Composites Manufacturing最新文献

In the pressforming of thermoplastic composite sheet, the heated laminate is rapidly formed into a mould. The moulding force is transmitted using either matched metal dies or by a rubber pad/metal mould combination. Friction must occur between the metal or rubber mould surface and the heated composite as the laminate moves across the tool surface until it is fully formed. This paper describes work carried out to characterize and measure these frictional forces. Composites such as unidirectional carbon fibre-reinforced poly(ether ether ketone) and glass fibre fabric-reinforced PA-12 have been tested, with rubber and tool steel as the mould materials. Two methods of testing were used, one comprising two fixed heated platens, between which the surfaces to be tested were placed while the composite was sheared from between the surfaces. Pulling-out force was achieved using a variable velocity shearing rig and by using dead-weight loading. A heated friction sled was also built which allowed various samples of metal and rubber material to be dragged across a heated composite sheet. The effects of varying surface temperature, normal pressure, surface fibre orientation and mould release agent were investigated. An adhesive bond was found to occur if the surfaces were left in contact during heating. By varying the shearing velocity, the friction between the composite and tool surface was found to be hydrodynamic in nature, i.e. velocity-dependent, at forming temperature.

Filament winding of composite materials with thermoplastic matrices is more complicated than wer winding of thermosetting composites, due to the much higher viscosity of thermoplastics. Therefore, winding parameters have to be optimized to achieve both good impregnation and high consolidation quality. In this study, the material investigated was impregnated with poly(ethylene terephthalate) powder and had a thin matrix sheath surrounding the flexible glass fibre bundles. It offers a high degree of flexibility compared with stiffer tapes, but is much more difficult to process by a filament winding technique, hence a specially developed filament winding device for processing these flexible fibre bundles is presented. The filament winding technique is the so-called in situ consolidation process, where the incoming yarn is welded to the previously wound surface. The processing parameters in this winding process are mandrel temperature, preheating temperature, nip-point temperature, tow tension, compaction force and winding speed. For this technique, the winding parameters were optimized to obtain a bulk composite structure without any defects if possible. To characterize the consolidation quality, the composite's interlaminar shear strength was determined. Furthermore, the density, flexural modulus and residual stresses in the wound rings were measured. From the point of view of economics, it is very important to increase the winding speed. For this reason a hot air preheating zone was developed. Thus the in situ consolidation process involved a further processing parameter: the preheating temperature. Winding speeds of up to 30 m min⁻¹ were realized using this preheating zone, without diminishing good consolidation quality.

The design and manufacture of fibre preforms for structural parts remains the major technical challenge in liquid composite moulding processes such as resin transfer moulding and structural reaction injection moulding. This paper sets out to identify new methods for preform design based upon fibre architecture in 2.5-dimensional preforms via a drape analysis. The predicted fibre geometry is related to models for permeability and elastic properties to generate property distributions over the part. These may then be used within finite element analyses to predict mould filling and structural performance. Experimental results are presented which include fibre distribution, in-plane permeability, elastic properties and structural tests. The integration of the stages within a design framework is discussed.

A series of experiments was conducted at 2.45 GHz to study the physical extent of the effective heating regions of the resonant modes, the perturbation of the cavity by fibre composites, and to check the integrity of the construction of the microwave resonator. Material factors investigated include fibre length, fibre orientation, composite stacking sequence, sample dimensions, sample position, electrical conductivity of the fibres and permittivity of the sample. The effects of fibre properties and sample geometries are reported here, as they related to optimization of materials processing techniques in the cylindrical applicator. The results of the investigation contribute to the optimization of sample and resonant applicator parameters for microwave processing of fibre composite materials.

The resin transfer moulding (RTM) process involves the loading of dry reinforcement into a mould. After the mould is closed, resin is flowed into the mould cavity and cured. The RTM process has traditionally been used to produce low fibre volume fraction composites. There is now increasing interest in using the process to manufacture high fibre volume fraction composites for structural applications. Experiments have been conducted to monitor the force required to compress a typical plain-woven glass fibre reinforcement. The load displacement curves for monotonic loading, and for relaxation after repeated reloading cycles to a maximum load are presented. The loading cycle responses for the fabric have been fitted to power-law relationships, and the relaxation cycles have been fitted to exponential decay functions.