Zhongjia Yang

Mechanical properties of surface-treated ramie fiber fabric/epoxy resin composite fabricated by vacuum-assisted resin infusion molding with hot compaction

The optimization of composite manufacturing process is an important means for improving mechanical properties of natural fiber composites. In this paper, ramie fiber fabrics were, respectively, modified by NaOH, KMnO4, and ammonium polyphosphate flame retardant, and then ramie fabric/epoxy resin composite laminates were prepared using vacuum-assisted resin infusion molding. In order to increase ramie fiber content in composite, vacuum pressure compaction and hot compaction with high pressure and temperature were, respectively, used to compress the fabric stack before molding. The effects of precompaction process on fiber compaction and mechanical properties of ramie fiber yarns and composites were studied. The comparison with the ramie fiber fabric without surface treatment was also done. It is found that surface-treated ramie fiber fabric has lower compressibility than the untreated one. Moreover, hot compaction with suitable conditions is effective in increasing fiber content and mechanical properties of all studied ramie fabric composites.

Manufacture and characterization of carbon fiber composite stiffened skin by resin film infusion/prepreg co-curing process

I-shaped stiffened skin was manufactured by a new co-cured resin film infusion process (co-RFI) with fiber preform stiffener and prepreg skin. One kind of epoxy resin film and four kinds of carbon fiber prepreg were used. Resin flow behavior, processing quality, and mechanical performance were investigated for co-RFI stiffened skin. Sole prepreg/autoclave process and resin film infusion process were also adopted for comparison. Resin flow front and resin pressure were detected by self-developed monitoring systems. Optical micrographs and thickness measurement were employed to evaluate processing quality. Moreover, pull-off test was used to analyze the influences of core filler and prepreg systems in skin on the mechanical performance of stiffened skin. The results show that with reasonable processing conditions, good processing quality, and mechanical property at co-curing interface region can be achieved for co-RFI stiffened skin. Co-RFI process is suitable to fabricate composite structure with high flexibility in materials and structures.

Permeabilities along fiber direction of ramie bundles and through-thickness of ramie fabric stack for liquid composite molding

Natural fiber has been a focus for environmental and recyclable polymer composite. Liquid composite molding process is an attractive manufacturing technique for natural fiber-reinforced polymer composites with high quality and low cost. Understanding the permeability along different directions of fiber preform is important for liquid composite molding to design and optimize mold and processing parameters. This paper addresses issues of the permeabilities along longitudinal direction of ramie fiber bundles and through-thickness direction of ramie fabric stack. Two simple methods were designed to detect axial and transverse infiltration with assistance of external vacuum pressure in ramie bundles and ramie fabric stack, respectively. Different surface chemical treatments, including flame retardant, silane and alkali treatments, were done on ramie fabric. The effects of fiber content, liquid type and surface treating method on the permeability and capillary pressure were studied. The results show that surface treatment obviously changes the surface morphology and surface energy of ramie fiber. The relationships between defined relative velocities of penetration flow and applied pressure for ramie fiber bundles and fabrics perfectly follow linear relationships, indicating that Darcy’s law is suitable for describing permeation behavior in ramie fibers. Moreover, fiber content and liquid type, including silicone oil and epoxy resin, significantly impact axial permeability and capillary pressure. Surface treatment significantly decreases the permeability along the thickness direction of ramie fabric stack followed by increasing capillary pressure, which are attributed to the changes of treated ramie fibers in surface energy and morphology. Finally, a unique difference in the permeabilities along axial and thickness directions was pointed out.

Design and verification of a small-scale lift-type vertical axis wind turbine composite blade

In order to obtain the small lift style vertical axis wind turbine with excellent performances, this paper presented the technologies of design and manufacture of the composite blade with high lift coefficient. The manufacturing process was evaluated based on the dimensional accuracy of the blade. The structure of the composite blade was evaluated by means of finite element modeling (FEM) and the mechanical property. Moreover, the vibration property of the blade was studied by FEM, and the resonance of the wind turbine assembled with the blade was investigated.