Thesis DESARROLLO DE UN MÉTODO NUMÉRICO DE HOMOGENEIZACIÓN PARA LA OBTENCIÓN DE PROPIEDADES MECÁNICAS DE PATRONES DE FABRICACIÓN POR MANUFACTURA ADITIVA. APLICACIÓN EN PRÓTESIS DE PIE ARTICULADO
Date
2018
Authors
MONTERO AGUILERA, PABLO ESTEBAN
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Abstract
La presente investigación se enfoca en definir las propiedades mecánicas de dos tipos de patrones de impresión producidos por el método de impresión por deposición de material fundido (FDM) fabricados por medio de la impresora tridimensional Zortrax M200, donde los patrones difieren en el grado de relleno con el cual son construidos. La importancia de estos reside en que corresponden a la estructura interna de los objetos que se elaboran mediante este tipo de impresión 3D.Para analizar esta problemática es necesario indicar que una vez que la pieza ha sido construida, su estructura se compone de láminas anisotrópicas [1], por lo que las propiedades mecánicas del producto final no son las mismas en distintas direcciones y, por ende, son distintas al del material base con el cual se construyen.La empresa TakeaHand utiliza esta técnica de manufactura en la construcción de los componentes de su prótesis transtibial, donde el material que emplean corresponde al ABS (Acrilonitrilo Butadieno Estireno). De allí la importancia de este trabajo, dado que los resultados pueden ser utilizados, en un estudio posterior, para evaluar el comportamiento de la prótesis sometida a un sistema de cargas correspondientes al ciclo de caminata del ser humano [2].Para caracterizar las propiedades mecánicas, que son el módulo de Young, módulo de Poisson y módulo de Corte, se propone una vía basada en las teorías de Elasticidad y Homogeneización.Determinada la morfología de los patrones de impresión, se decide simplificar el modelo, removiendo los contornos de los patrones, con lo cual se trabaja como si solo la estructura de estos se conformara de cuadrículas. Esto facilita el empleo de la teoría de Homogeneización, dado que permite tratar el patrón de impresión como un material heterogéneo periódico permitiendo identificar un volumen representativo elemental (VRE). A partir de la teoría de Elasticidad se determinan las condiciones de borde que se deben fijar sobre el VRE. Aquello se lleva a cabo mediante simulaciones numéricas por medio del software comercial de elementos finitos Ansys Workbench.Los datos derivados de la simulación son procesados para obtener las propiedades mecánicas. Para corroborar aquellos resultados numéricos, es necesario contrastar el valor de la constante ingenieril Ezz con aquella alcanzada teóricamente mediante la teoría de Mezclas, dado que esta última solo permite la obtención de dicha propiedad.A partir de allí, se confirma que la vía propuesta en esta investigación es apropiada, debido a la similitud del valor de Ezz entre el resultado numérico y teórico. Lo que conlleva a validar las demás propiedades mecánicas derivadas de las simulaciones.
The following research focuses on defining the mechanical properties of two kinds of printing patterns produced by the fused deposition modeling (FDM) printing method, fabricated through the M200 Zortrax three-dimensional printer, where patterns differ according to the degree of resin that was used to make them. The importance of these is that they belong in the internal structure of the objects that are elaborated through this 3D printing.In order to analyze this situation, it is necessary to indicate that, once the piece has been built, its structure is composed by anisotropic layers. Hence, the mechanical properties of the final product are not the same in different directions and, therefore, are different from the base material on which they are based.TakeHand Company uses this manufacturing technique in the construction of the components in their transtibial prosthesis, being the employed material ABS (Acrylonitrile Butadiene Styrene). Thus the importance of this work, given that the results can be used in later work to evaluate the behavior of the prosthesis under a load that corresponds to the human walking cycle.A procedure based on the theories of elasticity and homogenization is proposed to characterize the mechanical properties. They are Young’s modulus, Poisson’s ratio and Shear modulus.Once the morphology of the printing patterns has been determined, it is decided to simplify the model by removing the edges of the patterns and consequently making it possible to work as if the structure of these were composed of grids. This facilitates the employment of the homogenization theory, given that this latter allows us to treat the printing pattern as a heterogeneous periodical material which permits the identification of a representative volume element (RVE). The edge conditions that must be set on the RVE are determined thanks to the elasticity theory. This is done through numeric simulations via the finite elements software Ansys Workbench.The data derived from the simulation are processed to obtain the mechanical properties. To confirm those numeric results, it is necessary to contrast the value of engineering constant Ezz with the one theoretically reached through the blending theory (given that this latter only allows the obtaining of said property).From that point on, it is confirmed that the procedure proposed in this research is appropriate, due to the similarity of the Ezz value between the numerical and theoretical result. This leads to the validation of all the other mechanical properties derived from the simulations.
The following research focuses on defining the mechanical properties of two kinds of printing patterns produced by the fused deposition modeling (FDM) printing method, fabricated through the M200 Zortrax three-dimensional printer, where patterns differ according to the degree of resin that was used to make them. The importance of these is that they belong in the internal structure of the objects that are elaborated through this 3D printing.In order to analyze this situation, it is necessary to indicate that, once the piece has been built, its structure is composed by anisotropic layers. Hence, the mechanical properties of the final product are not the same in different directions and, therefore, are different from the base material on which they are based.TakeHand Company uses this manufacturing technique in the construction of the components in their transtibial prosthesis, being the employed material ABS (Acrylonitrile Butadiene Styrene). Thus the importance of this work, given that the results can be used in later work to evaluate the behavior of the prosthesis under a load that corresponds to the human walking cycle.A procedure based on the theories of elasticity and homogenization is proposed to characterize the mechanical properties. They are Young’s modulus, Poisson’s ratio and Shear modulus.Once the morphology of the printing patterns has been determined, it is decided to simplify the model by removing the edges of the patterns and consequently making it possible to work as if the structure of these were composed of grids. This facilitates the employment of the homogenization theory, given that this latter allows us to treat the printing pattern as a heterogeneous periodical material which permits the identification of a representative volume element (RVE). The edge conditions that must be set on the RVE are determined thanks to the elasticity theory. This is done through numeric simulations via the finite elements software Ansys Workbench.The data derived from the simulation are processed to obtain the mechanical properties. To confirm those numeric results, it is necessary to contrast the value of engineering constant Ezz with the one theoretically reached through the blending theory (given that this latter only allows the obtaining of said property).From that point on, it is confirmed that the procedure proposed in this research is appropriate, due to the similarity of the Ezz value between the numerical and theoretical result. This leads to the validation of all the other mechanical properties derived from the simulations.
Description
Catalogado desde la version PDF de la tesis.
Keywords
IMPRESION 3D , MANUFACTURA ADITIVA , PROPIEDADES MECANICAS , SIMULACION NUMERICA , TEORIA DE ELASTICIDAD , TEORIA DE HOMOGENEIZACION