In this research, a method for producing gum tragacanth (GT) FIBERS is presented. Ribbon type GT of Astragalus Gummifer species were obtained from local production lands. The gum was treated with alkali to increase its process ability, and allowed to stand for a period of time to reach the proper viscosity and/or to “ripen”. Samples with different ripening times were prepared and their viscosities were measured to determine the effect of ageing time on viscosity. They were injected into a coagulation bath. Calcium chloride with different concentrations was applied as the coagulant agent. The consolidated samples were washed under different pH conditions. Finally, the mechanical properties of the FIBERS were measured and their scanning electron micrographs were taken. The results show that chemically modified GT can be processed into FIBERS with different qualities.

Carbon FIBERS are fabricated from different materials such as special polyacrylonitrile (PAN) FIBERS, cellulose FIBERS and pitch. But PAN FIBERS are recognized as the most widely used precursor for the present-day manufacture of carbon FIBERS. The process of fabrication carbon FIBERS from special PAN FIBERS is composed of two steps including oxidative stabilization at low temperature and carbonization at high temperatures in an inert atmosphere. Today carbon FIBERS are still expensive because of the high price of their raw material (special PAN FIBERS).This study focuses on making carbon FIBERS from commercial PAN FIBERS (low price PAN FIBERS used in textile industry). The results shows that in case of conducting complete stabilization process, it is possible to produce desirable carbon FIBERS from commercial PAN FIBERS. With some changes in conventional procedure of stabilization in terms of temperature and time of operation, the desirable conditions of complete stabilization are achieved.

This work deals with the thermal, mechanical and dynamic properties of hybrid composites reinforced with carbon FIBERS and aramid FIBERS, whose matrix is epoxy resin. In this study a series of hybrid fiber composite are prepared with carbon and aramid FIBERS as reinforcement. Thermal properties are obtained by thermal gravimetric analysis (TGA), Thermo-mechanical analysis (TMA) and hot plate analysis. Also mechanical properties are obtained by tensile and modal analysis tests. The experimental results are compared with the similar theoretical ones. Besides the effect of stacking sequence and hybrid ratio (adding the number of layers of carbon FIBERS), on the thermal and mechanical properties are investigated. The results show that by increasing the hybrid ratio although the weight of the sample is more, the thermal conductivity of the carbon FIBERS used is higher than that of the aramid FIBERS and this increase in thermal conductivity causes the heat to be transferred to the sample much faster and the temperature of the glass increases with the increase of the hybrid ratio. Due to the high stiffness of carbon FIBERS, adding it to the composite causes, the tensile modulus of the samples increases. By combining carbon FIBERS with aramid FIBERS, the toughness of carbon FIBERS can be increased and at the same time the brittle property of carbon FIBERS is removed due to the malleability of aramid FIBERS. It is concluded that aramid fiber has an effective role in improving failure strain due to its high toughness and malleability, while carbon fiber is very fragile. The lowest tensile strength occurs at the hybrid ratio of 29% with a value of 677. 66 MPa. which is very close to the theoretical critical hybrid ratio. The results also show when the carbon FIBERS and aramid FIBERS are on the outer and the middle layers of the beam respectively, the frequency has a larger value because the aramid FIBERS have a very high impact resistance.

Irregularities are inherent to virtually all FIBERS, including the conventional textile FIBERS, the high-performance brittle FIBERS and newly developed nano-FIBERS. These irregularities can fall into two main categories: dimensional or geometrical irregularity (external) and structural irregularity (internal). For natural FIBERS such as wool, diameter variation along fiber length is a typical example of fiber dimensional or geometrical irregularity, while the presence of flaws and defects within a fiber signifies structural irregularity. The irregularities of FIBERS are bound to have major impact on the mechanical behavior of FIBERS. In recent years, there has been a growing awareness of the importance of this particular fiber attribute – fiber irregularity, particularly the within-fiber diameter variation. Instruments have been developed to accurately measure fiber diameter variations. In addition, with the development of computing technology, numerical modeling technique has been applied to examine the impact of fiber irregularity on fiber mechanical properties. This paper reviews research progress in the area of fiber geometrical irregularity and its effect on important fiber mechanical properties.