Composites Manufacturing最新文献

The Advanced Research Projects Agency initiated a major technology effort to develop and demonstrate cost effective, advanced fabrication methods for marine structures. In situ consolidation of thermoplastic composite structures in concert with automated fibre placement offers the premise to produce affordable, high quality parts. In situ consolidation processing eliminates costs due to hand lay-up, bagging and autoclaving, as well as costs associated with acquiring, operating and maintaining an autoclave. Automated fibre placement with high quality and tight dimensional control offers the ability to make complex parts, to lay materials at any fibre angle and path, to vary bandwidth and to cure using in situ consolidation. This paper will present. process-related issues associated with the thermoplastic, hot gas, in situ consolidation of 61 cm diameter cylindrical demonstration models, NOL rings and test specimens to achieve low manufacturing costs. These process-related issues include process adaptation, throughput, part integration and scalability to larger diameter parts. Optimization of these factors in terms of manufacturing costs and quality (void content, mechanical properties) will enhance the development of the in situ consolidation fibre placement process into an affordable manufacturing technology. Thermoplastic materials investigated included carbon/poly(ether ether ketone) and carbon/poly(phenylene sulfide).

Macroscopic capillary pressure and microscopic interparticle forces due to surface tension are examined. A general equation for the capillary pressure during impregnation is derived and subsequently specialized to particular processes. For fibre composites, the capillary pressure can be of the order of ±10⁴ Pa, the sign depending on the contact angle between solid and liquid. Next, the attractive and repulsive forces between particles connected by liquid droplets are analysed by two different model geometries. At contact angles between π/2 and π, an equilibrium particle separation distance is obtained in the absence of applied force. At lower contact angles, spontaneous impregnation can be achieved. The effect of capillary action on impregnation rate may be significant if applied pressures are small (e.g. filament winding) but negligible at applied pressures greater than ∼100 kPa (e.g. compression moulding). The topology and concentration of voids may, however, be greatly influenced by surface energies.

This paper deals with increasing the speed of the infra-red (IR) heating cycle in the processing of thermoplastic composites. A constraint on the heating process is that all parts of the material must be within the recommended processing temperature range before forming can start. A mathematical model is used to predict the transient temperature distribution through the thickness of flat consolidated panels of continuous carbon fibre-reinforced poly(ether ether ketone) (APC-2) during heating. The model includes (i) natural convection, (ii) medium and long wave radiation and (iii) one-dimensional conduction through the material. Experimental validation of the model is conducted using an IR test rig. The following process parameters were varied to obtain optimum process conditions: (i) heater power: (ii) heater-to-composite distance: (iii) composite thickness; (iv) degree of oversizing of heater area compared with surface area of composite: and (v) one- or two-sided heating. Results presented show that reduction of the heater-to-composite distance from 100 to 50mm increases the steady-state temperature of the composite by 88%, whereas almost doubling the heater power density from 25.6 to 47.3 kWm² - increases the composite temperature by only 17%. Using one-sided heating, experimental results show that upward-facing heaters produce a more even temperature distribution across a panel surface than downward-facing heaters. Model results showing 1 R heating times for composite panels of thickness 0.5 to 9.5 mm are also presented.

The resin transfer moulding process involves the long-range flow of resin into a closed mould which is filled with dry fibre reinforcement. The rate of resin flow can be calculated using the Darcy and Kozeny-Carman equations. The flow rate is thus a function of the pressure drop across the fibre bed, the resin viscosity and the permeability of the fibre bed. The permeability constant is dependent on the fibre radius and the porosity of the bed. A number of reinforcement fabrics are now available commercially which promote faster resin flow than that in equivalent fabrics of the same areal weight at the same fibre volume fraction. The KozenyCarman equation includes a parameter known as the mean hydraulic radius. If this parameter is varied by calculating specific hydraulic radii, then the flow enhancement may be modelled. Calculations for model materials have been published and demonstrate that this approach predicts that significant changes in flow rate are possible. The commercial fabrics do not have model structures, but feature variations in the mesoscale architecture of the reinforcement: fibres clustered into tows and uneven distribution of pore space. The paper will report on the correlation of quantitative image analysis of optical micrographs with the flow rates in a range of reinforcement fabrics.