There is a strong desire among automobile manufacturers to reduce the fuel consumption and greenhouse gas emissions of their current vehicles. Reducing the overall weight of a vehicle represents the most practical opportunity to reduce fuel consumption. Replacing the current steel sheet structures with lightweight alternatives, such as aluminum, offers an excellent solution. Much of the attention in North America has been focused on copper-containing Al-Mg-Si aluminum alloys (6xxx series), such as AA6111. These alloys offer an excellent combination of good formability and precipitation-strengthening ability.<p> In this study, the effect of solute concentration on the strength and strain aging behavior of a proprietary Al-Mg-Si-(Cu) alloy was evaluated. The experimental design used was a 26 full factorial design, with the primary factors being the solute concentrations of magnesium, silicon, and copper, as well as the effects of applied strain (cold work), and natural and artificial aging heat treatments (e.g., a simulated paint bake process). The primary investigative techniques employed included tensile testing, microhardness measurements, and optical metallography.<p> The results show that cold work and artificial aging produce the most substantial strengthening in the alloys. The occurrence of natural aging prior to forming and artificial aging reduced strengthening. The highest strength levels in the naturally aged and paint baked condition, which most closely resembles what is found in industry, were achieved at a combination of low magnesium levels (i.e., 0.5 wt.%) and high silicon and copper levels (i.e., 0.9 and 0.3 wt.%, respectively).

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Member: Rhett Mayor; Committee Member: Shreyes Melkote; Committee Member: Steven Danyluk. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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Thesis (Ph. D.)--University of Sydney, 2008. / Includes graphs and tables. Includes list of publications co-authored with others. Title from title screen (viewed November 28, 2008) Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Civil Engineering. Includes bibliographical references. Also available in print form.

Thesis (M.M.)--Boston University

Les Sheet Moulding Compounds (SMC) sont des matériaux composites pré-imprégnés thermodurcissables. Ils sont largement utilisés dans l’industrie automobile pour fabriquer des pièces d’habillage ou semi-structurelles. Le développement de nouvelles formulations SMC hautes performances et de haute réactivité permettent d’envisager des cycles de production rapides et des propriétés convenant à des pièces de structure. Le procédé de mise en forme par compression impose à la matière des chargements thermo-mécaniques sévères couplés à la réaction de réticulation de la matrice (phase de cuisson). Le contrôle des dimensions et des propriétés finales des pièces nécessite la compréhension et la maitrise des phénomènes physiques se déroulant pendant ce procédé. Les travaux de cette thèse portent sur la caractérisation et la modélisation des transferts de chaleur, de la cinétique de réticulation et sur l’évolution des propriétés mécaniques résultant de la phase de cuisson. Tout d’abord, les propriétés thermo-physiques et la cinétique de réaction sont caractérisées afin de prévoir les champs de température, les champs d’avancement et les variations dimensionnelles pendant le cycle de moulage. Ensuite, le comportement rhéologique en cours de transformation est étudié en abordant la notion de gel d’un point de vue mécanique, à travers le concept de contrainte seuil. Enfin, un nouveau dispositif de caractérisation est présenté ; il permet une analyse fine du comportement de la matière pendant la totalité du cycle de compression, à travers le suivi des flux de chaleur et des niveaux de pression dans la cavité moulante. Mots clés Composite thermodurcissable, Sheet Moulding Compound / Sheet Moulding Compound (SMC) materials are thermoset prepregs. They are already extensively used in the automotive industry to manufacture semi-structural parts. The development of new formulations containing a high fibre content (40-60 wt%) and with higher reactivity is ongoing in the perspective of producing structural parts and reducing cycle times. SMC compression moulding process imposes strong thermo-mechanical loadings coupled with the crosslinking reaction of the matrix (curing step). The control of the final dimensions and properties of the moulded parts requires to understand and to predict the physical phenomena occurring during this process. This study is focused on the characterization and the modelling of heat transfer, the kinetic reaction and on the variations of mechanical properties resulting from the curing step. At first, thermo-physical properties and kinetics of reaction are characterized in order to predict the temperature and conversion degree fields but also the dimensional variations during the moulding cycle. Then, the rheological behaviour during the transformation is investigated by considering a mechanical approach for the gel point, based on the concept of yield stress. Finally, a new specific device is introduced; it allows a fine characterization of the material behaviour during the whole compression cycle, thanks to the measurement of heat flux and pressures in the moulding cavity.

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