Aurélie Benoit

Traditionnellement, les collecteurs d'échappement sont fabriqués en fonte, d'un seul tenant. En raison de l'augmentation des performances des moteurs, des tôles d'acier mécano-soudées sont maintenant utilisées pour améliorer la tenue mécanique du collecteur à haute température. Cette technologie permet de réduire la masse du collecteur et de répondre ainsi favorablement aux normes de dépollution les plus sévères. L'objectif de la thèse est de proposer un modèle numérique de soudure et un critère de ruine associé permettant de prédire la durée de vie de ces structures mécano-soudées soumises à des chargements thermiques anisothermes. La procédure de dimensionnement consiste à simuler plusieurs cycles de chargements et à évaluer le critère de fatigue sur le dernier cycle simulé, considéré comme stabilisé.Dans un premier temps, une étude théorique est menée sur la caractérisation des différents états asymptotiques (adaptation, accommodation et rochet). Elle permet, d'une part de vérifier que l'état stabilisé est effectivement atteint et éventuellement d'estimer le nombre de cycles nécessaires pour l'atteindre, d'autre part de déterminer la nature de l'état limite. Dans un second temps, des essais de durée de vie isothermes, réalisés sur des éprouvettes en tôle, en tôle soudée et en tôle soudée arasée (abrasion du cordon puis polissage de la zone utile) mettent en évidence l'influence de la géométrie et de la microstructure au niveau de la soudure sur la durée de vie de ces structures. Enfin, des essais de durée de vie anisothermes, inspirés de chargements effectivement observés sur le collecteur, ont été réalisés sur des éprouvettes en tôle et en tôle soudée.La rigidité du cordon de soudure est modélisée à l'aide d'éléments coques dimensionnés de sorte à reproduire la déformée des éprouvettes en tôle soudée observée expérimentalement. Différents critères de ruine sont mis au point sur le matériau de base pour caractériser l'endommagement induit par des chargements anisothermes puis sont adaptés à la zone soudée. Enfin, la simulation d'un essai de choc thermique sur un collecteur d'échappement permet de valider le modèle de soudure proposé et de tester la pertinence des critères vis-à-vis de l'application industrielle.

Backgroung/Aim: New resins for the additive manufacturing of mouthguards for contact sports are now available on the market. However, no study has evaluated the impact performance of these resins. The aim of this in vitro study was to compare the shock absorption capacities of custom‐made mouthguards produced by additive manufacturing with those of thermoformed mouthguards. Materials and Methods: Three types of custom‐made mouthguards were fabricated: 3D‐printed Keyguard and Dima resin mouthguards and thermoformed triple‐layer mouthguards. For each type of mouthguard, eight samples were produced. Each mouthguard was subjected to an impact performance test defined by the NF S72‐427 standard for industrial mouthguards. Mean transmitted deceleration must not exceed 230 g (g = 9.81 m/s ² ) and no individual impact should exceed 250 g. Mechanical performance was evaluated by a series of five consecutive impacts with a drop‐mass impact test on the inter‐incisal area. Peak force transmission and deceleration were measured. Thickness decrease was assessed by 3D scanning. Results: None of the mouthguards met the impact absorption standard. Thermoformed mouthguards exhibited major structural failure after the first impact. For 3D‐printed mouthguards, average peak deceleration ranged from 255 to 278 g for Dima and 292 to 299 g for Keyguard. Corresponding transmitted forces ranged from 2753 to 3106 N (Dima) and 3192 to 3292 N (Keyguard), with no significant difference between the two 3D‐printed mouthguards ( p > 0.05). Mean thickness decrease at the impact site was 0.2 mm for Dima mouthguards, 0.1 mm for Keyguard mouthguards, and 0.3 mm for thermoformed mouthguards. Conclusion: Although none of the tested mouthguards met the NF S72‐427 standard, 3D‐printed custom devices demonstrated promising shock absorption performance after repeated impacts. These results highlight the potential of additive manufacturing as a cost‐effective alternative to conventional thermoformed mouthguards, particularly for younger athletes requiring frequent replacements.

Background/Aim: 3D printing processes can be used to manufacture custom‐made mouthguards for sports activities. Few studies have compared the impact performance of industrial‐created mouthguards with that of custom‐made mouthguards manufactured by thermoforming or 3D printing. The objective of this in vitro study was to compare the shock absorption capacities of custom‐made mouthguards manufactured by 3D printing with industrial mouthguards and thermoformed ethylene vinyl acetate (EVA) mouthguards.Materials and Methods: For each type of mouthguard, eight samples were produced. 3D‐printed mouthguards were manufactured using digital light processing technology. Each mouthguard was subjected to an impact performance test defined by the standard AFNOR XP S72‐427, which evaluate maximum deceleration and force transmitted during impact. The thickness of each mouthguard before and after a series of five impacts was measured at the impacted inter‐incisal area.Results: The mean maximum decelerations during impact ranged from 129 to 189 g for industrial mouthguards, 287 to 425 g for thermoformed EVA mouthguards, and 277 to 302 g for 3D‐printed mouthguards. The mean reduction in mouthguard thickness at the impact zone after five tests was 1.2 mm for industrial mouthguards, 0.6 mm for 3D‐printed mouthguards, and 2.2 mm for thermoformed EVA mouthguards.Conclusions: Custom‐made 3D printed mouthguards showed slightly better shock absorption ability than thermoformed mouthguards with respect to the indicator proposed in XP S72‐427. They seemed to combine the practical advantages of thermoformed mouthguards in sports with better shock absorption capacity and lower cost. Furthermore, they had the least thickness variation during the test, and their shock absorption capacity was the least affected by repeated mechanical tests. Other types of 3D‐printing resin materials that will become available must continue to be tested for shock absorption to provide the best protection to users at low cost.

Attachment systems (AS) enhance retention and stability by anchoring the overdentures to implants. Since 2002, the McGill consensus statement recommends the 2-implant-retained overdentures as the standard choice for edentulous mandible (2-IRMO). Considering the large number of AS available, it remains difficult for a practitioner to make a reasoned choice. A systematic review was conducted in PubMed/Medline and carried out independently by three authors, on retention, wear, and maintenance of AS used clinically or in vitro specifically for 1- or 2-IRMO. The 45 selected studies include 14 clinical and 31 in vitro studies. The risk of bias was evaluated according to the revised Cochrane risk of bias tool for randomized trials (RoB 2). The initial retention force of the cylindrical system is higher than the ball system. The retention loss, related to the wear of the retention device, is responsible for the most common need of maintenance, requiring activation or replacement. Plastic retention devices wear out faster and more significantly than metal ones, implying a worse time behavior of cylindrical systems, but their maintenance rate is similar. Neither system appears categorically superior. Cylindrical systems provide higher initial retention than ball ones; this advantage reduces over time with wear without affecting their need for maintenance.