If the average is referred to the fluid phase volume of the REV, the following nomenclature is used: when it is taken the value of the property, N, in all phases and it is averaged regarding to the fluid phases volume, and when the value is taken only in the fluid phases and then averaged regarding to the same fluid phases. In porous media all properties are given in terms of averages in a Representative Element Volume (REV). The most known form of Darcys law in one direction, equation 1, can be described as : This property was initially studied experimentally in 1855 by French engineer Henry Darcy, who measured the water volume (Q) that crossed by time unit, through a saturated column of sand of length (L) and cross sectional area (A), when a difference of hydrostatic pressure (H) was applied between two points. Permeability can be defined as the easiness of a liquid to flow through porous media. In general, as is higher and/or the size of gaps between tows is smaller, the behavior of the preform tends to be like a single-scale preform, contrary to what happen when is lower and/or the size of gaps is greater, where the preform behaves like a dual scale preform and the differences between the micro-flow (flow inside the yarns) and the macro-flow (flow in the gaps) could be notorious. In double scale preforms, there are some circumstances where that difference could be significant, depending on many factors, such as the fiber volume fraction and the size of the bundles. Single scale preforms are the ones in which the difference among the permeability inside the bundles (micro-permeability) and the permeability in the gaps (macro-permeability) is not relevant in any situation. In general terms, the reinforced preforms used in LCM processes can be classified into single scale preforms and dual scale preforms ( Figure 1). ![]() The fibrous reinforced preforms have many types of geometrical configurations and its architecture is the main variable affecting the permeability. The most common preforms used in LCM are composed of inorganic materials, such as glass, carbon and aramid. The term fibrous reinforced preform is referred to the part of the composite material that provides mechanical resistance and stiffness, and that is impregnated by the resin when a LCM process is employed for the manufacturing of the part. ![]() Palabras Clave:Permeabilidad, preformas reforzantes,medición de permeabilidad, moldeo líquido de compuestos El presente artículo realiza una revisión y análisis de las diferentes técnicas establecidas para determinar la permeabilidad de preformas reforzantes, con el fin de presentar una referencia para posteriores estudios e investigaciones en el campo de la simulación y procesamiento de resinas reforzadas con preformas. Es importante conocer los diferentes métodos de medición de permeabilidad, sus alcances, ventajas y desventajas, ya que en algunos casos se pueden inducir errores considerables en la medición, por lo que es adecuado realizar una validación entre los métodos experimentales y teóricos. Esta variable determina, en el caso de procesos de moldeo líquido de compuestos (Liquid Composites Molding, LCM por sus siglas en Ingles), el patrón de llenado de moldes. La permeabilidad es la propiedad que determina la facilidad con la que un líquido fluye a través de un medio poroso. Keywords:Permeability, preforms, permeability measurements, liquid composite molding The review was done in order to provide a reference for future study and research in the field of processing and simulation of liquid composites molding reinforced with preforms. In this work, a review about different techniques used in the literature to determine the permeability of reinforcement materials was done. Therefore it is important to compare theoretical methods by experimental measurements. ![]() It is important to know the different methods used to measure permeability (scopes, advantages and disadvantages) since in some cases it is possible to obtain significant errors during the measurements. This property defines how a mold is filled in Liquid Composite Molding (LCM). Permeability is a property used to measure how a liquid flows through porous media. *Autor de correspondencia: teléfono:+ 574 4600727 ext. Campus Robledo, Portería Principal: Calle 73 No 76A - 354 Vía al Volador. Grupos Materiales Avanzados y Energía, MATyER, Instituto Tecnológico Metropolitano. Iván Patiño, Carlos Vargas*, Juan Vanegas Métodos para determinar la permeabilidad de preformas reforzantes fibrosas Methods for permeability measurements of fibrous reinforced preforms
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