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Abstract The development of a novel hot-stage microscopy technique to measure the level of cure shrinkage that occurs in an epoxy thermoset microdroplet with different epoxy-to-hardener ratios is presented. The equipment setup, sample preparation, and experimental procedure are described in detail. A comparable method to characterise cure shrinkage, a modified rheometry technique, is also reviewed. Shrinkage measurements using the hot-stage microscopy method are shown to characterise the full range of shrinkage that occurs both before and after the resin gel point, hence producing values greater than those found previously in the literature. However, when used in conjunction with the gel point values for the different ratios, measured using rheometry, the technique produces results for shrinkage post-gelation that concur well with literature values. The modified rheometry technique showed potential for measuring the level of cure shrinkage with a varying cure temperature profile, with more work required to perfect the method in defining the cross-over point for sample loading for different epoxy-to-hardener ratios. Highlights • A novel technique for measuring the cure shrinkage of an epoxy droplet is proposed. • The level of cure shrinkage that occurred was found to increase with the R value. • Hot-stage technique found to measure all possible shrinkage that would occur. • Gel point found to decrease with increases in R value. • Results were comparable to those in literature after accounting for gel point. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of polyamide 6 (PA 6) nanofibres and microfibres, as well as the effect of moisture present in these structures, on the curing kinetics of a diglycidyl ether of bisphenol A (DGEBA)-methylenedianiline (MDA) system. Modulated temperature differential scanning calorimetry measurements show that the initial reaction rate follows a linearly increasing trend as a function of the moisture content present in the nanofibrous structures. Compared to PA 6 microfibrous structures, incorporating PA 6 nanofibrous structures exposed to the same humidity resulted in a higher initial reaction rate, which is in agreement with the higher water absorption of the nanofibrous structure, measured with differential vapour sorption. Overall, the nanofibres themselves affect the curing characteristics, and the moisture present in the structures enhances this effect. [ABSTRACT FROM AUTHOR]

A certified aerospace resin (RTM 6) normally utilised for resin transfer moulding is considered for vacuum infusion. The resin was subjected to simulated vacuum infusion conditions by using a specialised thermogravimetric analysis that enables control of pressure as well as temperature. By varying conditions, it was possible to investigate the expected occurrence of volatile loses during infusion that could cause mechanical or cosmetic defects in a part. With particular reference to RTM6, it was determined that full vacuum could be used for infusion provided that the temperature was kept below ∼130 °C. Higher temperatures could be used, but the applied vacuum should be significantly reduced. Of note is that the manufacturers datasheet recommends processing parameters that could result in volatile loss. As such, the pressure enhanced TGA method may be considered more widely for providing processing conditions supplemental to the manufacturers recommendation for any liquid resin used under vacuum conditions. • Thermogravimetric assessment of RTM-6 resin with pressure and temperature control. • Mass loss begins to occur at > 130 °C, independent of pressure. • Cessation of mass loss appears to correlate with gel point. • Pressure and temperature region predicted to avoid mass loss. [ABSTRACT FROM AUTHOR]

In situ monitoring of resin flow, impregnation of carbon fiber fabrics, and curing during composite manufacturing are very important for determining the quality of composite parts. In conventional methods, sensors, such as optical fibers and strain gages, are bonded to or embedded in the composites for measuring the changes in mechanical and chemical properties. Although they can detect resin curing behavior and impregnation of carbon fibers, they may adversely affect the manufacturing process or structural integrity of the composites. In this study, carbon fiber itself was used as a sensor that minimizes the degradation of mechanical properties and increases the efficiency of monitoring the manufacturing process. The change in the electrical resistance of carbon fiber fabrics was monitored during the various manufacturing processes when the resin flowed through the carbon fiber fabric and curing progressed. The effectiveness of this monitoring method was confirmed, and it is expected to be applicable in monitoring the quality of the finished composite parts. Real-time, in situ monitoring of: •Resin flow. •Resin impregnation of carbon fiber fabrics. •Curing behavior of the resin during the resin transfer molding process to fabricate fiber-reinforced composite, using electrical resistivity measurement. [ABSTRACT FROM AUTHOR]