Liquid Moulding Research Articles

Simulation of mono-ply and multi-ply woven composite reinforcements forming

The numerical simulation of composite forming permits to envisage the feasibility of a process without defect but also to know the directions of the reinforcements after shaping. These directions condition strongly the mechanical behaviour of the final textile composite structure. In addition, the angles between warp and weft yarns influence the permeability of the reinforcement and thus the filling of the resin in the case of a liquid moulding process. The forming of composite reinforcement can be made on a single ply or simultaneously on several plies. In this paper the different approaches for the textile reinforcement forming simulation are described. A three node element with arbitrary directions of the yarns with regard to the element sides is presented and used for the simultaneous hemispherical forming of three layers.

Simulation of mono-ply and multi-ply woven composite reinforcements forming

The numerical simulation of composite forming permits to envisage the feasibility of a process without defect but also to know the directions of the reinforcements after shaping. These directions condition strongly the mechanical behaviour of the final textile composite structure. In addition, the angles between warp and weft yarns influence the permeability of the reinforcement and thus the filling of the resin in the case of a liquid moulding process. The forming of composite reinforcement can be made on a single ply or simultaneously on several plies. In this paper the different approaches for the textile reinforcement forming simulation are described. A three node element with arbitrary directions of the yarns with regard to the element sides is presented and used for the simultaneous hemispherical forming of three layers.

The Effect of Lactobacillus buchneri 40788 on the Fermentation and Aerobic Stability of Ground and Whole High-Moisture Corn

Experiments were conducted to evaluate the effects of inoculating high-moisture corn (HMC) with Lactobacillus buchneri40788 on silage fermentation and aerobic stability. In the first experiment, HMC (73% DM) was ground and treated with nothing, L. buchneri40788 to achieve 6.6×105 cfu/g of HMC (LB), a mixture of enzymes (ENZ), LB + ENZ, or 0.1% (wet weight basis) of a liquid mold inhibitor and was ensiled in 20-L bucket silos for 90 d. Treatments with LB and LB + ENZ increased the concentrations of acetic acid and improved the aerobic stability of ground HMC relative to other treatments. Treatment ENZ had no effect on the chemical composition or aerobic stability of ground HMC. The only effect of the liquid mold inhibitor relative to untreated HMC was that it increased the concentration of propionic acid, but this did not improve its aerobic stability. In a second experiment, HMC (75% DM) was harvested as the intact, whole grain and treated with nothing, L. buchneri40788 to achieve 4×105 cfu/g of HMC, L. buchneri40788 to achieve 6×105 cfu/g of HMC, or L. buchneri40788 to achieve 8×105 cfu/g of HMC and ensiled for 120 d. Treatments with L. buchneri40788 resulted in whole HMC with lower concentrations of water-soluble carbohydrates; higher concentrations of lactic, acetic, and propionic acids; and greater numbers of lactic acid bacteria but fewer molds when compared with untreated corn. As a group, inoculated silages were more aerobically stable than untreated silage, but increasing levels of application did not further improve the response. These experiments showed that addition of L. buchneri40788, but not addition of an enzyme mixture or a liquid mold inhibitor, improved the aerobic stability of ground and whole HMC harvested between 73 and 75% DM.

Permeability of stitched preform packages

To obtain useful flow simulations to support mould design, it is necessary to use accurate permeability values. In the work described here, the permeability of carbon fibre preforms with and without stitches was measured. A preform is a multilayer package of material ready to be impregnated using liquid transfer moulding technology. The main parameters which vary in the preforms are the stitching pattern, meaning the distance between the stitch rows through the preform, the stitching thread tension and the stacking sequence of the layers. The permeability measurements were carried out using a continuous, two-dimensional radial-flow measurement technique. The measuring device consists of an aluminium mould with integrated dielectric sensors (surface treated to prevent short circuit). The sensor system relies on the change in the dielectric properties of the material as saturation takes place. The results showed that stitching has a positive influence on the permeability. The stacking sequence was found to be the most effective way to influence permeability.

Optimization of Liquid Molding Cycle for a Phenylethynyl Terminated Polyimide Composite

This article presents a robust resin transfer molding (RTM) process window of a phenylethynyl terminated imide (PETI) oligomer with melt viscosity lower than 1 Pa s over 15 min and 10 Pa s for 2 h at 280 C. Curing occurs rapidly only above 350 C. Curing should be over 30 min at 370 C. Molding optimization reduces the melt viscosity. The oligomer is heated rapidly from 265 to 280 C for the minimum viscosity being lower. The melt is further heated for easier flow in injection and early permeation. The mechanical properties of the prepared composite remain almost constant up to 280 C, facilitating the fabrication of large, complex, high-quality aerospace parts.

Resin transfer moulding of anionically polymerised polyamide 12

Liquid composite moulding of Lactam 12 monomer and activating system (APLC12) into satin weave carbon fabrics is investigated, with emphasis on minimising the void content in the final part. The main sources for void formation are identified. The solidification shrinkage is quantified to account for at most 9% in the matrix. Optimal flow conditions are determined to minimize void content during liquid moulding. Finally, as the monomer is kept under Nitrogen prior to processing, diffusion and solubility of Nitrogen in the monomer are characterized, to indicate that Nitrogen coalescence during injection is a major cause of voids in the final part. The average void content is reduced from initially 15% to below 1% in polyamide 12 based composite plates with optimised process conditions.

Low Dimensional Particle Patterning

We developed novel processes to fabricate micro‐patterns of particle assembly by the use of capillary force in the drying process of colloidal solution. Liquid mold method was developed to fabricate particle wires through self‐assembly on hydrophilic regions of self‐assembled monolayers (SAMs). Ethanol or water containing particles was dropped onto a patterned SAM which has hydrophobic regions and hydrophilic regions. The solution was separated into two droplets with a liquid bridge between the droplets along the hydrophilic regions of a patterned SAM. The droplets and the liquid bridge were used as a mold for fabrication of a two‐dimensional pattern of colloid crystals. Particle wire was formed between two droplets and colloid crystals such as an opal structure were formed at both ends of the particle wire after drying the solution. The particle wires constructed from a close‐packed structure or non‐close‐packed structure, i.e., square lattice, were fabricated through self‐assembly at room temperature by using this method. Furthermore, we developed a self‐assembly process to fabricate an orderly array of particle wires constructed from a close‐packed structure from colloidal solution without preparation of patterned templates. A substrate was immersed into the solution containing particles perpendicular to the liquid surface and the liquid surface was moved downward by evaporation of solution. Particles formed a mono/multi‐particle layer and the particle layer was cut by the periodic drop‐off of the solution. This process allowed us to fabricate the orderly array of particle wires and to show the high ability of the self‐assembly process for fabrication of nano/micro‐structures constructed from nano/micro‐particles or blocks.

Effect of Crystallinity on Thermal Diffusivities of Mould Fluxes for the Continuous Casting of Steels

The thermal diffusivities of mould flux having the glassy and crystalline states were measured as a function of temperature by the laser flash method to obtain the relationship between the thermal diffusivity and the degree of crystallization. The thermal diffusivities of the liquid mould flux were also measured to compare the data with those of the solid samples. The thermal diffusivity increases roughly linearly with an increase in the degree of crystallization. The thermal diffusivities of glassy and liquid samples having the ratios of NBO/T=1.48, 1.65 and 2.11 exhibit roughly the same values of 4.6×10−7 m2 s−1 and 4.0×10−7 m2 s−1, respectively. It is considered that because the silicate network is largely broken down, there is not a significant change of the structure for these samples.

Foam Core Deformation During Liquid Molding of Sandwich Structures: Modeling and Experimental Analysis

The rapid manufacturing of composite parts by liquid molding containing foam cores introduces potential processing issues that could lead to degradation in part quality and performance. This paper addresses the key issue of the flow-induced foam core deformation and its effect on the molding pressure. A set of molding experiments are carried out to investigate mechanisms linked to the foam core and fabric deformation during the filling stage. A simplified two-dimensional model is proposed to predict the pressure evolution resulting from the combined deformation of foam core and the fabrics. Computed results show reasonable agreement with the experimental results.

Two-Dimensional Self-Assembly of Spherical Particles Using a Liquid Mold and Its Drying Process

We developed a novel process to fabricate particle wires through self-assembly on hydrophilic regions of SAMs (self-assembled monolayer). A SAM of octadecyltrichlorosilane was formed on a silicon substrate and modified by UV irradiation to create a pattern of hydrophobic octadecyl and hydrophilic silanol groups. Ethanol or water containing particles (550 or 800 nm diameter) were dropped onto a patterned SAM. The solution was separated into two droplets with a liquid bridge between the droplets along the hydrophilic regions of a patterned SAM. The droplets and the liquid bridge were used as a mold for fabrication of a two-dimensional pattern of colloid crystals. Particle wire was formed between two droplets and colloid crystals such as an opal structure were formed at both ends of the particle wire after drying the solution. The particle wires constructed from a close-packed structure or non-close-packed structure, i.e., square lattice, were fabricated through self-assembly at room temperature using this method.

Preliminary study on cost optimisation of aircraft composite structures applicable to liquid moulding technologies

This paper details the initial development of a method for determining the associated recurring labour costs for the manufacture of a aircraft component that will form the basis for a computerised methodology for determining the optimum manufacturing method for a component design. The research focuses on the flow of process steps to manufacture an aircraft component for the vacuum-assisted resin transfer moulding and resin transfer moulding manufacturing process. The methodology developed is based on applying MIT cost equations to process steps from which cost variables and constants are established to represent an estimated costing of the aircraft structure. This research will assist in providing a swifter and more accurate conceptual design/manufacturing system that includes an analysis of cost and will assist the production of trade studies that consider the manufacture of aircraft components using cost-effective technologies, such as liquid moulding.

液体の界面張力を利用したプラスチックの光成形 球面体成形の試み

In this paper, spherical surface molding of polymer using a liquid mold system is described. A liquid droplet has spherical surfaces at the liquid-liquid interface due to interfacial tension. The curvature of the spherical surface is determined by the degree of interfacial tension applied at each interface. Interfacial tension between some liquids was measured, and the shape of a photopolymer droplet between the liquids was calculated. Ultraviolet light was irradiated onto a photopolymer droplet located at the liquid-liquid interface, using a superhigh-pressure mercury lamp. Photopolymer droplets solidified and lens-shaped objects were produced. Cross sections of these objects were observed, and the curvatures of the spherical sufaces were found to correlate with the interfacial tension. A spherical solid was formed at a water/salt solution interface. The possibility of forming various spherical surfaces by exploiting liquid-liquid interfaces was revealed.

Process modelling for liquid moulding of braided preforms

Prediction of the fibre architecture within reinforcement preforms is required to model subsequent processing and performance characteristics. In recent years, a number of studies has been published in which forming or draping of fabric reinforcements has been examined, and links between draping and subsequent processing and mechanical properties have been established. Similar work on 2D braiding is limited, with existing models restricted to cylindrical geometries or surfaces of revolution. This paper presents a model for the braiding of a general mandrel cross-section, which is composed of a number of flat facets. A relatively simple geometric procedure is used, based on the paths of key braid tows that bound each flat facet. Locking or jamming of the braid is accounted for by considering the effects of tow spacing and braid angle on the fibre architecture. Experimental results are presented for a range of geometries to demonstrate the validity of the model, including a range of rectangular mandrels and a prototype automotive component. In all cases agreement is reasonably good, given the appropriate locking angle. The consequences of variations in fibre architecture on subsequent flow are demonstrated. The relationship between ply angle and the principal permeabilities is shown to be different from that observed for woven fabric reinforcements. At low braid angles, flow within the large inter-tow spacings appears to dominate the measured permeability. Finally the effect of fibre architecture on the subsequent eprocessing is demonstrated using a PC-based flow model. This demonstrates that the associated variations in permeability and porosity may result in a non-uniform flow pattern during liquid moulding.

Oil Bleeding Behaviour of Self-Lubricating Liquid Silicone Rubbers

The term liquid silicone rubber (LSR) covers a whole range of two-pack, heat-curing products, which may be processed using liquid injection moulding (LIM), a technique similar to thermoplastic injection moulding. Although this product group only accounts for about one thousandth of the world rubber market (corresponding to approximately 18 000 t/a) and is therefore a speciality rubber (ref. 1), due to their excellent properties, such as thermal stability, low-temperature flexibility, constantly good mechanical properties over a wide temperature range and good physiological compatibility to name but a few, products made of LSR are used in a wide variety of applications in many different fields. The most important fields of application include household appliances and the food industry, electronics and electrical engineering, sports and leisure activities and the automotive and aerospace industries (ref. 2). As a result of their low-temperature flexibility and heat stability, silicone rubbers are used for numerous applications in the automotive sector. Examples include spark-plug socket jackets, radiator seals, exhaust mountings, O-rings, seals and membranes. Nowadays, it is standard practice to use weather packs made of special silicone rubbers to which has been added a silicone oil incompatible with rubber and which exudes slowly after the product has cured for sealing cable connectors for wiring harnesses.

Mold Filling Simulation of Sandwich Composite Structures Manufactured by Liquid Molding: A Parametric Study

The mold filling stage in the manufacturing of sandwich composite structures with fiber reinforced foam core was studied with numerical simulations. Three different geometries of sandwich core reinforcement were considered in the form of fiber layers forming angles of 450 or 900 with the facings or in the form of equally spaced separate strands (webs). The influence of variable core and face reinforcement permeability and location of the injecting edge on the flow front progression and filling time was explored. The results suggest that permeability of the core has a significant influence on filling pattern and mold filling time. Experimental and predicted flow front developments and flow rates for a radial injection case under constant pressure were compared.

Mold Filling Simulation of Sandwich Composite Structures Manufactured by Liquid Molding: A Parametric Study

Mold Filling Simulation of Sandwich Composite Structures Manufactured by Liquid Molding: A Parametric Study

Physical and biocompatibility properties of poly- ε-caprolactone produced using in situ polymerisation: a novel manufacturing technique for long-fibre composite materials

Preliminary investigations into a novel process for the production of poly- ε-caprolactone (PCL) to be used as a matrix material in a bioabsorbable composite material are detailed. This material is primarily being developed as a bone substitute for use in maxillofacial reconstructive surgery, however, the technique described could be adapted to other areas where bioabsorbable composite materials may be used. The development of a totally bioabsorbable long-fibre composite material would allow a two-stage degradation to occur with the matrix material degrading first leaving a scaffold structure of degradable fibres which would be absorbed at a later stage. Caprolactone monomer was polymerised in situ within a tool cavity to produce a net shape moulding. Inclusion of a fibre preform within the tool cavity which was impregnated by the liquid monomer produces a long-fibre composite material. PCL with a range of molecular weights has been produced using this liquid moulding technique to assess the physical and biocompatibility properties compared to commercially available PCL. Osteoblast-like cells derived from human craniofacial bone (CFC) have been used to assess the in vitro biocompatibility of the PCL. The results show that high-quality PCL with a narrow molecular weight distribution and properties similar to commercially available PCL can be produced using this technique. Polymerisation of the monomer around a woven fibre preform made of a poly(lactic acid) (PLA)/poly(glycolic acid) (PGA) copolymer (vicryl mesh) produced a bioabsorbable long-fibre composite material. Further work is ongoing to develop this system towards a method for improving craniofacial bone reconstruction.

Solidification process and characterisation of a mass–gravity foundry ingot

The first step in the processing of metals is often a liquid moulding operation. Numerous defects can appear, which depend on the material, the process conditions and the thermal parameters and it is very important to know how they can evolve in order to obtain finally more homogeneous and defect-free ingot. In this study, the authors have looked at a special alloy of uranium, containing 6% of niobium. The casting operation is made up of different steps: melting of the metals; homogenisation of the liquid through stirring; and finally pouring into a graphite mould in order to obtain an ingot. In this case, the authors want to be able to validate a model that will be created after this study with the aim at minimising both the segregation that can occur in this kind of alloy, the porosities which are very common in the foundry process. To be presented are: (i) the conditions, the material and the parameters used in this case; (ii) some parameters concerning the alloy (phase diagram, inclusions and their morphologies, thermal properties); (iii) the location of the thermocouples in the ingot and in the mould which were used in order to see how the solidification evolves; (iv) the temperature recordings; and (v) the results of the characterisation of this ingot, through metallography and chemistry analysis; so that it is possible to obtain a full chart of the niobium content in this ingot. This set of experimental measurements constitutes a complete collection of data that can be used on one hand as input for the numerical model and on the other hand as results for comparison with the numerical simulations.

The Measurement Of In-plane Permeability For Sheared Preforms

Computer simulations of composites manufacturing processes such as liquid moulding require accurate permeability data. Increasingly sophisticated models have been proposed for the prediction of the permeability of fibrous reinforcements; however these analytical tools are not yet able to account for the actual structure of the preforms. Parameters such as the textile structure or the level of imposed deformation in compaction and shear are known to modify the principal permeability values, as well as the orientation of the inplane permeability tensor. If such parameters are to be considered within the simulations, their effects must be known with a level of accuracy that allows them to be separated from the natural variability observed with permeability data. In this paper, a method for the analysis of permeability measurements obtained from a planar apparatus instrumented along three axes is described. The principal permeabilities, as well as the values for the anisotropy ratio and orientation of the in-plane permeability tensor, are obtained without making any assumption relating the warp and weft directions of the materials to the orientation of the tensor. A metal cavity is used, allowing tests to be performed at high fibre volume fractions. Using this method, values can be obtained in a fraction of the time required for an equivalent work to be done using rectilinear measurements. Typical experimental data is presented to illustrate the potential of the method, and simplifying hypothesis used in other published methods are commented. Transactions on Engineering Sciences vol 21, © 1998 WIT Press, www.witpress.com, ISSN 1743-3533

Yarn Compaction and Migration in Woven Composites

The geometry of a woven fabric is predicted accounting for process information. The processing information includes basic weave configurations as well as applied transverse compressive displacement during liquid moulding operations and yarn-yarn interaction within the fabric. The compaction and migration of individual yarns within the woven structure are modelled. To consider the usefulness of the developed model, the predicted geometries are used as input to a stiffness prediction model and the results are compared with experimental data on a range of woven composites - plain weave, orthogonally woven, and angle-interlock.