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.

En este artículo se analizan tres tipos de resinas poliéster in-saturado comerciales de amplio uso en el mercado nacional y se evalúa su conveniencia de uso en procesos de transferencia de resina en molde cerrado (RTM), de acuerdo con criterios de visco-sidad y reactividad. Se compara la viscosidad de las resinas entre 15 y 50°C, así como la reactividad mediante curvas de curado a temperatura ambiente, con porcentajes de catalizador del 1, 1.5 y 2%. De acuerdo con los resultados se determinó que algunas de las resinas son susceptibles de uso en procesos RTM, por su apropiada viscosidad, estabilidad en la reactividad y su velocidad de curado. Estas características son de gran importancia al momento de seleccionar las resinas poliéster insaturado, de acuerdo con las condiciones del proceso en molde cerrado.

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.

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Some fibrous reinforcements used in the manufacturing of parts by Liquid Composite Molding (LCM) have a dual-scale nature, which supposes flow imbalances between the tows and channels at mesoscopic scale, which in turn, cause uncontrolled defects (voids, dry points, among others) and could considerably affect the global flow behavior during the filling of cavities at macroscopic scale. In the present work, a new approach to conduct filling simulations of dual-scale fibrous reinforcements at mesoscopic scale is proposed. This consists of prescribing a pressure gradient along the Representative Unitary Cell, and imposing Stokes-Darcy matching conditions between the tows and the channel sub-domains to determine the filling of the former ones. Contrarily to the traditional approach, where a uniform pressure is assumed for the channels and only the porous media fluid is modeled, the present one allows considering the fluid pressure gradient at channels (fluid motion), air compressibility and dissolution, flow-direction dependent capillary pressure, and vacuum pressure, as well as capturing several phenomena involved in the dynamic evolution of intra-tow voids, namely, compression, mobilization at constant volume and migration from tows towards channel. The velocity vectors and streamlines in the tows and channel subdomains, when these phenomena take place, are analyzed as well.

A numerical fragmentation model is proposed to predict the mechanical response of intermingled, unidirectional hybrid composites under tensile loads. The model is based on a previously developed for unidirectional composites considering the critical number of fiber breaks and the correction of the fiber-matrix interfacial strength. Hybrids comprising two reinforcements are considered, and the energetic contribution of reinforcements is evaluated during the damage process. Additionally, the pseudo-ductile strain, yield strength, and the level of degradation of each reinforcement are estimated. The present model is compared with a progressive failure model and micromechanical finite element simulations, obtaining some similarities in the stress-strain behavior.  Results show that both low elongation and high elongation fiber sub-composite experience a linear tensile response where fibers remain intact (IF), and fragmentation (FM) where breaking appears. The sliding/separation phenomenon (SS) occurs in one of the sub-composites when crack saturation is obtained, and failure occurs when the other one undergoes the crack saturation. Results also show that the IF, FM, and SS phenomena are conditioned by the fiber mixing ratio, α. The model allows estimating the optimal value of α for which the highest pseudo-ductile strain and hybrid effect are reached.