Numerical Method to Predict Void Formation during The Liquid Composite Molding Process

Void formation during the injection phase of the liquid composite molding process can be explained as a consequence of the non-uniformity of the flow front progression. This is due to the dual porosity within the fiber perform (spacing between the fiber tows is much larger than between the fibers within in a tow) and therefore the best explanation can be provided by a mesolevel analysis, where the characteristic dimension is given by the fiber tow diameter of the order of millimeters. In mesolevel analysis, liquid impregnation along two different scales; inside fiber tows and within the open spaces between the fiber tows must be considered and the coupling between the flow regimes must be addressed. In such cases, it is extremely important to account correctly for the surface tension effects, which can be modeled as capillary pressure applied at the flow front. Numerical implementation of such boundary conditions leads to illposing of the problem, in terms of the weak classical as well as stabilized formulation. As a consequence, there is an error in mass conservation accumulated especially along the free flow front. A numerical procedure was formulated and is implemented in an existing Free Boundary Program to reduce this error significantly

Mass Conservation Enhancement of Free Boundary Mesolevel Flows during LCM Processes of Composites Manufacturing

Undesirable void formation during the injection phase of the liquid composite moulding process can be understood as a consequence of the non-uniformity of the flow front progression, caused by the dual porosity of the fibre perform. Therefore the best examination of the void formation physics can be provided by a mesolevel analysis, where the characteristic dimension is given by the fibre tow diameter. In mesolevel analysis, liquid impregnation along two different scales; inside fibre tows and within the open spaces between them; must be considered and the coupling between these flow regimes must be addressed. In such case, it is extremely important to account correctly for the surface tension effects, which can be modelled as capillary pressure applied at the flow front. Numerical implementation of such boundary conditions leads to ill-posing of the problem, in terms of the weak classical as well as stabilized formulation. As a consequence, there is an error in mass conservation accumulated especially along the free flow front. This contribution presents a numerical procedure, which was formulated and implemented in the existing Free Boundary Program in order to significantly reduce this error

Novel epoxy powder for manufacturing thick-section composite parts under vacuum-bag-only conditions. Part I: Through-thickness process modelling

Thick-section composite parts are difficult to manufacture using thermosetting resins due to their exothermic curing reaction. If processing is not carefully controlled, the build-up of heat can lead to warpage or material degradation. This risk can be reduced or removed with the use of a low-exotherm resin system. Material and process models are presented which describe vacuum-bag-only processing of thick-section composites using a novel, low-exotherm epoxy powder. One-dimensional resin flow and heat transfer models are presented which govern the fabric impregnation and temperature evolution, respectively. A semi-empirical equation is presented which describes the sintering of the epoxy powder. The models are coupled via laminate thickness change, which is determined for a simplified ply microstructure. The resulting system of equations are discretised and solved numerically using a finite difference code. A case study is performed on a 100-ply laminate, and the advantages and disadvantages of using epoxy powders are discussed

Fuel Cell Research at the University of Delaware

The grant initiated nine basic and applied research projects to improve fundamental understanding and performance of the proton exchange membrane (PEM) fuel cells, to explore innovative methods for hydrogen production and storage, and to address the critical issues and barriers to commercialization. The focus was on catalysis, hydrogen production and storage, membrane durability and flow modeling and characterization of Gas Diffusion Media. Three different types of equipment were purchase with this grant to provide testing and characterization infrastructure for fuel cell research and to provide undergraduate and graduate students with the opportunity to study fuel cell membrane design and operation. They are (i) Arbin Hydrogen cell testing station, (ii) MTS AllianceâÃÂâ RT/5 material testing system with an ESPEC custom-designed environmental chamber for membrane Durability Testing and (iii) Chemisorption for surface area measurements of electrocatalysts. The research team included ten faculty members who addressed various issues that pertain to Fuel Cells, Hydrogen Production and Storage, Fuel Cell transport mechanisms. Nine research tasks were conducted to address the critical issues and various barriers to commercialization of Fuel Cells. These research tasks are subdivided in the general areas of (i) Alternative electrocatalysis (ii) Fuel Processing and Hydrogen Storage and (iii) Modeling and Characterization of Membranes as applied to Fuel Cells research.. The summary of accomplishments and approaches for each of the tasks is presented belo

Demonstration of cellular immunity in chronic myeloid leukaemia using leucocyte migration inhibition assay.

Peripheral blood leucocytes from chronic myeloid leukaemia patients in remission were tested for inhibition of migration in presence of solubilized membrane antigens from leukaemic cells in 15 cases. Eight out of 9 autochthonous combinations (88-8%) and 35/49 allogenic combinations (71-4%) showed inhibition of migration. Antigens prepared from relapse leukaemic cell samples in 4 cases showed inhibition of migration of autochthonous as well as allogeneic remission leucocytes. The same batch of CML antigens inhibited migration of normal leucocytes at the level of 22-2%. The difference between inhibition of migration shown by remission leucocytes and normal leucocytes in presence of CML antigens was statistically significant. Solubilized antigens, similarly prepared from normal leucocytes, showed inhibition of migration of remission leucocytes to the extent of 15% only. The difference between the reactivity of CML remission leucocytes to normal and CML antigens was also statistically significant. No enhancement of migration of remission leucocytes was seen with CML antigens

Método Numérico de Predição de Formação dos Vazios durante os Processos de Fabrico de Moldação Líquida

Apresenta-se simulação do escoamento de resina durante a fase de enchimento do processo de fabrico de moldação líquida. Nesta modelação não se pode desprezar a influência da tensão de superfície que corresponde a introdução da pressão capilar aplicada na fronteira livre. Esta condição de fronteira torna o problema mal posto quer em termos da formulação fraca clássica, quer estabilizada, e em consequência existe um error na conservação local de massa de resina, acumulado especialmente ao longo da fronteira livre. Apresenta-se uma metodologia numérica, que permite significativamente diminuir este error, e que no caso de escoamento de Stoke ainda não foi publicada. Esta metodologia está implementada no Programa de Fronteira Livre (PFL), apresentado em [1-4]