This study investigates scaling effects in a novel fibre-metal laminate (FML) system based on a thermoplastic matrix. The material is based on an aluminium alloy, a selfreinforced polypropylene composite and a polypropylene film acting as an interlayer adhesive. Initially, the mechanical characterisation of the FMLs and 'their constituents are characterised in tension, flexure and under impact loading. Additionally, the level of adhesion between the composite and aluminium constituents is characterised using fracture mechanics procedures. The performance of the FML is investigated aI!d compared to that offered by its constituents, enabling the advantages of these novel hybrid systems to be highlighted. Two different laminate constructions are employed here, these being an [AI, 0°/90°]5 FML and an [AI, +/- 45°]5 FML. Pronounced differences were observed between the two laminates, with the strain to failure of the latter being approximately 50% greater than the former. Interestingly, flexural tests revealed that the fibre orientation did not affect either the maximum stress or the strain at failure of the FML. Abstract ABSTRACT J. G. Carrillo The second part of the study focuses on investigating scaling effects in this FML system. Here, scale model tests are used to predict the full-scale behaviour of fibremetal laminates. Two laminates are investigated in this part of the research programme, these being [Aln, 00/900 n]5 and [Aln, +/- 45°n]5 with n = '14, Y2, % and 1. Tensile tests are undertaken on laminates prepared using three different scaling approaches, these being ID (scaling the thickness dimension), 2D (scaling the inplane dimensions) and 3D scaling, where all of the dimensions are scaled appropriately. Here, a small decrease in the value of these parameters was observed with increasing specimen size, suggesting that modest scaling effects do exist. Additionally, flexural tests are carried out using a 3D scaling approach, giving a direct comparison with the results generated in tension. The final part of this section investigates scaling effects in the low velocity impact response of the FMLs. Here, it is shown that the impact energy to initiate fracture in the FMLs does not exhibit any size dependency. Other test parameters, such as the impact duration are shown to obey the scaling law, with less than ten percent deviation from the normalised data being observed.

No description available.

No description available.

No description available.

No description available.

No description available.

La Fabrication Additive (FA) ouvre des perspectives nouvelles pour mettre en forme des matériaux à base de polymères naturels et ainsi tirer parti de leurs propriétés intrinsèques, telles que comestibilité et biorésorbabilité. Cette thèse se concentre sur le procédé d’impression 3D par dépôt de fil fondu (FA-DFF) appliqué à la zéine, une protéine de réserve du maïs pouvant être mise en œuvre à l’état fondu en présence de plastifiants. Après avoir établi un cahier des charges déclinant les critères « matière » pour ce procédé, une formulation plastifiée par 20% de glycérol a fait l’objet d’une caractérisation complète des propriétés concernées. Son comportement thermomécanique et rhéologique peut être compatible avec un procédé FA-DFF alimenté par des filaments préalablement extrudés : Suffisamment rigide à 20°C, le matériau peut être extrudé à des températures supérieures à 120 °C. Son comportement rhéofluidifiant et son aptitude à la fusion-adhésion sont alors similaires à ceux de polymères standards tels que l’ABS et le PLA. Cependant, une réticulation progressive due à l’agrégation de la protéine à l’état fondu, mise en évidence par des caractérisations structurales, vient limiter sa fenêtre de mise en oeuvre. Néanmoins, il est possible de pallier à ce phénomène soit en modifiant le système d’alimentation matière du procédé, soit en modulant la formulation. Outre la combinaison du glycérol avec des additifs réducteurs ou dénaturants, l’intérêt de sa substitution par des liquides ioniques est mis en évidence, ces composés pouvant apporter des fonctionnalités pharmaceutiques aux objets imprimés, ce qui ouvrirait un champ d’applications nouvelles pour la zéine. / Additive Manufacturing (AM) opens new perspectives for the processing and shaping of materials based on natural polymers. Their intrinsic properties such as edibility and bioresorbability could thus be exploited. This thesis focuses on 3D printing by molten Material Extrusion (AM-ME). It is applied to zein, a corn storage protein which is melt processable in presence of plasticizers. After listing the relevant material specifications for the AM-ME process, all the properties concerned were characterized for a formulation plasticized by 20% of glycerol. Its thermomechanical and rheological behaviour can be compatible with an AM-ME process fed by previously extruded filaments : While rigid enough at 20°C, the material can be extruded above 120°C. Its shear thinning behaviour and fusionbonding ability are similar to those of standard polymers such as ABS and PLA. However, a progressive crosslinking due to protein aggregation in the melt was shown by structural characterizations. The processing window is thus limited, but this issue can be addressed either by modifying the feeding system of the process, or by adapting the formulation. Glycerol can be combined with reducing or denaturing agents, or substituted by ionic liquids. The interest of these plasticizers is to allow bringing pharmaceutical functionalities to printed parts. This would open the field of new applications for zein.

Fatigue crack initiation and propagation in aluminium butt welds has been investigated. It is shown that the initiation of cracks from both buried defects and from the weld reinforcement may be quantified by predictive laws based on either linear elastio fracture mechanics, or on Neuber's rule of stress and strain concentrations. The former is preferable on the grounds of theoretioal models of crack tip plasticity, although either may be used as the basis of an effective design criteria against crack initiation. Fatigue lives fol1owing initiation were found to follow predictions based on the integration of a Paris type power law. The effect of residual stresses from the welding operation on both initiation and propagation was accounted for by a Forman type equation.This incorporated the notional stress ratio produced by the residual stresses after various heat treatments. A fracture mechanics analysis was found to be useful in describing the fatigue behaviour of the weldments at incrodsed. temperatures up to 300°C. It is pointed out however, that the complex interaction of residual stresses, frequency, and change in fracture mode necessitate great caution in the application of any general design criteria against crack initiation and growtn at elevated temperatures.

Les alliages de plomb-antimoine permettent à 1 milliard de véhicules thermiques de démarrer quotidiennement mais sont également utilisés dans le secteur médical et de l’énergie pour réaliser des équipements de radioprotection. Or la littérature montre une grande disparité des propriétés mécaniques et électrochimiques de ces alliages en fonction des conditions de sollicitation. La cause de cette confusion est liée à une sous-estimation de la sensibilité de ces matériaux à la température et à la vitesse de déformation. La température ambiante représente en effet la moitié de la température de fusion du plomb (en Kelvin) qui subit alors un recuit permanent. Les phénomènes thermiquement activés tels que la restauration et la recristallisation ne sont donc pas négligeable dans la modélisation du comportement mécanique de ces alliages. Après avoir modélisé l’influence de l’antimoine et de la vitesse de solidification sur les propriétés des microstructures de fonderie, une modélisation du comportement mécanique lors de grandes déformations est proposée. Le modèle déterminé est fidèle aux données expérimentales et intègre la sensibilité du matériau aux conditions de déformation sous la forme du paramètre de Zener- Hollomon. Les hétérogénéités de propriétés mécaniques qui sont issues de l’assemblage par soudage TIG sont expliquées par la présence conjointe des deux microstructures : une morphologie de solidification dans le cordon de soudure et une morphologie de déformation dans les laminés. Dans les alliages de plomb-antimoine, une microstructure hybride est créée à l’interface par un phénomène de fusion partielle des joints de grains. / Lead-antimony alloys allow 1 billion thermal vehicles to start daily but are also used in the medical and energy sector to produce radiation protection equipment. However, the literature shows a great disparity in the mechanical and electrochemical properties of these alloys depending on the conditions of stress. The cause of this confusion is related to an underestimation of the sensitivity of these materials to temperature and strain rate. The ambient temperature represents in fact half the melting temperature of the lead (in Kelvin) which then undergoes a permanent annealing. The thermally activated phenomena such as restoration and recrystallization are therefore not negligible in the modeling of the mechanical behavior of these alloys. After modeling the influence of antimony and the rate of solidification on the properties of solidification microstructures, a modeling of the mechanical behavior during large deformations is proposed. The determined model is faithful to the experimental data and incorporates the sensitivity of the material to the deformation conditions thanks to the Zener-Hollomon parameter. The heterogeneities of mechanical properties that arise from the TIG welding are explained by the presence of two microstructures: a solidification morphology in the weld bead and a deformation morphology in the rolls. For leadantimony alloys, a hybrid microstructure is created at the interface by a phenomenon of partial melting of the grain boundaries.

Research concerning the surface of technical ceramics is carried out from the viewpoint of their mechanical performance subjected to relevant operating conditions. The selected materials are silicon nitride, zirconia and alumina. They are subjected to cavitation erosion and other wear processes. When polished ceramics are subjected to cavitation, a pseudoplastic deformation pit is discovered, as well as a delayed phase transformation or ageing of the zirconia stored at room temperature. Measured ageing times recorded are of the order of one month. These two discoveries are novel and a full explanation is explored. The creation of cracks that release the slip planes of ceramic grains allowing plastic deformation is proposed to be the main mechanism. In order to understand the relationship of the zirconia surface degradation with its oxides (yttria or magnesia), several material compositions are tested. It is concluded that the delay of phase transformation relies on the existence of partially stabilized tetragonal zirconia regardless of the oxide used to stabilize it. Part of this research consists of understanding the effects of the experimental procedure that is utilised on the behaviour of the material. An unexpected non homogeneous cavitation erosion shape is obtained when an ultrasonic horn of small diameter is used to produce the bubbles. This non homogeneous region, referred to as ring region for this research, affects the erosion pattern of the material and it differs from the typical ones obtained when following the standard test. The acoustic theory does not explain this phenomenon. Therefore, a new approach is followed. This approach consists of using fluid mechanics equations combined with analytical mechanics principles. It is concluded that the location of cavitation clusters fulfils a condition of minimum energy. On the other hand, there are important differences between this experimental set up and the set up suggested by the published standards. These differences are discussed and a criterion for cavitation erosion resistance is developed. The comparison of cavitation resistance of materials is achieved by means of surface loss as criterion instead of volume loss.