Portail HAL IMT Mines Albi
Not a member yet
5440 research outputs found
Sort by
Numerical modeling and advanced characterization techniques to study the influence of process-inherited local deformation on in-service behavior of an Inconel 718
No full textInternational audienceThis work’s long-term objective is to assess the continuity of material deformation at the grain- and mesoscopic scale from processing to subsequent mechanical loading using crystal plasticity strain gradient models. To that end, advanced experimental characterization techniques are deployed on different pre-deformed microstructures of an Inconel 718. They include advanced digital image correlation (HR-DIC) and high angular resolution orientation (HAR-EBSD) imaging, in order to provide lattice rotations, dislocation substructures and slip events necessary to instantiate simulation volumes. A numerical non-local crystal plasticity model has been developed, and implemented using FFT spectral method, to take into account initial deformation gradients and to describe their evolution under different loading conditions. Advanced experiment/simulation dialogue is expected to prove the ability of the model to predict both localisation of plastic strain and overall material behavior, as well as to predict the influence of pre-deformation history on subsequent microstructure evolution
Stress corrosion cracking behavior of austenitic stainless steel 316L produced using laser-based powder bed fusion
No full textInternational audienceAustenitic stainless steel UNS S31603 (SS316L) is widely used in the resources industry due to its excellent corrosion resistance, ductility, and weldability. Recently, laser-based powder bed fusion (LPBF) manufacturing has gained popularity for creating SS316L components with complex geometries and superior mechanical properties. However, the rapid melting and solidification of the deposited layers during the thermal cycle of LPBF produce residual stresses. Components manufactured through LPBF are frequently used under applied stress in corrosive environments. Thus, it is crucial to understand their susceptibility to stress corrosion cracking (SCC) and the impact of residual stresses. This study investigated the combined effects of applied stress and temperature on the SCC behavior of LPBF SS316L using custom-made C-ring test specimens. Cold-drawn wrought SS316L was included for comparison. Stress relief heat treatment, microhardness testing, partial immersion testing, and microanalysis techniques, such as light optical microscopy (LOM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD), were used to quantify the SCC behavior. The outcomes of this study showed that stressed and unstressed LPBF SS316L specimens were highly susceptible to cracking around their printed holes. The SCC susceptibility was attributed to the residual stresses introduced by the printed supports, as both polished and as-printed holes showed similar cracking behavior. This work provides valuable insights and lays a foundation for further research into the impact of using C-ring samples to investigate SCC susceptibility and sheds light on the SCC susceptibility of as-printed components of complex geometry printed with supports due to the influence of residual stresses
Thermal conductivity of glass/talc filled Polyamide 12 as function of tapping level
No full textInternational audienceSelective laser sintering is a layer-by-layer process that allows complex shapes to be processed butrequires specific properties for the powder used to build the final object. The advantages of freecrucible processing and freedom of design makes this process interesting for several applications.Despite the large number of SLS printer available in the market, a deep understanding of the physicalphenomena of this process is still lacking, due to the number of parameters involved, directlyinfluencing the final part’s properties through the microstructure. In this work, glass beads or talc wereadded to Polyamide 12 (PA 12) matrix in order to evaluate these filler’s influence on powder bed. Westarted with PA 12 and glass beads (PA90/GB10 in wt%) untill 70/30 wt%, with a 5 wt% increment. AsSLS operates with CO2 laser working at 10.6μm to melt powders, it is fundamental to investigate howheat will be conducted through the different sintered layer. Various parameters can influence thermalconductivity of filled Polyamide 12 powder bed such as particle shape, aspect ratio, chemicalcomposition, presence of impurities and also the packing of the particles from powder bed. Hence,porosity is such an important parameter as air inside is highly insulating the material and reduces itsthermal conductivity by convection between pores. This convection is also governed by the pores size.(Rayleigh criterion) Several experiments were carried out in order to evaluate the thermal conductivityas a function of porosity which highly depends on how particles are settled, thus how the powder bedis tapped. These results were obtained using a hot wire conductivity meter from Neotim which cangive thermal conductivity through a powder bed. To determine samples porosity, we used a powdertester which returned powder densities for different tapping levels. As we are working with filledpolyamide 12 matrix, a huge drop of flowability has to be considered upon addition of filler whichcan cause issues during the process. Changes of processing parameters could be required due tosignificant modifications of the thermal behavior resulting from the presence of fillers
The mechanisms of calcium-catalyzed graphenization of cellulose and lignin biochars uncovered
No full textInternational audienceA recent study has shown that highly crystalline graphene-based materials can be obtained from poorly organized carbon precursors using calcium as a non-conventional catalyst. XRD and TEM analyses of calcium-impregnated cellulose and lignin biochars showed the formation of well-ordered graphenic structures (L c > 7 nm, d 002 2000 °C). Herein, we propose new insights on the mechanism controlling the formation of highly graphenic biochars using Ca as a catalyst. We postulate that the calcium-catalyzed graphenization occurs through the formation of a metastable calcium carbide by reaction between CaO particles and amorphous carbon between 1000 and 1200 °C. CaC 2 decomposes into calcium vapor and a graphenic shell covering the CaC 2 particles as confirmed by TEM analysis. The thickness and planarity of the graphenic shell increase with the CaC 2 initial particle size (between 20 and 200 nm), and its growth is controlled by the diffusion of the calcium vapor through the graphene layer. A much effective graphenization was obtained for the lignin biochars compared to cellulose, with L c > 10 nm and d 002 < 0.340 nm, attributed to the insertion of sulfur in the graphenic shells, which favors their ruptures and the decomposition of CaC 2 into graphene. We believe that these findings would enable the reduction of costs and environmental impact of graphene-based materials synthesis using cheap and abundant renewable feedstocks and catalysts as well
Evaluate the Potential of the Physical Internet for Last Mile Delivery in Developing Countries
No full textInternational audienceLast mile delivery is a crucial component of the supply chain process, particularly in developing countries. However, traditional delivery methods are often characterized by inefficiencies, such as high costs, long delivery times, and poor delivery accuracy. The rise of e-commerce and the growth of online retail have added further pressure to last mile delivery in these countries. To address these challenges, Physical Internet (PI) has emerged as a promising solution. PI is a new paradigm for logistics and supply chain management that aims to increase the efficiency, sustainability, and resilience of the supply chain. This study aims to assess the impact of PI on last mile delivery in developing countries, using a digital model-based approach. By analyzing the potential benefits and limitations of PI, this study will contribute to the literature and provide insights and recommandations into the implementation of PI-based scenarios in last mile delivery in developing countries
The influence of activity coefficient and equilibrium constant models on the speciation of aqueous solutions of H2SO4-MgSO4-Al2(SO4)3 at 235 and 250 °C
No full textInternational audienceSupersaturation occurs in many industrial applications promoting reactive crystallisation between the reactants to form solutes. These solutes accumulate during precipitation, leading to the formation of scales on the inner walls of the reactor and particularly around the stirrer, causing modifications in the hydrodynamics. This encrustation is responsible for process shutdowns in continuous crystallisation processes. Supersaturation control is essential for industrial processes aimed at controlling or inhibiting the formation of these solids. Knowledge of mineral solubility and chemical speciation is required to account for the composition of the complexes in the system in their various solid or aqueous forms. This speciation is obtained by considering the thermodynamic equilibrium constants of the dissociation/complexation reactions involved in the system, the pressure, and the activity coefficients of the chemical species in their molecular or electrolyte form. From these thermodynamic quantities and the state of the system, we can predict the direction of the reaction.This study highlights the risk of the lack of experimental information on equilibrium constants at high temperatures and moderate pressures. Our goal is to evaluate the accuracy of existing models classically used to predict the equilibrium constant in such very hard conditions encountered in hydrometallurgical processes. Furthermore, we demonstrate the influences of equilibrium constants estimation and activity coefficient models on the speciation of H2SO4–Al2(SO4)3 and H2SO4–MgSO4 systems, forming hydronium alunite and kieserite respectively, in the laterite liquor of hydrometallurgical processes
A Go/No-Go Decision-Making Model Based on Risk and Multi-Criteria Techniques for Project Selection
No full textInternational audienceThe realization of infrastructures and the deployment of processes can follow project formalism. Generally, a project goes through a design and a realization phase. Between these two phases, there is a crucial milestone: Launching the project. Making this decision is not easy at all, and constitutes a real problem-- the main reasons to this are the numerous numbers of criteria (for technical, economic, social, environmental dimensions) and risks in the sense of feared events. Criteria and risks are most of the time not considered due to lack of time (for formalization) and the difficulty to handle them. The objective of this paper is to propose a relevant approach to make the decision of launching the project or not. The proposal outlined is innovative in that it can consider indicators based on several appropriate criteria, the associated risks, and their ways of management. The fact of considering several criteria and risks increases the probability of making the good decision
Multi-criteria performance analysis based on Physics of Decision — Application to COVID-19 and future pandemics
No full textInternational audienceThe purpose of this study is to present a novel perspective on decision support based on the conventional SEIR pandemic model paradigm considering the risks and opportunities as physical forces deviating the expected performance trajectory of a system. The impact of a pandemic is measured by the deviation of the social system’s performance trajectory within the geometrical framework of its Key Performance Indicators (KPIs). According to the overall premise of utilizing Ordinary Differential Equations to simulate epidemics, the deviations are connected to several alternative interventions. The model is essentially built on two sets of parameters: (i) social system parameters and (ii) pandemic parameters. The ultimate objective is to propose a multi-criteria performance framework to control pandemics that includes a combination of timely measures. On the one hand, the current study optimizes prospective strategies to manage the potential future pandemic, while on the other hand, it explores the COVID-19 epidemic in the state of Georgia (USA)
Application of design of experiments (DoE) for optimised production of micro- and mesoporous Norway spruce bark activated carbons
No full textInternational audienceIn this work, Norway spruce ( Picea abies (Karst) L.) bark was employed as a precursor to prepare activated carbon using zinc chloride (ZnCl 2 ) as a chemical activator. The purpose of this study was to determine optimal activated carbon (AC) preparation variables by the response surface methodology using a Box–Behnken design (BBD) to obtain AC with high specific surface area (S BET ), mesopore surface area (S MESO ), and micropore surface area (S MICR ). Variables and levels used in the design were pyrolysis temperature (700, 800, and 900 °C), holding time (1, 2, and 3 h), and bark/ZnCl 2 impregnation ratio (1, 1.5, and 2). The optimal conditions for achieving the highest S BET were as follows: a pyrolysis temperature of 700 °C, a holding time of 1 h, and a spruce bark/ZnCl 2 ratio of 1.5, which yielded an S BET value of 1374 m 2 g −1 . For maximised mesopore area, the optimal condition was at a pyrolysis temperature of 700 °C, a holding time of 2 h, and a bark/ZnCl 2 ratio of 2, which yielded a S MESO area of 1311 m 2 g −1 , where mesopores (S MESO% ) comprised 97.4% of total S BET . Correspondingly, for micropore formation, the highest micropore area was found at a pyrolysis temperature of 800 °C, a holding time of 3 h, and a bark/ZnCl 2 ratio of 2, corresponding to 1117 m 2 g −1 , with 94.3% of the total S BET consisting of micropores (S MICRO% ). The bark/ZnCl 2 ratio and pyrolysis temperature had the strongest impact on the S BET , while the interaction between temperature and bark/ZnCl 2 ratio was the most significant factor for S MESO . For the S MICRO , holding time was the most important factor. In general, the spruce bark AC showed predominantly mesoporous structures. All activated carbons had high carbon and low ash contents. Chemical characterisation indicated that the ACs presented disordered carbon structures with oxygen functional groups on the ACs’ surfaces. Well-developed porosity and a large surface area combined with favourable chemical composition render the activated carbons from Norway spruce bark with interesting physicochemical properties. The ACs were successfully tested to adsorb sodium diclofenac from aqueous solutions showing to be attractive products to use as adsorbents to tackle polluted waters