Surface analysis of environmentally exposed painted composites manufactured from Quickstep and autoclave processes

The surface finishes of laminates produced by Quickstep™ and autoclave processes for use in automotive outer skin panels were compared. Automotive quality, painted carbon fibre samples, manufactured via both processes, were exposed to typical exposure environments including combinations of temperature (70, 120, 170°C), UV-B, humidity (95% RH) and immersion in water.

The microscopy and surface roughness results demonstrated that the surfaces produced by the Quickstep process were less susceptible to damage in the aging environments than the surfaces of the autoclaved samples. Quickstep samples displayed surface bubbling of only 5 μm, compared to the autoclaved surface bubbles which reached a diameter of 30 mm before bursting, with complete delamination occurring between the paint and the composite. The surface roughness measurements revealed the autoclave samples (Ra = 0.72 μm) were up to three times the roughness of the Quickstep samples (Ra = 0.23 μm).

Characterisation of an out-of-autoclave resin film infusion process for textile composites

A new method to manufacture damage tolerant textile composites, which combines Resin Film Infusion with a fast and cost·efficient curing technology QuickstepTM, was investigated. The effect of process parameters on resin flow through carbon fibre preforms was analysed and model-based parameter optimisation resulted in considerable improvement of resin flow properties.

Characterisation of out-of-autoclave carbon fibre composites

Out-of-autoclave processing parameters were tailored to investigate the effect of resin viscosity on mechanical performance. Faster heating rates improved the shear and fracture mechanisms of carbon fibre composites by improving their fibre to matrix adhesion, as a result of a decrease in resin viscosity.

Rapidly cured out-of-autoclave laminates: understanding and controlling the effect of voids on laminate fracture toughness

Voids are one of the most significant defects found within composites and have been demonstrated to reduce the performance of composite structures. The understanding of the impact of the size and distribution of voids on laminate properties is still limited because voids have proven difficult to deliberately control. This study aims to understand the mechanisms by which voids are generated within out-of-autoclave cured laminates. In this study, a process of prepreg conditioning was developed to control the level of voids within test laminates. Non-conditioned laminates highlighted signs of void growth (1.5%), while conditioned laminates showed consistently low levels of voids (<0.3%). Mass spectrometry indicated higher levels of aqueous and solvent volatiles within the non-conditioned prepreg. Finally, Mode II fracture testing revealed a 21% improvement in toughness for the non-voided laminates. A model on the effect of voids within the Mode II stress state has also been proposed.

Effect of the manufacturing process on the interlaminar fracture toughness of 2/2 twill weave fabric carbon/epoxy composites

A 2/2 twill weave fabric carbon fibre reinforced epoxy matrix composite MTM56/CF0300 was used to investigate the effect of different manufacturing processes on the interlaminar fracture toughness. Double cantilever beam tests were performed on composites manufactured by hot press, autoclave and 'Quickstep' processes. The 'Quickstep' process was recently developed in Perth, Western Australia for the manufacture of advanced composite components. The values of the mode I critical strain energy release rate (G1d were compared and the results showed that the composite specimens manufactured by the autoclave and the 'Quickstep' process had much higher interlaminar fracture toughness than the specimen produced by the hot press. When compared to specimens manufactured by the hot press, the interlaminar fracture toughness values of the Quickstep and autoclave samples were 38% and 49% higher respectively. The 'Quickstep' process produced composite specimens that had comparable interlaminar fracture toughness to autoclave manufactured composites. Scanning electron microscopy (SEM) was employed to study the topography of the mode I interlaminar fracture surface and dynamic mechanical analysis (DMA) was performed to investigate the fibre/matrix interphase. SEM micrography and DMA spectra indicated that autoclave and 'Quickstep' produced composites with stronger fibre/matrix adhesion than hot press.

An experimental study of low velocity impact response in 2/2 twill weave composite laminates manufactured by a novel fabrication process

A novel fabrication process for advanced composite components—the QuicktepTM process was described. 2/2 twill weave MTM56/CF0300 carbon epoxy composite laminates were manufactured by the Quickstep and the autoclave processes. The response of these laminates to drop-weight low velocity impact at energy levels ranging from 5 to 30 J was investigated. It was found that the laminates fabricated by the Quickstep had better impact damage tolerance than those fabricated by the autoclave. Optical microscopy revealed extensive matrix fracture in the center of the backside of the autoclave laminates indicating the more brittle property of the epoxy matrix cured by the autoclave process. Interfacial shear strength (IFSS) for two composite systems were measured by micro–debond experiments. The MTM56/CF0300 material cured by the Quickstep showed stronger fibre matrix adhesion. Since the thickness and density of the impact targets produced by two processes were different, finite element analysis (FEA) was performed to study the effect of these factors on the impact response. The simulation results showed that the difference in thickness and density affects the stress distribution under impact loading. Higher thickness and lower density caused by processing lead to less endurance to drop weight impact loading. Therefore the better performance of Quickstep laminates under impact loading was not due to the thickness and density change, but resulted from stronger mechanical properties.

Characterization and analysis of delamination fracture and nanocreep properties in carbon epoxy composites manufactured by different processes

Delamination resistance and nanocreep properties of 2/2 twill weave carbon epoxy composites manufactured by hot press, autoclave, and Quickstep^TM process are characterized and analyzed. Quickstep is a fluid filled, balanced pressure heated floating mold technology, which is recently developed in Perth, Western Australia for the manufacture of advanced composite components. Mode I and Mode II interlaminar fracture toughness tests, and nanoindentation creep tests on matrix materials show that the fast ramp rate of the Quickstep process provides mechanical properties comparable to that of autoclave at a lower cost for composite manufacturing. Low viscosity during ramping process and good fiber wetting are believed to be the reasons that this process produces composites with high delamination and creep-resistant properties. Nanocreep properties are analyzed using a Kelvin–Voigt model.

Rapid composite tube manufacture utilizing the quickstep™ process

In this study, a novel method for manufacturing composite tubes utilizing the Quickstep^TM process has been developed. Tubes manufactured from `quick-cure' Toray G83C prepreg have demonstrated highly repeatable axial crush behavior with an average specific energy absorption (SEA) of 86 kJ/kg. The cure cycle is optimized by comparing the results from compression, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and porosity testing. The tube lay-up is optimized using compression and porosity test results. The effect of changes in fiber-orientation on SEA is also investigated. Process development has resulted in a robust manufacturing method capable of producing fully cured, high performance composite tubes with a cure cycle of 7 min. This corresponds to a 95% reduction in time compared to an equivalent autoclave cycle.

Manufacturing influence on the delamination fracture behavior of the T800H/3900-2 carbon fiber reinforced polymer composites

'Torayca' T800H/3900-2 is the first material qualified on Boeing Material Specification (BMS 8-276) which utilizes the thermoplastic-particulate interlayer toughening technology. Two manufacturing processes, the autoclave process and the fast heating rated Quickstep™ process, were employed to cure this material. The Quickstep process is a unique composite production technology which utilizes the fast heat transfer rate of fluid to heat and cure polymer composite components. The manufacturing influence on the mode I delamination fracture toughness of laminates was investigated by performing double cantilever beam tests. The composite specimens fabricated by two processes exhibited dissimilar delamination resistance curves (R-curves) under mode I loading. The initial value of fracture toughness GIC-INIT was 564 J/m2 for the autoclave specimens and 527 J/m2 for the Quickstep specimens. However, the average propagation fracture toughness GIC-PROP was 783 J/m2 for the Quickstep specimens, which was 2.6 times of that for the autoclave specimens. The mechanism of fracture occurred during delamination was studied under scanning electron microscope (SEM). Three types of fracture were observed: the interlayer fracture, the interface fracture, and the intralaminar fracture. These three types of fracture played different roles in affecting the delamination resistance curves during the crack growth. More fiber bridging was found in the process of delamination for the Quickstep specimens. Better fiber/matrix adhesion was found in the Quickstep specimens by conducting indentation-debond tests.

Characterization of melded carbon fibre/epoxy laminates

‘Melding’ is a novel in situ method for joining thermosetting composite structures, without the need of adhesives. Laminate joining is achieved using uncrosslinked resin matrix of the pre-preg. This study used Hexply914C pre-preg material to characterize melded CFRP structures produced using the melding method. A designated area of a laminate was maintained at temperatures below 40 °C retaining uncured (B-staged) material, while the remainder of the laminate was cured at 175 °C. After a 2.5 h cure cycle, the cured region showed a high degree of cure (0.88) and glass transition temperature (176 °C). The uncured area of the same laminate was cured in a second stage, simulating an in situ melded joint. By controlling the temperature and duration of the intermediate dwell and affecting minimum viscosity values prior to final cure, low values of porosity (<0.5%) were achieved. The mechanical properties of the resulting joint were consistent throughout the melded laminate. Flexural strength (1600 MPa), flexural modulus (100–105 MPa) and short beam strength (105–115 MPa) values observed where equivalent or greater than those found in the recommended autoclave cured control specimens. After the entire laminate was post cured, glass transition temperatures of 230 °C (peak tan δ) were observed in all areas of the laminate.

The effect of cure cycle heating rate on the fibre/matrix interface

Development of civil aerospace composites is key to future “greener” aircraft. Aircraft manufacturers must improve efficiency of their product and manufacturing processes to remain viable. The aerospace industry is undergoing a materials revolution in the design and manufacture of composite airframes. The Airbus A350 and Boeing 787 (both due to enter service in the latter part of this decade) will push utilisation levels of  composite materials beyond 50% of the total airframe by weight. This  change requires massive investment in materials technology, manufacturing capability and skills development. The Quickstep process provides the ability to rapidly cure aerospace standard composite materials whilst providing enhanced mechanical properties. Utilising fluid to transfer heat to the   composite component during the curing process allows far higher heat rates than with conventional cure techniques. The rapid heat-up rates reduce the viscosity of the resin system greatly to provide a longer processing window introducing greater flexibility and removing the need for high pressure during cure. Interlaminar fracture toughness (Mode I) and Interfacial Shear Strength of aerospace standard materials cured using Quickstep have been    compared to autoclave cured laminates. Results suggest an improvement in fibre-matrix adhesion.

Manufacturing process effects on the mode I interlaminar fracture toughness and nanocreep properties of CFRP

Quickstep ™ is a fluid filled floating mould technology which was recently developed by an Australian company of the same name. The Quickstep and conventional autoclave manufacture of composites were compared by investigating the mode I interlaminar fracture toughness and nanocreep propeties of HexPly914 carbon epoxy composites. It was found that composites cured using the Quickstep technology had significantly higher fracture toughness (1.8 times) than the composites cured via autoclave for this system. DMTA (dynamic mechanical thermal analysis) results showed a higher Tg (glass transition temperature) for the material manufactured by the Quickstep than that cured by the autoclave. FTIR (Fourier transform infrared spectroscopy) spectra did not indicate any difference in cure chemistry between the two processes. Nanocreep experiments were performed to explore the viscoelastic properties of the epoxy matrix of composites. The KelvinVoigt three-element model was applied to analyse the indentation creep behaviour of both composites.

Inspection of drop-weight impact damage in woven CFRP laminates fabricated by different processes

The influence of manufacturing process on the drop-weight impact damage in woven carbon/epoxy laminates was inspected by visual observation, dyepenetrant X-ray technique, and optical microscopy observation. The MTM56/ CF0300 woven quasi-isotropic laminates were fabricated by two processes: the autoclave and the Quickstep processes. Quickstep^TM is a novel composite manufacturing process, which was designed for the out-of-autoclave production of high-quality composite parts at lower cost. It utilizes higher heat conduction of fluid other than gas to transfer heat to components, which results in much shorter cure cycles. The laminates cured by this fast heating process showed different impact failure modes from those cured by the conventional autoclave process. The residual indentation in the top side of the Quickstep-cured laminates had a bigger diameter, but a smaller depth at the same impact energy level. Dye-penetrant X-ray revealed more intense and connected impact damage regions in the autoclave-cured laminates. Optical micrography as a supplementary method showed less severe matrix damage in the quickstep-cured laminates indicating a more ductile property of the resin matrix cured at a faster heating rate.