Composites Manufacturing最新文献

As the technology of composite structures matures, the use of thermoplastic composite materials in aircraft increases, offering reduced structural weight and improved payload. However, primary load-bearing applications demand optimum structural integrity in harsh environmental conditions, and the total installed manufacturing cost has previously restricted the use of thermoplastic materials. This paper describes a programme of work to develop a carbon fibre-reinforced thermoplastic transverse floor beam for a commercial jet. Component selection, material selection, design optimization, equipment, processing methods and testing are discussed. A cost model for the composite component is presented in comparison with that of the incumbent aluminium alloy beam. A key element of the work has been “design for manufacture”.

The pressure forming, or thermoforming, of preconsolidated continuous fibre-reinforced thermoplastic sheets offers a promising fabrication option for structural composite components. Modern thermoplastic polymers have improved mechanical and physical properties compared with their thermoset counterparts and, perhaps most important for industry, offer the possibility for rapid part production. As in tradational metal stamping, the current process and part design for thermoforming rely heavily on ‘trial and error’ practices which are costly, inefficient and provide little scope for optimization and understanding of the forming process. For efficient thermoforming information regarding temperature and pressure distribution, part thickness distribution, fibre orientations and potential regions of material defects must be determined. This paper presents some first results of an explicit finite element solution to simulate the forming process. At present a constant temperature process is assumed, however work is presently underway to include this effect.

Filament winding is one of the most challenging technologies to produce axisymmetrical or even nonsymmetrical structural thermoplastic composite shells with continuous fibre reinforcement. The aims of this contribution are: (1) to present results on laser-assisted high speed filament winding of pre-impregnated thermoplastic tapes and quasi-axial helical filament winding with direct flame, and (2) to compare different heating and pre-heating methods. The key issue in the application of thermoplastic tape winding is heating. Proper heating of pre-impregnated tapes during the on-line winding process can be achieved by a variety of methods: laser and infra-red radiation, hot gas and direct flame. It will be considered how the above heating methods affect the equipment and process costs, energy efficiency and response time.

When a rectangular sample of aligned, continuous fibre-reinforced composite is subjected to normal pressure, it has been observed that resin is squeezed out parallel to the fibres and the fibres flow transversely. The fibres deform so that the sample becomes barrel-shaped. A three-dimensional code has been developed to simulate this flow. The material is modelled as a transversely isotropic continuum in which the fibre direction is specified at each point by a vector a. The system of coupled equations is solved using a finite difference technique. The transverse and longitudinal viscosities are assumed to be functions of the fibre volume fraction which increases as the resin is forced to percolate parallel to the fibres. The stress equations of motion are discretized using central differences for a fixed orientation and the discretized equations are solved using a pseudo-time technique. The converged solution is then used to determine the change in fibre direction at each point of the continuum. The process is repeated in real time using the new fibre orientation. In the momentum equations, the viscous terms are treated explicitly and the pressure gradient implicitly. A projection method is used to ensure that the mass is conserved at each time step. The results are in broad agreement with the experimental observations and demonstrate the success of the continuum model to predict flow behaviour.

The paper investigates the suitability of the idealized fibre-reinforced fluid (IFRF) model for the thermoforming of fabric-reinforced thermoplastic sheets, and a strategy is proposed for determining the materials parameters required to characterize the sheet theological behaviour. The IFRF theory for a viscous fluid with two inextensible directions is developed for modelling fabric sheets and specific forms of the constitutive equation are derived. Some simple flows are analysed and it is shown that in throughthickness shear flows, as for example in a torsion rheometer experiment, the fabric angle ϖ remains constant, whereas in in-plane flows ϖ is a function of the strain rate. Trellis deformations are investigated by considering the in-plane stretching flow of a fabric with fibres inclined to the load direction. The torsion rheometer test is analysed for a fabric pre-deformed to a fabric angle ϖ. In this case, tests on rectangular specimens with different aspect ratios and fabric angles are proposed which enable the three viscosities in the model to be determined.