Boron fibers application

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. 

Applications. Boron fibers are used as unidirectional reinforcement for epoxy composites in the form of preimpregnated tape. The material is used extensively, mostly in fixed and rotary wing military aircrafts for horizontal and vertical stabilizers, mdders, longerons, wing doublers, and rotors. They are also used in sporting goods. Another application is as reinforcement for metal matrix composites, in the form of an array of fibers pressed between metal foils, the metal being aluminum in most applications. 

CVD silicon carbide fibers are a recent development with prom-ising potential which may take over some of the applications of CVD boron fibers or other refractory fibers, providing that the production cost can be reduced. 

Boron fibers have been used in connection with aluminum, magnesium, and titanium for such applications as compressor blades and structural supports, antenna structures, and jcl-cngine fan blades. 

Because they are relatively expensive, epoxy polymers have not been used very widely as binders in PC products. Therefore, epoxy PC is used for special applications, in situations in which the higher cost can easily be justified, such as mortar for industrial flooring to provide physical and chemical resistance, skid-resistant overlays (filled with sand, emery, pumice, quartz) in highways, epoxy plaster for exterior walls (e.g., in exposed aggregate panels), and resurfacing material for deteriorated areas (e.g., in flooring). Epoxy PC reinforced with glass, carbon, or boron fibers is used in the fabrication of translucent panels, boat hulls, and automobile bodies [2,6],... 

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. 

Boron/tungsten fiber applications include the use of filaments and of boron/tungsten fiber reinforced prepreg tape, aluminum matrix composites, and boron/graphite structures. The major applications for these structures are found in the aerospace market and about 25% in sporting goods markets [36]. SiC/carbon fiber reinforced products include aluminum, titanium, and ceramic matrix composites. Major applications for these structures are also found in the aerospace market, minor uses in the industrial market [37]. 

Vega-Boggio, J. and Vingsbo, O. (1976) Application of Griffith criterion to fracture of boron fibers. J. Mater. Sci., 11 2242-2246. 

Although alloys do not typify the concept of structural composites or composite materials, they do demonstrate that the principle of their functionality applies on both very small and very large scales. The application of those principles on that small scale is increasingly relevant in the development of new and useful materials and methods and is intimately bound to the manipulation of atoms and molecules to produce specific atomic and molecular structures. Two examples illustrate the formation of structural composites from the atomic scale boron fiber and the combination of materials to produce specific electronic properties or physical structures. 

Metallized metal, polymer and carbon. Types la, lb, and Ic, are variants of the solid metal fibers and are distinguished therefrom by a metal layer upon the base fiber s periphery. They are fabricated by electrochemical deposition or grafting of a suitable metal, such as nickel, copper, aluminum, and their alloys, as a thin layer upon the fiber s surface. In general, these variants evolved in attempts to improve upon one, or more, properties of the Type 1 fibers. Applications of metal-on-metal. Type la, are typified by the structures described in 1972 by McNab(26) who used refractory, non conducting, base fibers for example, aluminum oxide and boron nitride, upon which were deposited films of noble metals. McNab s objective was to improve upon the strength and flexibility of Type 1 fibers by selecting a base fiber for its mechanical... 

In the aircraft industry advanced composites are penetrating into large markets. The first application of advanced composites was in the F14 Fighter in 1971. At that time, boron-fiber reinforced composite was used. Today, the materialsused to make the "Harrier AV-8B" consists of 25 wt advanced composites reinforced by carbon or aramid fibers. For commercial aircraft, advanced composites were applied for the first time in 1977, for the secondary structural parts of the DC-10. Afterward, the proportion of advanced composites used has risen from 3 wt on the Boeing 767 in 1982 to 20 wt of the Air-Bus A320 in 1987. Moreover, the application of advanced composites has extended into the primary structural parts of aircraft. In the future, we expect, the next generation aircraft will consist of more than 30 vjt% of advanced composites. 

FRPs are usually constructed of unidirectional or woven fibers imbedded in a specifically formulated resin matrix. The fibers are usually of glass and/or carbon although some specific applications call for aromatic polyamide (e.g., Kevlar ), quartz, or even boron fibers. 

Boron-reinfixced aluminum is a technologically mature continuous-fiber MMC (Fig. 2). Applications for this composite include tubular truss members in the mid-fiiselage structure of the space shuttle orbiter and cold plates in electronic microchip carrier multilayer boards. Fabrication processes for boron/aluminum composites are based on hot-press diffusion bonding of alternating layers of aluminum foil and boron fiber mats (foil-fiber-foil processing) or plasma-spraying methods. 

Fiber-reinforced composite materials such as boron-epoxy and graphite-epoxy are usually treated as linear elastic materials because the essentially linear elastic fibers provide the majority of the strength and stiffness. Refinement of that approximation requires consideration of some form of plasticity, viscoelasticity, or both (viscoplasticity). Very little work has been done to implement those models or idealizations of composite material behavior in structural applications. 

The second special case is an orthotropic lamina loaded at angle a to the fiber direction. Such a situation is effectively an anisotropic lamina under load. Stress concentration factors for boron-epoxy were obtained by Greszczuk [6-11] in Figure 6-7. There, the circumferential stress around the edge of the circular hole is plotted versus angular position around the hole. The circumferential stress is normalized by a , the applied stress. The results for a = 0° are, of course, identical to those in Figure 6-6. As a approaches 90°, the peak stress concentration factor decreases and shifts location around the hole. However, as shown, the combined stress state at failure, upon application of a failure criterion, always occurs near 0 = 90°. Thus, the analysis of failure due to stress concentrations around holes in a lamina is quite involved. 

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