Multilayer interlocked woven fabrics: simulation of RTM mold filling operation with preform permeability properties

The simulation of resin flow during the resin transfer molding (RTM) process through multilayered textile fabric of known permeability and porosity has been attempted in this study. A simple three-dimensional computational fluid dynamics (CFD) simulation model has been developed and the results of the simulation are compared with the experimental RTM resin flow through multilayer interlocked woven structures. A multiphase simulation model is observed to reasonably predict the time for RTM mold filling. Fabric structural influence in terms of an Interlacement Index (I) has significant influence on the resin flow behaviour of the multilayered preform. A higher I of the preform means a longer time to fill the mold in both the experimental and simulated results. Images of the simulated flow front has been compared with the experimental results and it is observed that not only the mold filling time, but also the area of resin flow in the multilayer perform, is influenced by a fabric structural factor, I.(undefined

Critical thickness in silicone thermosets

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005.Includes bibliographical references (leaves 147-151).Critical thickness effects are utilized to achieve high fracture toughness in brittle polymers. The postulate of critical thickness, which is: "Macroscopically brittle polymers deform in a ductile fashion below a critical dimension" is validated for silicone thermosets and polystyrene using novel "direct" methods by measuring failure strain in thin films. A discussion on polymer intrinsic deformation mechanisms is presented. Using these intrinsic deformation mechanisms as bases, it is argued that all polymers are ductile at the molecular level. Accordingly, it is suggested that polymer properties below a certain length scale (defined as critical thickness) are dominated by intrinsic deformation characteristics. Two analytical models have been developed which predict critical thickness based on the physical properties of the polymer. The first model is based on an energy criterion according to which crack initiation does not take place if the crack driving force is less than the crack resistance. Such a condition for a brittle polymer is achieved at the critical thickness. The second model is based on a mechanics criterion according to which a minimum film thickness (critical thickness) is required for typical fracture features like crazes to exist within it. Further, using these theoretical models as a basis, the effect of network density, temperature and strain rate on critical thickness is discussed. It is also shown that fracture strain is the characteristic material property to measure film toughness. A variety of silicone thermosets are studied to demonstrate engineering applicability of critical thickness.(cont.) The selected polymers include a commercial laminate poly-phenyl- methyl-silsesquioxane resin, an experimental high temperature poly-methyl- silsesquioxane resin and an optical polysiloxane resin. In addition to silicone thermosets, polystyrene is studied as a reference polymer. A bending technique has been developed in order to determine failure strain of thin films (on substrates) of these materials. Using this technique, the failure strain is evaluated as a function of film thickness. Further, from a plot of failure strain as a function of film thickness the critical thickness is determined. For polystyrene, a critical thickness value of approximately 0.1 um is observed. The strain to failure of polystyrene films below the critical thickness is >15%, a marked increase over bulk material fracture strain (-2%). For each of the silicone thermosets, a range of curing temperatures is investigated to determine the influence of curing temperature on critical thickness. For the poly-phenyl-methyl-silsesquioxane resin, the optimum thin film properties are observed when it is cured at 225 ⁰C. The critical thickness is observed to be -5 gm with a strain to failure of -13% (bulk strain to failure <2%). Molecular engineering of the poly-phenyl-methyl-silsesquioxane by modifying the chemical structure using functionalized PDMS is shown to increase critical thickness to 0lm. For this PDMS modified poly-phenyl-methyl-silsesquioxane, critical thickness values have been determined over a range of test temperatures from -40 ⁰C to 75 ⁰C. Results indicate that the test temperature does not influence the critical thickness. For the poly-methyl- silsesquioxane, the critical thickness is observed to be greater than 2.51um with a strain to failure of 15% when cured at 250 ⁰C.(cont.) Two optical polysiloxane resins are studied. The first resin, commercially called the PF-1202 resin is studied for a single cure temperature and is observed to have a critical thickness of -0.2-0.3um. The properties of the second resin, named MP-101, are studied for a range of cure temperatures. The best performance, with 8% strain to failure and a 0.5um critical thickness, is observed for a 50 ⁰C cure temperature. Infrared spectroscopy measurements in reflection mode are carried out to compare orientation effects in thin (below critical thickness) vis-A-vis thick (above critical thickness) films for polystyrene, poly-phenyl-methyl-silsesquioxane and PDMS modified poly-phenyl-methyl-silsesquioxane. It is observed that both the thick as well as thin films do not exhibit any substantial orientation. A correlation between molecular orientation and fracture properties cannot be made. Infrared spectroscopy has also been used to determine the "nature" of strain (elastic or plastic) these thin films (below critical thickness value) exhibit when stretched to values higher than their bulk counterparts.by Manish Deopura.Ph.D

Influence of preform interlacement on the low velocity impact behavior of multilayer textile composites

Impact property of composite material is influenced not only by the type of fiber/matrix, but also by the woven structure of the reinforcement. Presence of 3D fibers in reinforcement is reported to enhance the performance of textile composites in an impact event. This article attempts to study the influence of interlacements in the multilayer woven interlocked 3D structures on the impact properties of the composite material reinforced with them. Low velocity impact testing was carried out on an instrumented drop weight impact tester to obtain loadelongation- time plots of the impact event. It has been observed that increased interlacement in the structure improves the impact resistance of the multilayer textile composites. Further, damage area maps have been developed to understand and analyze the interlacement effect on the impact behavior

Compression and permeability properties of multiaxial warp-knit preforms

Textile preform properties such as compression and permeability greatly influence the quality of the composite material and its performance, particularly those prepared by injection moulding techniques like resin transfer moulding (RTM). Directionally oriented warp-knit biaxial, triaxial and quadraxial glass fabrics have been studied for these preform properties. The preform compression properties were tested on the universal testing machine up to a maximum force of 250 N. The rate of test liquid flow through these preforms has been measured using the horizontalwicking test method. The permeability of these preforms has been analyzed based on the liquid flow-rate data. Fibre orientation and fibre volume fraction of the preforms are observed to be important factors influencing these preform properties

Studies on preform properties of multilayer interlocked woven structures using fabric geometrical factors

Structure property correlation is a critical textile research area explored by various researchers and many factors have been proposed over the years to predict/compare/design the woven fabrics. Cross-over firmness factor (CFF) and floating yarn factor (FYF) have been recently proposed as parameters to understand weave effect on fabric properties (Morino, H., Matsudaira, M. and Furutani, M. (2005). Predicting Mechanical Properties and Hand Values from the Parameters of Weave Structures, Textile Research Journal, 75(3): 252—257). Redefined CFF and FYF factors using fabric fields in terms of interlacement index (I) and float index (F), respectively have been proposed in this article. This new approach provides better understanding of the interlacements and floats in the woven structure and further they are applied on multilayer interlocked fabrics to quantify the structural influence on the properties. Multilayer interlocked woven fabrics with different interlacement patterns have been developed. Influence of fabric structure on preform properties relevant for resin transfer molding composite manufacture, such as compression, permeability, and tensile behavior were studied with respect to the interlacement and float indices. Tensile and compression tests were conducted on universal testing machine. Liquid permeability of these structures was evaluated based on horizontal wicking and contact angle wettability tests. Results show that influence of structural factor is greater on tensile and permeability properties than the compression properties of these multilayer fabricsThis work has been conducted within the Asia-Link Programme RPO1736, project no IN/ASIA-LINK/002 (82158). The authors wish to thank the European Commission for awarding research programme under the EU Asia-link project to the University of Minho (Portugal) and Indian Institute of Technology-Delhi (New Delhi, India)

Tribological properties of the directionally oriented warp knit GFRP composites

Recently, directionally oriented warp knit structures have gained prominence as reinforcements in composite materials due to their superior isotropic behaviour compared to other types of textile reinforcements. In the present study, composites prepared from four types of directionally oriented warp knit glass preforms with three different thermoset resins have been considered for the tribological characterisation. The tribological tests have been conducted on a reciprocating sliding test rig with ball-on-plate configuration. The tests were conducted in dry (unlubricated) and wet (aqueous) conditions at a fixed applied load (100 N) by varying the sliding distance. E-glass warp knitted preforms were used for the study including biaxial, biaxial non-woven, triaxial and quadraxial fabrics. The matrices were three different thermoset resins namely polyester, vinyl ester and epoxy resin. 13 14 15 16 17 18 19 The main aim of the study was to identify a composite having the best tribological performance, with regard to types of preform and matrix resin. Moreover, the results obtained from the tests have been used to develop a wastage map for these composites, as a function of sliding distance and type of preform in order to have a clear understanding of the tribological process.Fundação para a Ciência e a Tecnologia (FCT

Soil-release behaviour of polyester fabrics after chemical modification with polyethylene glycol

The ease of cleaning the fibers depends, among other characteristics, on their hydrophilicity. Hydrophilic fibers are easy-wash materials but hydrophobic fibers are difficult to clean due to their higher water-repellent surfaces. This type of surfaces, like polyester (PET), produce an accumulation of electrostatic charges that adsorbs and retain dirt. Thus, the polyester soil-release properties can be increased by finishing processes that improve fiber hydrophilicity [1, 2]. In present study, PET fabric modification was described by using polyethylene glycol (PEG) and dimetilol dihidroxy ethylene urea chemically modified resin. Briefly, the modification process was carried out in two steps, one to hydrolyse the polyester and create hydroxyl and carboxylic acid groups on surface and the other to crosslink the PEG chains. The resulting materials were characterized by contact angle, DSC and FTIR- ATR methods. Additionally, the soil release behavior and mechanical properties of modified PET were evaluated. For the best process conditions, the resulted PET presented 0º contact angle, stain release grade of 5 and acceptable mechanical performance.Programme - COMPETE and by national funds through FCT – Foundation for Science and Technology within the scope of the project POCI-01-0145-FEDER-007136.info:eu-repo/semantics/publishedVersio

Structure-property relationships in structural glass fibre reinforced composites from unsaturated polyester and inherently fire retardant phenolic resin matrix blends

The effects of matrices from co-cured blends of an unsaturated polyester (UP) with inherently fire-retardant and char-forming phenolic resoles (PH) on the mechanical and fire performances of resultant glass fibre-reinforced composites have been investigated. Three different phenolic resoles with increasing order of compatibility with UP have been used. These are: (i) an ethanol soluble resin, (PH-S), (ii) an epoxy-functionalized resin (PH-Ep), and (iii) an allyl-functionalized resin (PH-Al). The mechanical properties of the composites increased with increasing compatibility with two resin types as might be expected, but not previously demonstrated. However, even with the least compatible resin (PH-S), the impact properties were unaffected and the flexural/tensile properties while reduced, were still acceptable for certain applications. Fire properties were however, in reverse order as previously observed in cast resin samples from these composites. Moreover, the reduction in flammability was less compared to those of the cast resin samples, reported previously, explained here based on the insulating effect of glass fibre reinforcement

Gradient Optics of subwavelength nanofilms

Propagation and tunneling of light through subwavelength photonic barriers, formed by dielectric layers with continuous spatial variations of dielectric susceptibility across the film are considered. Effects of giant heterogeneity-induced non-local dispersion, both normal and anomalous, are examined by means of a series of exact analytical solutions of Maxwell equations for gradient media. Generalized Fresnel formulae, visualizing a profound influence of gradient and curvature of dielectric susceptibility profiles on reflectance/transmittance of periodical photonic heterostructures are presented. Depending on the cutoff frequency of the barrier, governed by technologically managed spatial profile of its refractive index, propagation or tunneling of light through these barriers are examined. Nonattenuative transfer of EM energy by evanescent waves, tunneling through dielectric gradient barriers, characterized by real values of refractive index, decreasing in the depth of medium, is shown. Scaling of the obtained results for different spectral ranges of visible, IR and THz waves is illustrated. Potential of gradient optical structures for design of miniaturized filters, polarizers and frequency-selective interfaces of subwavelength thickness is considered