Sulfonated Styrene-(ethylene-co-butylene)-styrene/Montmorillonite Clay Nanocomposites: Synthesis, Morphology, and Properties

Sulfonated styrene-(ethylene-butylene)-styrene triblock copolymer (SSEBS) was synthesized by reaction of acetyl sulfate with SEBS. SSESB-clay nanocomposites were then prepared from hydrophilic Na-montmorillonite (MT) and organically (quaternary amine) modified hydrophobic nanoclay (OMT) at very low loading. SEBS did not show improvement in properties with MT-based nanocomposites. On sulfonation (3 and 6 weight%) of SEBS, hydrophilic MT clay-based nanocomposites exhibited better mechanical, dynamic mechanical, and thermal properties, and also controlled water–methanol mixture uptake and permeation and AC resistance. Microstructure determined by X-ray diffraction, atomic force microscopy, and transmission electron microscopy due to better dispersion of MT nanoclay particles and interaction of MT with SSEBS matrix was responsible for this effect. The resulting nanocomposites have potential as proton transfer membranes for Fuel Cell applications

Optimization of mechanical systems: engineering design tool

The present work focuses the problem of mechanical systems automated structural synthesis by means of case studies related to the design of components belonging to the automotive industry. A bibliographic review about the synthesis fundamental techniques (in the context presented here) is done: the analysis by the finite element method, the non-linear optimization and the model reduction or approximation techniques. Two first tier software tools were chosen (VMA/GENESIS and MSC/NASTRAN) in order to apply the aforementioned methodology in three case studies: the shape optimization of a part obtained by iron casting, the optimization of the dynamic behaviour of a structure excited by the vehicle’s powertrain and the comparisson between two difierent optimization techniques applied to an air suspension component. Finally, for one of the studied situations, a photoelastic experimental application is developed.Dissertação (Mestrado)O presente trabalho enfoca o problema da síntese automatizada de sistemas mecânicos, através de estudos de casos relacionados ao projeto de componentes da indústria automotiva. E feita uma revisão bibliográfica das técnicas fundamentais da síntese no contexto aqui colocado: a análise pelo método dos elementos finitos, a otimização não-linear e os métodos de redução de modelos ou técnicas de aproximação. Foram escolhidas duas ferramentas computacionais de destaque (VMA/GENESIS e MSC/NASTRAN) para a aplicação da referida metodologia em três estudos de caso: otimização de forma de uma peça obtida por fundição, otimização do comportamento dinâmico de uma estrutura excitada pela fonte de potência do veículo e comparação de diferentes técnicas de otimização aplicadas sobre um componente de suspensão a ar. Finalmente, para uma das situações estudadas, é desenvolvida uma aplicação experimental através da técnica da fotoelasticidade

Dynamical Modelling, Stochastic Simulation and Optimization in the Context of Damage Tolerant Design

This paper addresses the situation in which some form of damage is induced by cyclic mechanical stresses yielded by the vibratory motion of a system whose dynamical behaviour is, in turn, affected by the evolution of the damage. It is assumed that both phenomena, vibration and damage propagation, can be modeled by means of time depended equations of motion whose coupled solution is sought. A brief discussion about the damage tolerant design philosophy for aircraft structures is presented at the introduction, emphasizing the importance of the accurate definition of inspection intervals and, for this sake, the need of a representative damage propagation model accounting for the actual loading environment in which a structure may operate. For the purpose of illustration, the finite element model of a cantilever beam is formulated, providing that the stiffness matrix can be updated as long as a crack of an assumed initial length spreads in a given location of the beam according to a proper propagation model. This way, it is possible to track how the mechanical vibration, through its varying amplitude stress field, activates and develops the fatigue failure mechanism. Conversely, it is also possible to address how the effect of the fatigue induced stiffness degradation influences the motion of the beam, closing the loop for the analysis of a coupled vibration-degradation dynamical phenomenon. In the possession of this working model, stochastic simulation of the beam behaviour is developed, aiming at the identification of the most influential parameters and at the characterization of the probability distributions of the relevant responses of interest. The knowledge of the parameters and responses allows for the formulation of optimization problems aiming at the improvement of the beam robustness with respect to the fatigue induced stiffness degradation. The overall results are presented and analyzed, conducting to the conclusions and outline of future investigation