In the present study, the feasibility of the Friction Spot Joining technique on magnesium AZ31-O / glass fiber and carbon fiber reinforced poly(phenylene sulfide) joints is addressed. The thermo-mechanical phenomena associated with the Friction Spot Joining process promoted metallurgical and polymer physical-chemical transformations. These effects resulted in grain refinement by dynamic recrystallization and changes in local (microhardness) and global strength (lap shear). Friction spot lap joints with elevated mechanical performance (20-28 MPa) were produced without surface pre-treatment. This preliminary investigation has successfully shown that Friction Spot Joining is an alternative technology for producing hybrid polymer-metal structures.

The main accomplishment of compounding wood-flour with thermoplastics is an increase in rigidity and specific strength. Filler-matrix interactions play a key role in the composite performance and the strength of the interface is determined by the nature of the coupling agents employed. The coupling efficiency of maleated polypropylene (PP-MAH) with varying MAH content and melt flow index in polypropylene-wood composites has been investigated. A method based on a simplified single rule of mixtures aiming to compare differences in interface adhesion in the presence of PP-MAH is proposed in terms of relaxation spectra of polypropylene-wood composites obtained by dynamic-mechanical thermal analysis (DMTA). The criterion is an attempt to determine an adhesion factor as derived from the relative mechanical damping (tan ) of the composite as a function of the filler content and temperature. Experimental results deviate from model predictions possibly owing to assumptions of wood-flour as a rigid filler as well as neglect of an interphase volume fraction and its damping characteristics. However, good correlations of coupling efficiency and yield properties have been found for wood composites with homopolymer and copolymer matrices within a range of varying wood-flour content and type of coupling agent. Further evidences of improved matrix-filler interactions, wettability, and filler dispersion in the presence of the PP-MAH are observed by scanning electron microscopy.

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Friction spot joining is an alternative technique to produce metal-composite overlap joints. The main process parameters are tool rotational speed, plunge depth, joining time and joining force. In this study, the individual effect of the process parameters on the microstructure and mechanical strength of hybrid AA6181-T4/CF-PPS double lap joints was investigated using Taguchi method and analysis of variance (ANOVA). Produced joints presented mechanical performance from 2107 N to 3523 N. Joints failed by brittle fracture at the interface between aluminum alloy and composite, with displacement-at-peak load values from 0.7 mm to 0.9 mm. Tool rotational speed was the parameter with the largest influence on the joint shear resistance, followed by the joining time, plunge depth and joining force. Higher strength was correlated to the extension of the bonding area and macro-mechanical interlocking related to the formation of a metallic indentation (metallic nub) slightly inserted into the composite. Larger bonding areas were shown to be related to higher heat input (as a result of longer joining times and intermediate rotational speeds) leading to larger consolidate polymeric layers at the metalcomposite interface. Higher macro-mechanical interlocking was obtained at larger plunge depths. Joining force was shown to be related to crevice and pore filling of the metal surface by supporting spreading of the molten polymer. Higher joining forces led to better wetting of the interface increasing adhesive forces and joint mechanical performance. Nevertheless excessive joining forces caused squeezing flow of the molten layer reducing joint strength, since a large adhesive area was lost.

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Resumo: Dentre muitas fibras naturais de interesse tecnológico, o resíduo de madeira substitui com vantagens as cargas e reforços tradicionalmente empregados em compostos e compósitos poliméricos, particularmente os de origem mineral, tais como talco, CaCO 3 e fibra de vidro. A tecnologia dos chamados Wood-Plastic Composites (WPC´s) envolve conceitos de compatibilidade e processabilidade e apresenta grandes desafios tecnológicos para a formulação e estabilização da mistura devido à baixa estabilidade térmica da celulose. Muitos dos avanços tecnológicos em WPC's dependem de uma análise criteriosa das características físicas de seus componentes e das condições de processamento do sistema, particularmente aspectos relacionados a sua compatibilização. No presente trabalho são apresentados estudos sobre a reatividade do polipropileno modificado com anidrido maleico (PP-MAH) utilizado como compatibilizante em compósitos termoplásticos de polipropileno com farinha de madeira. A influência da carga celulósica e a eficiência do compatibilizante nas propriedades reológicas, térmicas, mecânicas e morfológicas do sistema foi avaliada através de medidas de rigidez, grau de cristalinidade, temperatura de cristalização e fusão cristalina levando-se em conta as características da resina, a distribuição granulométrica e o teor de umidade da farinha de madeira. Observou-se que os compósitos compatibilizados com PP-MAH apresentaram ganhos significativos de rigidez em relação aos compósitos não-modificados independentemente do tipo de farinha de madeira empregada. As propriedades térmicas do polímero mostraram-se sensíveis à distribuição granulométrica e algumas composições apresentaram tendência ao escurecimento e à elevação da temperatura de cristalização do polímero na presença do reforço celulósico. Imagens obtidas por microscopia eletrônica de varredura ilustram o molhamento da fibra celulósica pela resina termoplástica quando na presença do compatibilizante indicando a possível ocorrência de reações de esterificação na interface polímero-madeira. Palavras-Chave: Compósitos termoplástico-celulósicos, tecnologia polímero-madeira, compatibilização, reometria de torque, análise térmica. Wood-Plastic CompositesAbstract: Wood waste fibers (WWF), mostly known as wood flour, can replace mineral fillers such as talc, CaCO 3 and fiberglass in the reinforcement of thermoplastics with great advantage. Wood-plastics composites (WPC's) technology includes concepts of compatibility and processing and yet presents technical challenges in grade formulation and stabilisation of the composite system. Owing to thermal constraints in wood flour processing, commodities such as polyolefins (PP, PEAD/PEBD), styrenics (PS e HIPS) and vinyls (PVC) represent the bulk of the thermoplastics used in WPC's applications. In the present work, a brief overview of the latest developments in WPC's processing technology is discussed in the light of technical characteristics and performance of this novel class of thermoplastics composites in emerging applications...

In this work the feasibility of Friction Spot Welding of thermoplastics was investigated on poly (methyl methacrylate) plates. Preliminary results have shown that the weld strength is comparable to other available welding techniques, while joining times are equal or shorter. Light optical microscopy and Vickers microhardness measurements showed the presence of a heat affected zone and a thin, consolidated stir zone, where physical-chemical transformations related to thermo-mechanical processing led to changes in local mechanical strength. The work has demonstrated for the first time that the welding of thermoplastic materials by Friction Spot Welding is feasible.

ABSTRACT:The effect of processing conditions and elastomer content on the toughening of Polypropylene (PP) by melt blending with styrene/ethylene-butylene/styrene triblock copolymer (SEBS) in a twin-screw extruder has been investigated. The parameters analyzed were: temperature profile, screw speed, and feed rate of the blend components. Their effect was evaluated through the mechanical properties (tensile strength and Izod impact resistance at room temperature) as well as the morphology of the dispersed phase by means of scanning electron microscopy (SEM). The results showed that the impact resistance increases with increasing rotor speed and feed rate and decreases when the temperature profile is increased. The parameter with the greatest effect on the mechanical properties was the variation in rotor speed. Despite the fact that impact resistance as high as 25 times that of neat PP has been achieved with blends containing 20 wt % SEBS, no significant modification in phase morphology has been observed.