120 research outputs found
Thermal and Mechanical Numerical Modeling of Extrusion-based 3d Printed Reinforced Polymers for Selecting Manufacturing Process Parameters
Extrusion-based 3D printing of thermoplastic polymer composites manufactures parts that have nonhomogenous, orthotropic, and process-dependent macro-scale material properties. As a part of the dissertation, research works were carried out to: • improve the interlayer mechanical properties and reduce the orthotropy, • use experimentally homogenized orthotropic material properties to numerically model the mechanical behavior of the non-homogenous orthotropic 3D printed parts, • create an efficient numerical thermal model to predict the process-dependent thermal history of the 3D printed part, and • aid the manufacturing process by selecting a suitable set of processing parameters based on a simplified sequentially coupled thermomechanical model. The dissertation presents four studies that improve the understanding of the mechanical behavior and aid the manufacturing process of the 3D printed thermoplastic polymer composites. Three journal publications that resulted from the research work carried out are listed below: • Bhandari, S., Lopez-Anido, R. A., & Gardner, D. J. (2019). Enhancing the interlayer tensile strength of 3D printed short carbon fiber reinforced PETG and PLA composites via annealing. Additive Manufacturing, 30, 100922. iii • Bhandari, S., Lopez-Anido, R.A., Wang, L. et al. (2020). Elasto-Plastic Finite Element Modeling of Short Carbon Fiber Reinforced 3D Printed Acrylonitrile Butadiene Styrene Composites. JOM 72, 475– 484. • Bhandari, S.; Lopez-Anido, R.A. (2020). Discrete-Event Simulation Thermal Model for Extrusion-Based Additive Manufacturing of PLA and ABS. Materials, 13, 4985
Polymers and Their Application in 3D Printing
Dear Colleagues, Fused filament fabrication, also known as 3D printing, is extensively used to produce prototypes for applications in, e.g., the aerospace, medical, and automotive industries. In this process, a thermoplastic polymer is fed into a liquefier that extrudes a filament while moving in successive X–Y planes along the Z direction to fabricate a 3D part in a layer-by-layer process. Due to the progressive advances of this process in industry, the application of polymeric (or even composite) materials have received much attention. Researchers and industries now engage in 3D printing by implementing numerous polymeric materials in their domain. In this Special Issue, we will present a collection of recent and novel works regarding the application of polymers in 3D printing
Free Form Extrusion : extrusion of 3D components using complex polymeric systems
Tese de doutoramento - Programa Doutoral em
Ciência e Engenharia de PolÃmeros e CompósitosFree Form Extrusion (FFE) is a 3D fabrication process that involves depositing an
extruded filament onto successive horizontal planes, in order to build a physic part with
a specific geometry. The method is an adaptation of Fused Deposition Modeling
(FDM), whereby a commercial pre-extruded ABS filament is replaced by a miniextruder
capable of processing a wide range of materials, including homopolymers,
polymer blends and nanocomposites.
The mechanical performance of FFE parts is controlled by the bonding quality between
adjacent filaments both in the horizontal and vertical plans. Adjacent filaments must be
sufficiently hot to ensure adhesion, but should then cool down fast enough to avoid
excessive deformation due to gravity and weight of the filaments on top. Therefore, it is
important to know the evolution in time of the filaments temperature and how it is
affected by the major process variables.
Although several heat transfer models have been proposed in literature, most assume
simplifications without verifying their effective importance. In this work, a detailed
analysis of the contributions to the global heat transfer was made using the ABAQUS®
software. Heat exchanges with ambient by convection and between adjacent filaments
by conduction were found to be the most important. Consequently, these were taken in
the energy balance, in order to obtain a rigorous FFE heat transfer analytical model.
This analytical solution was then embedded into a routine capable of considering three
different deposition patterns, for parts with specific geometries. Moreover, an adhesion
criterion was implemented, in order to predict whether the operating conditions and
deposition patterns selected for the manufacture of a given part are adequate. The
deformation of the filaments was investigated by performing computational experiments
with the ABAQUS® software, assuming a temperature dependent viscoelastic response.
Since the maximum differences were shown to be quite small (< 0.2%), this
phenomenon was considered negligible The consequence of this work is then a computer code that rigorously considers and
inter-relates the three phenomena, with the potential of assisting the FFE user in
selecting the ideal process parameters in order to obtain a part with good performance.
This also allows testing the influence of many process variables and concluding about
the most important.Free Form Extrusion (FFE) é um processo 3D de fabricação que envolve a deposição de
um filamento extrudido em planos horizontais sucessivos, por forma a obter uma peça
com uma geometria especÃfica. O método é uma adaptação do Fused Deposition
Modelling (FDM), através do qual um filamento de ABS comercial pré-extrudido é
substituÃdo por uma mini-extrusora com a capacidade de processar uma grande
variedade de materiais, incluindo homopolÃmeros, misturas de polÃmeros e
nanocompósitos.
O desempenho mecânico das peças obtidas através da técnica FFE é influenciado pela
qualidade de adesão entre filamentos adjacentes, nos planos horizontais bem como
verticais. Os filamentos adjacentes devem ser suficientemente quentes para assegurar a
adesão, mas ter um arrefecimento suficientemente rápido para evitar a deformação
excessiva devido à gravidade e ao peso dos filamentos posicionados nas camadas
superiores. Consequentemente, é importante o conhecimento da evolução da
temperatura dos filamentos em função do tempo, e como este é afetado pelas principais
variáveis do processo.
Apesar de vários modelos de transferência de calor terem sido propostos na literatura,
na maior parte, simplificações são assumidas sem verificar a sua efetiva importância.
Neste trabalho, uma análise detalhada dos intervenientes na transferência de calor foi
elaborada usando o software ABAQUS®. Trocas de calor com o ambiente por
convecção e entre filamentos adjacentes por condução mostraram ser os mais
importantes. Consequentemente, estes foram incluÃdos no balanço de energia, a fim de
obter um modelo analÃtico rigoroso de transferência de calor para o processo FFE.
Esta solução analÃtica foi então incorporada numa rotina com a capacidade de
considerar três tipos diferentes de deposição, para peças com geometrias especÃficas.
Além disso, um critério de adesão foi implementado, a fim de prever se as condições
operatórias e os tipos de deposição selecionados para a construção de uma dada peça
são adequados A deformação dos filamentos foi investigada através da realização de experiências com
o software computacional ABAQUS®, assumindo uma resposta viscoelástica
dependente da temperatura. Uma vez que as diferenças máximas mostraram ser muito
baixas (< 0.2%), este fenômeno foi considerado negligenciável.
A consequência deste trabalho é portanto um código computacional que considera
rigorosamente e inter-relaciona os três fenómenos, com a potencialidade de auxiliar o
utilizador do processo FFE na seleção ideal dos parâmetros de processo, a fim de obter
uma peça com bom desempenho. Também permite testar a influência de diversas
variáveis de processo e concluir quais são as mais importantes
Effect of the interface geometry on the structural integrity of the ceramic crown-tooth complex
The effect of the interface lute on the structural integrity of the tooth adhesively restored with an all-ceramic crown remains is an unknown parameter especially in relation to the interface geometry (thickness and uniformity).
Traditionally, the structural integrity of a restored tooth system (tooth-lute-crown) is tested by laboratory based mechanical testing. However, a more sophisticated FEA computer modelling seems to provide a non-destructive way of understanding the structural integrity of the system, which may complement mechanical testing
Bending control and stability of functionally graded dielectric elastomers
A rectangular plate of dielectric elastomer exhibiting gradients of material properties through its thickness will deform inhomogeneously when a potential difference is applied to compliant electrodes on its major surfaces, because each plane parallel to the major surfaces will expand or contract to a different extent. Here we study the voltage-induced bending response of a functionally graded dielectric plate on the basis of the nonlinear theory of electroelasticity, when both the elastic shear modulus and the electric permittivity change with the thickness coordinate. The theory is illustrated for a neo-Hookean electroelastic energy function with the shear modulus and permittivity varying linearly across the thickness. In general the bending angle increases with the potential difference, and this enables the material inhomogeneity to be tuned to control the bending shape. We derive the Hessian criterion that ensures stability of the bent configurations in respect of a general form of electroelastic constitutive law specialized for the considered geometry. This requires that the Hessian remains positive. For the considered model we show that the bent configuration is stable until the voltage reaches the value for which the cross section of the bent configuration forms a complete circle
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