Thèses sur le sujet « Fatigue fonctionnelle »
Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres
Consultez les 19 meilleures thèses pour votre recherche sur le sujet « Fatigue fonctionnelle ».
À côté de chaque source dans la liste de références il y a un bouton « Ajouter à la bibliographie ». Cliquez sur ce bouton, et nous générerons automatiquement la référence bibliographique pour la source choisie selon votre style de citation préféré : APA, MLA, Harvard, Vancouver, Chicago, etc.
Vous pouvez aussi télécharger le texte intégral de la publication scolaire au format pdf et consulter son résumé en ligne lorsque ces informations sont inclues dans les métadonnées.
Parcourez les thèses sur diverses disciplines et organisez correctement votre bibliographie.
Jutand, Luce. « Fatigue et contrôle des muscles inspiratoires à l'exercice ». Poitiers, 2009. http://www.theses.fr/2009POIT2276.
Texte intégralThis work aimed firstly to determine the duration and intensity of the exercice inducing diaphragmatic central fatigue. We tested the presence of the diaphragmatic central fatigue for three exercice durations (5,15 and 40 minutes) keeping the same intensity of exercice (55% of V̇O2max). The diaphragmatic central fatigue was present for a duration of 40 minutes. This fatigue would settle in progressively with time. On a second time, we checked if the exercice intensity influenced this fatigue. We checked the presence of diaphragmatic central fatigue for different intensities of exercice (40%, 55%, 75% of V̇O2max) keeping the same duration (15 minutes). The central diaphragmatic fatigue was absent, whatever the intensity of exercice. In a third work, we studied the ventilatory control during exercice. We checked if premotor potentials, which are evidences of the premotor cortex activation, were present during exercices of different intensities (40% et 70% of V̇O2max) and during a moderate exercice with resistive inspiratory load (40% de V̇O2max with a load of 5cmH2O). We did not observe any premotor preinspiratory activity, suggestive of an absence of cortical contribution of human ventilation during exercise
Berriri, Ahmed. « Caractérisation fonctionnelle des muscles respiratoires : effets de l'entraînement et du désentraînement ». Electronic Thesis or Diss., Amiens, 2017. http://www.theses.fr/2017AMIE0025.
Texte intégralThe aim of thesis was on one hand to characterize the respiratory muscles during an incremental effort until exhaustion and on the other hand, to study the effects of specific inspiratory muscle training and detraining. We first confirmed the development of respiratory muscle fatigue during a maximal incremental exercise. Through recording of oxygenation at the 7th intercostal space, the second study showed reduced intercostal muscle deoxygenation and inspiratory muscle fatigue with a prior inspiratory exercise. Then, we showed that 5 weeks of specific inspiratory muscle training (IMT), whether at high or low intensity, reduces respiratory muscle fatigue induced by maximal incremental exercise. This reduction corroborates the parallel decrease observed in the intercostal muscle oxygen utilization and therefore in their metabolic demands in relation to their fatigability decrease (Study 3 and 4). This may reflect an increase in the oxygen supply of the locomotor muscles. These improvements were greater with high-resistance IMT. However, the IMT induced adaptations were lost after 10 weeks of detraining (Study 5). Nevertheless, reducing training frequency by up to two sessions per week while preserving the same training load was sufficient to maintain the already achieved adaptations. These results highlighted the respiratory muscle implication in the limitation of incremental effort until exhaustion and have contributed to a better understanding of the mechanisms underlying the improvement of performance after IMT particularly respiratory muscle oxygenation and fatigue
Nédélec, Mathieu. « Fatigue et récupération en football ». Thesis, Lille 2, 2012. http://www.theses.fr/2012LIL2S014.
Texte intégralDuring periods when the schedule is particularly congested (i.e. two matches per week over several weeks), the recovery time allowed between two successive matches may be insufficient. As a result, players may experience underperformance and/or injury. The overall aim of the present thesis was to identify underlying factors (environmental and intrinsic factors, playing position) that contribute to fatigue and recovery time of professional soccer players after a match. Four experimental studies were conducted to investigate the influence of soccer running activity profile, playing actions performed during a match (i.e. contact, jump, shot/long pass, tackle, change of direction) and playing surface (natural grass versus artificial turf) on the recovery kinetics of physical performance, cognitive performance, subjective ratings and biochemical parameters. Results showed that soccer running performance does not appear to be the main cause for post soccer match-induced fatigue. Post-match fatigue and recovery time depend on playing actions performed during the match (contact, jump, shot/long pass and change of direction). Post-match fatigue depends on playing position (goalkeepers versus outfield players). Playing surface does not impact recovery kinetics among regular artificial turf players. Present results may promote the prescription of more efficient and individualized recovery practices after soccer match
Berriri, Ahmed. « Caractérisation fonctionnelle des muscles respiratoires : effets de l'entraînement et du désentraînement ». Thesis, Amiens, 2017. http://www.theses.fr/2017AMIE0025/document.
Texte intégralThe aim of thesis was on one hand to characterize the respiratory muscles during an incremental effort until exhaustion and on the other hand, to study the effects of specific inspiratory muscle training and detraining. We first confirmed the development of respiratory muscle fatigue during a maximal incremental exercise. Through recording of oxygenation at the 7th intercostal space, the second study showed reduced intercostal muscle deoxygenation and inspiratory muscle fatigue with a prior inspiratory exercise. Then, we showed that 5 weeks of specific inspiratory muscle training (IMT), whether at high or low intensity, reduces respiratory muscle fatigue induced by maximal incremental exercise. This reduction corroborates the parallel decrease observed in the intercostal muscle oxygen utilization and therefore in their metabolic demands in relation to their fatigability decrease (Study 3 and 4). This may reflect an increase in the oxygen supply of the locomotor muscles. These improvements were greater with high-resistance IMT. However, the IMT induced adaptations were lost after 10 weeks of detraining (Study 5). Nevertheless, reducing training frequency by up to two sessions per week while preserving the same training load was sufficient to maintain the already achieved adaptations. These results highlighted the respiratory muscle implication in the limitation of incremental effort until exhaustion and have contributed to a better understanding of the mechanisms underlying the improvement of performance after IMT particularly respiratory muscle oxygenation and fatigue
Allaf, Oula. « Le Muscle epitrochlearis de rat et son adaptation à la demande fonctionnelle ». Compiègne, 1997. http://www.theses.fr/1997COMP0998.
Texte intégralSince a long time, the humanity has given a particular place to the study of athletic gestures. It was discovered that a wide category of muscles existed in living beings and that their evolution occurred due to alterations imposed by their environment. Ln new conditions, some muscles respond in a new pattern and hence adapt themselves to a newly imposed function. This induces a structural and functional re-ordering of the muscles, leading to changes in biochemical and mechanical characteristics which tend to reflect muscle plasticity. Ln our work, a rats were suspended to induce hyperactivity of postural nature in a phasic muscle of the forelimb : the epitrochlearis. Thus, the rat has to use its forelimb to move around or to maintain his posture. Results show that, after 21 days, the epitrochlearis behaves as a slower muscle : fibbers and myosin heavy chains of type 1 are increased, maximal shortening velocity is decreased, resistance to fatigue is improved and stiffness is increased. Thanks to a model including the force-velocity relationship, the role of the myosin light chains in this adaptative process is emphasized. Moreover, an increase in the total number of muscle fibbers is observed. This could be the result of a mitotic division of satellite cells which are able to generate new undifferentiated fibbers. These fibbers should transform themselves into slow fibbers. This study confirms the relationship between fibber types, contractile proteins and mechanical properties. The observed plasticity is certainly related to the original work by the muscle during suspension, notably, the need of an important postural activity
Lopes, Leal Junior Marcos. « Méthode de conception et de dimensionnement en fatigue d'actionneurs à base d'Alliage à Mémoire de Forme pour des applications automobiles ». Electronic Thesis or Diss., École nationale d'ingénieurs de Brest, 2024. http://www.theses.fr/2024ENIB0001.
Texte intégralIn the current automotive industry context, numerous actuators are essential, necessitating optimized solutions. Shape memory alloy (SMA) actuators are well-suited for this purpose. However, implementing this technology in the automotive sector faces challenges due to complex behavior and a lack of design tools. This thesis aims to establish a multidisciplinary approach to designing SMA actuators to meet automotive industry requirements. The method comprises three main parts: characterizing NiTi wires’ thermomechanical and electrical behavior, proposing a numerical model based on experiments to simulate SMA actuator behavior under electrical activation via the Joule effect, and determining fatigue behavior for estimating lifespan and degradation impact on performance. Finally, a validated design method for SMA wire-based actuators is presented
Pigot, Annick. « Explorations fonctionnelles respiratoires au lit du malade en réanimation : étude en vue de l'optimisation de l'assistance ventilatoire asservie ». Compiègne, 1996. http://www.theses.fr/1996COMPD979.
Texte intégralMarqueste, Tanguy. « Plasticité fonctionnelle et post-traumatique du système neuromusculaire chez l'Homme et l'animal : effets de l'électromyostimulation et de l'exercice physique ». Aix-Marseille 2, 2003. http://www.theses.fr/2003AIX22028.
Texte intégralConsequences of the maintenance in activity of muscle by chronic electrostimulation (comparing two types of current) or following rehabilitation on treadmill, are studied in order to induce a functional neuromuscular recovery succeeding a section-suture of a mixed peripheral nerve. This plasticity is evaluated in the rat through contractile, neurophysiological, histochemical and biochemical data. We also studied the mechano- and metabosensitive reafferentation. In order to evaluate the importance of this metabosensitive activity on the sensorimotor regulation and during muscular activity, we used capsaïcine to carry out a selective suppression (pharmacological knocked-out) of this sensitivity in the new-born rats. Finally chronic electromyostimulation was carried out at the healthy human sujects in order to evaluate the adaptive modifications on the neuromuscular system, before an application of this technique to the traumatized subjects. In the animal capsaïcine removes most of the group IV muscle afferent fibres of and strongly deteriorates metabosensitivity. The time of endurance time measured at the end of an exhaustive exercise on treadmill is also reduced. The muscular atrophy related to denervation is removed at the time of a electromyostimulation by a biphasic current modulated in frequency during the reinnervation period. Twitch characteristics is restored. Moreover muscular typology and the enzymatic activities (citrate synthase and lactate dehydrogenase) are close to control values. Rehabilitation on treadmill during post-operative period restores the metabolic sensitivity in response to the tested stimuli. The mechanical sensitivity is little affected, and all the mechanical parameters tested are restored (fatigue index, twitch). Chronic electrostimulation on healthy subjects led to an increase in the maximum force, a fall of RMS and a shift towards higher frequencies in the power spectrum density function (measured in surface EMG) during an endurance exercise at 60% of the maximal voluntary force. These changes persist 6 weeks after the end of the electrostimulation session. This could represent an adaptation of the central order in a facilitation of fast twitch muscle fibres activation, surely implying the muscular afferents. In conclusion the results obtained in Human and animals, indicate the key role of the muscular metabolic sensitivity involved in physical exercise. The two techniques used to maintain in activity the muscle during the reinnervation period produce complementary results. Protocol combining the electromyostimualtion and the voluntary physical exercise should improve the functional restorations, following the neuromuscular traumatisms in Human
Ponchel, Amélie. « Fatigue post-accident vasculaire cérébral : facteurs associés et impact des troubles cognitifs et émotionnels ». Thesis, Lille 2, 2016. http://www.theses.fr/2016LIL2S049/document.
Texte intégralPost-stroke fatigue (PSF) is frequent and debilitating. However, PSF is up to date a poorly understood and unrecognized phenomenon. In this thesis, we have done an exhaustive synthesis of scientific literature on factors associated with PSF. It indicates that PSF is frequently related with depressive and anxious symptoms but there is a lack of understanding of its physiopathological mechanisms. We conducted a study of PSF on 153 patients from the hospital-based cohort study STROKDEM (NCT01330160), followed-up for 6 months after an ischemic stroke. In a first study, we have shown that PSF was not a side effect of drugs use. PSF more reflects presence of disturbances frequently observed after stroke such as depression, anxiety, or sleep disturbances. In a second study, we have observed a strong association between PSF and subjective cognitive complaints that contrasted with the absence of association with objective cognitive performances during the neuropsychological evaluation, regardless of the considered cognitive domain. In a third study, we explored neuronal mechanisms underlying PSF. With an exploratory analysis, without a priori, we did not demonstrate any difference in functional connectivity at rest between patients with or without PSF. As a whole, these data give us pieces to progress in the understanding of the complex phenomenon named PSF
Callier, Jacqueline. « La décomposition acido-basique comme facteur limitant de l'exercice musculaire : effets d'une alcalinisation exogène sur la capacité d'endurance a puissance sub-maximale et maximale du sujet sportif ». Paris 5, 1991. http://www.theses.fr/1991PA05S018.
Texte intégralZhang, Xiang Qin. « Estimation du couple généré par un muscle sous SEF à la base de l’EMG évoquée pour le suivi de la fatigue et le contrôle du couple en boucle fermée ». Thesis, Montpellier 2, 2011. http://www.theses.fr/2011MON20191/document.
Texte intégralFunctional electrical stimulation (FES) has the potential to provide active improvement to spinal cord injured (SCI) patients in terms of mobility, stability and side-effect prevention. In the domain of lower limb FES system, elicited muscle force must be provided appropriately to perform intended movement and the torque generation by FES should be accurate not to lose the posture balance. However, muscle state changes such as muscle fatigue is a major cause which degrades its performance. In addition, most of the complete SCI patients don't have sensory feedback to detect the fatigue and in-vivo joint torque sensor is not available yet. Conventional FES control systems are either in open-loop or not robust to muscle state changes. This thesis aims at a development of joint torque prediction and feedback control in order to enhance the FES performance in terms of accuracy, robustness, and safety to the patients.In order to predict FES-induced joint torque, evoked-Electromyography (eEMG) has been applied to correlate muscle electrical activity and mechanical activity. Although muscle fatigue represents time-variant, subject-specific and protocol-specific characteristics, the proposed Kalman filter-based adaptive identification was able to predict the time-variant torque systematically. The robustness of the torque prediction has been investigated in a fatigue tracking task in experiment with SCI subjects. The results demonstrated good tracking performance for muscle variations and against some disturbances.Based on accurate predictive performance of the proposed method, a new control strategy, EMG-Feedback Predictive Control (EFPC), was proposed to adaptively control stimulation pattern compensating to time-varying muscle state changes. In addition, this control strategy was able to explicitly avoid overstimulation to the patients, and conveniently generate appropriate stimulation pattern for desired torque trajectory
Weil, Hadrien. « Modélisation du besoin fonctionnel pour la nitruration gazeuse ». Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0037.
Texte intégralGaseous nitriding is a thermochemical treatment that improves fatigue strength by providing important mechanical properties such as increased hardness and residual compressive stresses. This study is carried out on a 33CrMoV12-9 steel used in the aeronautical industry. A complete model adapted to this grade allows to quantify the residual stress and hardness profiles as a function of the nitriding parameters. Taking into account the contribution of these mechanical properties is possible thanks to the use of fatigue criterion such as Crossland. This type of criterion is integrated in a methodology in order to calculate the fatigue limit in a nitrided layer and to predict the resistance of the workpiece, as well as the potential initiation zone of rupture according to a load, a lifetime And a given break probability. The combination of the model for the calculation of mechanical properties (hardness and residual stresses) and the prediction of the initiation of rupture in a nitrided material, makes possible an inverse method allowing to calculate the nitriding parameters adapted to a load suffered. This approach is justified in the case of gaseous nitriding because it has been demonstrated in this study that this treatment remains robust against the loading undergone by the workpiece
Guion, Vincent. « Prise en charge de la douleur et de la fin de vie en EHPAD : prévention, anticipation et accès aux soins palliatifs ». Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30107.
Texte intégralNursing home residents (NHRs) accounted for a quarter of all decedents in France in 2015, 87% of which died from predictable causes. About 130,000 NHRs could require palliative care at the end of life every year. Yet, previous works suggested about a fourth of these NHRs were in "a severe physical discomfort" in their last week of life and nursing home medical directors' training on end of life management was scarce. In addition, one fourth of NHRs get transferred to hospital in emergency in their last two weeks of life or die in hospital. Palliative care in NHRs needs to be developed in its dimensions of prevention, anticipation, and access to care. The objective of the first study was to determine whether a strong intervention involving auditing and feedback plus a cooperative work between a hospital geriatrician and the nursing home (NH) staff around quality indicators of care compared to a light intervention involving auditing and feedback only decreases the number of residents with a pain complaint. We also investigated whether this type of intervention improves pain management in NHs. The objectives of the second study were to describe the trajectories of functional ability of NHRs before the emergency department (ED) transfer, during hospital stay, and after hospital discharge, and to examine the determinants of both functional ability and mortality after a transfer to ED. The objectives of the third study were to describe the joint trajectories of pain, dyspnea, fever, confusion, agitation, and fatigue in NHRs from a week before their transfer to ED until the week following their discharge back to NH, and identify predictive factors of symptomatic outcomes. Data from the IQUARE and FINE studies were used to address these objectives. Statistical analyses included survival models, mixed-effects logistic and linear models and latent-class mixture models. Our results support that a general geriatric intervention based on education and professional support to NH staff not only improved the quality of pain management in the IQUARE study but was also associated with a lower number of residents who complained about pain. Almost one-half of NHRs declined on their functional ability or died after being transferred to ED in the FINE study, but the majority either remained stable or even improved. Functional decline across trajectory groups was mainly driven by transfer characteristics, such as condition during transfer (number of distressing symptoms, fracture, or stroke) and care pathway after ED (length of hospital stay and discharge department). Functional trajectories allow us to better understand the resilience capacities of residents facing the challenging stress of a transfer to ED. The course of symptom burden in the FINE study shows distinct trajectories depending on the nature of symptoms: specific symptoms were well alleviated, but non-specific symptoms, i.e. related to comorbidities or disease burden, were frequently uncontrolled.[...]
Nay, Kevin. « Le fer et le microbiote intestinal : deux nouvelles cibles pour améliorer les capacités fonctionnelles et musculaires en condition d'hypoactivité ». Thesis, Rennes 2, 2019. http://www.bu.univ-rennes2.fr/system/files/theses/2019theseNayK.pdf.
Texte intégralHypoactivity is characterized by a lack of mechanical constraints on the musculoskeletal system, and affects a wide range of individuals, from bedridden and hospitalized patients, to astronauts subjected to hypoactivity. Specifically, hypoactivity reduces functional abilities by altering, among others, muscle function and oxygen transport. To improve astronauts’ health during and after missions, or bedridden patients’ care, understanding its underlying mechanisms is necessary. Since they seem to interact with skeletal muscle, iron metabolism and gut microbiota could play a key role in functional disorders related to hypoactivity. The aim of this PhD thesis was to study the crosstalk between gut microbiota, iron and skeletal muscle during hypoactivity and to identify the underlying mechanisms. Based on animal and human models, our work highlights that iron misdistribution occurs during hypoactivity, especially due to hepcidin upregulation. By demonstrating for the first time the effect of gut microbiota on skeletal muscle endurance, our results support that glucose homeostasis plays a key role in this mechanism. Furthermore, some indicators of gut dysbiosis are suggested in hypoactivty. Our work opens promising and innovative countermeasures for therapeutic strategies destined to improve astronauts‘ health and patients’ care
Aubry, Anaël. « Compréhension du phénomène de surmenage fonctionnel induit par le travail en endurance : implications pour l’entraînement et la performance ». Thesis, Université Côte d'Azur (ComUE), 2016. http://www.theses.fr/2016AZUR4104/document.
Texte intégralThe purpose of this work is to examine whether performance supercompensation during taper is maximized in endurance athletes after experiencing overreaching during an overload training period. This first study showed that 1) greater gains in performance and V˙O2max can be achieved when higher training load is prescribed before the taper but not in the presence of functional overreaching (F-OR); 2) peak performance is not delayed during taper when heavy training loads are completed immediately prior; and 3) F-OR provides higher risk for training maladaptation, including increased infection risks. The second study confirms sleep disturbances and increased illness in endurance athletes who present with symptoms of F-OR during periods of high volume training. The third study shows a lower cardiac output and systolic blood pressure with greater arteriovenous O2 difference were reported in F-OR subjects at all exercising intensities, while no significant change was observed in the control and acute fatigue (AF) groups. A concomitant decrease in epinephrine excretion was reported only in the F-OR group. All values returned to baseline at Post. Following an overload endurance training program leading to F-OR, the cardiac response to exhaustive exercise is transiently impaired, possibly due to reduced epinephrine excretion. This finding is likely to explain the complex process of underperformance syndrome experienced by F-OR endurance athletes during heavy load programs
Gautier, Alexis. « Intégrité de surface et performances fonctionnelles de surfaces de roulement en usinage haute précision ». Compiègne, 2007. http://www.theses.fr/2007COMP1725.
Texte intégralThe aims of this thesis were to carry out integrity and functional performances of AISI 51200 bearing ring surfaces machined by High Precision Turning machine lathe (HPT, hard turning). The functionality of these surfaces, which are nowadays finished by grinding, is life in contact fatigue. Machine developments and adjustment setup have increased the machine performances and then allow to obtain following presented surfaces which analysis and measures have shown the influence of the feed rate on the surface roughness and the residual stresses level: at the opposite of grinding, material is in high compression on the surface and in deep. Contact fatigue tests have been done until 100,000 cycles and have shown the stability of residual stresses which keep in high compression. These last results should be confirmed by several million cycle tests. As machined surfaces present similar level of roughness than the one obtain by grinding, different other studies have been carried out in order in a first band to determine limitations and relevance of measurements techniques (tactil profiler, AFM, interferometric microscope) in function of the surface nature; and in an other hand to choose the most relevant roughness parameter by a multi scale analysis. This last one has shown that roughness parameters used in industry or in standards are not always the most relevant. This study will be applied to other manufacturing processes
Dureau, Clément. « Fatigue d'aciers inoxydables austénitiques traités par grenaillage ultrasonore sévère : contributions expérimentales et numériques à l'étude de l'amorçage et la propagation des fissures ». Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0143.
Texte intégralIn the high cycle fatigue, cracks initiate most of the time at the surface of workpieces. Therefore, in addition to the overall mechanical properties, surface and sub-surface characteristics such as roughness and residual stresses affect the fatigue life. Roughness essentially influences the cracks initiation phase. Indeed, the presence of surface irregularities induces stress concentrations producing high local strains potentially leading to the formation of crack-like defects. Besides, the presence of residual stresses affects both the crack initiation and propagation phase. They affect the plasticity close to the surface and influence the crack initiation. Moreover, superposed with the macroscopic loading, they locally modify the stress field and therefore may affect the crack propagation behavior as well.The ultrasonic shot peening (SMAT) is a surface mechanical treatment which consists in impacting a sample with shots put in motion by a vibrating device operating at frequencies up to 20 kHz. The repeated impacts lead to a surface plastic strain allowing the formation of compressive residual stresses as well as a microstructure gradient characterized by highly deformed zones in the sub-surface and submicronic grain size just below the surface. Such treatment was carried out to austenitic stainless steels in order to study the fatigue crack initiation and propagation in the complex microstructure and residual stress field induced by the SMAT.Uniaxial high cycle fatigue tests have been conducted for two different load ratios (under tension-compression at RTC=-1 and under tension-tension at RTT=0.1). They allowed to highlight the variable effectiveness of the SMAT with regard of the cyclic loading conditions. Indeed, at RTC, an increase of the fatigue limit was measured whereas for RTT a reduction of the fatigue limit was observed. In order to explain this difference, an in-depth study of the initial state and SMAT treated broken and run-out samples was carried out. It turns out that under the studied loading conditions the modifications of residual stress state can be considered as the primary factor governing the varying fatigue performances and the observed triggering at different initiation sites. Considering the stabilized surface residual stress after fatigue loading, the use of a Crossland criterion allowed to explain both the effects of load ratio and SMAT on the high cycle fatigue behavior of the stainless steel.A modelling method of the mechanical properties and residual stresses gradients was then developed using the finite elements method (via ABAQUS) in order to understand and predict the residual stresses redistributions. The results of the simulations were compared to the experimental measurements, and a good agreement was observed. The capacity of the model to simulate both the strain- and stress-controlled fatigue behavior was evaluated and a good consistency between the numerical and experimental results were obtained.Specimens with an artificial surface defect were then prepared in order to evaluate the surface anomalies sensitivity, and also to study the fatigue crack propagation behavior using the surface replication method. It was shown that the SMAT samples do not exhibit an increased sensitivity to the presence of defects compared to the initial state when loaded at RTT, whereas for RTC a slightly increased sensitivity was identified. Studying the crack propagation at the surface of the specimens highlighted different behaviors for different load ratios. Also, despite the presence of a defect, the crack initiation phase remained important. Finally, crack fronts were marked by different methods which permitted plotting the fatigue crack growth curves. It was then shown that at RTC, fatigue crack growth behavior in the SMAT layer is drastically different from the initial material, whereas at RTT no difference was revealed
Baudoin, Pierre. « Caractérisation et identification de propriétés de matériaux métalliques à gradients de microstructure ». Thesis, Lille 1, 2015. http://www.theses.fr/2015LIL10015/document.
Texte intégralThe main objective of this thesis is to design a consistent methodology for the characterization and simulation of functionally graded metals. This approach should allow the assessment of the high cycle fatigue response of forged railway axles produced by Valdunes, in the context of the Innovaxle project. The tests conducted on the forged material reveal a very heterogeneous microstructure, whose grain size varies in the width of the axle. A procedure based on recrystallisation is designed to reproduce this grain size gradient on a smaller scale, on a reference material (ARMCO iron). The characterization of the obtained graded microstructure shows heterogeneities in the local elasto-plastic response of the specimen. This behaviour is tentatively described by a heterogeneously distributed elasto-plastic law over the microstructure, the local yield strength being obtained from the local grain size through a Hall-Petch formulation. This model is used to simulate the response of graded microstructures under heterogeneous loadings in the high cycle fatigue regime. The interests of functionally graded materials are outlined by these simulations. The finite element simulations run in this work make use of the Code Aster software, and the digital image correlation program YADICS is used for image registration purposes
Tadros, Rafik. « Caractéristiques et origine fonctionnelle des propriétés fréquentielles du noeud auriculoventriculaire ». Thèse, 2010. http://hdl.handle.net/1866/5135.
Texte intégralThe atrioventricular (AV) node is the sole electrical connection between atria and ventricles, and is of utmost importance in both normal and perturbed cardiac function. Through slow conduction, it generates a delay between atrial and ventricular systoles, thereby optimising cardiac output. The AV node also has a long refractory period which confers it a filtering role during supraventricular tachyarrhythmias. Because of this ventricular rate watchdog role, the AV node has become a primary therapeutic target in atrial fibrillation, a frequent arrhythmia with major clinical burden. Not withstanding intense research, understanding of AV nodal function remains restrained by many controversies, some of which have persisted for almost a century. Major obstacles concern the definition of nodal recovery time and nodal refractoriness. The objective of our studies is to untangle some of these controversies regarding rate-dependent AV nodal function in an experimental model of superfused rabbit heart preparations. Our first study concerns the definition of AV nodal recovery time used to assess rate-dependent nodal function. The dependence of conduction time through the node (atrio-His interval; AH) on time elapsed since last activation i.e., recovery time (RT), is a well accepted fact but its assessment is controversial for nearly a century. This problem arises from the fact that the nodal recovery function shows different characteristics depending upon whether RT is assessed from the preceding atrial cycle length (AA) or His-atrial (HA) interval. Moreover, the rate- and time-dependent increase in AH, known as fatigue, also shows different characteristics depending on RT index used. Furthermore, the third rate-dependent AV nodal property known as facilitation and that tends to shorten AH with penultimate cycle length, is obviously present or virtually absent when studying it with HA or AA index, respectively. Our first study sought to identify the source of this paradoxical apparent dependence of nodal rate-dependent properties on selected RT index. For this purpose, we varied two known independent modulators of AV nodal function, the basic (BCL) and pretest cycle length (PTCL), in 30 different combinations and assessed how the resulting 30 nodal functional states alter the recovery and the fatigue property as assessed with both recovery indexes. We found that, for each functional state, the shape of the nodal recovery curve and the level of fatigue was identical regardless of selected recovery index. We thus documented for the first time that recovery and fatigue properties are consistent whether assessed with HA or AA. However, we also found that PTCL effects appeared different on the two recovery curve formats. In a second study, using the same data, we investigated the origin of PTCL related variations of nodal recovery curves constructed with different recovery indexes. We found that PTCL shortening induced rightward AA curve shifts and leftward HA curve shifts proportional to the increase in pretest conduction time. Moreover, these curve shifts affected all data points equally. This finding suggests that both AA and HA indexes are biased by increases in pretest conduction time. These increases appeared to delay nodal recovery for an identical AA, and to hasten nodal recovery for an identical HA. Uncontrolled changes in pretest conduction time during fast rates thus produce apparent different effects depending on nodal recovery index. Taking into account changes in pretest conduction time results in unified rate-dependent nodal conduction properties regardless of chosen recovery index. Another major problem in AV nodal physiology relates to rate-dependent changes in nodal refractoriness. Two indexes of nodal refractoriness, effective (ERPN) and functional (FRPN) refractory periods, are commonly determined. ERPN and FRPN correspond to the longest AA resulting in nodal block and shortest interval between successive His bundle activations, respectively. For unclear reasons, increasing rate typically results in ERPN prolongation but FRPN shortening, and these effects vary greatly with individuals, ages and species. In a third study, we assessed the functional origin of rate-induced changes in ERPN and FRPN. BCL shortening prolonged ERPN but did not significantly affect FRPN. This ERPN prolongation mainly arose from an increase in pretest conduction time. PTCL shortening also prolonged the pretest conduction time and hence ERPN, but this prolongation was partly counterbalanced by a decrease in the His-atrial subinterval at ERPN. Similar PTCL-induced His-atrial shortening also fully accounted for FRPN shortening. Notably, we found that when ERPN is corrected for the increase in pretest conduction time, ERPN and FRPN vary in parallel according to their respective His-atrial subintervals. Combined BCL and PTCL shortening, including those corresponding to standard commonly used protocols, result in net changes in refractory measures predictable from the sum of their individual effects. These observations not only support a new functional scheme for rate-dependent AV nodal refractoriness but also establish a relationship between ERPN and FRPN which, for a long time, were thought to reflect different nodal properties. In conclusion, rate-dependent AV nodal function reflect the net sum of concurrent yet independent cumulative and non-cumulative effects arising from BCL and PTCL changes, respectively. Nodal recovery and fatigue properties are independent of recovery index. Rate-induced non-cumulative variations in nodal recovery curves originate from changes in pretest conduction time and reflect current limitations of recovery indexes to precisely measure exact nodal recovery time. Changes in pretest conduction time also explain opposite rate-induced changes in ERPN and FRPN. When these changes are taken into account, FRPN and ERPN vary in parallel with heart rate and largely depend on His-atrial interval. These data support a new functional model of rate-dependent nodal conduction and refractoriness, which may help guide studies on underlying cellular and ionic mechanisms as well as on nodal behaviour during supraventricular tachyarrhythmias.