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On the use of modal works of cutting forces to optimize machining conditions in the presence of vibrations
Full text linkThe use of Virtual Machining models may be a valuable approach in the designing stage of a machining operation as long as the models are sufficiently accurate. When vibration risks are suspected, stability analysis approaches to predict regenerative chatter phenomena are generally used. However, although these approaches, when applicable, allow efficient numerical optimization of the process around an operating point, they often require other strong assumptions such as neglecting transient phenomena or oversimplifying kinematics. On the other hand, time domain approaches with detailed matter removal modelling allow to monitor the continuous evolution of cutting conditions and represent various phenomena that the models can reproduce (regenerative chatter, forced vibrations, non-linear behaviours). The amount of data produced is, however, considerable and often costly to analyse. It may therefore be interesting to deduce, from these data, scalar indicators allowing easier and more relevant analysis of the simulation results.
In this work, the modal work of the cutting forces upon the workpiece vibratory displacements is proposed as an indicator to discriminate different tool paths. A one degree of freedom theoretical problem and a face milling operation on extruded aluminum profiles extracted from automotive structural part are used to explain and show the relevance of such indicator
As-scanned point cloud generation using structured-light simulation and machine learning-based coverage prediction
No full textAlthough several methods have been proposed for generating as-scanned point clouds, i.e. point clouds incorporating various realistic artefacts that would appear if the corresponding real objects were digitized for real, most of them still fail to take into account the complex phenomena that occur in a real acquisition devices. This paper presents a new way of artificially generating point clouds by combining simulation and machine learning. Starting from the CAD model of the object to be virtually scanned and from a scan configuration, structured light simulation first allows reconstructing a preliminary 3D point cloud. Then, a coverage prediction network is used to predict the regions that would be acquired if a real acquisition was to be done. The prediction model has been trained from a large database of scan configurations and point clouds scanned for real. Finally, filtering and cropping are performed to fine-tune the generated point cloud. Experiments confirm that this method can generate point clouds very close to those that a real scanner would acquire, as shown by several metrics characterizing both local and global similarity. Such a virtual scanning technique enables the rapid generation of large quantities of realistic point clouds, especially when compared to the time-consuming and costly processes involved in using physical acquisition systems. This opens up new perspectives in terms of access to realistic point cloud databases, in particular for the development of various AI-based approaches
Hierarchical micromechanical modeling for CNT-coated fuzzy fiber composites accounting for viscoplasticity and interfacial damage
Full text linkThis study investigates fuzzy fiber composites, characterized by a viscoplastic matrix and fuzzy fibers, i.e. fibers coated with radially aligned carbon nanotubes (CNTs). A comprehensive micromechanical framework is developed to model and optimize these composites, with a particular emphasis on interfacial damage mechanisms introduced through microvoids growth in the region between the fuzzy fibers and the matrix. By developing an equivalent fiber model, the complexity of the multi-phase structure is effectively reduced, facilitating efficient parametric analyses. Various homogenization techniques, including Composite Cylinder Assemblage (CCA), Transformation Field Analysis (TFA), and periodic homogenization, are combined to predict the overall stress-strain responses of the equivalent fiber approach and then the full fuzzy fiber composite. The identification of the framework and model parameters enabled a parametric/sensitivity analysis to study the effect of varying key parameters, including the volume fraction. The results of this paper contribute to a deeper understanding of unidirectional fuzzy fiber composites and establish a foundation for future parametric investigations and fuzzy fiber composite applications accounting for nonlinear regimes
Comparison of experimental and simulated behaviour of Solid-liquid expression using predictive model
Full text linkThis study compares the experimental and simulated behaviour of solid–liquid expression using a nonlinear predictive model. The model is based on power-law constitutive equations for the local filter cake parameters (permeability, specific resistance, compressibility modulus, and consolidation coefficient), and describes the compressive pressure distributions and consolidation ratio under different pressures. Experimental data from kaolin and bentonite suspensions are compared to model simulations. The experiments involve the formation of semi-solid and pre-compressed by filtration cakes, which are then subjected to solid–liquid expression. The study highlights the influence of initial cake structure on consolidation behaviour and evaluates the applicability of conventional filtration-consolidation theory to non-uniform cakes formed by filtration. The results demonstrate that the predictive model generally aligns with the experimental data, although deviations may occur due to unmodeled effects and experimental inaccuracies
Experimental fatigue characterization and modeling of a bi-component structural acrylic adhesive: Application to single-lap joints
Full text linkThe aim of this paper is to predict the fatigue behavior of bonded joints made of a bi-component structural acrylic adhesive. The approach considered is based on a characterization of the fatigue properties of the bulk adhesive combined with a finite element modeling of the bonded joint to provide the heterogeneous stress field within the adhesive. The identification of the fatigue model is conducted with experimental bulk adhesive tests under two loadings (tensile–compression and tensile–tensile) in order to account for the effect of the mean stress. A modified Crossland criterion, in the limited life time domain, is used to predict the fatigue life of the bonded joint assembly. The numerical fatigue life determined with this approach is compared to the experimental fatigue life of the assembly. A good correlation is found between the numerical model and the experimental results
Geometrical comparison between instrumented and non-instrumented mouthguards for rugby: A pilot study
No full textRugby is a sport with a high injury rate. Much has been done to make the sport safer, particularly in terms of limiting and identifying concussions. Recently, instrumented mouthguards have been developed and used to measure events that may lead to concussion. However, these instrumented mouthguards may not have an appropriate geometry regarding shock absorption and comfort. In addition, there is no specific international standard for instrumented mouthguards. This study proposed a geometric analysis of both instrumented and non-instrumented mouthguards. Ten instrumented mouthguards were analysed and compared with three non-instrumented mouthguards. They were inspected visually, with a 3D envelope scan and with a CT scan. The results showed that the mouthguards did not comply with recommendations such as indentation with the lower teeth which may increase injury or fracture risk
Impact of cognitive Effort, Social Interaction, Enjoyment of Learning, and Immersive Presence on Academic Achievement with Virtual Reality
Full text linkImmersive technologies represent significant advancements that allow users to engage in interactive and captivating environments, both perceptually and sensorily. This study aims to enrich the understanding of the relationship between several key variables and the achievement of academic objectives when using VR. An experiment was conducted with first-year university institute of technology students who participated in a virtual visit to a biology laboratory. The primary objective is to evaluate how each of the studied variables influences academic goals. By providing insights into the key factors that determine academic success in immersive environments, this research aims to optimize the use of these technologies in educational contexts, thereby enhancing students' learning outcomes
Towards Efficient Monitoring for WAAM Processes on a Robotized and Reconfigurable Manufacturing Cell
No full textWire Arc Additive Manufacturing (WAAM) is an efficient technology for producing metal parts. It offers high deposition rates, low material waste and reduced machining costs. However, the process's complex multi-physics nature presents several challenges, particularly with regard to residual stresses, deposition accuracy, and internal defects. Internal defects that occur during the WAAM process are difficult to detect in real time or immediately after fabrication without the use of non destructive testing methods.This study focuses on enhancing an experimental protocol that employs a monitoring method
analysing the geometry of each deposited layer using a laser sensor. This approach, combined with segmentation techniques, aims to identify and locate internal defects. Specifically, the proposed method relies on segmenting individual layers and comparing normalised values to detect and localise defects. This paper presents the developed methodology and an initial validation of its effectiveness
MONITORING AND CONTROL OF STRUCTURES SUBJECT TO VIBRATION AND DAMAGE USING THE KOOPMAN OPERATOR
No full textDue to the effects of fatigue and excessive vibration, structures may present a different health condition than initially observed. The change in system behavior due to damage also causes the system to demand more energy, which can saturate the actuators and make the system unstable. In this context, this work proposes to estimate in real-time the dynamics of a structure and control the undesired effects of vibration and damage. A data-driven model will be developed based on the Koopman operator, analyzing only data from sensors and actuators already installed by the control system. The information obtained by this updated model can be used to monitor changes in structural health and adapt a controller to meet performance specifications, even if the system dynamics vary over time. Changes in the spectral
characteristics of the Koopman operator can help identify damage in the structure. In addition, an adaptive model predictive controller can incorporate the possible changes in dynamics in real time, adjusting the optimization problem according to the current estimated model. Therefore, our results have demonstrated the benefits and limitations of this online monitoring and control strategy based on data already measured by the controller.
REFERENCES
[1] N. Mechbal and E. G. O. Nóbrega, Damage tolerant active control: Concept and state of art. IFAC Proceedings Volumes, vol. 45, no. 20, pp. 63–71, 2012.
[2] M. Korda and I. Mezić, Linear predictors for nonlinear dynamical systems: Koopman operator meets model predictive control. Automatica, vol. 93, pp. 149–160, 2018
Barycentremetry, spine disorders, posture and motion analysis
No full textPurpose of the research
Prevention of spine disorders and their management require better understanding of related biomechanical issues. While tremendous progress has been performed for musculoskeletal modelling of the spine, subject specific modelling of the gravitational loads and their effects on the spine is still an issue. Recently, 3D reconstruction of the skeleton from biplanar head to feet X-rays in erect position has been completed by the external body envelope. An approach named “barycentremetry” based on density models to estimate the mass and centre of mass of each body segment, yielding a force plate less estimation of the gravity line, together with the estimation of the gravitational loads and the associated lever arm at each vertebral level.
Principal results
Due to vertebral pose, gravitational loads effect on intervertebral disc shows wide variation. Studies exploring barycentremetry clinical relevance were analysed, particularly for adolescent idiopathic scoliosis, adult spinal deformities and osteoporosis. They progressively yield a better comprehension of the potential vicious circles linking postural disorder to increase of spine loads to increase of postural disorder.
Barycentremetry was also explored within gait and motion analysis research, allowing to estimate subject specific body segments inertial parameters for patient specific dynamic analysis. Indeed, 3D musculoskeletal modelling of posture and motion could benefit from subject specific dynamic analysis based on barycentremetry.
Major conclusions
Such approaches progressively provide a better understanding of the stability of this complex system and compensation strategies that could be useful for early detection of disorders that are responsible of a biomechanical cascad