Conchur O Bradaigh

Processing and mechanical properties evaluation of a commingled carbon-fibre/PA-12 composite ☆

A carbon-fibre/PA-12, hybrid yarn, woven fabric material has been processed into laminates and mechanically tested to evaluate its suitability for high performance applications. The processing technique used was compression moulding. A process parameter investigation was carried out to determine the most suitable values of pressure, temperature and time at temperature required to economically produce laminates of high quality. Laminates were subsequently produced for a detailed material-testing programme. It was found that the hybrid yarn material exhibits excellent mechanical properties, particularly tension, open-hole tension, fracture and impact properties.

Process investigation of a liquid PA-12/carbon fibre moulding system

A new RTM-type process has been developed to process complex geometry components utilising a thermoplastic matrix. The matrix is an anionically polymerised liquid PA-12 (APLC-12) system which may be injected into a fibre preform, with polymerisation occurring in-situ. The initially low melt viscosity can be utilised to good effect for the impregnation of all types of composite fabrics, yielding fibre volume fractions as high as 60%. Large, complex-shaped components can be manufactured using low injection pressures. A melt processing system was established and a test mould was constructed. Different geometries were used to investigate the processing characteristics and residual stress build-up effects of the unreinforced PA-12, composite plates and composite sandwiches. An industrial-scale dosing/mixing unit was also designed and developed, and used to produce carbon-fibre/PA-12 laminates for measurement of mechanical properties. Mechanical properties were tested and the results obtained were found to be comparable to those obtained from commingled carbon-fibre/PA-12 laminates.

A preliminary design methodology for fatigue life prediction of polymer composites for tidal turbine blades

Tidal turbine blades experience significant fatigue cycles during operation and it is expected that fatigue strength will be a major consideration in their design. Glass fibre reinforced polymers are a candidate low-cost material for this application. This article presents a methodology for preliminary fatigue design of glass fibre reinforced polymer tidal turbine blades. The methodology combines: (a) a hydrodynamic model for calculation of local distributions of fluid–blade forces; (b) a finite element structural model for prediction of blade strain distributions; (c) a fatigue damage accumulation model, which incorporates mean stress effects; and (d) uniaxial fatigue testing of two candidate glass fibre reinforced polymer materials (for illustrative purposes). The methodology is applied here for the preliminary design of a three-bladed tidal turbine concept, including tower shadow effects, and comparative assessment of pitch- and stall-regulated control with respect to fatigue performance.

Fibre structure and anisotropy of glass reinforced thermoplastics

Abstract The fibre structure and orientation distribution of two commercially available glass mat thermoplastics reinforced by continuous glass fibre was studied to investigate the anisotropic behaviour under compression moulding and mechanical loading, and to investigate the influence of the fibre structure and orientation on the anisotropic behaviour. Circular samples were deformed into ellipses when moulded, due to the anisotropic fibre orientation. The fibre content and orientation were examined in different locations of the elliptically deformed specimens. X-ray pictures were taken of the material in order to develop images of the fibres, before and after compression moulding. In another procedure, the matrix was burned off and the fibre network structures were studied in each case. A CCD camera was used to scan the fibres as digital images to measure the orientation distribution functions of the fibres. The fibre orientation measuring process was facilitated by subroutines implemented in the source code of the public domain NIH-image analysis software using simulated Fraunhofer diffraction.

Self-tapping ability of carbon fibre reinforced polyetheretherketone suture anchors

An experimental and computational investigation of the self-tapping ability of carbon fibre reinforced polyetheretherketone (CFR-PEEK) has been conducted. Six CFR-PEEK suture anchor designs were investigated using PEEK-OPTIMA® Reinforced, a medical grade of CFR-PEEK. Experimental tests were conducted to investigate the maximum axial force and torque required for self-taping insertion of each anchor design. Additional experimental tests were conducted for some anchor designs using pilot holes. Computational simulations were conducted to determine the maximum stress in each anchor design at various stages of insertion. Simulations also were performed to investigate the effect of wall thickness in the anchor head. The maximum axial force required to insert a self-tapping CFR-PEEK suture anchor did not exceed 150 N for any anchor design. The maximum torque required to insert a self-tapping CFR-PEEK suture anchor did not exceed 0.8 Nm. Computational simulations reveal significant stress concentrations in the region of the anchor tip, demonstrating that a re-design of the tip geometry should be performed to avoid fracture during self-tapping, as observed in the experimental component of this study. This study demonstrates the ability of PEEK-OPTIMA Reinforced suture anchors to self-tap polyurethane foam bone analogue. This provides motivation to further investigate the self-tapping ability of CFR-PEEK suture anchors in animal/cadaveric bone. An optimised design for CFR-PEEK suture anchors offers the advantages of radiolucency, and mechanical properties similar to bone with the ability to self-tap. This may have positive implications for reducing surgery times and the associated costs with the procedure.

Monitoring the Degree of Conversion of Cyclic Butylene Terephthalate using Dielectric Analysis

Dielectric analysis (DEA) is the most common technique used to determine the state of cure in-process for many thermosetting resins systems such as epoxies, polyesters, polyurethanes, polyimides, silicones, bismaleimides, and phenolics. The objective of this work is to investigate the processing characteristics of cyclic butylene terephthalate (CBT) (supplied by Cyclics Corporation) which polymerises to form a thermoplastic, polybutylene terephthalate (PBT). This paper reports on the interim results of ongoing experimental investigations in which DEA is used to correlate the process cycle to composite structural features and mechanical performance of a complex composite part. Through adjustments in process cycle, the significant processing parameters have been identified which optimise the production of thermoplastic PBT composite parts. The recorded ion viscosity is used to indicate change in material viscosity, conversion rate and process time. These results have been analysed and presented as a guide for correct process control.

Chapter 7 Implicit finite element modelling of composites sheet forming processes

Abstract This chapter discussed implicit finite element methods of simulating composite sheet forming problems. Each ply is assumed to behave as a transversely isotropic, incompressible Newtonian fluid at forming temperature. The presence of high volume fractions of continuous elastic reinforcing fibres in the molten polymer leads to the kinematic constraint of inextensibility in the fibre direction, and associated arbitrary tension stresses. A mixed penalty numerical formulation is constructured by discretizing the weak forms of the constraint and governing equations for creeping flow, using independent interpolation of the velocity and tension stress fields. Numerical solutions are given for two types of planar problems, plane stress which is used to simulate the problem of diaphragm forming a small indentation in the centre of a large composite sheet, and plane deformation which is used to simulate single-curvature forming situations. The plane stress analysis calculates the stress and deformation patterns which are responsible for shear-buckling under rapid forming conditions, by considering uniform radial velocity or pressure boundary conditions applied at the inner radius of an annular sheet. Experimental results are presented which correspond with the numerical predictions. For multi-ply lay-ups, each ply is analysed individually, and average stress predictions for the laminate are obtained on this basis. A detailed comparison between numerical stress predictions and experimental buckling patterns is presented for central identation of circular uni-directional, cross-ply and quasi-isotropic preforms. Parameters influencing the magnitude and location of peak tangential stresses include tangential fibre lengths and diaphragm/composite viscosity ratios. The effect of sheet width and shape on the instability patterns is investigated for quasi-isotropic laminates using both numerical and experimental techniques. The plane strain finite element model presented can model isothermal shearing and plane transverse flows encountered in forming composite laminates into single-curvature shapes. These flows are the dominant mechanisms in the forming of important industrial shapes such as J- and U-beams for aerospace applications. The finite element formulation uses a mixed penalty approach with independent interpolation of the velocity, pressure and fibre tension stress fields. Results are shown which agree well with available analytical studies for both single-ply and multi-ply deformations. Experimental characterizations of the inter-ply slip behaviour are used to develop a general-purpose contact-friction algorithm for forming situations. The results shown are an important step towards the development of a simulation tool for single-curvature composite forming.

Use of carbon fibres for reinforcement of thin geopolymer cement sections

An alkali-activated aluminosilicate geopolymer cement was reinforced with polyether ether ketone-wound carbon fibre layers to improve the mechanical properties of the cement in flexion. Such a material, which is heat resistant and has a low coefficient of thermal expansion, will be of use in the development of out-of-autoclave processing routes for large area composite components. The mechanical and physicochemical properties of both the neat and reinforced cement were examined using Charpy impact and three-point bend testing and Fourier transform infrared spectroscopy. A five-fold improvement in flexural strength was observed for the fibre-reinforced geopolymer samples, while a three-fold improvement was observed in the impact strength. The coefficient of thermal expansion of the composite was determined using dilatometry. A number of different curing cycles were also examined using differential scanning calorimetry. The fibre reinforcement led to flexural strength improvement of up to 5 times as well as increasing the strain to failure.

Industrial cure monitoring of CBT using DEA for wind energy

Dielectric Analysis (DEA) is a widely used method to measure the cure of many common thermosetting resins systems such as epoxies, polyesters, polyurethanes, polyimides, silicones, bismaleimides and phenolics. The objective of this work is to investigate the curing characteristics of a thermoplastic, Cyclic Butylene Terephthalate (CBT) (supplied by Cyclics Corporation) which polymerises to form Polybutylene Terephthalate (PBT). This paper reports on the results of ongoing experimental investigations in which DEA is used to relate the curing cycle to composite structural features and mechanical performance of a complex composite part. Through adjustments in curing parameters, the significant processing parameters have been identified which optimise the production cycle for thermoplastic PBT composite parts. The recorded ion viscosity is used to determine change in material viscosity, cure rate and cure time. These results have been analysed and presented as a processing guide for correct process control.