S.M. Grove

Resin Infusion under Flexible Tooling (RIFT): a review

Abstract Increasing legislation to limit styrene emissions (mainly from polyester resin systems) into the work place has been the key factor in promoting new technology in the manufacture of fibre reinforced plastics composites. Styrene emissions can be reduced by the development of: resin systems with low styrene emission; improved ventilation and air filtering systems; closed moulding techniques. It is the final area on which this paper concentrates. RIFT is a variant of vacuum-driven RTM in which one of the solid tool faces is replaced by a flexible polymeric film. The process is known by several acronyms—in this paper it is referred to as RIFT (Resin Infusion under Flexible Tooling). Potentially a very clean and economical composites manufacturing method, the process draws resin into a dry reinforcement on an evacuated vacuum bagged tool using only the partial vacuum to drive the resin. It reduces worker contact with liquid resin whilst increasing component mechanical properties and fibre content by reducing voidage compared to hand lay-up. For higher performance composites, RIFT offers the potential for reduced tooling costs where matched tooling (RTM or compression moulding) is currently used. This paper reviews the progress of RIFT from its first development as the Marco method in 1950 to the Seemann Composites Resin Infusion Manufacture Process (SCRIMP) today. Development of the process has been slow (compared to RTM) and generally lacking in scientific rigour. Current research is reviewed and the potential for scientific development is discussed.

The compression response of fibre-reinforced plastic plates during manufacture by the resin infusion under flexible tooling method

Abstract Resin infusion under flexible tooling (RIFT) is a variant of vacuum-driven resin transfer moulding in which one of the solid mould faces is replaced by a polymeric film. One variant of the process is known commercially as SCRIMP. In comparison with traditional hand lay-up, the process has obvious health and safety advantages, through reductions in worker contact with liquid resin and in reduced emissions to the environment. Additionally, laminate mechanical properties are improved by higher fibre contents and lower voidage. In comparison with conventional (matched mould) resin transfer moulding, the process can offer a substantial reduction in tooling costs, especially for large parts. As one of the tool faces is flexible, the moulded laminate thickness depends in part on the compressibility of the reinforcement and on its interaction with the flowing resin. This paper describes a preliminary experimental study of the measurement of fabric compression and the effects of the interaction between reinforcement and resin flow on the final component thickness.

Energy Use in the Production of Flax Fiber for the Reinforcement of Composites

A comparative quantitative life cycle assessment (LCA) should consider the eight environmental impact classification factors listed in ISO/TR 14047:2003. This paper reports on the energy requirement for production of flax fibers to be used as reinforcement in composite materials. Data are compiled from a number of published sources. Only 5% of the harvested plant mass is converted into long fibers, while the other 95% could be regarded as waste; the respective coproducts (short fiber for paper manufacture, shives for animal bedding, and dust for fuel) can be collected, processed, packaged, and sold. The analysis here assumes that these coproducts are disposed of at a cost that covers the postseparation handling and hence they are not included in the flax burdens. The analysis suggests that sliver (postcarding fiber) has an embodied energy comparable to glass fiber reinforcement mat at approximately 55 GJ/tonne. Spinning fibers to produce yarn for weaving dominates the embodied energy. In the event that best agricultural practice is taken into account, and that some energy usage is apportioned to coproduct, then the claim that flax is a sustainable “green” alternative may be justified for random mat reinforcement. If the fiber is spun to yarn, then the embodied energy for flax exceeds that of the glass fiber equivalent.

The effect of reinforcement architecture on the long-range flow in fibrous reinforcements

Abstract The resin transfer moulding process involves the long-range flow of resin into a closed mould which is filled with dry fibre reinforcement. The rate of resin flow can be calculated using the Darcy and Kozeny-Carman equations. The flow rate is thus a function of the pressure drop across the fibre bed, the resin viscosity and the permeability of the fibre bed. The permeability constant is dependent on the fibre radius and the porosity of the bed. A number of reinforcement fabrics are now available commercially which promote faster resin flow than that in equivalent fabrics of the same areal weight at the same fibre volume fraction. The KozenyCarman equation includes a parameter known as the mean hydraulic radius. If this parameter is varied by calculating specific hydraulic radii, then the flow enhancement may be modelled. Calculations for model materials have been published and demonstrate that this approach predicts that significant changes in flow rate are possible. The commercial fabrics do not have model structures, but feature variations in the mesoscale architecture of the reinforcement: fibres clustered into tows and uneven distribution of pore space. The paper will report on the correlation of quantitative image analysis of optical micrographs with the flow rates in a range of reinforcement fabrics.

Relationship between mechanical performance and microstructure in composites fabricated with flow-enhancing fabrics

Abstract The resin transfer moulding process involves the long-range flow of resin into a closed mould which is filled with dry reinforcement. High-performance composites require a high volume fraction of fibres, which results in low porosity of the fibre pack and therefore slow rates of mould filling. Commercial reinforcement fabrics are becoming available which promote faster resin flow than conventional fabrics, by engineering regions of large pore space into the reinforcement stack. However, theoretical models of the property-microstructure relationships have indicated that resin-rich areas (corresponding to filled large pore space) and fibre clustering will lead to degradation of the mechanical performance of the laminate. This report describes a series of compression and interlaminar shear tests on a range of twill-weave fabrics having ‘flow-enhancing’ tows substituted in the warp direction. The results provide some experimental support for existing theoretical models.

Quantitative microstructural examination of RTM fabrics designed for enhanced flow

The resin transfer moulding (RTM) process involves the long-range flow of resin through a mould packed with dry reinforcement. The process can be considered as similar to the flow of fluids through porous media, and hence the situation can be modelled by the Darcy and Kozeny-Carman equations. The Kozeny-Carman equation predicts the effect of changes in the pore structure of the reinforcement on flow rate, through a parameter known as hydraulic radius, which is itself a function of the wetted surface in any given volume. Laminates have been manufactured, from fabrics which include flow-enhancing tows, in a transparent RTM mould. The cured laminates were sectioned for quantitative microscopy and image analysis. An analysis of the effect of substituting spiral-wound flow-enhancing tows for conventional tows in the reinforcement fabric is presented.

The effect of microstructure on flow promotion in resin transfer moulding reinforcement fabrics

The resin transfer moulding (RTM) process is becoming increasingly important for the manufacture of continuous fibre‐reinforced thermosetting resin matrix composites. The RTM process is a closed mould technique which reduces volatile emissions relative to traditional hand lay‐up methods. The fibres, generally as several layers of fabric, are prepared as a preform and laid in the closed mould. The resin is injected, at one or more points, and flows through the mould to form the finished product. In the manufacture of high‐performance composite structures, the flow of resin is constrained by the high volume fraction of reinforcement fibres required to achieve the performance. Commercial fabrics are becoming available which are woven with specially designed mesoscale architecture to promote flow of the resin. The flow rates in a series of such fabrics have been studied. The microstructures of the resulting composites have been examined using brightfield optical microscopy. A Quantimet image analyser was used to quantify the structures on both the mesoscale and the microscale. The flow rate has been shown to be related to the presence of both large and more modest sized pore space in the reinforcement architecture.

Canoe do physics

How disappointing that Olympic canoeist David Florence, who has a degree in physics, sees no direct applications of physics in his sport (March p65).