Aijun Li

Thermal analysis and gelation property of multifunctional epoxy resins used for pultruded composite ropes

Non-isothermal curing reactions of three different multifunctional epoxy resin systems were investigated by differential scanning calorimetry. The Kissinger equation was applied to calculate the apparent activation energy, and the Levenberg–Marquardt algorithm was used to fit the curing kinetic data. It was observed that the two-parameter model was in good match with the curing kinetics. In addition, dynamic mechanical thermal analysis was used to obtain the glass transition temperature (Tg). Furthermore, the thermal stabilities of the systems were studied by thermogravimetric (TG) analysis, the integral procedure decomposition temperature and temperature index Ts were used to characterize the thermal stability. Finally, the gelation time was measured by plate–knife method of a home-made device, and the relationship between gelation time and temperature was established, according to which the pultrusion process parameters were predicted.

Thermal characterizations of multifunctional epoxy/anhydride systems used for pultruded composite ropes

The viscoelastic characterization and thermal stability property of some multifunctional epoxy/anhydride systems cured at different schedules were investigated by dynamic mechanical thermal analysis (DMTA) in single cantilever mode at fixed frequency, and by non-isothermal thermogravimetric (TG) analysis, respectively. According to the DMTA results, three obviously different glass transition temperatures (Tg), were observed, among which TGDDM/MHHPA system exhibits the largest Tg. While from the TG curves, the results of the mass loss and thermal stability showed that, after cured for a prolonged duration, the TGDDM/MHHPA system possessed the most excellent performance in heat resistance.

Dynamic Mechanical Thermal Analysis of Pultruded Carbon Fiber/Resin Composite Cable Cores

The viscoelastic property of the CTC composite cores was investigated through dynamic mechanical thermal analysis (DMTA) in single cantilever mode. The effect of the frequency on the glass transition temperature (Tg) was studied. The results show that the peaks were shifted to higher temperatures with increasing frequencies. Tgof CTC was approximately 180 °C, much higher than that of a home-made composite core (Composite I). The activation energy ΔH of CTC is also greater than that of Composite I. The CTC sample exhibit better stiffness and toughness.

Effect of DLC Film on Tribological Properties of Carbon/Carbon Composites

The effect of DLC film on tribological properties of C/C composites was investigated with a ball-on-disk tribometer in dry air, compared with the result of specimen without DLC film. The DLC film was prepared on the surface of C/C composites substrate by plasma enhanced chemical vapor deposition method (PECVD). After PECVD, structural characterization of the film, adhesion strength of film to substrate, surface morphology and linear wear were studied by Raman spectroscopy, Rockwell-C apparatus, Scanning Electron Microscopy (SEM) and Optical Microscopy (OM), respectively. The result showed that the film deposited on the surface of C/C substrate exhibited typical Raman spectroscopy fingerprints of DLC films and a good adhesion to the substrate surface was found. A stable friction coefficient was observed during the friction tests. With the DLC film, the friction and wear properties of C/C composites were improved significantly. The average friction coefficient of the C/C specimen with DLC film (0.08637) was reduced by 65.56% than that of the one without DLC film (0.2508) and the linear wear was decreased by 84.7% ( from 148.47μm to 22.71 μm) as well.

Microstructure and Micromechanical Property of C/C-SiC Composites

The C/C-SiC composites are prepared by the reaction molten infiltration process of silicon powders, using porous C/C composites as preform. C/C composite frameworks with various bulk densities are prepared by the chemical vapor infiltration (CVI) combined with the resin impregnation-pyrolysis methods, using needled-carbon fiber felts as preform. Characterization of the microstructure was conducted with a digital microscope (VHX-500) and a polarized light microscopy, respectively. The hardness (H) and the elastic modulus (E) of the composites are measured using a nano indentor. The results show that the indentation behaviors of the pyrolytic carbon and resin carbon are elastic while silicon and silicon carbide show a plastic deformation behavior. The hardness of the resin carbon as well as the pyrolytic carbon is 2.1GPa and 1.3~1.6GPa, respectively. E of SiC varied from 360 to 259GPa and H from 36 to 21GPa. For Si, the value of E and H are 155-170GPa and 11.7GPa, respectively. The relationship between microstructure and mechanical properties of C/C-SiC composites were analyzed.