On the measurement of relative powder-bed compaction density in powder-bed additive manufacturing processes

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.matdes.2018.06.030 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Experimental studies in the literature have identified the powder-bed compaction density as an important parameter, governing the quality of additively manufactured parts. For example, in laser powder-bed fusion (LPBF), the powder-bed compaction density directly affects the effective powder thermal conductivity and consequently the temperature distribution in melt pool. In this study, this physical parameter in a LPBF build compartment is measured using a new methodology. A UV curable polymer is used to bind powder-bed particles at various locations on the powder-bed compartment when Hastelloy X was used. The samples are then scanned using a nano-computing tomography (CT) system at high resolution to obtain an estimation of the relative powder-bed compaction density. It is concluded that due to the interaction between the recoater and the variation in the powder volume accumulated ahead of the recoater across the build compartment, the relative powder-bed compaction density decreases along the recoater moving direction (from 66.4% to 52.4%.). This variation in the powder-bed compaction density affects the density and surface roughness of the final printed parts that is also investigated. Results show that the part density and surface quality decrease ~0.25% and ~20%, respectively, along the build bed in direction of the recoater motion.Natural Sciences and Engineering Research Council of Canada (NSERC) Federal Economic Development Agency for Southern Ontario (FedDev Ontario

Additively manufactured metallic biomaterials

Metal additive manufacturing (AM) has led to an evolution in the design and fabrication of hard tissue substitutes, enabling personalized implants to address each patient's specific needs. In addition, internal pore architectures integrated within additively manufactured scaffolds, have provided an opportunity to further develop and engineer functional implants for better tissue integration, and long-term durability. In this review, the latest advances in different aspects of the design and manufacturing of additively manufactured metallic biomaterials are highlighted. After introducing metal AM processes, biocompatible metals adapted for integration with AM machines are presented. Then, we elaborate on the tools and approaches undertaken for the design of porous scaffold with engineered internal architecture including, topology optimization techniques, as well as unit cell patterns based on lattice networks, and triply periodic minimal surface. Here, the new possibilities brought by the functionally gradient porous structures to meet the conflicting scaffold design requirements are thoroughly discussed. Subsequently, the design constraints and physical characteristics of the additively manufactured constructs are reviewed in terms of input parameters such as design features and AM processing parameters. We assess the proposed applications of additively manufactured implants for regeneration of different tissue types and the efforts made towards their clinical translation. Finally, we conclude the review with the emerging directions and perspectives for further development of AM in the medical industry.National Institutes of Health || The Natural Sciences and Engineering Research Council of Canada || Network for Holistic Innovation in Additive Manufacturin

Rapid Thermo-mechanical Modeling of Laser Powder-Bed Fusion Additive Manufacturing using an Effective Heat Source

Laser powder-bed fusion (LPBF) is one of the most common types of additive manufacturing (AM) processes that has gained a lot of attraction by industries. This process induces a high magnitude of a temperature gradient within the fabricated part due to fast thermal and cooling cycles. Therefore, the existence of residual stresses and deformation of produced parts is inevitable. There are a tremendous number of process parameters involved in LPBF that affect the quality of final products, such as laser power, scanning speed, layer thickness, hatching distance, etc. Modeling and simulation of LPBF provide an opportunity for predicting residual stresses and deformation of LBPF-made parts. Therefore, optimizing process parameters for minimizing residual stresses and deformation is required. Extensive computational time and implementing a proper heat source model are some of the existing challenges in the modeling and simulation of LPBF. Due to micro-scale features of the LPBF melt pool zone, as well as the high-speed process (up to 5 m/s), the computational cost of the simulation process of making macro-scale large parts is highly expensive. On the other hand, extremely fine mesh is required for capturing heat transfer in the laser interaction zone accurately. Consequently, a large number of elements need to be analyzed for solving the problem, which requires a strong resource for computation. This work presents the multi-scale modeling approach based on two groups of micro/mesoscale and macroscale simulations. Firstly, melt pool dimensions of Hastelloy X material single tracks were measured experimentally. Afterward, the micro/mesoscale simulation of LPBF single track was conducted, while implementing a volumetric heat source model (conical-Gaussian) to extract the transient temperature profile and melt pool dimensions. The percentage difference of melt pool depth and width dimensions derived from simulation results and experimental ones are 13% and 6%, respectively. The validated model was then used for multi-track multi-layer simulation. The effect of thin-wall thicknesses on the melt pool dimensions has been studied as an application of the multi-track simulation process. In the macroscale simulation, the thermo-mechanical model was developed for obtaining residual stresses and deformation of the fabricated part. As a major contribution, novel effective heat flux is proposed and applied for accelerating the simulation. Thermo-mechanical modeling of the cube building process is carried out using an effective heat flux. The residual stress is experimentally measured using an X-Ray analyzer machine. The simulation results show a good agreement with experimental ones while a significant reduction in computational costs is achieved. The average percentage difference in predicting residual stress in longitudinal and transverse directions was 11% and the total computational time was 90 minutes

Polarisation X-UV a l'aide de miroirs interferentiels polariseurs-analyseurs

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Etude par resonance magnetique nucleaire de la dynamique du directeur des nematiques en rotation dans un champ magnetique

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Vibration analysis of composite laminated shells using 2D spectral Chebyshev method and lamination parameters

This study presents a modeling approach to accurately and efficiently predict the dynamics of laminated composite structures. The governing equations are derived based on the first order shear deformation theory kinematic equations following the Hamilton’s principle. To express the strain energy of the shells, in-plane and bending lamination parameters are used. A two-dimensional spectral approach based on Chebyshev polynomials is implemented to solve the governing equations. The developed framework including the spectral Chebyshev approach and lamination parameters results in an accurate and computationally efficient solution method. To demonstrate the performance of the presented solution approach, various case studies including straight panels, curved shells, truncated conical shells, and sandwich panels are investigated. The benchmarks indicate that the calculated nondimensional natural frequencies and critical buckling loads excellently match the results found using finite element method and the simulation duration can be decreased by 100 folds. To leverage the computational performance of the presented approach, a stacking sequence optimization is performed to maximize the fundamental frequency of a shell geometry, and the corresponding fiber angles are retrieved from the optimized lamination parameters. Furthermore, a parametric analysis is performed to investigate the effect of geometry on the optimized lamination parameters (and fiber angles) based on fundamental natural frequency maximization

The role of collateral against the asymmetric information phenomenon in the Bank lending market and the requisite for effectively play the role in movable collaterals.

Information inequality of the parties to the contract is known as an asymmetric information phenomenon. This causes two other phenomena called adverse selection and moral hazard that are seen in the banking loans market more effectively. In this paper, the role of collateral against this phenomenon has been examined by considering the economic importance of movable property and the need to use these assets for collateralization and attraction of credit. In addition, the requirement of movable collaterals for playing this role has come to light.  This article argues that the use of collateral will efficiently handle adverse selection and moral hazard phenomena within the Iranian banking loans market, especially with respect to the weakness of the tools necessary for tackling with this issue and will also prevent from accumulation of dues. However, the lack of information transparency and confidence in the security rights within movable property weakens the function of this type of collateral and reduces its potential for collateralization. The creation of a public register system of security rights in movable property as the most effective tool for ensuring transparency and confidence in movabl

Design of laminated conical shells using spectral Chebyshev method and lamination parameters

This study presents a modeling approach to accurately and efficiently predict the dynamics of laminated conical shells. The governing equations are derived based on the first order shear deformation theory kinematic equations following the Hamilton's principle. To express the strain energy of the shells, in-plane and bending lamination parameters are used. A two-dimensional spectral approach based on Chebyshev polynomials is implemented to solve the governing equations. The developed framework including the spectral-Chebyshev approach and lamination parameters results in an accurate and computationally efficient solution method. To demonstrate the performance of the presented solution approach, various case studies including straight panels, curved shells, and truncated conical shells are investigated. The benchmarks indicate that the calculated non-dimensional natural frequencies excellently match the results found using finite element method and the simulation duration can be decreased by 100 folds. To leverage the computational performance of the presented approach, a stacking sequence optimization is performed to maximize the fundamental frequency of a shell geometry, and the corresponding fiber angles are retrieved from the optimized lamination parameters. Furthermore, a parametric analysis is performed to investigate the effect of geometry on the optimized lamination parameters (and fiber angles) based on fundamental natural frequency maximization