Jianjun Sha

Influence of carbon fiber’s surface state on interlaminar shear properties of CFRP laminate

In order to investigate the influence of carbon fiber’s surface state on the interlaminar shear properties of carbon fiber-reinforced plastic (CFRP) laminate, the carbon fiber’s surface state was modified by thermal treatment at elevated temperatures. The interlaminar shear strength (ILSS) of CFRP laminates reinforced with treated fibers was measured by means of short-beam shear test, and the surface state of fiber was characterized by Electron Spectroscopy for Chemical Analysis (ESCA) analysis to reveal the dominate factor for controlling the ILSS. Combining the ILSS measurement with the ESCA analysis, the results indicated that: (1) the ILSS is strongly dependent on the oxygen-containing functional groups on the surface of carbon fiber; (2) the fiber treated at 600 °C has the highest oxygen-containing functional groups that lead to the highest ILSS of CFRP; and (3) at temperatures beyond 600 °C, the oxygen-containing functional groups decrease with increasing the heat treatment temperature, resulting in a low ILSS of CFRP laminates. Furthermore, from the microstructure observation, it was found that the CFRP mainly failed in the mode of multi-interlaminar shear. The multi-interlaminar shear failure in the CFRP laminates with low ILSS is more severe due to a weak fiber-matrix interface.

Synthesis and growth mechanism of SiC nanofibres on carbon fabrics

The SiC nanofibres with a length of few millimetres were synthesized successfully on carbon fabrics using a catalyst-free method. The Si and SiO2 powder mixtures functioned as a source for the generation of gaseous species. Following the chemical vapour reaction route, abundant SiC nanofibres with near stoichiometric composition and high crystallinity were grown on the surfaces of carbon fibres. The phase, morphology and crystal structure were characterized to reveal the nucleation and growth mechanism. SiC nanofibres presented a pagoda structure, which is a consecutive stacking of hexagonal segments with a high density of stacking faults. Combining the fabrication process with an analysis of the morphology and crystal structure, both the vapour–solid mechanism and the screw dislocation-driven mechanism are responsible for the nucleation and the growth of SiC nanofibres in the current study. The significant advantage of the present process is that it can be conveniently implemented and provides an approach to allow the fabrication of SiC nanostructures on a variety of carbonaceous substrates without the assistance of a catalyst, leading to less expensive, long length and high purity production of nanostructures.

Synthesis of novel hierarchical SiC–SiO2 heterostructures via a catalyst free method

Novel hierarchical SiC–SiO2 heterostructures were synthesized on a graphite paper substrate via a catalyst free method. The morphology, microstructure and composition were characterized by SEM, HR-TEM, EDS and XRD. Results revealed that the hierarchy of SiC–SiO2 heterostructures consisted of nanochain structures and nanoweb structures located in different layers of the graphite paper substrate. The nanochain structures were SiC–SiO2 nanochains coated by an exterior SiO2 shell, in which the SiO2 beads were chained to the SiC nanostructure. The nanoweb structures showed that many intersecting SiC nanostructures were encapsulated in irregular SiO2 agglomerates. The formation of hierarchical SiC–SiO2 heterostructures was dependent on the synthesis temperature. The VS process followed by a modulation process was proposed to elucidate the formation mechanism of such hierarchical SiC–SiO2 heterostructures.

Influence of Fiber’s Surface State on Mechanical Properties and Fiber-Matrix Interaction of CFRP

In order to investigate the influence of carbon fiber’s surface state on the mechanical properties and the fiber-matrix interaction of CFRP, the change of surface state was achieved by thermal treatment of carbon fibers at elevated temperatures, and the surface state was characterized by XPS. The mechanical properties were measured from the flexural test. The CFRP reinforced with 600 °C treated fabrics containing the highest reactive functional groups, showed the highest flexural strength and modulus. But in the case of CFRP reinforced with 1500 °C treated fabrics containing the lowest reactive functional groups, exhibited the lowest flexural strength and modulus. Combining the mechanical properties with the microstructure analysis, the results indicated that the fiber-matrix interaction (strong or weak) depends on the relative percentage of reactive functional groups present on the carbon fiber surface.