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Mechanical characterization and behavior modelling of Ti-6Al-4V alloy in hot forming conditions
No full textInternational audienceTi-6Al-4V is a widely used titanium alloy in superplastic forming process which requires high temperatures (T≈900 °C) and low strain rates (ε ˙≈〖10〗^(-3) s^(-1)). One way to reduce the costs of the process is to use a lower forming temperature and/or higher strain rate, up to 〖10〗^(-2) s^(-1). However, the behavior of Ti-6Al-4V alloy still need to be modeled at such forming conditions and for different initial microstructure. In order to characterize the mechanical behavior of Ti-6Al-4V at temperature between 400 °C and 700 °C, relaxation and tensile tests performed under small and large deformation conditions were conducted. Depending on the test, the deformations were evaluated through two kinds of measurements, respectively with an extensometer and with a digital image correlation technique (DIC). Similar experimental results were obtained, validating the use of DIC at high temperature to evaluate high strain levels. Two different microstructures of Ti-6Al-4V alloy were tested to study the impact of the initial microstructure on the mechanical behavior. For similar conditions of strain rate and temperature, representative of the forming process, a fine-grained microstructure exhibits an enhancement of mechanical behavior in comparison with the classical coarse-grained microstructure used in the current industrial process. Finally, an elasto-viscoplastic has been identified for each microstructure
Numerical and experimental studies of molten pool phenomena influence on dissimilar materials coatings by L-PBF
No full textInternational audienceOver the past few years, Laser Powder Bed Fusion (L-PBF) has become increasingly popular, as this method enables energy and material savings during the manufacturing process. 3D L-PBF parts, based on computer-designed geometries, are generated layer by layer using laser energy. Since the beginning of these studies several decades ago, significant progress has been made in the understanding of additive manufacturing, particularly with regard to properties, structure and in situ monitoring. However, the scientific manufacturing community has yet to achieve optimal operational reliability. Presently, numerous defects remain a major problem for parts produced by L-PBF. These defects are mainly caused by the movement of the molten material and its rate of solidification within the melt, which is also influenced by the thermal phenomena of the process. In the L-PBF manufacturing process, the main challenge is to control the complex interdependence of these phenomena [1]. The aim of this work is therefore to study the various physical aspects during a Laser Powder Bed Fusion (L-PBF) process. For this purpose, it is necessary to provide a numerical model with specific works on experimental characterizations of materials at high temperature (up to 1000 °C) as a model’s input parameters, such as the thermal or optical properties of cobalt based powder (CoCrMo) used in our study. In addition to material characterization, theoretical model studies have been used to determine the thermal properties of L-PBF powder [2], in particular thermal diffusivity. This model is also validated by specific experimental characterizations, involving the dilution of iron substrates in a CoCrMo alloy deposit and temperature measurements during the manufacturing process. Furthermore, the amount of iron transferred from the substrate to the coating can be used as an indicator of the molten metal movement in the melt and, ultimately, of the operating parameters used to apply the coating. Too much iron on the surface impairs the mechanical strength of the substrate-coating assembly, thus indicates poor control of the parameters used for this purpose
Analysing the modifications of carbon black and other fillers after pyrolysis of model tyres
No full textInternational audienceCarbon blacks (CBs) that are used as fillers to reinforce rubber contribute to tyre recycling issues. Although recovered carbon black (rCB) produced from the thermoconversion of waste tyres has poor reinforcing abilities in non-polar rubbers, the exact origin of the difference between rCBs and CBs is not elucidated. The characteristics of the rCBs produced from the steam pyrolysis of model laboratory-reinforced rubbers, with or without silica added, were analysed and compared to the pristine CB. X-Ray Diffraction revealed that the quantity of unorganised carbon in the rCB increased by about 25% after pyrolysis, revealing the occurrence of carbonaceous deposits originating from rubber carbonisation. They affected the filler texture, and part of the ultra-microporosity (i.e., pores within the diameter range 0.34–0.76 nm), which had a three-fold decrease in the rCB sample. The recovered fillers, with and without silica, had more oxygenated functional groups than the CB. The dispersibility and stability of the colloidal suspensions were affected by the increased surface oxygen functional groups. Reductive hydrogenation was utilised to remove the excess oxygen allowing an improved understanding of the rCBs. This is a promising method to maximise material reutilisation in the circular value chain of tyres
Evaluation of the printability of agar and hydroxypropyl methylcellulose gels as gummy formulations: Insights from rheological properties
No full textInternational audienceThe trial-and-error method currently used to create formulations with excellent printability demands considerable time and resources, primarily due to the increasing number of variables involved. Rheology serves as a relatively rapid and highly beneficial method for assessing materials and evaluating their effectiveness as 3D constructs. However, the data obtained can be overwhelming, especially for users lacking experience in this field. This study examined the rheological properties of formulations of agar, hydroxypropyl methylcellulose, and the model drug caffeine, alongside exploring their printability as gummy formulations. The gels’ rheological properties were characterized using oscillatory and rotational experiments. The correlation between these gels’ rheological properties and their printability was established, and three clusters were formed based on the rheological properties and printability of the samples using principal component analysis. Furthermore, the printability was predicted using the sample’s rheological property that correlated most with printability, the phase angle , and the regression models resulted in an accuracy of over 80 %. Although these relationships merit confirmation in later studies, this study suggests a quantitative definition of the relationship between printability and one rheological property and can be used for the development of formulations destined for extrusion 3D printing
Antiproliferative in Vitro Evaluation of Terpenic Amines Synthesized via a Rhodium‐catalyzed Hydroaminomethylation
No full textInternational audienceTerpene‐derived alkaloids show a variety of biological activities, including antioxidant, anti‐inflammatory, antimicrobial and cytotoxicity effects. In this work, homologated monoterpene amines have been prepared via a rhodium‐catalyzed hydroaminomethylation of biomass‐based alkenes, such as (R)‐limonene, linalool, myrcene and camphene, in combination with secondary amines of aliphatic and aromatic nature, namely morpholine and N‐methylaniline, leading to highly chemo‐ and regioselective processes. The as‐prepared amines were obtained in 50‐99% overall yields, and in vitro tested on a human colon cancer cell line (HCT‐116) to evaluate their cytotoxic potential. The lead compound of the series (3a) showed cytotoxicity in the micromolar range (IC50 52.46 µM) via the induction of cell death by apoptosis, paving the way towards further structure‐activity relationship studies
Effect of creep loading on the oxygen diffusion of Ti6242S at 650°C
No full textInternational audienceThe influence of low and steady loading on the oxidation behaviour and oxygen diffusion within Ti6242S was investigated at 650 °C in air. Electron probe microanalyser (EPMA), secondary-ion mass spectrometry (SIMS) and high energy synchrotron X-ray diffraction (S-XRD) were used to quantify the oxygen distribution within the oxygen-enriched layer beneath the external oxide scale. Rietveld and peak by peak methods were used to evaluate the average response versus the crystal-oriented response of this diffusion process under load. Interestingly, a thermo-mechano-chemical coupling occurs during the creep-oxidation experiment even for moderate applied stresses (25-70 MPa) and demonstrates: (i) a decrease of the oxygen concentration at the metal/oxide interface, and (ii) a curvature change of the oxygen diffusion profile with load application. A qualitative thermo-mechano-chemical approach is proposed to model the modification of the diffusion law of the oxygen within Ti6242S due to application of a mechanical loading to explain observed experimental results
Analyse microstructurale et comportement mécanique de CMCs oxyde/oxyde élaborés par imprégnation de mèches en continu
No full textInternational audienceThis paper focuses on the analysis of the mechanical behaviour of alumina/alumina ceramic matrixcomposites (CMCs) developed by a continuous tow impregnation method, in relation to their microstructures. The influence of the aqueous slurry formulation on the microstructures of the materials and their tensile and bending properties is studied. A combination of a hygroscopic plasticizer (glycerol) and a gelling powder (boehmite) within the slurry is needed to obtain a good interply cohesion in the composite. A large amount of glycerol (20 wt.% relative to the alumina mass) allows a fine-scale porosity distributed throughout the matrix with few large pores which allows to reach a high Young’s, around 130 – 150 GPa. Moreover, reducing the plasticizer amount induces the apparition of delaminations and defects appear the microstructure, hence decreasing the stiffness. Then, increasing the boehmite amount (from 5 wt.% to 10 wt.%), the damage tolerance is enhanced, likely due to a higher densification level induced by the presence of the boehmite powder.Cet article porte sur l'analyse du comportement mécanique des composites à matrice céramique (CMC) alumine/alumine développés par une méthode d'imprégnation de mèches en continue, en relation avec leurs microstructures. L'influence de la formulation de la suspension aqueuse sur les microstructures des matériaux et leurs propriétés en traction et en flexion est étudiée. La combinaison d'un plastifiant hygroscopique (glycérol) et d'une poudre gélifiante (boehmite) dans la suspension est nécessaire pour obtenir une bonne cohésion inter-plis dans le composite. Une grande quantité de glycérol (20 % en poids par rapport à la masse d'alumine) permet d'obtenir une porosité à échelle fine répartie dans toute la matrice avec peu de pores de grande dimension, ce qui permet d'atteindre un module de Young élevé, de l'ordre de 130 à 150 GPa. Diminuer la quantité de plastifiant provoque l'apparition de délaminages et de défauts dans la microstructure, ce qui diminue la rigidité. Au contraire, augmenter la quantité de boehmite (de 5 % en poids à 10 % en poids) améliore la tolérance à l'endommagement, probablement grâce à une densification plus élevée induite par la présence de la poudre de boehmite
Influence of strain rate on the behavior of natural fiber reinforced thermoplastic composites, experimental and numerical approaches.
No full textInternational audienceThese studies aim to explore the behavior of natural fiber-reinforced thermoplastic matrix composites by examining their response to strain rate during traction, focusing particularly on the longitudinal elastic modulus variation in 0° composites and in plane shear elastic modulus for the ±45° laminates.Utilizing bamboo, flax, and basalt fibers as unidirectional reinforcements and Arkema's semi-crystalline polyamide-11 and ELIUM amorphous resin as matrices, experiments are conducted to characterize the materials. Static and dynamic tensile tests are performed using advanced equipment. Numerous explicit numerical simulations are iterated to match experimental data. Results reveal that composites with 0° plies show limited sensitivity to strain rates below 100 s-1, with bamboo and flax composites exhibiting little change in Young's modulus, while basalt-reinforced composites exhibit a slight increase. However, composites with ±45° stacking display heightened sensitivity, primarily influenced by the resin. This comprehensive investigation provides insights into the complex behavior of these composites under different loading conditions, guiding their optimization and application
Clay/phosphate-based ceramic materials for high temperature thermal energy storage – Part II: Validation of high temperature storage performance at pilot scale
No full textInternational audienceThe performances of a pilot scale packed bed thermal energy storage system filled with 162 kg of developed phosphate-based ceramic materials (cylinders of 1.5 cm × 4 cm) was experimentally investigated under different operating conditions of inlet air temperature for the charge (334 +/- 21 °C, 531 +/- 23 °C and 760 +/- 15 °C), air flowrate for charging and discharging (26.5 to 74 kg/h), as well as under consecutive cycles.The packed bed performed well at different temperature and charge / discharge flowrate. The cylindrical shape of the produced clay/phosphate-based ceramic combined with the horizontal implementation of the storage tank did not provoke a significant preferential path for the air inside the storage medium and did not create a significant thermal de-stratification during the charging and discharging phases. Furthermore, under consecutive cycles, the TES system could be quickly stabilized demonstrating the robustness and flexibility of the developed TES system, which can cover a wide range of application cases. The production of the developed ceramics is mastered by ceramic industries allowing the availability at industrial scale worldwide with competitive cost and carbon footprint.This work opens new prospects for using phosphates-based ceramics as alternative promising media to build new generation of flexible and reliable high temperature TES system for industrial assets decarbonation, grid services as well as renewable energies high penetration into the grid
Influence of the coating brittleness on the thermomechanical fatigue behavior of a -NiAl coated R125 Ni-based superalloy
No full textThe brittleness of an aluminide diffusion coating protecting a Ren\'e 125 Ni-based polycrystalline superalloy was investigated over a wide range of temperatures in its as-received and thermally aged form. Isothermal and thermal cycled aging were performed on the coated system at a maximum temperature of 1100 {\deg}C. Microstructure evolutions and damage initiation within the coating were characterized. Interrupted tensile tests and thermomechanical fatigue tests were conducted to document critical stress-strain conditions leading to the coating cracking and lifetime for the case of thermo-mechanical fatigue loading. Advanced digital image correlation and acoustic emission techniques were used to detect coating cracking. Isothermal oxidation or cyclic oxidation led to improved strain-to-failure due to metallurgical evolutions and also longer fatigue life under thermomechanical fatigue conditions