Carbon Fiber-reinforced Thermoplastic Composites Research Articles

A novel route for injection moulding of long carbon fibre-reinforced LLDPE

The scope of our work has been the development of a new type of coupling agent by which processing of long carbon fibre-reinforced thermoplastic composites by conventional injection moulding can be possible. The experimental additive was expected to hinder fibre breakage and to simultaneously improve the mechanical properties of the composites. Resistance of LLDPE reinforced with 1–10 wt% long carbon fibres against tensile, flexure and impact stresses has been investigated. Tensile strength of carbon fibre/LLDPE composites has increased by 10–30%; flexure strength has gained 15–90% related to the neat polymer depending on the fibre concentration. The effect of a blowing agent on the mechanical properties has also been investigated. At least 20% higher yield strength has been measured for the foamed sample with 5% carbon fibre related to the nonfoamed one with the same fibre content. The higher the fibre content was, the higher the improvements in the mechanical properties became. Fibre–matrix interaction has been studied on scanning electron microscopy graphs where a well-connected polymer layer has been observed to the fibre surface.

Surface modification of carbon fibers by a polyether sulfone emulsion sizing for increased interfacial adhesion with polyether sulfone

Interests on carbon fiber-reinforced thermoplastic composites are growing rapidly, but the challenges with poor interfacial adhesion have slowed their adoption. In this work, a polyether sulfone (PES) emulsion sizing was prepared successfully for increased interfacial adhesion of carbon fiber/PES composites. To obtain a high-quality PES emulsion sizing, the key factor, emulsifier concentration, was studied by dynamic light scattering technique. The results demonstrated that the suitable weight ratio of PES to emulsifier was 8:3, and the resulting PES emulsion sizing had an average particle diameter of 117nm and Zeta potential of −52.6mV. After sizing, the surface oxygen-containing functional groups, free energy and wettability of carbon fibers increased significantly, which were advantageous to promote molecular-level contact between carbon fiber and PES. Finally, short beam shear tests were performed to evaluate the interfacial adhesion of carbon fiber/PES composites. The results indicated that PES emulsion sizing played a critical role for the enhanced interfacial adhesion in carbon fiber/PES composites, and a 26% increase of interlaminar shear strength was achieved, because of the improved fiber surface wettability and interfacial compatibility between carbon fiber and PES.

Influence of residual thermal stress in carbon fiber-reinforced thermoplastic composites on interfacial fracture toughness evaluated by cyclic single-fiber push-out tests

Cyclic thermal expansion measurements and single-fiber push-out tests performed with a flat-end indenter tip have been conducted on unidirectional carbon fiber-reinforced thermoplastic composites. The cyclic thermal expansion measurements revealed process-induced residual thermal stress. By annealing the composite above the glass transition temperature of the Polyphenylene sulfide matrix, the residual thermal stress can be reduced. This is attributed to structural relaxation processes. The influence of residual thermal stress on the interfacial fracture toughness was investigated by push-out measurements. Using a cyclic loading schedule consisting of subsequent unloading–reloading cycles, the dissipative and non-dissipative energy contributions during push-out test can be evaluated separately. An adapted energy-based method allows the evaluation of the interfacial fracture toughness. Reducing the amount of residual thermal stress causes a change in failure behavior from brittle to quasi-ductile failure. The altered failure behavior leads to an increase in interfacial fracture toughness by a factor of 2.4.

Electrically conductive recycled carbon fibre-reinforced thermoplastic composites

Polypropylene (PP) thermoplastic composites were fabricated using recycled carbon fibres (rCFs; recovered from composite parts) and waste CFs (wCFs; generated during post-manufacturing processes). Both staple CFs (average 60 mm long) were blended with staple PP resin fibres (60 mm long) and then converted into yarns prior to the composite fabrication using hot-pressed moulding technique. It is found that the composites fabricated from wCFs contained longer CFs (40 mm long) and exhibited better electrical and mechanical properties (conductivity: 10.75 × 103 S m−1; tensile strength 160 MPa and modulus 45 GPa) compared with the composites fabricated from rCFs. It was concluded and recommended that both composite materials could be used as cost-effective and heating elements in lightweight applications.

Finite element analysis of an inelastic interface in ultrasonic welded metal/fibre-reinforced polymer joints

The ultrasonic welding technology is an innovative method to produce hybrid joints for multi-material components. In this contribution, the behaviour of an interface layer of metal/fibre-reinforced polymer single overlap tensile specimens is considered. The investigations are carried out using the ultrasonic metal welding technique (UMW) for joining carbon fibre reinforced thermoplastic composites (CFRP) with aluminium alloys. An interfacial traction-separation-law based on elastoplasticity with Lemaitre-type damage is applied. The finite element method is used for the analysis of damage evolution. Two-dimensional interface elements are employed for modelling the solid interface in a 3-D problem. Numerical simulations are carried out for three different interface geometries: square, elongated rectangle and cross rectangle. It is shown that damage develops slower in the specimen with square interface than in the specimen with rectangle interface. The damage parameter reaches the maximum value in every loadstep in the specimen with cross-rectangle interface. Comparison with experimental data shows that the damage process and the fractured zone are identical to simulated results for the specimen with square interface.

Ultrasonic Metal Welding of Aluminium Sheets to Carbon Fibre Reinforced Thermoplastic Composites

The ultrasonic welding technology is an innovative method to produce hybrid joints for multi-material components. The investigations described in this paper were carried out using the ultrasonic metal welding technique for joining carbon fibre reinforced thermoplastic composites (CFRP) with sheet metals like aluminium alloys or aluminium-plated steels. The achievable mechanical properties as a function of the process parameters are presented. Additionally, microscopic investigations of the bonding zone are discussed. One important advantage of ultrasonic metal welding is the possibility to realise a direct contact between the load bearing fibres of the reinforced composite and the metallic surface without destroying the carbon fibres.

Frequency Analysis and Process Monitoring in Drilling of Composite Materials

Drilling experiments were conducted using carbide and cryogenic treated carbide drills into carbon fiber-reinforced thermoplastic composites, namly Graphite/PIXA-M (PIXA-M) composites. Drilling force signals were collected from all conditions and analysed using fast Fourier transformations and autoregressive (AR) time series models. Power spectrums were used to examine the cutting characteristics in the drilling process. AR coefficients were used to distinguish the cutting signals of autoclaved and induction heated PIXA-M composites, and conventional and cryogenic treated carbide drills.

Experimental determination of the effects of industrial oil immersion on polymer-based composites

This paper presents a unique set of experimental data on the long-term oil immersion effects on various carbon fiber-reinforced thermoplastic composites. Five materials—unidirectional AS4/PEEK, unidirectional AS4/PPS, unidirectional AS4/PEI, woven AS4/PEI, and short random AS4/PFA—were immersed in oil and water for several months at four temperatures between room temperature and 80 °C. The weights of the four samples were monitored. The samples exposed to oil were tested via Dynamic Mechanical Analysis (DMA). The results show that the four AS4/PEEK, AS4/PPS, AS4/PEI and woven AS4/PEI composites did not exhibit any changes in thermo-mechanical properties. However, the Teflon-based composite showed significantly altered behavior despite no changes in weight. The glass transition temperature was lowered by 30 °C after a 2-month immersion in oil (independently of the temperature). No change in the glass transition temperature but a stiffness degradation was observed after immersion in water. A dramatic decrease in the glass transition temperature of reinforced PFA can be attributed solely to prolonged industrial oil contact including that at room temperature.

Impact behaviour and damage tolerance of woven carbon fibre-reinforced thermoplastic composites

Instrumented drop weight impact and compression after impact test methods were used to assess the impact performance and damage tolerance of firm-stacked, woven carbon fibre-reinforced PEEK and woven carbon fibre-reinforced PPS composite systems. The tests were performed at three energy levels with a constant velocity, and at three velocity levels with a constant energy. Extreme energy of the levels were also determined. While the effect of the impact velocity was found to be significant within the range of the velocities used, the impact energy significantly affected the impact performance of the panels. Carbon fibre PPS panels evinced a high resistance to perforation by way of extensive delamination. On the other hand, carbon fibre PEEK panels showed an ability to confine the damage zone and hence, to markedly increase the damage tolerance of the panels. A set of material selection criteria for impact applications, based on the results of this study, has bee proposed

Processing and properties of pultruded thermoplastic composites (I)

A feasibility study of pultrusion of fibre-reinforced thermoplastic composites has been conducted using a proprietary method. The thermoplastic matrices studied included Nylon 6. pmm and tpu. The fibre reinforcements investigated included glass fibre, carbon fibre and Kevlar 49 aramid fibre. Mechanical and thermal properties of unidirectional fibre-reinforced Nylon 6, pmma and tpu composites were measured. Experimental results for tensile strength agree with the prediction of the rule of mixtures. Kevlar fibre-reinforced thermoplastic composites possess the highest notched Izod impact strength and specific tensile strength, whereas carbon fibre-reinforced thermoplastic composites show excellent tensile strength and flexural strength. A scanning electron microscopic study was conducted to investigate the interfacial adhesion between fibre and matrix. Results showed that the fibre can be well impregnated by thermoplastic matrices.

Impact behaviour and damage tolerance of woven carbon fibre-reinforced thermoplastic composites

Instrumented drop weight impact and compression after impact test methods were used to assess the impact performance and damage tolerance of film-stacked, woven carbon fibre-reinforced PEEK and woven carbon fibre-reinforced PPS composite systems. The tests were performed at three energy levels with a constant velocity, and at three velocity levels with a constant energy. Extreme energy levels were also determined. While the effect of the impact velocity was found to be insignificant within the range of the velocities used, the impact energy significantly affected the impact performance of the panels. Carbon fibre PPS panels evinced a high resistance to perforation byway of extensive delamination. On the other hand, carbon fibre PEEK panels showed an ability to confine the damage zone and hence, to markedly increase the damage tolerance of the panels. A set of material selection criteria for impact applications, based on the results of this study, has been proposed.