Yingdan Zhu

Interfacial Microstructure and Properties of Carbon Fiber Composites Modified with Graphene Oxide

The performance of carbon fiber-reinforced composites is dependent to a great extent on the properties of fiber-matrix interface. To improve the interfacial properties in carbon fiber/epoxy composites, we directly introduced graphene oxide (GO) sheets dispersed in the fiber sizing onto the surface of individual carbon fibers. The applied graphite oxide, which could be exfoliated to single-layer GO sheets, was verified by atomic force microscope (AFM). The surface topography of modified carbon fibers and the distribution of GO sheets in the interfacial region of carbon fibers were detected by scanning electron microscopy (SEM). The interfacial properties between carbon fiber and matrix were investigated by microbond test and three-point short beam shear test. The tensile properties of unidirectional (UD) composites were investigated in accordance with ASTM standards. The results of the tests reveal an improved interfacial and tensile properties in GO-modified carbon fiber composites. Furthermore, significant enhancement of interfacial shear strength (IFSS), interlaminar shear strength (ILSS), and tensile properties was achieved in the composites when only 5 wt % of GO sheets introduced in the fiber sizing. This means that an alternative method for improving the interfacial and tensile properties of carbon fiber composites by controlling the fiber-matrix interface was developed. Such multiscale reinforced composites show great potential with their improved mechanical performance to be likely applied in the aerospace and automotive industries.

Barrier properties of latex/kaolin coatings

The inclusion of plate-like pigments such as kaolin to a styrene–butadiene dispersion is a well-known approach for enhancing barrier properties. Latex coatings containing kaolin with different treatments were evaluated. The in situ dispersion of kaolin in latex-bound coatings were characterised by Focused Ion Beam (FIB) imaging, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The effects of parameters such as the kaolin particle size distribution (PSD) and aspect ratio (AR), and the particle orientation distribution on the barrier properties of coatings were investigated. It is found that the barrier properties of the composites are independent of PSD and are mainly dominated by the AR distribution range and the degree of disorientation of the kaolin platelets (given a similar volume concentration of flakes). Large platelets with high AR contribute more to the improvement of barrier properties than do small platelets with low AR. Finally, the influence of platy pigments on the water vapor permeability was simulated using traditional models, which shows good agreement with the experimental data.

Structural slotted waveguide antennas for multirotor UAV radio altimeter

Z-slots are presumed to offer a structural advantage over conventional inclined slots for narrow wall slotted waveguide antennas, in that the corners of the rectangular waveguide are not cut and consequently will not weaken a structural tube as much. Initial structural simulations are shown to confirm this assumption. This slot configuration was also further investigated as radiating slots in standing wave type slotted waveguide antennas. Fan-beam antennas having 10 to 30 slots were successfully designed for 10GHz using a commercially available antenna simulator, having directivities from 16 to 21dBi and aperture efficiency of 60%.

Properties of polymerized cyclic butylene terephthalate and its composites via ring-opening polymerization:

Continuous glass fiber (GF)-reinforced polymerized cyclic butylene terephthalate (pCBT) composites were prepared via vacuum-assisted resin transfer molding using butyltin tris(2-ethylhexanoate) as the catalyst. The relationship between melt viscosity and polymerization time was examined in the ring-opening polymerization of CBT resin. The effects of polymerization conditions such as catalyst content and polymerization temperature on viscosity average molar mass (Mv ), crystallization, mechanical properties, and microstructure of GF/pCBT composites were also investigated in detail. It is found that both high molecular weight and high degree of crystallinity of resin matrix can lead to high mechanical properties of composites. The composites prepared with 0.5% catalyst at 190°C show the best mechanical properties with tensile strength of 549 MPa, flexural strength of 585.2 MPa, and interlaminar shear strength of 47.1 MPa. The scanning electron microscopy analysis also demonstrates that good interfacial adhesion exists between fiber and resin, which agrees very well with experimental results.

Compression Buckling Response of Tow-placed, Variable Stiffness Composite Panels with Sine Curved and Tangent curved Fibers

Fiber-reinforced composites have been widely used in aerospace, automotive, and other industries due to their high stiffness to weight ratio and unique tailoring advantages1-4. Traditional laminates usually consist of multiple layers with a constant fiber orientation in each ply, typically 0°, 90°, and ±45°. Recently research has shown that greater structural performance of composites can be achieved by steering variable fiber orientation as a function of location through the ply5-7. Variable Angle Tow (VAT) placement is one of the methods capable of steering individual curvilinear fibers. Two general approaches such as the shifted ply and the parallel ply based on a reference fiber path through the center of the panel are often used to construct variable stiffness composite laminates by VAT8-9. Buckling performance is often an important criterion in the design of composite laminates. It is well known that 45o ply performs excellently for initial buckling while cross-ply (0°/90°) has better post-buckling performance. Hybrid lay-ups including both 45° and cross-ply angles within a single layer can be realized by VAT placement, which can improve buckling behaviors by redistributing loads more efficiently than straight fiber laminates8,10-11.Tailoring of composite laminated panels by Variable Angle Tow (VAT) steering fibers in their optimal spatial orientations provides a unique opportunity to maximize performance. Increased buckling response of the laminates by VAT steering technique may directly provide significant weight savings by redistributing loads in a benign manner. The aim of this work is to design tow-placed, variable stiffness composite panels with resistance to buckling by steering sine curved and tangent curved fibers. Buckling behaviors of two types of VAT panels and three typical types of straight fiber panels ([45/-45/0/90]s,[±45]2s, [0/90]2s) are investigated by finite element numerical simulations. It is found that the VAT panels with sine curved and tangent curved fibers show much better buckling performance to traditional straight fiber panels, with 9.25%-30.75% and 8.18%-29.47% improvement in buckling load respectively and a more uniform stress distribution. These results demonstrate that the design of composite laminate...