Zuoguang Zhang

Rapid Curing Epoxy Resin and Its Application in Carbon Fibre Composite Fabricated Using Vartm Moulding

A rapid curing resin system made from the diglycidyl ether of bisphenol A epoxy, modified imidazole and modified aliphatic amine was developed. The curing behaviour and following characteristic of the resin were evaluated by differential scanning calorimetric and rheological analysis, respectively. Carbon fibre-reinforced polymer composite (CFRP) laminates using this resin system were manufactured through vacuum-assisted resin transfer moulding (VARTM) under short-term curing schedule. Subsequently, studies were performed on the processing quality, mechanical properties and heat resistance of the composites. The effects of post-cure duration on the interfacial bonding and the properties of the composites were investigated. The results showed that the curing time of a CFRP laminate using the studied resin under 120 °C could be controlled within 13 min with more than 95% curing degree and few defects. There were variations of the mechanical and thermal properties of the composites with different post-cure durations. The optimum properties were obtained after a post-cure process of 60 min, and extended post-cure treatment were detrimental. The corresponding mechanism was discussed from the viewpoint of interfacial bonding between carbon fibre and epoxy matrix.

Effects of Processing Parameters on the Forming Quality of C-Shaped Thermosetting Composite Laminates in Hot Diaphragm Forming Process

In this study, the effects of processing temperature and vacuum applying rate on the forming quality of C-shaped carbon fiber reinforced epoxy resin matrix composite laminates during hot diaphragm forming process were investigated. C-shaped prepreg preforms were produced using a home-made hot diaphragm forming equipment. The thickness variations of the preforms and the manufacturing defects after diaphragm forming process, including fiber wrinkling and voids, were evaluated to understand the forming mechanism. Furthermore, both interlaminar slipping friction and compaction behavior of the prepreg stacks were experimentally analyzed for showing the importance of the processing parameters. In addition, autoclave processing was used to cure the C-shaped preforms to investigate the changes of the defects before and after cure process. The results show that the C-shaped prepreg preforms with good forming quality can be achieved through increasing processing temperature and reducing vacuum applying rate, which obviously promote prepreg interlaminar slipping process. The process temperature and forming rate in hot diaphragm forming process strongly influence prepreg interply frictional force, and the maximum interlaminar frictional force can be taken as a key parameter for processing parameter optimization. Autoclave process is effective in eliminating voids in the preforms and can alleviate fiber wrinkles to a certain extent.

Correlation of temperature dependences of macro- and micro-interfacial properties in carbon fiber/epoxy resin composite

The short beam shear test and single fiber fragmentation test with an energy-based model were conducted to characterize the interfacial properties of two types of carbon fiber–reinforced epoxy resin composites. The temperature dependences of interlaminar shear strength and interfacial fracture energy (Γi) from room temperature to 130°C were investigated. The correlation between interlaminar shear strength and the micro-interfacial property at elevated temperature was discussed. The scanning electron microscope images of fractographic cross-sections of the composite laminates were used to analyze the failure mode transition as the temperature rising. The results show that the interfacial properties of the two carbon fiber composites with the same matrix are obviously different, especially at high temperature. The changes of interlaminar shear strength and interfacial fracture energy are different at elevated temperature, mainly ascribed to the different treating ways of thermal residual stress and matrix property in the two methods. The similar temperature sensitivities in the changes of Γi and the amount of matrix adhering on carbon fibers in the short beam shear failure images suggest the variations of the micro-interfacial properties in the short beam test as increasing temperature.

Interfacial adhesion and micro-failure phenomena in multi-fiber micro-composites using fragmentation test

Statistical fragments and micro-failure modes in the multi-fiber-reinforced micro-composites were investigated by fragmentation test. The specimen consisted of three fibers using carbon fibers (CFs) and glass fibers (GFs), embedded in the epoxy resin with three-dimensional arrangement. Fracture morphology and micro-failure behavior from the progressive fragmentation of fibers and fiber/matrix interfacial adhesion were observed via polarized-light microscope. The interfacial shear strength of CF/epoxy micro-composites is higher than that of the GF/epoxy micro-composites measured by the single fiber fragmentation test. The results show that fragment number on monofilament demonstrates obvious differences between multi-fiber and single fiber systems, and the location of the breakpoint is determined by the CFs that fracture firstly, indicating clustering fracture modes. This is because stress concentration around the breakpoints influences the stress redistribution on the adjacent fibers. Distinct micro-failure modes were observed in three-fiber and the hybrid systems, where matrix cracks around the CFs and interfacial debonding occurs around the GFs. The mixture of CFs and GFs demonstrates distinctive hybrid effect by the changes of the fragment number and initial fracture strain of fibers in hybrid systems.