Vérification de la cohérence d'une solution mécanique associée à diverses représentations d'un produit

En utilisant un critère mécanique a posteriori caractérisant l'influence des variations de forme d'un objet sur la solution mécanique associée, il est possible de quantifier la cohérence des différentes formes produites d'un point de vue mécanique. Cette cohérence indique dans quelle mesure des objets de formes différentes ont un comportement mécanique pouvant être considéré comme identique lorsqu'ils sont soumis à des conditions aux limites identiques. Nous présentons une ébauche de plateforme permettant de vérifier automatiquement cette cohérence dans différents scenarii du processus de développement d'un produit

Interoperability between CAD and simulation models

No abstract availabl

QUALITY AND PRODUCTIVITY IMPROVEMENTS IN ADDITIVE MANUFACTURING

Additive manufacturing (AM) is a relatively new manufacturing technology compared to the traditional manufacturing methods. Even though AM processes have many advantages, they also have a series of challenges that need to be addressed to adapt this technology for a wide range of applications and mass production. AM faces a number of challenges, including the absence of methods/models for determining whether AM is the best manufacturing process for a given part. The first study of this thesis proposes a framework for choosing specific AM processes by considering the complexity level of a part. It has been proven that the method works effectively through numerical experiments. Optimization of process parameters through expensive and time-consuming experiments is another issue with AM. To address this issue, an empirical model is presented in the second study to optimize parameters for minimizing building costs through maximizing the trade-off between productivity and quality. The proposed model proves to be effective in reducing building costs at any quality level. The results indicate that process parameters can be optimized quickly and accurately, as compared to the time-consuming and expensive experimental methods. Another limitation of AM is the lack of capability to use multiple materials, which is a concern when adapting this technology to mass production. To address this issue, a new scheduling model with considering multi-material types is introduced in the third study. Based on the numerical results, the proposed model can provide optimal sequence by maximizing the trade-off between tardiness and material switching cost

Experimental and numerical investigation of biomass mechanical pre-processing

"July 2014."Dissertation supervisor/advisor: Dr. Ali Bulent Koc.Includes vita.In this study, mechanical properties of switchgrass and miscanthus were determined by tensile, compressive and shear tests in longitudinal (along the fiber) and transversal (cross the fiber) directions with special designed tools. A linear cutting platform and a data acquisition system were developed to investigate the biomass cutting performances using conventional cutting and ultrasonic-assisted cutting. Three different blades with 20 kHz vibration frequency were designed by using finite element analysis and verified by experimental modal analysis. Finite element analysis models of biomass cutting were developed to simulate the biomass cutting process. The simulation results showed that finite element analysis method could be used to design the ultrasonic blade and simulate the biomass cutting process. Biomass cutting experiments were carried out to investigate the effects of cutting speed, shear angle, blade profile and ultrasonication on the cutting force and energy consumption of switchgrass and miscanthus cutting. Experimental results showed that ultrasonic cutting could reduce the cutting force and the entire cutting energy consumption. The optimized energy consumption could be achieved when the cutting speed was about 1/3 of the ultrasonic blade vibration speed. For the biomass conventional cutting, the tested cutting speeds did not show obvious effects on cutting performances.Includes bibliographical references (pages 144-150)

Tribological optimisation of the internal combustion engine piston to bore conjunction through surface modification

Internal combustion (IC) engines used in road transport applications employ pistons to convert gas pressure into mechanical work. Frictional losses abound within IC engines, where only 38- 51% of available fuel energy results in useful mechanical work. Piston-bore and ring-bore conjunctions are fairly equally responsible for circa 30% of all engine friction - equivalent to 1.6% of the input fuel each. Therefore, reduction in piston assembly friction would have a direct impact on specific performance and / or fuel consumption. In motorsport, power outputs and duty cycles greatly exceed road applications. Consequently, these engines have a shorter useful life and a high premium is placed on measures which would increase the output power without further reducing engine life. Reduction of friction offers such an opportunity, which may be achieved by improved tribological design in terms of reduced contact area or enhanced lubrication or both. However, the developments in the motorsport sector are typically reactive due to a lack of relative performance or an ad-hoc reliance, based upon a limited number of actual engine tests in order to determine if any improvement can be achieved as the result of some predetermined action. A representative scientific model generally does not exist and as such, investigated parameters are often driven by the supply chain with the promise of improvement. In cylinder investigations are usually limited to bore surface finish, bore and piston geometrical form, piston skirt coatings and the lubricant employed. Of these investigated areas newly emerging surface coatings are arguably seen as predominate. This thesis highlights a scientific approach which has been developed to optimise piston-bore performance. Pre-existing methods of screening and benchmarking alterations have been retained such as engine testing. However, this has been placed in the context of validation of scientifically driven development. A multi-physics numerical model is developed, which combines piston inertial dynamics, as well as thermo-structural strains within a thermoelastohydrodynamic tribological framework. Experimental tests were performed to validate the findings of numerical models. These tests include film thickness measurement and incylinder friction measurement, as well as the numerically-indicated beneficial surface modifications. Experimental testing was performed on an in-house motored engine at Capricorn Automotive, a dynamometer mounted single-cylinder ‘fired’ engine at Loughborough University, as well as on other engines belonging to third party clients of Capricorn. The diversity of tests was to ascertain the generic nature of any findings. The multi-physics multi-scale combined numerical-experimental investigation is the main contribution of this thesis to knowledge. One major finding of the thesis is the significant role that bulk thermo-structural deformation makes on the contact conformity of piston skirt to cylinder liner contact, thus advising piston skirt design. Another key finding is the beneficial role of textured surfaces in the retention of reservoirs of lubricant, thus reducing friction