The changes in interfacial fracture energy of three kinds of commercially sized carbon fiber (CF)/epoxy resin composites in the range from ambient temperature to 130°C were investigated using the single‐fiber fragmentation test to evaluate the heat resistance of the interphase. The effects of CF sizing on the interfacial bonding property were studied using desized CF/epoxy resin composites. Thermogravimetric analysis and differential scanning calorimetry of the combination of sizing and matrix were employed to investigate the role of sizing on the variations in the fiber/matrix interfacial property under elevated temperature. The interfacial fracture energy values of all the studied CF composites were found to decrease quickly during the initial stage of temperature rise and drop gradually at higher temperature. At elevated temperature, the desized CF composites had higher heat resistance than the corresponding sized fiber composites. The differences in the interfacial heat resistance among the three kinds of CF composites and the difference in the interfacial thermal stability between the sized and the desized fiber composites were related to different glass transition temperatures of the interphases. The interaction between sizing and the matrix and the chain motion of the crosslink structure of the interphase has been suggested to determine the interfacial heat resistance. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

To diminish the brittleness of glass fiber reinforced polymer tubes and syntactic foams, a novel composite tube filled with syntactic foam was proposed, in which thin-walled tubes were reinforced by ribs and the syntactic foam core reinforced with multiwalled carbon nanotubes (MWCNTs). The influence of the ribs and the type and content of MWCNTs on the lateral crashworthy characteristics of composite tubes was investigated. Crushing experimental results indicated that the ribs contributed to improving the crashworthy performance for both hollow and foam-filled tubes. The effect of the ribs on the energy absorption was more pronounced for the hollow tubes. Incorporation of straight or helical MWCNTs lead to improvement of the crush resistance and energy absorption for foamfilled tubes. With the same MWCNT content, the peak load and absorbed energy of specimens with helical MWCNTs were nearly 14% and 13% higher than those of specimens with straight MWCNTs, respectively. Furthermore, analytical models were proposed to predict the load-displacement responses for foam-filled tubes in the linear-elastic, postcrushing, and foam-compaction stages. The predicted results agreed well with experimental results. The resulting composite tubes are potential light-weighted and crashworthy structures, which could be applied as collapsible energy absorbers in engineering fields.