Composites Manufacturing最新文献

For the double diaphragm forming process, laminate wrinkling is a major failure mode for both thermoplastic and thermoset composites. In this paper, we compare experimental observations on the wrinkling of aligned fibre thermoset composites with theoretical scaling laws based on ideal kinematics (i.e. constant interfibre spacing and constant thickness). Differences between the ideal predictions and actual results are explained in terms of deviations from ideal kinematics. Differences between thermoplastic and thermoset composites are discussed, and an empirical scaling law for the effect of part size on wrinkling is given.

The anisotropic rheology of a model composite consisting of a temperature-sensitive viscous liquid matrix reinforced by aligned and virtually inextensible fibres of nylon has been studied experimentally using a custom-built linear oscillator. The composite was characterized dynamically both along and transverse to the fibre direction over a wide frequency range and for different fibre volume concentrations. Towards the limit of zero shear the composite was found to exhibit a yield stress. The temperature dependence of the matrix dynamic viscosity was used to study the dependence of the longitudinal and transverse dynamic viscosities of the composite on the dynamic viscosity of the matrix. The dependence of the composite dynamic viscosities on fibre volume concentration is compared with models of the steady shear dependence for aligned fibre systems that have been reported in the literature.

Powder impregnation techniques have been developed to increase design and manufacturing flexibility with thermoplastic composites. The effect of pressure, temperature, mould closing rate and time on the consolidation of poly(ether ketone ketone) (PEKK) powder impregnated glass fibre towpregs in compression moulding were studied. A design of experiments approach was used. Isothermal pultrusion experiments using nylon 11 and PEKK powder impregnated glass fibre tows were conducted. These experiments were repeated at different temperatures and pulling speeds. The microstructural changes during coating and consolidation of the powder impregnated tows were studied. Temperature and mould closing rate were observed to be the significant parameters affecting consolidation in compression moulding. Superposition of the pulling force-pulling speed data at different processing temperatures was demonstrated in pultrusion.

This paper presents a detailed statistical analysis on geometric imperfections recorded on two series of nominally identical composite cylinders. These defects can be classified in two categories, both due to the particular manufacturing method used: out-of-roundness and change of thickness due to the overlapping of various layers. The statistical analysis is developed for various purposes: to evaluate the common properties of cylinders with different laminations, to build up a characteristic model for the geometric imperfections suitable for probabilistic simulations in buckling analysis and to identify the parameters for quality control processes. The analysis of the change in thickness due to overlapping layers allows evaluation of the stiffening effects of the manufacturing process that, in some cases, could affect the buckling behaviour of composite cylinders. A standard procedure for the characterization and qualification of manufacturing processes for composite shells, with particular attention to the factors that influence their buckling behaviour, is proposed.

In this paper, the change of fibre orientation that occurs during the moulding flow of a composite material, based on a thermoplastic matrix reinforced by chopped fibres, is investigated. The fibre orientation is described by a distribution function which is divided into two elementary distribution functions, each being concerned with part of the fibres. The model presents the changes of these functions, taking into account the interaction between all fibres and the transverse shear. The model agrees with experimental data obtained in the flow of composites in a plate-type compression moulding process.

A novel process has been developed to manufacture pultruded fibre-reinforced furfuryl alcohol (FA) resin composites. In this paper, the effects of fibre reinforcement type and content on the static, dynamic mechanical and thermal properties of the FA resin pultruded composites are investigated. The mechanical properties increase with increasing volume content of the glass or carbon fibres, with the glass fibre-reinforced furfuryl alcohol (GF/FA) composite exhibiting maximum mechanical property values at a filler content of 5 phr. High catalyst content and die temperatures are necessary for manufacturing FA pultruded composites with high filler content. GF/FA pultruded composites retain their mechanical properties at elevated temperatures better than do unsaturated polyester pultruded composites. Dynamic mechanical analysis revealed that the dynamic storage modulus of the GF/FA pultruded composites increases with increasing post-cure time. Tan δ of GF/FA decreases and its glass transition temperature increases with decreasing pulling rate or increasing post-cure time. The glass and carbon fibre-reinforced FA pultruded composites possess high heat distortion temperature and good flexural properties, in comparison with other pultruded composites.

Furfuryl alcohol (FA) prepolymer was developed to fabricate pultruded fibre-reinforced FA resin composites. FA monomer with p-toluene sulfonic acid was used to synthesize the FA prepolymer, which provided a good balance between processing parameters (including pot life, reactivity and wetting ability) and properties of the composites. The reactions occurring during synthesis of the FA prepolymers and the post-curing treatment were investigated by ¹H n.m.r. and i.r. spectroscopies. It was found that the mechanical properties of the composites increase with increasing die temperature or decreasing pulling rate. From the study on the mechanical properties of the composites, it was found that an optimum post-cure time exists when the post-cure temperature is above 200°C. It was also found that three kinds of reaction - crosslinking, chain extension polymerization and the transformation of the methylene ether linkage to a methylene linkage -occur during the post-curing treatment.