical properties of this new material were compared with those of other superelastic alloys. The different ingots have been made in a cold crucible from pure metals. Several thermomechanical treatments have been performed on the microstructure of four alloys among them (TiHfZr)(NbTa) 26 alloy. The microstructure of each alloy has been characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and x-ray diffraction technique (XRD) and the mechanical behavior was investigated through three-point bending tests between - 40 and 200C, in quasi-static monotonic and low cycle loading conditions. The effects of the thermomechanical treatments on the static and cyclic thermomechanical mechanical responses have been analyzed in combination with the microstructure investigations of the four studied alloys. It has been shown that the (TiHfZr)(NbTa) 26 alloy presents a martensitic transformation and a superelastic effect over the studied range of temperatures, in the cold-worked state or after solution treatment. Finally, the obtained experimental results have been compared with those of other superelastic alloys demonstrating the features of the developed high-entropy high-temperature superelastic alloy.

International audience; The numerical approach of topological optimization allows determining the optimal distribution of the material in a given volume in the function of an objective. This approach has recently regained interest thanks to the development of additive manufacturing, which makes it possible to manufacture its resulting parts with complex geometries. In the biomedical field, this numerical approach can also improve the performance of medical devices. Most of the time, the objective of topological optimization is to maximize the stiffness of the considered part while reducing its mass or volume. For example, this criterion has been applied for the optmisation of craniofacial reconstruction prosthesis (Al-tamimi et al. 2017). Some studies have integrated biomechanical considerations in the form of geometrical constraints in taking into account anatomical areas to be avoided (Sutradhar et al. 2016).To our knowledge, no study considers the phenomenon of “stress-shielding” between the bone and the implant in its optimization process. In this work, the originality is the optimization approach which does not only consider the mechanical characteristics of the optimized part (such as its stiffness) but also the mechanical characteristics of the surrounding bone. Thus, it involves specifically taking into account the mechanical behavior of the surrounding bone to topologically optimize the geometry of the medical device and improve the load transfer between the bone and the implant. For that, a numerical simplified Finite Element (FE) model is developed in this paper with a simplified geometry to highlight the possibility of controlling the load transfer bone and implant.

Porous structures, including those with lattice geometries, have been shown to mimic the mechanical properties of the human bone. Apart from the widely known strut-based lattices, the Triply Periodic Minimal Surfaces (TPMS) concept has been introduced recently to create surface-based lattices and to tailor their mechanical behaviors. In this study, the numerical investigation of the effective elastic properties, the anisotropic behavior, and the local stress distributions of a broad range of topologies provide us with a complete numerical tool to assist bone implant design. The comparison database of the lattices includes TPMS-based lattices, both sheet, and skeletal, as well as strut-based lattices. The lattices are subjected to periodic boundary conditions and also, a homogenization method is deployed to simulate the response of the lattice unit cells determining their apparent equivalent stiffness. A correlation among the lattice topologies, their effective mechanical properties, and the local Von Mises stress concentrations in them is observed. The stress distribution of various topologies with the same elastic modulus is examined to combine all the investigations. Finally, a large variety of numerical results are presented to allow the comparison of the lattice structures and the selection of the optimal configuration that mimics the elastic properties of the bone. The authors acknowledge Arts et Metiers Foundation for the finan­cial support in the framework of ENSAM Health Network.

International audience; Additive manufacturing (AM) processes are particularly interesting to reduce the weight of a part by associate lattice structures to thin skin. To ensure a finished product with the dimensional and structural requirements of an industrial part, a post-machining is necessary. The proposed work studied the surface integrity after the dry precision turning of a thin wall of Ti-6Al-4V part produced by sintering laser melting (SLM), using uncoated carbide tool with various cutting angles and tool nose radius. A design of experimental approach (DOE) is used. Different techniques are combined to characterize cutting performance and surface integrity including cutting forces, residual stresses, micro-hardness, and SEM microscopy. Observation reveals that the finish-cutting of near net shape part obtain by SLM induces a minimal effect on surface integrity. Even the dry condition, the low thermal conduction of titanium alloys and the 1 mm skin thickness obtained after cutting operation, damages on surface and subsurface are negligible (

International audience; The objective of this study was to develop multifunctional protective biocompatible (Cu, Zr)/a-C: H coatings with good mechanical properties and high corrosion resistance using a sputtering system on the surface of TC4 alloy. Coatings with a higher Zr/Cu ratio showed higher hardness, Young's modulus, and superior bio-corrosion resistance. It was demonstrated that charge transfer resistance of the coating with a higher Zr/Cu ratio enhanced from ∼40 kΩ. cm2 to ∼990 kΩ. cm2 after 168 h of immersion time. The results also showed strong synergistic effects of Cu and Zr, as well as the formation of the zirconium carbide phase on the surface.

International audience; New high temperature shape memory alloyswith five or more elements are under development and present attractive performances for several functional applications. These active metallic materials are called high entropy and high temperature shape memory alloys (HE-HT-SMAs). This work deals with the characterization of an alloy that combines high temperature shape memory effect and high entropy effect features, a NiCuTiHfZr alloy. The evolution of the phase transformation and the shape memory effect during thermal fatigue was compared with a ternary alloy NiTiZr. Ingots were prepared in a cold crucible and alloys were characterized after thermal cycling at 600 K without a protective gas atmosphere. Optical microscope, X-ray diffraction, and scanning elec- tron microscopy observations showed the presence of martensite in this unpublished alloy at room temperature. The differential scanning calorimetry (DSC) tests showed that martensitic transformation takes place at high temperature. High temperature thermal cycling was performed during a three-point bending tests under constant load without a protective atmosphere. Thermomechanical results showed that high entropy effects increase the operating behavior at high temperature. Hence this new composition of NiCuTiHfZr alloy can be used as an actuator for aerospace and aeronautic application.

International audience; In this study, the potential of microporous 3D metal–organic framework (MOF) for curing epoxy resin has been discussed. First, MIL-101 (Cr), a chromium based MOF, was synthesized under hydrothermal condition and then characterized by using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermogravimetric (TGA) measurements. Epoxy nanocomposites containing 0.1, 0.3 and 0.5 wt% of MOF nanocrystals were subsequently prepared and their curability was studied in terms of the universal dimensionless Cure Index (CI) criterion under nonisothermal differential scanning calorimetry (DSC). Based on calculations made on the basis of the CI, epoxy nanocomposites containing 0.1, 0.3, and 0.5 wt% of MOF were labeled Good and Excellent thanks to an enhanced chemical interaction between MOF and epoxy matrix, where the heat of cure in the system was surprisingly even higher than that of the neat epoxy. It was demonstrated that introduction of MOF into epoxy significantly improved the heat release during crosslinking process of epoxy, as indicated by a 63% rise in the enthalpy of cure at MOF loading of 0.1 wt%. Addition of thermally stable MOF nanomaterials to the epoxy resin improved thermal decomposition resistance of epoxy. Up to 0.3 wt% loading, the system revealed acceptable thermal stability at elevated temperature featured by more residue remained at the end of test, while sample containing 0.5 wt% MOF resisted against decomposition at early stages of degradation due to higher thermal stability of MOF with respect to epoxy resin.

Recent works have shown that the elastic mismatch observed at the bone / implant interface could be responsible for stress shielding issues causing bone resorption phenomena and potentially implant failures. In the present study, new advanced thermomechanical approaches leading to titanium alloys with graded elastic properties are proposed. The underlying philosophy and the whole methodology is detailed here, from the selection of candidates with large elastic variability to the creation of gradients, involving the identification of microstructure-properties relationships and the use of appropriate thermo-mechanical treatments. Applied on Ti-Nb-Zr alloys, these original routes enabled to get the following graded properties: elastic modulus from 85 to 65GPa over 400μm for TNZ alloy by surface deformation, and from 130 to 75GPa over 100μm for Ti-13-13 by preferential dissolution. These promising results thus validated the previously designed material-strategy-process combinations.

International audience; Additive manufacturing allows the manufacture of parts made of functionally graded materials (FGM) with a chemical gradient. This research work underlines that the use of FGM makes it possible to study mechanical, microstructural or biological characteristics while minimizing the number of required samples. The application of severe plastic deformation (SPD) by surface mechanical attrition treatment (SMAT) on FGM brings new insights on a major question in this field: which is the most important parameter between roughness, chemistry and microstructure modification on biocompatibility? Our study demonstrates that roughness has a large impact on adhesion while microstructure refinement plays a key role during the early stage of proliferation. After several days, chemistry is the main parameter that holds sway in the proliferation stage. With this respect, we also show that niobium has a much better biocompatibility than molybdenum when alloyed with titanium.

There have been several attempts to improve the cellular and molecular interactions at the tissue&ndash, implant interface. Here, the biocompatibility of titanium-based implants (e.g., Grade 2 Titanium alloy (Ti-40) and titanium&ndash, niobium alloy (Ti-Nb)) has been assessed using different cellular and molecular examinations. Cell culture experiments were performed on three substrates: Ti-40, Ti-Nb, and tissue culture polystyrene as control. Cells number and growth rate were assessed by cell counting in various days and cell morphology was monitored using microscopic observations. The evaluation of cells&rsquo, behavior on the surface of the implants paves the way for designing appropriate biomaterials for orthopedic and dental applications. It was observed that the cell growth rate on the control sample was relatively higher than that of the Ti-40 and Ti-Nb samples because of the coarse surface of the titanium-based materials. On the other hand, the final cell population was higher for titanium-based implants, this difference was attributed to the growth pattern, in which cells were not monolayered on the surface. Collagen I was not observed, while collagen III was secreted. Furthermore, interleukin (IL)-6 and vascular endothelial growth factor (VEGF) secretion were enhanced, and IL-8 secretion decreased. Moreover, various types of cells can be utilized with a series of substrates to unfold the cell behavior mechanism and cell&ndash, substrate interaction.

International audience; In today's business environment, the trend towards more product variety and customization is unbroken. Due to this development, the need of agile and reconfigurable production systems emerged to cope with various products and product families. To design and optimize production systems as well as to choose the optimal product matches, product analysis methods are needed. Indeed, most of the known methods aim to analyze a product or one product family on the physical level. Different product families, however, may differ largely in terms of the number and nature of components. This fact impedes an efficient comparison and choice of appropriate product family combinations for the production system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster these products in new assembly oriented product families for the optimization of existing assembly lines and the creation of future reconfigurable assembly systems. Based on Datum Flow Chain, the physical structure of the products is analyzed. Functional subassemblies are identified, and a functional analysis is performed. Moreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of thyssenkrupp Presta France is then carried out to give a first industrial evaluation of the proposed approach.

Human health is one of the challenging issues which have necessitated the accompaniment of various fields of science. Therefore, the diverse multidisciplinary scope of human health has been emerged using miscellaneous materials with specific applications. Photosensitizers are among the unique materials being utilized in medicine, in particular in cancer treatment. Though they have been partially studied for the treatment of cancer diseases, it is still believed that these materials are on the verge of a new era in the near future. Research on nanotechnology is expected to act as a game changer in this field by changing the basic characteristics of currently available photosensitizers. Photodynamic therapy as a non-invasive therapeutic method is one of the important applications of photosensitizers for disease treatment. The adjuvant methods can assist photosensitizers and phototherapy methods in an optimal way for a more efficient therapeutic result. Nano-sized photosensitizers can be synthesized for enhanced efficiency compared to the conventional techniques. Here, the emerging applications of nano-sized photosensitizers have been highlighted for medical research.

International audience; This paper presents the results of functionally graded Ti6Al4V-Mo alloy manufactured with directed energy deposition called CLAD ® (Construction Laser Additive Direct) process. Single track width sample with five gradients of composition, from 0 to 100 wt.% Mo, was manufactured using a coaxial nozzle. Both Ti6Al4V and Mo ratios were modified with a 25 wt.% increase or decrease in the chemical composition of each gradient. A two-powder feeder was used to input the correct ratio of each powder, so as to obtain the desired chemical composition. XRD analysis allowed to define the phases present in each deposition, as well as the lattice parameter. SEM observations showed microstructural evolution from 25 wt% Mo on, namely where the ␤-phase becomes dominant. Moreover, dendrites appear from 50 wt.% Mo on. Microhardness analysis revealed variation along the deposition depending on the chemical composition. The homogeneity of the powder mixture under laser beam was highlighted thanks to tomography on the manufactured samples, which validates the processability of functionally graded material (FGM) by CLAD ® process.

This paper investigates the mechanical properties of hyper deformed wires of Ti-26 at.%Nb (Ti-26Nb) alloy that can be equally expressed as Ti-40.5 wt.%Nb. These wires obtained by hot drawing process have a diameter of 85 μm and 285 μm, respectively. The effect of a short heat treatment at 748 K for 600 s was also investigated. The influence of the heat treatment and the diameter of the wires evaluated by mechanical tests, such as nano indentation, quasi-static tensile, and fatigue tests, and microstructure investigations. The quasi-static tensile tests show that the mechanical properties, like elasticity modulus and ultimate tensile strength, are improved with the decrease of the diameter. An increase of 55% and 26% in strength is obtained for the non-treated state and the heat treated state, respectively. The improvements in the mechanical properties for the 285 μm diameter wire are due to the refinement of grains to submicron scale between 100 and 200 nm. The short heat treatment induces an increase of the Young's modulus and a decrease of the ultimate tensile strength by the emergence of a dual phase (α and β) microstructure. For fatigue tests, the increase of frequency from 4Hz to 30Hz leads to an increase of 45% of the fatigue life time. Keywords: Ti-Nb alloy, Mechanical properties, Microstructure, Fatigue, Hyper deformed wires

International audience; Parts produced by Selective Laser Melting (SLM) presents a roughness due to thickness of fusion layers but also to partially sintered particles stuck to the edge of the parts. In order to ensure a finished product with the dimensional and structural requirements of an industrial part, a post processing by machining is necessary. The aim of the proposed study is to compare the machinability of Ti-6Al-4V obtained by SLM process and that of a cast alloy. Micro-cutting tests are conducted to examine the effect of operating conditions on cutting forces, chip formation and on surface and sub-surface microstructure. .

International audience; Various amounts of a phosphonium ionic liquid (IL169) were used as curing agents as well as flame retardants of epoxy prepolymer in order to prepare epoxy networks with improved fire properties. The flame retardancy of these resins was investigated using thermogravimetric analysis (TGA), pyrolysis combustion flow calorimetry (PCFC) and cone calorimetry. Phosphonium ionic liquid significantly reduced flammability without further addition of flame retardants due to the high amount of phosphorus (up to 3.69 wt%). The Peak of heat release rate decreases from 1099 kW/m(2) to 300 kW/m(2) in cone calorimeter at 35 kW/m(2) when incorporating 30 phr of IL169. Phosphorus modifies pyrolysis pathway, promotes charring and may act as flame inhibitor. The char layer protects the underlying polymer, leading to a high unburnt polymeric fraction. Char properties were studied using PCFC, Raman spectroscopy and X-ray tomography. Phosphorus improved the graphitization of the char and its thermooxidative stability.

International audience; The aim of this paper is twofold: firstly, to compare the microstructural and the mechanical properties of Ti-44Nb samples manufactured pre-alloyed powder and differential injection, and secondly, to demonstrate the feasibility of the differential injection method included in the DED-CLAD ® process, to manufacture functionally graded Ti-Nb alloys. Functionally graded materials (FGM) are promising new materials which are perfectly adapted to custom-made parts with various properties for specific applications. In FGMs, titanium and niobium ratios were modified in different steps to create the variation in alloy composition owing to a double-powder feeder. Mechanical analysis and SEM observations show the variation along the deposition depending on the chemical composition. Chemical analysis revealed the homogeneous repartition of the powder mixture as well as the nominal composition of each deposition. Mechanical tests showed a decrease of the microhardness with the increase of Nb content. The elastic modulus was found to be the lowest for Ti-40Nb.

International audience; When it is difficult to deposit a material A on a material B, it is possible to create a Functionally Graded Material (FGM) using a buffer material between them to avoid the appearance of defects. The literature shows that it is very difficult, nay impossible, to have an efficient metallurgical bond between Ti6Al4V and Inconel-Mo alloys without cracks, porosities or delamination. A buffer material is therefore needed (here 25% Ti6Al4V-75% Mo) and the fine analysis of the two interfaces thus created makes it possible to define the relevance of the choice of the buffer. Moreover, the understanding of the phenomena taking place at the interface allows the preservation of the structural integrity of a FGM made by additive manufacturing. CLAD® powder-based directed energy deposition allows the building of parts containing FGM and/or buffer materials directly during the process. The study of the interfaces at both sides of the buffer material is essential. In this paper, the first interface 100 Ti6Al4V / 25 Ti6Al4V-75 Mo (in wt%) is smooth, suggesting that there has been diffusion between both alloys. The second one, 25 Ti6Al4V-75 Mo / 30 Inconel 718-70 Mo, contains numerous exotic structures between both alloys. For such a sharp interface, we show in this paper that a microscopic study is not sufficient, but a finer scale is necessary to have a good metallurgical insight. Thus, EDS, TKD and X-ray crystallography were performed right on this interface and revealed three main structures: a hexagonal matrix, a cubic structure and an ordered hexagonal one. The hexagonal matrix appears to consist of Ni 3 Ti and the ordered hexagonal one of NiMo.

A semi-analytical model for orthogonal cutting taking into account microstructure evolution and its influence on the chip formation process is developed for polycrystalline materials. To describe the 2D material flow in the chip, a thermomechanical crystal plasticity constitutive model was combined with the flow line approach. The microstructure evolution, as well as material flow stress and temperature rise, are obtained through a Visco-Plastic Self-Consistent (VPSC) mean field crystal plasticity model combined with a Mechanical Threshold Stress (MTS) physical-based hardening law. The proposed approach allows capturing in a relative simple way the variations of thermomechanical fields such as stress, strain, strain rate and temperature in the primary shear zone. The model validation is conducted by successful comparisons with experimental results of Shi and Liu [63] in terms of cutting forces and chip thickness during orthogonal cutting of a HY 100 steel alloy. The predicted results indicate that equivalent strain and temperature increase from the chip free surface to the tool tip. In contrast, the equivalent stress exhibits a reverse trend.

International audience; Additive manufacturing techniques, such as Selective Laser Melting (SLM) are considered for making some Ti6Al4V parts. However, in some assemblies, such parts may be subjected to severe sliding.A Ti6Al4V tribopair was subjected to sliding under high speed and pressure (40 m/s and up to 300 MPa). This research focuses on the influence of the manufacturing process (machining or SLM) and the building orientation (for SLM) of one tribopair element on the friction coefficient and wear.Results were mostly insensitive to SLM orientation. However, with the SLM parts, there was a higher friction coefficient and a lower wear than with machined parts. An energy-based approach revealed a single pattern for wear regardless of the manufacturing technology, consistent with previous results.

International audience; The thermal degradation and flame retardancy of poly(methyl methacrylate) containing three mineral fillers, with different geometry, MMT: plate-like, sepiolite: fibrilar and zirconium oxide ZrO2: spherical, in combination with ammonium polyphosphate (APP) were studied. The flame behavior of composites was investigated using pyrolysis-combustion flow calorimeter, cone calorimeter and LOI tests. The results revealed that the composites containing APP and sepiolite present the best fire behavior. A rheological study was performed on composites to establish a relationship between viscosity and flammability. The residues of samples after cone calorimeter test were studied using X-ray diffraction and micro-tomography in order to investigate their chemical composition and also repartition of fillers. A better repartition of sepiolite during combustion could be the origin of the best results obtained for sample containing this filler.

International audience; Study: Implantation of a Left Ventricular Assist Device (LVAD) may produce both excessive local tissue stress and resulting strain-induced tissue rupture that are potential iatrogenic factors influencing the success of the surgical attachment of the LVAD into the myocardium. By using a computational simulation compared to mechanical tests, we sought to investigate the characteristics of stress-induced suture material on porcine myocardium.Methods: Tensile strength experiments (n = 8) were performed on bulk left myocardium to establish a hyperelastic reduced polynomial constitutive law. Simultaneously, suture strength tests on left myocardium (n = 6) were performed with a standard tensile test setup. Experiments were made on bulk ventricular wall with a single U-suture (polypropylene 3-0) and a PTFE pledget. Then, a Finite Element simulation of a LVAD suture case was performed. Strength versus displacement behavior was compared between mechanical and numerical experiments. Local stress fields in the model were thus analyzed.Results: A strong correlation between the experimental and the numerical responses was observed, validating the relevance of the numerical model. A secure damage limit of 100 kPa on heart tissue was defined from mechanical suture testing and used to describe numerical results. The impact of suture on heart tissue could be accurately determined through new parameters of numerical data (stress diffusion, triaxiality stress). Finally, an ideal spacing between sutures of 2 mm was proposed.Conclusion: Our computational model showed a reliable ability to provide and predict various local tissue stresses created by suture penetration into the myocardium. In addition, this model contributed to providing valuable information useful to design less traumatic sutures for LVAD implantation. Therefore, our computational model is a promising tool to predict and optimize LVAD myocardial suture.

International audience; The effects of bare and starch-modified ZnO (ZnO-St) nanoparticles on viscoelastic and mechanical properties are studied by dynamic mechanical and tensile analyses. Transparent epoxy-based nanocomposite films are prepared by incorporating bare or starch-modified ZnO particles into the epoxy matrix. The results demonstrated that ZnO particles hindered the curing reactions and hence the final properties of the cured epoxy. As a result, glass-transition temperature (Tg) and crosslinking density demoted. However, starch as a surface modifier compensated for the undesired effects of ZnO in a way that by enhancing the curing reactions through autocatalytic mechanism, Tg and crosslinking density increased. The storage moduli for epoxy, epoxy/ZnO and epoxy/ZnO-St are accordingly as 13.84, 3.95 and 19.54 MPa. Therefore, the molecular weight between the entanglements is calculated as 0.2878, 1.0089 and 0.2039 in the same order. Moreover, considering the peaks of the tanδ diagrams, Tgs for epoxy, epoxy/ZnO and epoxy/ZnO-St are obtained as 95.95, 100.16 and 101.24 °C, respectively. Comparing epoxy/ZnO-St nanocomposite to epoxy, it can be inferred that the network becomes tougher in the elastic region and then becomes softer passing this region. Mechanistic sketches of epoxy network formation in the presence of bare and surface-treated nanoparticles are discussed.

This original work proposes to investigate the transposition of crystallography rules to cubic lattice architectured materials to generate new 3D porous structures. The application of symmetry operations provides a complete and convenient way to configure the lattice architecture with only two parameters. New lattice structures were created by slipping from the conventional Bravais lattice toward non-compact complex structures. The resulting stiffness of the porous materials was thoroughly evaluated for all the combinations of architecture parameters. This exhaustive study revealed attractive structures having high specific stiffness, up to twice as large as the usual octet-truss for a given relative density. It results in a relationship between effective Young modulus and relative density for any lattice structure. It also revealed the opportunity to generate auxetic structures at will, with a controlled Poisson ratio. The collection of the elastic properties for all the cubic structures into 3D maps provides a convenient tool for lattice materials design, for research, and for mechanical engineering. The resulting mechanical properties are highly variable according to architecture, and can be easily tailored for specific applications using the simple yet powerful formalism developed in this work. The authors acknowledge the financial support from French National Research Agency ANR (LabEx DAMAS, Grant no.ANR-11-LABX-0008-01).

International audience; Layered double hydroxide (LDH) has a particular place in clay family because of its flame retardant action. The nanoplatelet-like structure of LDH makes possible development of polymer composites with cationic or anionic nature structures in which macromolecules are positioned in between nanoplatelet galleries. In this work, neat epoxy and its transparent nanocomposite coatings with sodium dodecylbenzene sulfonate (SDBS)-modified LDHs; Mg-Al and Zn-Al LDHs, were prepared and their cure kinetics and viscoelastic behavior were tracked through nonisothermal calorimetric and dynamic mechanical analyses. The higher progression of crosslinking in the epoxy network was observed for epoxy/Zn-Al LDH nanocomposites, while activation energy of cure reaction took a higher value for Mg-Al LDH-incorporated systems. Moreover, epoxy/Mg-Al LDH system revealed higher value of storage modulus and glass transition temperature thanks to larger galleries of Mg-Al nanoplatelets. Network formation in the presence of SDBS-modified Zn-Al LDH nanoplatelets was facilitated due to the action of Zn metal as an adduct with a lone-pair of oxygen atom of epoxy leading to an enhanced epoxy ring-opening. Viscoelastic behavior of transparent coatings containing Zn-Al LDH and Mg-Al LDH was studied through temperature- sweep test at various frequencies to compare the results of calorimetric and thermo-mechanical analyses.