Characterisation and prediction of mechanical properties of injection moulded polypropylene

Dissertação de mestrado em Engenharia de PolímerosThe characterisation of an automotive grade polypropylene, using a Taguchi L8 orthogonal array, was carried out in order to evaluate and quantify the differences in morphological features such as: skin ratio (Sa), bulk and skin crystallinity (χbulk and χskin), molecular orientation (Ωs) and β-phase content (k-value), and tensile properties: yield stress (σy), elastic modulus (E) and strain at break (εb) induced by different processing conditions. The morphological features were assessed by polarised light microscopy, differential scanning calorimetry and wide angle x-ray diffraction, respectively. The mechanical properties by quasi-static (20 mm/min) and high speed tensile (1 and 3 m/s) tests. Afterwards, Autodesk Moldflow Insight 2012 was used to calculate thermomechanical variables using a dual domain mesh model to later apply the thermomechanical indices methodology. It was used to describe the variation of both morphological and mechanical properties and to subsequently establish mathematical equations to describe straightforward relationships between the TMI and these properties. Such regression equations allow the prediction of mechanical properties as a function of the injection moulding conditions. Finally, an industrial-like case-study was carried out (using samples supplied by an industrial company) in order to identify the processing conditions that display the highest values of peak force and puncture energy measured in a falling weight impact test and subsequently establish the TMI methodology to predict the impact responses of the used material. Analysis of Variance was used to quantify the effect of the processing conditions on all morphological and tensile properties. Globally it was found a strong influence of the injection velocity (vi) and injection temperature (Ti) on the morphological parameters. A decrease of Ti seems to increase the majority of the morphological features, whereas a contrary effect was observed for vi. Sa increased for low values of vi and all other morphological properties increased with the increase of the injection velocity. Regarding the mechanical properties, the mould temperature (Tw) and holding pressure (Ph) were the most significant processing conditions. A low value of Tw resulted in the increase of the majority of tensile properties. On the other hand, an opposing effect was observed for the holding pressure. σy and E presented a low variation within each microstructure which can be due to the coupled effect of opposing effects on these properties (Ωs and k- value) promoted by the same processing variables and the fact that the bulk crystallinity showed virtually no variation. In the case-study, a lack of variation on the impact properties was also observed which in due turn compromised the use of the full extent of the TMI. This methodology is still under development but shows a great potential to predict both morphological and mechanical responses as a function of the existent thermomechanical environment.A caracterização de um polipropileno de grau automóvel, utilizando uma matriz ortogonal Taguchi L8, foi realizada a fim de avaliar e quantificar diferenças produzidas por diferentes condições de processamento em propriedades morfológicas, tais como: rácio casca- núcleo (Sa), cristalinidade média (χbulk) e da casca (χskin), orientação molecular (Ωs) e população de esferulites na fase β (k- value), e em propriedades mecânicas medidas à tração: tensão de cedência (σy), módulo de elasticidade (E) e deformação à rutura (εb). As características morfológicas foram avaliadas, respetivamente, através de microscopia de luz polarizada, calorimetria diferencial de varrimento e difração de raio-X. As propriedades mecânicas por ensaios de tração realizados a velocidades quase-estáticas (20 mm/min) e a alta velocidade (1 e 3 m/s). Posteriormente, o software Autodesk Moldflow Insight 2012 foi utilizado para calcular variáveis termomecânicas utilizando um modelo com malha dual domain de forma a aplicar a metodologia dos índices termomecânicos (TMI). Esta foi utilizada para descrever a variação nos parâmetros morfológicos e mecânicos e subsequentemente estabelecer relações matemáticas diretas entre os TMI e as propriedades avaliadas. Por fim, um caso de estudo foi realizado (utilizando amostras fornecidas por uma empresa) de forma a identificar as condições de processamento que apresentam maiores valores de força de pico e energia à rutura medidas num ensaio de queda de dardo e, posteriormente, aplicar a metodologia dos TMI para prever as respostas de impacto deste material. Análise de variância foi utilizada para quantificar a influência das condições de processamento nas propriedades morfológicas e mecânicas medidas à tração. Verificou-se que a temperatura (Ti) e velocidade de injeção (vi) são as variáveis operatórias que mais influenciam as propriedades morfológicas. Uma diminuição de Ti levou ao aumento da generalidade dos parâmetros avaliados ao passo que vi apresentou um efeito contraditório. Sa aumentou para baixos valores de vi e os restantes parâmetros morfológicos para um aumento da velocidade de injeção. Em relação às propriedades mecânicas, a temperatura do molde (Tw) e a pressão de manutenção (Ph) foram as variáveis mais importantes. Uma redução de Tw conduziu a um aumento da generalidade das propriedades à tração, por outro lado um efeito contraditório foi observado por parte de Ph. A tensão de cedência e módulo de elasticidade dentro das diferentes microestruturas apresentaram uma baixa variação. Tal pode ser devido a um efeito sinergético provocado por efeitos antagónicos (Ωs e k-value) que são promovidos pelas mesmas variáveis operatórias e ao facto de a cristalinidade média se apresentar praticamente constante nas diferentes microestruturas. No caso de estudo, uma falta de variação nas propriedades ao impacto também foi observado comprometendo a utilização dos TMI. Esta metodologia ainda se encontra em desenvolvimento mas mostra grande potencial para prever propriedades mecânicas e morfológicas em função do ambiente termomecânico existente no processo de injeção

On the simulation of the filling stage of thermoplastic injection molding using the open-source solver openInjMoldSim

NORTE-07-0162-FEDER-000086 and the Minho Advanced Computing Center (MACC) for providing HP

Enhancing the interface behavior on polycarbonate/elastomeric blends: morphological, structural, and thermal characterization

A systematic study was performed to provide better understanding of the effect of elas tomeric materials on the behavior of polycarbonate blends (PC). Thus, blends of PC with different amounts of elastomers, such as copolyether ester elastomer (COPE), acrylonitrile–butadiene–styrene (ABS), maleic anhydride-grafted ABS (ABS-g-MA), and styrene–ethylene–butylene–styrene (SEBS g-MA) were prepared in a co-rotating twin-screw extruder. The materials were characterized by an electronic microscopy (SEM), an infrared spectroscopy (FTIR), and thermal (DSC) and thermo mechanical (DMA) techniques. The incorporation of elastomeric phases was observed by changes in the FTIR band’s intensity, whereas a new shoulder of the ester band of COPE at 1728 cm−1 indicates the occurrence of a transesterification reaction. Unmodified and modified ABS (5% and 10%) did not affect the glass transition temperature (Tg) of PC, while 1% SEBS-g-MA slightly increased this value. PC/10% COPE showed that a decrease in Tg of 25 ◦C has a result of better compatibilization between both phases, which is visible via SEM. SEM analysis identified three main toughening mechanisms, depending on the type of elastomer. Unlike any other study, this work deepens the knowledge, in a comparative way, to understand the elastomeric effect at the interface and consequently, on the mechanical behavior of PC systems.This work was founded by Portugal 2020, and Fundo Social Europeu (FSE) through Programa Operacional Regional do NORTE (NORTE-08-5369–FSE-000034), developed under the pro gram “IMPULSE—Polímeros e Compósitos: Drivers da inovação tecnológica e da competitividade industrial”. The authors also acknowledge the Portuguese Foundation of Science and Technology (TSSiPRO—TECHNOLOGIES FOR SUSTAINABLE AND SMART INNOVATIVE PRODUCTS— NORTE-01-0145-FEDER-000015) and UID/CTM/50025/2013 for the financial support

A semi-automatic approach based on the method of manufactured solutions to assess the convergence order in OpenFOAM

Code verification is an intricate but crucial part of numerical code development. Due to the complexity of the partial differential equations, an analytical solution might not exist. In those situations and aiming at proving that the code is solving appropriately the governing equations, the method of manufactured solutions (MMS) is a powerful tool. In this method, a source term is derived to enforce the solution to a predetermined function. By performing a mesh refinement study, one can verify if the code is correctly solving the desired equations. In this work, a methodology that allows the automation of the MMS within the OpenFOAM© framework is proposed. The developed computational framework comprises a set of tools prepared, in an open-source environment, for the symbolic computation of the associated source term, and to generate the code required for its implementation as well as appropriate boundary conditions and functions to calculate the error norms