Composite characteristics fiber diameters

Several characteristics of fibers are targeted by forensic analysis. As shown in Figure 14.8, the chemical composition of the fiber is just one of many important characteristics. The diameter and cross section are useful for determining how a fiber is used. For example, carpet fibers are relatively thick and often have hollowed-out cross sections compared with those of fibers used in clothing. Cotton fibers have a characteristic flat ribbon geometry. Fiber color and how it... 

Because carbon fibers of different diameters are available and because construction parameters can be varied, it is possible to engineer composites having desired characteristics. By varying the orientation, concentration, and type of fiber, materials can be developed for specific applications. The fibers can be layered at different angles to minimize directional differences in properties. Also, layers of fibers can be impregnated with epoxy resin to form sheets that can be shaped prior to polymerization of the resin. 

Whiskers are synthetic crystalline fibers of variable size, but with diameters of usually less than 25 microns. An upper limit in diameter exists because the physical and chemical properties approach those of the bulk material as the diameter of fibrous sample increases. Since the purpose of synthesis is to take advantage of some characteristic property of the material in fibrous form, such as enhanced strength for small volume, the optimum material has a small diameter. For similar reasons the aspect ratio of useful whiskers is often well over 100. Whiskers can be single crystals, but many are polycrystalline aggregates of fibrils with preferred orientations. The compositions and crystal structures of the compounds synthesized as crystalline fibers also have the broadest possible variety (Brenner, 1958). 

Experimental research was performed on models of reinforced concrete beams (10 x 20 x 120 cm) with polymeric concrete layers. B 25 class concrete was used main longitudinal reinforcement of A-III class was used in the form of two 8-mm diameter rods and the 5-mm diameter stirrups of the same class arranged, so that destruction would be along normal sections. Epoxy-rubber compositions were used as covering layer materials. All compositions were made on ED-20 epoxy-based resin. Besides fiber glass-reinforced plastic glued by ED-20 compositions based on liquid rubbers, RubCon was used. The composition of the polymer layers and some of their mechanical characteristics are given in Table 6.3. 

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