No abstract

A fragmentation model based on global load sharing (GLS) theory is developed to obtain stress-strain curves that describe the mechanical behavior of unidirectional composites. The model is named + * because it is based on the Critical Number of Breaks model (CNB) and on the correction of the fiber matrix interfacial strength, *. Model allows both obtaining the ultimate tensile strength of CFRP and GFRP composites, and correcting the vs curve to match its peak point with the predicted strength, which is more accurate than the one obtained by previous GLS-based models. Our model is used to classify the mechanical response of the material according to the energetic contributions of two phenomena up to the failure: intact fibers (IF) and fragmentation (FM). Additionally, the influence of fiber content, , on the tensile strength, , failure strain, , and total strain energy, , is analyzed by means of novel mechanical-performance maps obtained by the model. The maps show a dissimilar behavior of , and with between GFRP and CFRP composites. The low influence of on the percent energetic contributions of IF and FM zones, as well as the larger energetic contribution of the FM zone, are common conclusions that can be addressed for both kinds of composites.

The main advances in the modeling and simulation of the filling phenomenon that takes place in dual-scale fibrous reinforcements used in liquid composites molding processes are grouped and classified in the present work. Special emphasis is done in the classification of the simulation methods according to the dimension of the mesh, the identification of the interface conditions porous medium-free fluid, the comparison between the most used fluid-front tracking techniques and the survey of researches dealing with the non-uniform filling of representative unitary cells, which in turn is responsible for the void formation at mesoscopic scale and the sink effect at macroscopic scale. As an original contribution to this field of study, a new methodology to quantify the sink effect in macroscopic fillings is presented and subsequently assessed by comparing the results of experimental radial injections with numerical results obtained by the dual reciprocity-boundary element method. The proposed methodology is physically consistent and leads to results that are closer to the experimental ones than the results obtained when the sink effect is neglected; however, the accuracy is liable to be improved.

High performance composites are exposed to severe loading and environmental conditions. In this work, mechanical properties of Fiberglass Reinforced Polyester (FRP) manufactured by resin transfer molding were evaluated. The effect of the strain rate on mechanical properties under three quasi-static testing conditions, four fiber contents and several orientations was studied using instrumented tensile tests. A model was fitted to predict Tensile strength, Young's modulus and shear modulus and the failed samples were analyzed to understand the failure mechanisms. The results showed that the fitted model is reliable enough to conclude about the effect of the fiber volume fraction and the strain rate on the mechanical properties. Young's modulus and tensile strength increased when the strain rate is higher. Tensile strength also increased with fiber content (Vf) up to 41%. The predominant failure mechanism is fiber rupture for the main directions and for the off-axis directions, the failure mechanisms are fiber pullout and delamination.

Los vacíos por atrapamiento mecánico se constituyen en unos de los tipos de defectos más comunes en el procesado de Composites por moldeo líquido. Debido a la gran influencia que tienen estos vacíos en el desempeño de la pieza final, una cantidad considerable de investigaciones se han centrado en el estudio de los mecanismos de formación de los mismos, de la influencia que éstos tienen en las propiedades mecánicas del compuesto y de las estrategias para su reducción durante el procesado. El presente trabajo pretende realizar una revisión de algunas investigaciones relevantes que se han hecho en el tema de vacíos formados por atrapamiento mecánico de aire en el procesado de compuestos por LCM (Moldeo Líquido de Composites, por sus siglas en inglés), con el objetivo de generar un material de referencia dirigido a investigadores interesados en esta importante temática relacionada con las áreas del procesado y comportamiento mecánico de materiales compuestos. Serán abordados temas como: el mecanismo de formación por desbalance entre macroflujo y microflujo, y su relación con el número capilar modificado y el efecto de sumidero; los fenómenos de compresibilidad, disolución y movimiento de burbujas en preformas de doble escala; la influencia de los vacíos en las propiedades mecánicas del composite y en los mecanismos de daño; y las estrategias más comunes que pueden ser implementadas a nivel industrial para la reducción de este tipo de defectología.