Plastics,Rubber and Composites: Macromolecular Engineering

There is growing interest in the use of thermoplastic composites for wind turbine blades. This paper presents preliminary work on the design, analysis and manufacture of a thermoplastic composite blade for a vertical axis wind turbine. The blade design featured a sandwich construction with commingled woven E-glass fibre/polypropylene thermoplastic composite skins and a polyethylene terephthalate (PET) foam core. A finite element modelling methodology has been developed for predicting the natural frequency and structural performance of the blade. For structural analysis, the skin was modelled with a composite damage model for which an inverse calibration procedure was developed. Vibration and static bending tests were conducted on a subscale prototype blade to validate the finite element models. A one-step vacuum moulding process was adopted to manufacture the prototype blade. The validated finite element models were then used to determine the natural frequency of the full sized blade and predict its performance under in-service aerodynamic loads. The results show that the thermoplastic composite blade design meets the desired structural requirements.

The usage of actual reinforced thermoplastic composites for structural aircraft applications is very limited because materials with higher mechanical and physical properties are needed. In the recent years, aircraft manufacturers have requirements for new continuous fibre reinforced thermoplastic composites with a significant improved performance/costs ratio for new, structural aircraft applications. That is why a new affordable reinforced composite with a poly(phenylene sulphide sulphone) (PPSS) matrix, presenting high mechanical and thermal resistance properties, is introduced in this paper. Mechanical characterisations have been performed and microscopy analyses have also been achieved to control the internal structure of the composite. It was found that PPSS reinforced material has high mechanical and thermal properties, but low chemical resistance.

The aim of this paper is to analyse fibre/matrix debond crack growth during high stress cyclic tension–tension loading of unidirectional composites. The debond crack evolution analysis is based on fracture mechanics concepts that mode II energy release rate calculations are performed analytically for long debonds, where crack growth is self-similar, and numerically for short debonds by finite element method in combination with virtual crack closure technique. From the calculation results simple expressions are derived for an arbitrary mechanical and thermal loading case. Finally, the obtained expressions are applied in Paris law for debond growth simulations in cyclic tension–tension loading.

Full scale tests carried out on polymer composite sandwich panels, which model the loads experienced by aircraft secondary wing structure, are described. The results from the tests form the basis of a performance assessment of the sandwich construction. The sandwich panel face sheets were manufactured from five different carbon fibre material architectures and were consolidated with epoxy resin using a variety of approaches. In previous work, it was shown that it was possible to significantly reduce the manufacturing costs of producing the sandwich structure by replacing the standard certificated process of unidirectional prepreg cured in an autoclave with a method that used non-crimp fabric infused in a conventional oven. In the present paper, thermoelastic stress analysis (TSA) is used during the full scale tests to obtain stress data from the five different panel types. The TSA data and measured deflection data are used to validate finite element (FE) models of each panel. The experimental validation highlighted some interesting features in the modelling approach. The face sheet materials were treated as homogeneous orthotropic blocks, which resulted in a conservative prediction of deflections. The models did not consider the woven and stitched material face sheet material configurations and therefore, omitted some of the features apparent in the experimental work. However, the validation showed that this did not affect the performance evaluation and most importantly, the validated FE showed that using different face sheet materials had little effect on the stresses in the panels.

Structural, fibre reinforced, battery prototypes with two types of electrolyte matrix material (a gel and a solid polymer) have been manufactured. This was to confirm the concept of using carbon fibres as current collector in the anode as well as providing a mechanical load-carrying functionality. As a result, functioning batteries with gel electrolyte have been produced and their properties have been characterised.

A route for the recovery and reuse of carbon fibres is presented with a summary of technological advances and areas requiring further development. Critical issues in size reduction of recyclate are presented along with results from a study considering comminution of a variety of time expired prepregs. High quality recovered carbon fibres have been incorporated in moulding compounds and preimpregnated composite materials. Fibre alignment is shown to be a critical factor in attaining high mechanical properties and high recovered fibre utilisation. A number of demonstrator materials have been developed and used to manufacture automotive parts which have shown excellent mechanical properties when compared with commercial glass fibre based moulding compounds.

The creep rupture of aramid fibre yarns (Twaron 1000 and Kevlar 29) was studied experimentally at different temperatures. The failure stress and strain data were analysed by statistical techniques. The reliability analysis, including extraction of Weibull parameters and distribution estimation, allows useful conclusions on the long term creep rupture behaviour of aramid fibre yarns, mainly on the properties variability and on temperature influence.

The use of ytterbium triflate as a catalyst for the cure of nano modified epoxy resins is described. Incorporation of γ-valerolactone was explored as a means of reducing the fragility of the material. The cure profiles were measured using the Strathclyde curometer over the temperature window of 90 to 120°C. The gelation time was sensitive to the concentration of the catalyst present. Incorporation of nanosilica particles, created using a sol–gel method, allowed enhancement of the physical properties of the base resin matrix. The addition of γ-valerolactone influenced the cure rate and the physical properties of the matrix formed. The mechanical and thermal properties of the materials were studied using dynamic mechanical thermal analysis and differential scanning calorimetry. The incorporation of the γ-valerolactone at certain levels leads to a reduction of the glass transition temperature with increasing level of nanofiller rather than the expected increase.

The debonding of Glare skin–stringer configurations for aerospace applications has been studied. Fatigue life curves were produced experimentally for two types of skin–stringer configurations. Using the double cantilever beam specimen configuration and applying different loading conditions, material models for pure mode I and mixed mode I and mode II fatigue loading were generated for the adhesive used to bond the skin to the stringer. These material models describe the crack growth rate, da/dN, as a function of the maximum cyclic strain energy release rate, G _max, and were used together with finite element analysis of the cracked skin–stringer configuration to derive predictions of the fatigue life. The predicted fatigue life was compared to the experimental results.

This work deals with three-dimensional numerical simulations of damage caused by air blast on fully clamped rectangular plates. The study examines the performance of both metallic and CFRP laminates subjected to blast loads using commercial LS-DYNA software, including a cohesive damage model to represent delamination. The blast load was simulated using a CONWEP algorithm and MMALE approach with fluid–structure interaction between the Eulerian blast and Lagrangian target models. The simulation results are presented and compared with the experimental data, showing good agreement in terms of dynamic deflection, damage morphology and residual deformation.

Herein a new series of all aromatic thermotropic liquid crystalline thermosetting polymers (LCTs) is presented. Liquid crystalline thermosetting polymers offer excellent thermal (T _g>200°C, T^5%_d>450°C) and mechanical properties (E′>4 GPa), and they can be melt processed into fibre reinforced composites with superior mechanical and physical properties over PPS or PEEK based composites. The fully cured polymers exhibit excellent mechanical properties, i.e. TA/HQ/HNA(25)-5K displays a flexural strength of 110 MPa, flexural modulus of 8 GPa, a tensile strength of 66 MPa and a room temperature elongation at break of 5·5%. These LCTs were also successfully applied as high temperature (150°C) adhesives for metal substrates. When used as resins in carbon fibre reinforced composites, significant improvements in critical composite properties were found, such as a high in-plane shear strength (154 MPa) and tensile strength (696 MPa).

A controllable impregnation of glass fibre structures used in high performance fibre reinforced cement composites can nowadays only be obtained by hand lay-up means, constraining possible structural applications of this promising composite. This paper discusses an innovative manufacturing process designed for the mechanical impregnation of textile reinforcements by a suitable cement matrix. The basic principles of this self-compacting impregnator (SCI) as well as the manufacturing of the cement based laminates will be explained. For comparison, uniaxial tensile strength and interlaminar shear strength were measured on specimens obtained by both production techniques, hand lay-up and SCI. The quality obtained with the laboratory prototype SCI is comparable with the quality obtained by hand lay-up.

‘Conventional' or certified repair procedures for impacted composite structures (i.e. patches) are time consuming, and must be performed by highly qualified staff. In this paper, a cost effective and simple repair method by liquid resin infiltration is studied. As damages on aircraft structures are generally due to impact, this kind of damage is characterised and compared to quasi-static indentation with ultrasonic inspection and micrographic cuts. The repair by liquid resin is used to fill in the very special damage pattern region organised as a crack network (delamination and transverse cracks). In order to study this new repair method, an experimental set-up has been manufactured and different configurations have been studied. Mechanical testing (CAI, DCB and ENF) was then performed to evaluate the strength of this repair. As good results were achieved, further exploration under complex loading should be performed to ensure the quality of the repair for an industrial application.

A model is proposed to optimise the processing parameters for the consolidation of glass/polyphenylene sulphide (PPS) laminates using a film stacking procedure. In a split approach, the heating and consolidation phase are treated separately. The heating phase is modelled using the one-dimensional heat conduction equation with variable thermal diffusivities. The model shows good agreement with experimental results. The consolidation phase is modelled using Darcy's law to predict the bundle impregnation time. The model predicts an impregnation time in the order of seconds, which is significantly shorter than the typical consolidation time of approximately 15 min used in practice. The impregnation model is validated in a comprehensive experimental programme, which included optical microscopy and mechanical testing. The experiments show that the consolidation time can indeed be shortened significantly for the glass/PPS system under consideration.

Details are presented of a novel carbon/epoxy spray deposition process for producing high performance, net shape charges for low flow compression moulding. The Bentley–Raycell automated carbon composite charge deposition (BRAC3D) process sprays powdered epoxy and chopped carbon bundles onto three-dimensional (3D) tools, offering a fully automated process with no touch labour. It has been demonstrated that fibre volume fractions of up to 54% are achievable for random discontinuous fibre architectures, with low void content (1·6%). This extends the volume fraction range currently offered by liquid moulding/preforming processes and potentially reduces part scrap rate, since the resin flow direction is through thickness rather than in-plane. Results from an experimental programme are presented, which aims to benchmark the BRAC3D material against commercial advanced moulding compounds. Ultimate tensile strength, tensile modulus and Charpy impact values are reported to be 272 MPa, 44·4 GPa and 128 kJ m^–2 respectively, for the random fibre architecture at a fibre volume fraction of 54%. This equates to a 99% stiffness retention and a 59% strength retention compared to a continuous fibre, quasi-isotropic counterpart. Observed trends for increasing fibre volume fraction and fibre length have been compared against finite element predictions and an analytical inclusion model. Simulations from a parametric cost model indicate that the BRAC3D process is cost effective for production volumes exceeding 1100 ppa for a structural demonstrator component, compared with prepreg and resin transfer moulding.

This paper presents the determination of the unsaturated permeability of a carbon fibre woven fabric using an experimental method of constant injection pressure and radial flow. Two effects in permeability measurement are reported: the error introduced by assuming constant injection pressure and the evolution of permeability dispersion with volume fraction. For the first, a simple approach that uses a set of values instead of just one to define the injection pressure is proposed. For the second, results showed a reduction in the dispersion with higher fibre volume fractions, which is believed to be due to the reduction of the variability of the size of the pores of the reinforcement.

The Royal Navy has adopted composites technology for use in its advanced technology mast. The mast has been designed, installed and is currently in-service on one of the UK's aircraft carriers, HMS Ark Royal. The multifunctionality of the materials has enabled the varied and complex design drivers to be met.