Development of the Resin Infusion between Double Flexible Tooling process : assessment of the viability of in-mold coating and implementation of UV curing.

As composites gain wider acceptance in all sectors of the economy, new methodologies must be developed to increase their cost effectiveness in manufacturing. The neoteric Resin Infusion between Double Flexible Tooling (RIDFT) process is undergoing modifications to improve its cost-effectiveness by developing methodologies for in-mold coating and the incorporation of UV curing. In-mold coating is desired by the composites industry since it eliminates the current paint process, which is not only laborious and time consuming, but expensive, and presents safety issues. Two methodologies (paint films and coinfusion) for implementing in-mold coating were investigated. It was demonstrated that thermoformable paint films could be used to produce coated RIDFTed components. Coinfusion was also successfully implemented. This work also investigated the feasibility of designing and incorporating a Cure on Demand system into the RIDFT process, using ultraviolet (UV) light for the curing of composite laminates. The objective was to develop a process for the RIDFT that would eliminate or reduce the inflexibility in the current production process, resulting in shortened production cycle times. UV-cured laminates were produced at a fraction of the time required to produce catalyst-cured laminates. Mechanical and material characterization tests were performed on each of the UV-cured laminates produced. The results were referenced against those obtained for laminates produced using a catalyst curing system to determine their overall quality. The UV-cured laminates, after undergoing tensile and rheological thermal tests, were found to have mechanical and material properties comparable, or in a few instances slightly better, than that of thermally cured laminates

The effects of strain rate and failure modes on the failure energy of fibre reinforced composites

The utilisation of polymer composite materials in safety critical structures necessitates their full characterisation. This will bring about the much needed boost in confidence for their application to industrial situations, especially where high speed impact is a concern. Impact performance can in some way be measured by the energy absorbed or expended to failure of a material. Hence, establishing the rate effect on energy absorption is of paramount importance when designing for impact. Tensile, shear and 3-point bend tests were conducted on a woven glass/epoxy laminate at increasing rates of strain. The results suggest a linear relationship between expended energy and the log of strain rate in the laminate tested. Furthermore, it was found that a relationship exists between the flexural energy obtained at low strain rate and the high speed (2-4 m s-1) test values. Magnified views of the failed specimen surfaces, viewed under a scanning electron microscope, indicate a change in failure modes as strain rate is increased, which brought about the increase in energy observed. © 2001 Elsevier Science Ltd. All rights reserved

In-mold coating of composites manufactured by the resin infusion between double flexible tooling process by means of co-infusion

As composite materials gain wider acceptance within the transportation industry, it is pertinent to investigate the available coating processes with a view to reducing emissions and associated costs. This work aims to develop a methodology for in-mold coating components manufactured using the resin infusion between double flexible tooling (RIDFT) process. RIDFT is a neoteric two-stage manufacturing process that involves (1) infusion of resin between two flexible silicone membranes until thorough wetting of the fibers is achieved and (2) vacuum forming, where the membranes are pulled over a one-sided mold. The viability of in-mold coating RIDFTed components is investigated. This work-in-process reports on successes and challenges presented during the co-infusion of a polyurethane enamel paint (DuPont Imron 5000) and a vinyl ester resin (Derakane 470-45). Methodologies for achieving co-infusion are investigated. It has been found that co-infusion is achievable with the use of an appropriate separation layer. © 2006 SAGE Publications

Aspects of the tensile response of random continuous glass/epoxy composites

The effect of strain rate on failure mechanisms was determined by viewing fractured surfaces of tensile specimens using a scanning electron microscope (SEM). The relationship between the energy dissipated and fiber content was also evaluated. Tensile tests were performed on a random continuous glass/epoxy laminate at increasing rates of strain. A second laminate with random continuous glass reinforcement was tested in tension at various fiber volume fractions to ascertain the relationship between fiber content and energy dissipated. Overall, significant results were obtained

Effects of process and materials on pressureless sintering of alumina

Ceramic materials are very sensitive to process factors. The interactions of these factors during processing are also highly significant in determining the properties of the resultant ceramic material. The effects of uniaxial compaction pressure, particle size, sintering temperature and the use of sintering aid as well as their interactions are investigated for pressureless sintering of alumina. The application of the techniques of Design of Experiments (DOE) employing 2K factorial design enables the determination of the magnitude or significance of each of these factors, and their various interactions in the emergence of physical and mechanical properties of alumina densified via pressureless sintering. Hence cost of production can be minimized and reproducibility enhanced for various categories of desired properties due to adequate knowledge and control of process parameters

Aspects of the tensile response of random continuous glass/epoxy composites

The impact properties of a material represent its capacity to absorb and dissipate energies under impact shock loading. If a material is strain rate sensitive, its static mechanical properties cannot be used in designing against impact failure. In addition, the failure modes in dynamic conditions can be quite different from those observed in static tests. The effect of strain rate on failure mechanisms was investigated by viewing fractured surfaces of tensile specimens using a scanning electron microscope (S.E.M.). The relationship between the energy dissipated and fibre content was also evaluated. Tensile tests were conducted on a random continuous glass/epoxy laminate at increasing rates of strain. A second laminate (with random continuous glass reinforcement) was tested in tension at varying fibre volume fractions in order to ascertain the relationship between fibre content and energy dissipated. The results suggest that although the fibres fail in a brittle mode, the matrix failure mode is dominant as strain rate is increased. In addition, increasing the test speed results in catastrophic failure due to enhanced crack propagation rate. The results also indicated that increasing the fibre volume fraction saw an initial increase in energy to a peak value, followed by a decrease as the fibre content was increased. This implies that there is a point where increasing the fibre volume fraction becomes detrimental to energy absorption. This has been identified as the point where there is poor wetting of the glass fibres, possibly due to the resin penetration of the glass being restricted by the packing density

Effect of 2-D regular channels and their configurations on properties of ceramic preforms

Regular channels of various sizes aligned in 2-D were fabricated in alumina using soft solder. The spaces between these channels were varied and their effects on the properties of alumina were investigated. It was found that these channels could significantly affect the fracture strength and elastic modulus of the specimen, depending on the channel diameter and spacing. After 3-point bend tests, it was seen that the presence of channels resulted in enhancement of modulus of rupture (MOR) and decrease in the scatter when compared to the solid specimen (specimen without channels). It was also observed that there exists an optimal spacing between the channels that imparts the highest MOR to the specimen. Beyond this value of spacing the MOR decreased, while the elastic modulus increased. The compressive strength also exhibited much less scatter for the porous specimen than for the solid specimen

An attempt at predicting failure in a random glass/epoxy composite laminate

The difficulties presented by inertial disturbances in the testing of fibre reinforced composite materials at elevated strain rates necessitated the development of a technique for the prediction of high strain rate material property data. These data have been used in a finite element analysis to simulate impact behaviour of a random glass epoxy composite. High strain rate properties obtained by extrapolating results of experiments conducted at low to intermediate strain rates were used in the finite element analysis of a simple three-point bend beam impact. Three point bend impact tests were performed on the laminates, and comparisons were made of the results predicted from this analysis and actual impact test data. The results show that the finite element model created may be used to predict the behaviour of random glass/epoxy laminates. However, the inclusion of flexible post-failure degradation rules to allow for progressive damage, will improve the accuracy of the analysis