الفهرس 
CHAPTER (1) INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 121 |  |  |
| | | from | 121 | | |
Abstract
Natural fiber strengthened polymer composites have raised great attention
and interests among materials scientists. This is due to the considerations of promoting an environmental friendly, high specific strength, low density. As well as cheaply and biodegradable compared to the synthetic fiber-reinforced composites. The various types of natural fibers such as jute, hemp, sisal, bananas, flax, and bamboo can be very cost-effective material for applications such as automotive interior, packing, building, construction industry, electric and electronic devices, and transportation. One of the main reasons for limitation using natural fibers is a high response of water absorption which reduced its mechanical properties. The combination between the synthetic fibers and natural fibers reinforced polymer leads to the reduction in water absorption. The present study aims to characterize the mechanical and electrical properties of interlayered hybrid composites based on unsaturated polyester resin reinforced with different combinations of flax, sisal, carbon and glass fibers. In addition, studying the effect of water absorption and swelling
thickness on the tensile properties of flax/sisal/carbon/glass fabrics reinforced
unsaturated polyester based hybrid composites before and after immersion is
of great importance. Hybrid composites reinforced with different natural and
synthetic fiber configurations have been processed using the Hand lay-up (HLU) technique. Water absorption test was carried out by immersing specimens in distilled water for different duration’s time up to 1344 hours. The results showed the minimum value of water absorption for fibers configuration [C/C/C/C/C/C] up to 1.45% while maximum value of water absorption for fiber configuration [S/S/S/S/S/S] up to 14%. The tensile strength of the laminated composites
before and after immersed in distilled water was evaluated. The result showed
that the tensile strength of fibers configuration [C/C/F/F/C/C] 73 MPa is
approaching to fibers configuration [C/C/C/C/C/C] 86 MPa at dry condition.
Fracture morphology of laminated composites was investigated using scanning electron microscopy (SEM) to evaluate the fibers/matrix interface before and after hydro aging. where it was possible to link the increase in tensile strength attributed to water penetrating is slight for hybrid composites with synthetic fibers at the outer layers but large for hybrid composites with natural fibers at outer layers. Dielectric spectroscopy of all investigated hybrid and non-hybrid
laminated composites were examined at various values of electric field frequency to widen our knowledge about the structure of composite. The results showed the maximum values of dielectric constant in the lower frequency region (0.5 kHz) were due to the interfacial polarization between different phases.