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.
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”.
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.
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.
Diaphragm forming offers several advantages over other forming techniques in the manufacture of advanced thermoplastic composites. The technique can be used in the forming of parts with complex curvature and can produce excellent surface finish. This work investigates the effect of buckling in both single- and double-curvature moulds, while forming carbon fibre-reinforced poly(ether ether ketone) (APC-2). A control system was set up to provide linear displacement of parts at rates of 1–100 mm min−1. Buckling was established for both cross-ply and quasi-isotropic lay-ups in a double-curvature elliptical dish mould. Forming rate experiments were also carried out on a single-curvature 90° mould, with no buckling occurring at forming rates up to 100 mm min−1 The conditions likely to cause buckling were calculated for the 90° female mould, using both the tensile properties of the diaphragm material and interply shear data for APC-2 laminates. An investigation was also made into the spring-forward effect on 90° parts formed using male and female tools for both APC-2 and carbon fibre-reinforced poly(ether imide) materials. The parts made from the male tool using these materials had a larger spring-forward effect in each case. The influence of part thickness was investigated and found to reduce the spring forward which occurred. The effect of mould radius of curvature was also investigated and found to be negligible. The effect on part quality when varying the consolidation pressure was investigated for [0°/90°]2S and [0°/±45°/90°]S APC-2 lay-ups in the male 90° mould. The parts were ultrasonically C-scanned to assess their quality; interlaminar shear tests were also carried out to validate the ultrasonic tests. It was found that a consolidation pressure in excess of 200 kPa was required to fully consolidate these parts.
The development of industrial-scale manufacturing techniques for thermoplastic composites requires new processing technologies. The filament winding of thermoplastic preforms, such as powder-impregnated or intermingled yarns, would be more economical than winding of thermosets, if similar fibre placement speeds could be achieved for similar costs of equipment and preforms. The present experimental work compares two different processing techniques based on hot air and short wave infra-red spot heating, and discusses the influence of preheating the preforms and mandrel. The research work is based on powder-impregnated poly(ether imide) preforms, which are processed to hoop wound tube specimens. These preforms were commercialized under the trade name FIT (Fibres Impregnated with Thermoplastic) in the early 1980s. Characterization of the laminate quality is based on micrographs. The results show the importance of continuous heating at low heating rate. Discontinuous temperature peaks above the matrix melting temperature lead to its thermal degradation and therefore to poor laminate 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.
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 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.
A novel porous micro-nanostructure based on nickel disulfide (Ni3S2) nanoparticles interconnected with carbon nanotubes (CNTs) has been synthesized through a facile vulcanization with sulphur in the Ar + H2 (5%) atmosphere at 550 °C. The superior structural integrity of the Ni3S2/CNTs composites with abundant mesopores can be controlled by adjusting the amount of CNTs. The CNTs not only homogenously embed into every micro-nanostructure but also bridge between micro-nanostructures to form excellent integral conductive network. In the electrode, every Ni3S2/CNTs unit has a micro-nanostructure, resulting in fast transportation of ions and electrons. The experimental proofs reveal that the stable solid electrolyte interphase films on the outer surface of micro-nanostructures can assure the high columbic efficiencies and prevent the polysulfides shuttle effect, which plays an important role in the excellent cycling performance. The charge capacity retention of the Ni3S2/CNTs-10 electrode is up to 82.2% after 200 cycles at the current density of 0.5 A g−1. It shows a high initial coulombic efficiency (up to 83.2%) and stable voltage platforms at different current densities, suggesting that the Ni3S2/CNTs micro-nanostructure is a promising applicable anode candidate for sodium ion batteries.
This work focuses on the Riemann problem of Euler equations with global constant initial conditions and a single-point heating source, which comes from the physical problem of heating one-dimensional inviscid compressible constant flow. In order to deal with the source of Dirac delta-function, we propose an analytical frame of double classical Riemann problems (CRPs) coupling, which treats the fluids on both sides of the heating point as two separate classical Riemann problems and then couples them. Under the double CRPs frame, the Riemann solution is self-similar, and three types of structures are found. The theoretical analysis is also supported by the numerical simulation. Furthermore, the uniqueness of the Riemann solution is established with some restrictions on the Mach number of the initial condition.
The in-plane dynamic compressive behavior of a 2D twill weave carbon fiber reinforced composite was investigated using the split Hopkinson pressure bar (SHPB) apparatus. Constant strain rate loading was achieved with the adoption of pulse shapers within the experiments. A non-dimensional parameter was adopted to verify the stress equilibrium state of the specimens, which ensured the effectiveness of the experimental results. The upper limit of constant strain rate for the composite, which determines the achievable range of constant strain rate, was analytically estimated and verified by the experimental results. On this basis, the dynamic compressive behavior of the composite was investigated within the strain rate range of 193/s-846/s. The stress-strain curves were obtained under the studied strain rates, an empirical equation for the strengths under different strain rates was summarized. Based on the experimental results, a viscoelastic constitutive model was adopted to characterize the dynamic stress-strain response. Finally, the deformation process of the specimens recorded through high speed photography was discussed. Together with the microscopic observations, typical damage modes of the specimens were summarized
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.
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.
When designing filament-wound parts, use of an integrated strategy is recommended to take advantage of the benefits of composites despite limitations of the filament winding process. This paper describes a computer-integrated methodology for the design of filament-wound parts which includes: (1) initial part design using a computer-aided design system; (2) preliminary finite element analysis to determine ideal fibre orientations; (3) fibre path generation, including non-geodesics, to obtain feasible fibre paths; (4) choice of final lay-up sequence; and (5) composite finite element analysis to adapt the final lay-up until strength and stiffness requirements are met. The proposed methodology, embodied in the computer code CAWAR, is illustrated by application to a conical filament-wound part.
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.
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.
