John Summerscales

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.

Carbon fibre and glass fibre hybrid reinforced plastics

Abstract A review of the literature on carbon fibre and glass fibre hybrid reinforced plastics is presented. There are indications that the incorporation of both fibres into a single matrix sometimes leads to better properties than would be expected from consideration of the rule of mixtures. The incorporation of glass fibres in cfrp appears to improve impact properties and to increase the strain to failure of the carbon fibre in tension. The addition of carbon fibres to the surface of grp beams markedly increases the flexural modulus. A system of nomenclature for the diverse types of hybrid composite lay up is proposed.

The compressibility of a reinforcement fabric

Abstract The resin transfer moulding (RTM) process involves the loading of dry reinforcement into a mould. After the mould is closed, resin is flowed into the mould cavity and cured. The RTM process has traditionally been used to produce low fibre volume fraction composites. There is now increasing interest in using the process to manufacture high fibre volume fraction composites for structural applications. Experiments have been conducted to monitor the force required to compress a typical plain-woven glass fibre reinforcement. The load displacement curves for monotonic loading, and for relaxation after repeated reloading cycles to a maximum load are presented. The loading cycle responses for the fabric have been fitted to power-law relationships, and the relaxation cycles have been fitted to exponential decay functions.

Microstructural image analysis applied to fibre composite materials: a review

Abstract Current definition of the microstructure of fibre-reinforced composite materials is usually limited to the definition of the materials used and the proportion and orientation of the fibres. Significant differences can be achieved within such a definition, particularly in respect of the spatial distribution of fibres within the material. The microstructure-mechanics relationship is gaining importance as the discipline of mesomechanics. Recent advances in computer hardware, and in software for image processing and analysis, have permitted the rapid definition of spatial microstructural parameters. This paper reviews the preparation of samples for optical microscopy and the use of image analysis for the definition of microstructure in fibre-reinforced composites.

Hybrids — a review: Part 2. Physical properties

Abstract The second section of a review, commenced in the previous issue, is presented, covering the subject of carbon fibre and glass fibre hybrid reinforced plastics (cghrp). The existence of a ‘hybrid effect’ is still the subject of some controversy, although a negative synergism has been reported in fracture at high interdispersion of the two fibres. Some attempts to quantify the residual thermal stresses from curing have been made, but these do not correlate well with the observed hybrid effect. A discrete burst of acoustic emission has been reported on the transfer of load to the glass fibres, coincident with the load drop associated with failure of the carbon fibres. The conclusions of the previous review would appear to be still valid. An outline of the areas of ignorance is included.

Modulus and Strength Prediction for Natural Fibre Composites

Abstract This paper presents a new micromechanical model for the prediction of the tensile modulus and strength of natural fibre reinforced polymer matrix composites. The model addresses issues linked to the statistical variation inherent in fibre reinforcements extracted from plants. The new model introduces a fibre area correction factor (FACF). Modulus and strength are estimated and compared to experimental data for a jute–epoxy composite. The predictions of tensile modulus and strength using the FACF show improvements over those from other micromechanical models presented in the literature.

Low-pressure (vacuum infusion) techniques for moulding large composite structures

Abstract Resin transfer moulding (RTM) involves the long-range flow of resin into a dry fibre pack that is preloaded into a defined mould cavity. Resin infusion under flexible tooling (RIFT) can be considered as a variant on RTM in which one tool face is replaced by a flexible film or a light splash tool. The flow of resin results only from the vacuum drawn under the film and any gravity effects. In RTM the dimensions of the component are defined by the separation of the mould faces, whilst in RIFT processes the thickness of the part is a function of the pressure history during the process. This paper reviews current developments in resin infusion processes.

An investigation into the effects of fabric architecture on the processing and properties of fibre reinforced composites produced by resin transfer moulding

Abstract The use of resin transfer moulding (RTM) as an economic and efficient means of producing high performance fibre-reinforced composites is critically limited by the permeability of the fabrics employed. Commercial fabrics are available where the architecture of their reinforcement is designed to cluster the fibres, giving higher permeabilities than conventional fabrics. This has been shown to improve processing times, but there is evidence that such clustering is detrimental to the mechanical performance of the resulting composite materials. The objective of this work was to relate variations in permeability and mechanical performance to differences in composite microstructure. This was achieved by producing carbon/epoxy plates of different weave styles by RTM in a transparent mould. The progress of the resin was recorded by a video camera during injection, and the images were processed by a frame-grabbing computer, permitting the permeabilities of the fabrics to be calculated. Further plates were manufactured using the same fabrics, and sectioned for microstructural image analysis and interlaminar shear strength (ILSS) testing to CRAG standards. Relationships were sought between measured permeabilities and finished microstructures using a Quantimet 570 automatic image analyser. It has been shown that variations in permeabilities and mechanical properties can be related to observed differences in the microstructure.

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.

Hybrids-a review: Part 1. Techniques, design and construction

Abstract A continuation of the previous review on carbon fibre and glass fibre hybrid reinforced plastics (cghrp) is presented. The first section covers fabrication techniques, design, cost-effectiveness and applications. The second section, to be published in the next issue, covers the thermal and mechanical properties of cghrp.