Publications

The performance and unsteady vortical flows of a 2-bladed cycloidal propeller are investigated using the SST γ �� Reθt transition model, under different pitch-pivot-point and blade camber conditions. Firstly, it shows that the results of the present computations match well with the previous numerical data and experiments, in terms of the instantaneous performance and internal flow structures. Then, due to the moderate propulsive force and low power, the cycloidal rotor with a pitch-pivot-point of x/c = 0.25 maximize the efficiency. Moving the pitching location to the leading edge increases the lift and leads to the earlier flow separation on the blade surface. However, as the pitch-pivot-point shifts to the middle chord, the power of the cycloidal rotor increases dramatically because of the massive flow separation, leading to the degradation of the performance. Simultaneously, the symmetrical profiles, involving NACA0012 and 0015, are recommended due to the wide operation condition with high efficiency. The thick symmetrical and asymmetrical airfoils produce the worst performance due to the large power that is consumed. Furthermore, owing to the change of the rotating speed only, the advance coefficient effect is more obvious than the Reynolds number. When analyzing the performance of the rotating system at any position, one should consider the performance, pressure difference, near-wall flows and forces (lift and drag) of each blade.

In this study, CrN/CrAlN multilayer coating with different periods (Ʌ = 1, 2, 3, 4) were deposited on stainless steel (90CrMoV8) and silicon Si (100) samples by DC magnetron sputtering. The results obtained exhibited that the increasing of the number of periods considerably improves the properties of multilayer coatings. All CrN/CrAlN multilayer coatings have a dense columnar microstructure, and the surface morphology showed a pyramidal shape with nanopores. The coating hardness and Young’s modulus of the CrN/CrAlNmultilayer coating increases with the increase of bilayers number and reach 40 and 392 GPa respectively. Friction coefficient in seawater environment was calculated and it show that the increase in bilayer number decreases friction contact and reduce the friction coefficient. Also, wear resistance improves with increasing interfaces and increasing hardness.

When long parts are machined in forged blanks, the variability of bulk residual stress (RS) fields leads to uncontrolled deformation after machining, requiring manual reshaping. An original hybrid digital twin of forged part is thus proposed to manage the bulk RS variability and reduce part distortion in machining. The behavior model of parts relies both on reduced models of thermomechanical simulations of the forging pro-cess variability, on-line measurements and machine learning from the previous parts deformations. Adaptive machining solutions can then be simulated for a rapid decision-making. The approach was validated on a series of aeronautic forged parts.

This paper addresses the problem of timber board positioning within the log where they were sawn from. The method takes as input log and board end cross-section images. It uses a two-step image matching method based on scale invariant feature transform (SIFT) and normalized correlation coefficient (NCC). In the first step, the scale factor and rotation angle of board end images are estimated from the board images that are correctly identified on the log end image by SIFT. Then, the accurate position of each board within the log end image is achieved by the NCC method. The method has been tested on 70 different log images and the 798 corresponding board images of various visual aspects and coming from three different species (Douglas fir, Norway spruce, and oak). The results fully demonstrate that the proposed method is not only rotation and scale invariant, but also has high accuracy properties.

Background: Patient-specific scapular shape in functional posture can be highly relevant to clinical research. Biplanar radiography is a relevant modality for that purpose with already two existing assessment methods. However, they are either time-consuming or lack accuracy. The aim of this study was to propose a new, more user-friendly and accurate method to determine scapular shape. Methods: The proposed method relied on simplified manual inputs and an upgraded version of the first 3D estimate based on statistical inferences and Moving-Least Square (MLS) deformation of a template. Then, manual adjustments, with real-time MLS algorithm and contour matching adjustments with an adapted minimal path method, were added to improve the match between the projected 3D model and the radiographic contours. The accuracy and reproducibility of the method were assessed (with 6 and 12 subjects, respectively). Findings: The shape accuracy was in average under 2 mm (1.3 mm in the glenoid region). The reproducibility study on the clinical parameters found intra-observer 95% confidence intervals under 3 mm or 3° for all parameters, except for glenoid inclination and Critical Shoulder Angle, ranging between 3° and 6°. Interpretation: This method is a first step towards an accurate reconstruction of the scapula to assess clinical parameters in a functional posture. This can already be used in clinical research on non-pathologic bones to investigate the scapulothoracic joint in functional position.

Titanium alloys, largely used for aeronautical applications, are difficult to machine. High cutting forces, chip serration and important tool wear reflect this poor machinability, limiting productivity. One way of improving the machinability of titanium alloys consists of controlling their microstructure. In the present work, the impact of the microstructure of the Ti5553 alloy on chip formation and cutting forces is investigated. For this purpose, a novel experimental approach is proposed. Orthogonal cutting tests are performed on eight different microstructures, which allows studying the impact of the α-phase fraction as well as the size and shape of α particles. Also, an original post processing method based on machine learning provides chip morphological information from images recorded with two high speed cameras. Such information is completed with the cutting forces measured with a dynamometer. In contrast with commonly used approaches, the proposed method is not limited to the formation of a few segments, but uses the full dataset acquired during a test. The results obtained for the different microstructures indicate that no direct link can be established between the cutting forces and their hardness as minimal cutting forces are obtained for microstructures with an intermediate hardness. For microstructures providing low hardness, high cutting forces result from a significantly thick chip. In opposition, for the microstructures leading to high hardness, an important flow stress generates high cutting forces. This study also suggests that chip morphology is primarily affected by the α-phase fraction while the size and morphology of α-phase particles have little influence.

The cost of manufacturing a structural ceramic component is a direct function of production quantity. Small-quantity production, such as prototypes manufactured by conventional methods, leads to long production times and high unit costs. The advent of fused flament fabrication of ceramic (FFFC) technology has created an opportunity to reduce lead time and cost and produce complex-shaped bodies with tailored sized and controlled porosity in small-quantity production runs, which is an advantage over traditional methods of fabrication of ceramic products. In this work, we propose to study the feasibility of manufacturing a low-cost composite flament, for FFFC processing, based on micrometric alumina (Al₂O₃) powder and polylactic acid (PLA) polymer as a binder system without any additive. Three compositions with the ceramic-to-polymer ratios (by volume) were considered: 70% Al₂O₃/30% PLA, 60% Al₂O₃/40% PLA, and 50% Al₂O₃/50% PLA. For that, the customized technological chain is adapted. It consists of four principal steps: (i) grinding in a ball mill and drying the raw powders; (ii) extrusion into ceramic-polymer flament; (iii) printing of ceramic-polymer samples; and (iv) thermal debinding and sintering samples to obtain the ceramic product. The physical, microstructural, and mechanical properties of raw materials, composite flament, and green and sintering samples are investigated and the optimal composition is chosen dependent on both homogeneous repartition of the Al₂O₃ powder and the printability of flament. The 3D sintered material obtained by 60% Al₂O₃/40% PLA composite flament shows the best fexural strength value of 332±21 MPa with a relative density of ~ 91%, which may be sufcient for several technical applications. Note that the 60% Al₂O₃/40% PLA flament composite can easily be used to print a complex geometry using a standard nozzle of 0.4 up to 0.8 and does not show signs of brittleness during the printing process allowing it to become a promising material for the FFFC process. Based on the results of this paper and previous studies, FFFC technology can be a technically feasible and economically viable process for manufacturing ceramic components under certain conditions.

The importance of natural reinforced bio-composite materials with desirable properties such as high modulus-to-weight ratio, good impact resistance, and the ability to be easily repaired is crucial in the industry. A woven flax/Elium® thermoplastic bio-composite is manufactured to challenge these needs. Elium® is the only resin that permits the manufacture of large parts with thermoset-like processes, as Liquid Resin Infusion presented in that work. The paper highlights the influence of stacking fibre orientation, moisture absorption, and repair aptitude on its impact resistance. An instrumented drop tower was needed to conduct low-velocity impact tests at several energies and high-speed image coupled with microscopic observations was used to assess the damage evolution. The impact resistance was improved for the dry (0/90)₆ orientation, but moisture absorption decreased its impact peak force by 20%. A three-point bending test was preferred to compression after impact for studying the residual properties after impact. The bio-composites with (±45)₆ orientation showed higher impact residual performance than the (0/90)₆ orientation, and corresponded to the reduction of maximum bending force by 20% than that of the reference. In addition, a thermo-compression process was applied to repair the impacted plates and conduct multiple impact/repair cycles which showed a significant recovery of stiffness and maximum impact force at 4J on (0/90)₆ plates, highlighting their potential for repair in the automotive and marine industries.

In this paper, the effect of gravity on the nonlinear extreme amplitude vibrations of a slender, vertically-oriented cantilever beam is investigated. The extreme nonlinear vibrations are modeled using a finite element discretization of the geometrically exact beam model solved in the frequency domain through a combination of harmonic balance and a continuation method for periodic solutions. The geometrically exact model is ideal for dynamic simulations at extreme amplitudes as there is no limitation on the rotation of the cross-sections due to the terms governing the rotation being kept exact. It is shown that the very large amplitude vibrations of dimensionless beam structures depend principally on two parameters, a geometrical parameter and a gravity parameter. By varying these two parameters, the effect of gravity in either a standing or hanging configuration on the natural (linear) modes as well as on the nonlinear modes in extreme amplitude vibration is studied. It is shown that gravity, in the case of a standing cantilever, is responsible for a linear softening behavior and a nonlinear hardening behavior, particularly pronounced on the first bending mode. These behaviors are reversed for a hanging cantilever.

The aim of this experiment was to characterize and compare the tracking systems of 5 HMDs (Microsoft Hololens 2; Vive Pro 2; Vive Focus 3; Varjo XR-3 with Vive lighthouse; Varjo XR-3 in standalone mode) on short distance displacements (max 50cm) for phygital applications. A UR5 robotic arm was used to move HMDs along square and round trajectories, at slow speeds, high speeds, and variable speeds. To study the accuracy of HMDs, their position data were compared to position data recorded by an external robust passive infrared tracking system which serves as a groundtruth. The results shown that the Varjo XR-3 has the best accuracy with an average error of 0.23 cm. The HMD with the worst accuracy is the Vive Pro 2 with an average error of 1.24 cm, followed by the Hololens 2, the Vive Focus 3 and the Varjo XR-3 SLAM with an average error of 1.22 cm, 0.58 cm, and 0.54 cm respectively. The analysis of the results shown that in the case of phygital applications in driving cockpits with a high demand of accuracy (up to 1mm), the Varjo XR-3 with Vive lighthouse or other optical tracking systems is a good solution. In the case of larger scale phygital applications such as vehicle exterior reviews, which require larger movements and lower levels of accuracy (up to 1cm), standalone HMDs such as the Vive Focus 3 are more beneficial.