Comparative studies were carried out on the cure kinetics of an epoxy resin Araldite LY 5052 and a hardener, 4 4’ Diaminodiphenyl sulfone. Differential scanning calorimetry and a microwave heating calorimeter were used to monitor the curing kinetics of conventionally and microwave cured epoxy samples. These studies were carried out under isothermal conditions using four different temperatures. There was a significant increase in the fractional conversion of the microwave cured samples compared to the conventionally cured samples. The curing reactions for samples cured using microwave heating took place over a smaller temperature range. Higher reaction rates were observed in the samples cured using microwave heating.During the isothermal curing, higher K1 and K2 kinetic parameters were observed in microwave cured samples. A lower K1 / K2 ratio was observed in microwave curing than in conventional curing. This is attributed to the enhancement of the catalytic reaction over the non-catalytic reaction by the microwave radiation which occurs as a result of the high activity of the [OH] group.

The thermo-mechanical performance of extruded wheat starch/flour containing different additives was examined via microwave-heated thermo-mechanical analysis. Additionally, the dielectric property of the wheat starch-based materials was also studied using a microwave calorimeter. It has been found that when glycerol or polyvinyl alcohol was used as single additive in wheat starch, a content limit existed and using the additives at a concentration higher than the limit will lead to deterioration of the material’s microwave foamability. A good initial thermal expansion is essential for a proper foaming of the wheat starch-based materials; however, high enough dielectric loss factor (ɛ″) is also required for the formation of foam structure under microwave radiation. Glass transition temperature ( Tg) for the extruded wheat starch materials was detected by microwave thermo-mechanical analysis at about 75–95°C when heated at 15°C/min; and for the foamable formulations, the foaming temperature ( Tf) is generally 10–20°C higher than the corresponding Tg. Impurities like proteins play important roles in the microwave foaming of extruded wheat flour. Overall, the extruded wheat flour with additives is more difficult to foam under microwave heating than the wheat starch extruded from the similar formulations.

Extruded pellets from starch-based materials have been heated and foamed under microwave radiation. The foaming mechanisms and effects of some additives on the dielectric properties of the materials have been investigated using a microwave calorimeter. A rapid increase in dielectric loss factor (ɛ″) has been found for all the tested materials foamable under microwave heating and the onset of the ɛ″ increase is considered to be correlated to glass transition. It has been found that extruded starch materials can be foamed at 15℃/min but the expansion level reduced compared with that of the same material foamed at higher heating rate. The incorporation of organic additives in starch-based materials generally led to significant decrease of their microwave foamability when glycerol and polyvinyl alcohol are used as the additives in the extruded pellets.

Fully cured epoxy samples of Araldite DLS 772 / 4 4' DDS with an amine to epoxy ratio of 0.8M were dissolved in 4M nitric acid in a microwave reaction system at a temperature of 120 o C for a total of 75 minutes. The dissolved compound was collected and dried. High Performance Liquid Chromatography was used to analyze and separate the components in the compound. Infrared spectroscopy, nuclear magnetic resonance spectroscopy and electrospray ionization mass spectrometry was used to identify the dissolved product. The dissolved product was identified as 1, 3 - di(ethyl ester)-5-(diethyl amino)-2-hydroxybenzene.

Samples of an epoxy resin system, based on Araldite DLS 772 and 4 4’ DDS (a hardener) with an amine / epoxy ratio of 0.8 were cured using conventional and microwave heating. The cured samples were cut into the required dimensions using ASTM standards, and then subjected to Density, Dynamic Mechanical Thermal Analysis and Flexural tests. It was observed that the microwave cured samples had a higher glass transition temperature (Tg), a higher flexural strength, higher cross-link density (ν) and lower molecular weight between cross-links than the conventionally cured samples. The results showed that the microwave cured samples had a more compact network structure, and suggest a better stiff ness and strength in the microwave cured samples. This improved stiffness is ascribed to a better molecular alignment and a greater homogeneity which is found in the microwave cured samples.

Comparative studies were carried out on the curing kinetics of an epoxy resin Araldite DLS 772 mixed with a hardener, 4 4’ Diaminodiphenyl sulfone. Differential scanning calorimetry and a microwave heating calorimeter were used to monitor the curing kinetics of conventionally and microwave cured epoxy samples. These studies were carried out under non-isothermal conditions using five different heating rates. There was a significant increase in the fractional conversion of the microwave cured samples compared to the conventionally cured samples. The curing reactions for samples cured using microwave heating took place over a smaller temperature range. Higher reaction rates were observed in the samples cured using microwave heating. The activation energies of the microwave cured samples of Araldite DLS 772 / 4 4’DDS epoxy system were about ten percent lower than activation energies of conventionally cured samples. Keywordscuring; differential scanning calorimetry; epoxy; microwave heated calorimeter; kinetics ————————————————————

While there are reports concerning the processing and properties of materials using Quickstep technique, little attention has been paid to the hygrothermal degradation of the flexural, interfacial and glass transition behaviours of polymeric composites cured at a relatively high ramp rate of 10Kmin−1 (typical of Quickstep processing). Composite laminates were manufactured in an autoclave and using Quickstep and then conditioned in a climatic chamber at 70°C and 85% RH until reaching the limit of saturation. The interfacial (interlaminar shear strength (ILSS)), flexural (flexural strength) and glass transition (Tg) properties of the conditioned and unconditioned panels were evaluated. The results demonstrated that the moisture absorption caused the deleterious effect on the properties and that the reduction in the flexural, interfacial and glass transition properties of Quickstep panels was comparable to that observed in autoclave cured panels. Thermal stability, reversible and irreversible effects of hygrothermal conditioning using TGA, DMTA and FT-IR spectroscopy was also investigated and discussed.

A woven fabric carbon fibre reinforced epoxy matrix composite (Cycom® 977-2A/6KHTA) has been used to investigate the effect of different processing techniques on its physical and mechanical properties. Composites are manufactured by oven curing, hot press and the ‘Quickstep’ processes. Quickstep is a novel polymer composite processing technique designed for out-of-autoclave processing of high quality, low cost components in comparatively shorter cure cycle time. Mechanical (Flexural strength, Interlaminar shear strength (ILSS)) and physical properties (fibre volume fraction, void content, glass transition temperature) of composites manufactured using Quickstep were found to be comparable with those made using thermal oven and a hot press. Oven cured and hot press panels were manufactured by the recommended cure cycle from the material manufacturer, however, the cure cycle employed for Quickstep was different based on the higher ramp rate achievable through Quickstep. Manipulation of cure cycle for Quickstep was done for further optimization to get the best properties at the shortest possible time. The time at two dwell temperatures (130 oC and 180 oC) was manipulated and the effects on physical and mechanical properties were evaluated. It was observed that when the dwell time decreases, resin rich areas formed in the panels resulted in the reduction of physical and mechanical properties.

T. Corbett et al. have successfully melded lap joints and it has been shown that the transition zone between the cured and uncured regions is less than 40 mm. [1] This work aims to manufacture a 160 ply (20 mm) by melding through the thickness of a laminate by joining two half cured 80 ply (10 mm) panels. Unidirectional Hexcel 8552 CFRPs were partially cured along the z-axis using a modified hot press, then joined using the Quickstep chamber. The fully melded panel was shown to have similar degree of cure (between 88% and 98% cured) as a panel cured by traditional methods. Although the panel was fully cured, a great deal Work is also underway to design a Quickstep chamber that will allow for through-thickness melding.

ABSTRACT This paper focuses on the development of a laminate containing optical sensors using a novel cure process and the detection of the load distribution in a structure. An array of Fiber Bragg Grating (FBG) sensors embedded in a carbon laminate has been manufactured using an out of autoclave process, called the Quickstep process, which permits shortening of cure time. The internal strain changes of FBG sensors were observed during the manufacturing process and static loading test. The sensors remain stable during manufacturing process and the temperature responses of sensors prove that the cure process was suitable. Embedded FBGs show the promising static loading sensitivity and repeatability.

The cure of a commercial epoxy resin system, RTM6, was investigated using a conventional differential scanning calorimeter and a microwave-heated calorimeter. Two curing methods, dynamic and isothermal, were carried out and the degree of cure and the reaction rates were compared. Several kinetics models ranging from a simple nth order model to more complicated models comprising nth order and autocatalytic kinetics models were used to describe the curing processes. The results showed that the resin cured isothermally showed similar cure times and final degree of cure using both conventional and microwave heating methods, suggesting similar curing mechanisms using both heating methods. The dynamic curing data were, however, different using two heating methods, possibly suggesting different curing mechanisms. Near-infrared spectroscopy showed that in the dynamic curing of RTM6 using microwave heating, the epoxy-amine reaction proceeded more rapidly than did the epoxy-hydroxyl reaction. This was not the case during conventional curing of this resin. (c) 2006 Wiley Periodicals, Inc.

Although the autoclave technique produces composite parts of high quality, the process is time consuming and has intrinsically high capital and operating costs. QuickstepTM is a novel polymer composite manufacturing technique designed for the out-of-autoclave processing of highquality, low-cost components with a reduction in cure-cycle times. This paper assesses the use of the Quickstep method for the processing of an epoxy-carbon fibre aerospace composite material. The Quickstep process is compared both to a thermal vacuum-bag only process and the manufacturer’s specifications for autoclave cured panels. Higher process ramp rates, achievable by using Quickstep, have been shown to reduce resin viscosity and facilitate void removal. Through manipulation of the Quickstep cure cycle while the resin is at low viscosity, significant effects on the mechanical properties of the product are demonstrated. Using Quickstep curing it has been found that better interlaminar properties than the manufacturers autoclave data could be obtained while the flexural strength was a little lower. The work identifies key parameters associated with the Quickstep process giving an insight into how it can be optimised further in an attempt to produce panel properties that rival those produced by autoclave methods.

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.

An instrument has been developed for monitoring cure processes under microwave heating conditions. The main function of the instrument was a calorimeter for performing microwave thermal analysis. A single mode resonant cavity was used as the heating cell in the microwave calorimeter. Thermal analysis measurements were obtained by monitoring the variation in the microwave power that was required to maintain controlled heating of the sample. The microwave thermal analysis data were analogous to conventional differential scanning calorimetry measurements. The dielectric properties of the sample, as a function of the extent of cure, have been obtained using perturbation theory from the changes in resonant frequency and quality factor of the microwave cavity during heating. Additionally, remote sensing fibre-optic probes have been employed to measure real time in situ infrared spectra of the sample during the cure reaction. In this paper, we describe the design and operation of the microwave calorimeter. Examples of experimental results are also presented.

SUMMARY A novel out-of-autoclave polymer composite material processing technology is described. The Quickstep manufacturing technique uses a liquid to transfer heat to the uncured laminate stack, enabling precise control of the stack temperature and a considerable reduction of cure-cycle times. Plant and tool structural requirements are significantly reduced compared to those of an autoclave process by eliminating the need for high consolidation pressures. This paper assesses the suitability of the Quickstep technique for the processing of a typical aerospace composite material, 914/40/G703 carbon epoxy prepreg. Laminate test specimens have been manufactured using various Quickstep process cycles and a conventional autoclave cycle. Physical and mechanical properties of the specimens have been measured and are reported. Comparable physical and chemical property data were obtained for the Quickstep and autoclave processed composites with the Quickstep process achieving a significant reduction in the overall process cycle time and estimated manufacturing costs.