Rowan Paton

Resin transfer moulding for aerospace structures

List of contributors. Preface. Acknowledgements. 1. Introduction to resin transfer moulding B. Rackers. 2. Injection equipment M. Petervary. 3. Materials M. Puckett, M. Petervary. 4. Advanced reinforcements M. Bannister, I. Herszberg. 5. Fabric drape modelling and preform design A.C. Long, C.D. Rudd. 6. Overview of fibre preforming V. Rohatgi, et al. 7. Preform permeability R. Parnas. 8. Modelling and simulation of flow, heat transfer and cure S.G. Advani, P. Simacek. 9. Tooling fundamentals for resin transfer moulding M. Wadsworth. 10. Tooling inserts for resin transfer moulding M. Thiede-Smet, M. Wadsworth. 11. Manufacturing and tooling cost factors T. Kruckenberg. 12. Data acquisition: monitoring resin position, reaction advancement and processing properties D.E. Kranbuehl, A. Loos. 13. Quality and process control B. Rackers, et al. 14. Qualification of resin transfer moulding for aerospace applications R.W. Stratton. Appendix A: Glossary. Appendix B: Conversion factors. Index.

The draping of woven fabric preforms and prepregs for production of polymer composite components

Drape trials were conducted on a simple shape and a number of aircraft parts. Predictions from computer drape simulation using the pin-jointed net model were compared with draping test results. The pin-jointed net model was evaluated. Yarn slippage, and how it is affected by the material properties and part geometry, were investigated. The criteria for optimal draping, and the means of manipulation of the drape simulation are discussed. The different methods of draping constraint are compared and their most useful applications are indicated. Some useful guidance for the application of drape simulation is given.

The shear properties of woven carbon fabric

This paper presents experimental and theoretical studies of the shearing properties of carbon plain weave fabrics and prepregs. The shearing characteristics of these materials are determined by the use of a picture frame shear rig which is loaded by a mechanical test machine. The shear force/angle curves are presented for the experiments conducted with the various test materials. A proposed shear model based on previous research which idealizes the fabric yarns as beam elements is presented. Using fabric geometric and material parameters, the model predicts the initial slip region of the fabric, as well as the more dominant elastic deformation range. Comparisons of the experimental and theoretical results were conducted to validate the model. A discussion of the findings from the analysis is also given, with particular focus relating to the accuracy, limitations and advantages offered by such a model. Results indicated that the slip model gives modestly accurate predictions, whilst the elastic modulus model showed very good correlation with experimental data.

Stresses and deformations induced during manufacturing. Part II : A study of the spring-in phenomenon

It has been observed that residual stresses always build up during the fabrication of composite components. Such stresses can change the shape of a component when it is removed from the mould. This paper examines the spring-in induced during fabrication of composite angle components by such residual stresses. The sample composite components were fabricated from unidirectional carbon/epoxy pre-preg tape and plain-weave carbon/epoxy pre-preg fabric, as well as from dry carbon fabric and resin using the resin transfer moulding (RTM) technique. The effects of lay-up, orientations, part thickness, tool angle, tool material, etc. were investigated. The results show that (1) the tool material has an insignificant effect on the degree of spring-in, (2) spring-in is insensitive to the lay-up sequence for symmetric lay-ups, (3) spring-in does not depend on ply orientation angles in the case of fabric laminates, (4) spring-in remains constant for almost all radius/thickness ratios and (5) spring-in decreases with an increase in the tool angle. Comparison with the theoretical model developed by Jain and Mai [1] is provided and good agreement is found.

Impact resistance and tolerance of interleaved tape laminates

This paper presents and discusses the results of low-velocity impact and compression-after-impact (CAI) tests conducted on interleaved and non-interleaved carbon/epoxy tape laminates. Olefin film interleaves provided a strong interface bond, resulting in a reduction in projected damage area. These interleaves changed the stress distribution under impact and restricted delamination formation at the ply interface. An investigation into the compression behaviour of these laminates revealed a reduction in undamaged strength using olefin interleaves. This was attributed to the lack of lateral support for fibres at the fibre/interleaf interface, allowing fibre microbuckling to occur at a low load. Low modulus copolyamide web interleaves resulted in an increase in damage area and minor changes to CAI strength. Examination of laminate cross-sections revealed that this was due to both the open structure of the interleaf and poor resin/interleaf adhesion. High shear modulus polyethylene interleaves resulted in a significant decrease in damage area at various impact energies, with CAI strength improved compared to the non-interleaved laminates.

Morphology of an Interface between Polyetherimide and Epoxy Prepreg

The morphology of the interface between a commercial epoxy prepreg resin (HexPly M18/1) and Polyetherimide (PEI) is studied. Different cure cycles prescribed by the supplier were investigated to determine the influence of temperature and pressure on interface formation. Atomic Force Microscopy (AFM) was used as the main means of investigation. A phase-separated interphase spanning 9-10μm was observed for the PEI/epoxy prepreg interface. It was found that the temperature profile of the cure cycle strongly influences the formation of this interphase. Rapid formation of these relatively large interphase areas suggests that mechanisms other than diffusion are responsible for this phenomenon.

Microanalysis Techniques for the Investigation of Interphases Formed between Thermoset and Thermoplastic Polymers: Scanning Electron Microscopy and Energy Dispersive X-Ray Analysis

Prepreg resin systems are typically of complex composition and require very specific manufacturing conditions. These characteristics restrict the use of some commonly used micro analysis techniques. This paper investigates the use of low acceleration voltage scanning electron microscopy and energy dispersive x-ray analysis for the characterization of diffused polymer interfaces. It is shown that, by operating at the dynamic charge balance, high resolution secondary electron images of polymer interfaces can be obtained and that conductive coating is not required. In addition, the effect of acceleration voltage on the interaction volume in EDX analysis is discussed using Monte Carlo simulation. X-ray intensity measurements in combination with afore mentioned Monte Carlo simulation is used to define practically obtainable spatial resolution limits. It is shown that by reducing the acceleration voltage below 5kV spatial resolution higher the 500nm can be obtained.

Glass transition and viscoelastic behaviour of partially cured composites

Abstract For this study, two tests were conducted in order to investigate the cure monitoring of composite parts utilizing XMTM-49 (carbon/epoxy composite) as the specimen. The first test involved the use of a dynamic mechanical thermal analyzer to investigate the nature of the loss modulus while the second test incorporated a differential scanning calorimeter to evaluate the degree of cure of the composite. From the results of the research, it was found that the loss modulus is an extremely sensitive cure monitoring indicator for composites beyond 70% cured. This is a significant finding since traditional ultrasonic procedures could only be effective in monitoring the cure of composite structures when the degree of cure reaches approximately 70% but decreases when the cure reaches 80% or more. Therefore, it is recommended that future developments should focus attention on a non-contact technique for measuring loss modulus for cure monitoring.

Measurements of Interface Fracture Strength between Fiber-Reinforced Composite Laminates and Thin Surface Films Using the Blister Test

The blister test is a promising test method to determine the interface fracture toughness of thin films adhering to rigid fibre reinforced plastics. In this paper nonlinear finite element analysis is used to determine a suitable layout for both the shaft loaded and the pressurised blister test. On the example of a PET film adhering to a quasi-isotropic fibre reinforced plastic, it is shown that energy release rates in a range of 0-1500N/m can be obtained for a 0.5mm thick film if test parameters are carefully selected. The two main causes for deviations of the analytic solution from the FEA results is attributed to infringement of the membrane limit condition and plastic deformation in the film.

Finite element simulations of the doublediaphragm forming process: Comparisons with experimental trials

This document provides a comprehensive evaluation of finite element simulations of double diaphragm forming of CF/EP plain weave prepreg. The simulations were performed using the PAM-FORM software, and incorporated critical advances recently achieved in composite forming simulations. The material properties were obtained from characterization tests, or estimated in conjunction with rationalization analyses. By using only one set of material and simulation parameters, the best-match simulations correlate well with all four experimental trials of different setups, which include one good and one wrinkled forming trail of rudder rib shape, and one good and one wrinkled forming trial of a simple cup shape. The simulations also highlight the effects of contact penalty, and the sensitivity to inter-ply friction, and re-confirm the necessity to scale-up the measured intra-ply shearing stiffness.