Boron Fibers strength

Boron fibers exhibit the highest stiffness and strength efficiencies in Figure 1-24. When placed in a lamina as unidirectional fibers, the... 

Fibers in which the basic chemical units have been formed by chemical synthesis, followed by fiber formation, are called synthetic fibers. Examples include nylon, carbon, boron fibers, organic fibers, ceramic fibers, and metallic fibers. Among all commercially available fibers, Kevlar fibers exhibit high strength and modulus. (Kevlar is a DuPont trademark for poly [p-phenylene diamine terephthalamide].) It is an aromatic polyamide (aramid) in which at least 85% of the... 

Fiber-reinforced plastics have been widely accepted as materials for structural and nonstructural applications in recent years. The main reasons for interest in FRPs for structural applications are their high specific modulus and strength of the reinforcing fibers. Glass, carbon, Kevlar, and boron fibers are commonly used for reinforcement. However, these are very expensive and, therefore, their use is limited to aerospace applications. 

Properties. CVD boron fibers have high strength, high modulus, and low density. Their properties are summarized and compared with SiC fibers and other inorganic fibers in Table 19.2 (data supplied by the manufacturers). 

Effect of laminate layup and stacking sequence on stress concentration and strength of boron fiber-epoxy matrix composites containing circular holes under uniaxial tension . 

Crystalline boron is a strong, hard, high-melting substance (mp 2075°C) that is chemically inert at room temperature, except for reaction with fluorine. These properties make boron fibers a desirable component in high-strength composite materials used in making sports equipment and military aircraft (see Section 21.8). Unlike Al, Ga, In, and Tl, which are metallic conductors, boron is a semiconductor. 

The intrinsic strength of boron can be estimated in a flexure test. Assuming that in a flexure test the core and interface are near the neutral axis, critical tensile stresses would not develop at the core or interface Flexure tests on boron fibers lightly etched to remove any surface defects yield a strength of 14 GPa (DiCarlo, 1985). Without etching, the strength is about half this value... 

Figure 10.2 Tensile strength of boron fiber as a function of gage length (after Herring, 1965).

Boron fibers possess good mechanical properties at low densities, which accounts for their use in composites for lightweight structures. Commercially obtainable boron fibers exhibit an elasticity modulus at room temperature of 400 Gpa, a tensile strength of 3-4 GPa and a thermal expansion coefficient from room temperature to 327°C of 4.9 10 /K. The maximum use temperature is 367°C, the elasticity modulus having dropped to 240 GPa at 627°C. 

Broken fibers, a result of impact damage, cause a reduction in tensile strength and thus shorten the life of composite laminates. Under cyclic loading, fiber fractures begin within the first third of the expected life of cross-ply laminates [6], If carbon or boron fibers are used, these tend to be more brittle, and cracking may occur more easily during onset of impacts, which reduces the structural integrity of composites made with such materials. 

A reinforcing fiber with high strength and modulus with 2.7 density. Primary purpose for this development was for the reinforcement of metal matrix and ceramic matrix composite structures used in advanced aerospace applications by the military. SiC fibers were developed to replace boron fibers in these RPs, where boron had its drawbacks principally degradation of mechanical properties at temperatures greater than 540C (lOOOF) and very high cost. 

Reinforced pol)nners are those to which fibers have been added that increase the physical properties—especially impact resistance and heat deflection temperatures. Glass fibers are the most common additions, but carbon, graphite, aramid, and boron fibers are also used. In a reinforced polymer, the resin matrix is the continuous phase, and the fiber reinforcement is the discontinuous phase. The function of the resin is to bond the fibers together to provide shape and form and to transfer stresses in the structure from the resin to the fiber. Only high-strength fibers with high modulus are used. Because of the increased stiffness resulting from the fiber... 

---