Multidirectional fibers

Fawaz Z, EUyin F. A new methodology for the prediction of fatigue failure in multidirectional fiber-reinforced laminates. Compos Sci Technol 1995 53 45-55. 

Multidirectional fiber preforms, fabricated from ex-PAN carbon fibers were used. Their main characteristics were given in a previous paper. ... 

Lamina (layer, ply) The arrangement of unidirectional or multidirectional fibers in a matrix to form a thin layer is called a layer, ply, or lamina of composite material. In general, several such layers are bonded together, with layer orientations chosen to form a single multilayered sheet having optimum material performance characteristics tailored for specific loading and environmental conditions. Three common types of lamina are unidirectional, woven, and random mat shown schematically in Figure 8.1. 

Pagano, N.J. and Tandon. G.P. (1990). Thermo-elastic model for multidirectional coated fiber composites Traction formulation. Composites Sci. Technol. 38, 247 269. 

Choi, N.S., Kinloch, A.J., Williams, J.G., (1999) Delamination Fracture of Multidirectional Carbon-Fiber/Epoxy Composites under Mode I, Mode II and Mixed Mode I/II Loading , / Comp. Mat. 33, No.l, pp. 73-100. 

The transferability of the mechanical properties of unidirectionally or multidirectionally incorporated reinforcing fibers to the entire composite material is determined by the interface between the fiber and the matrix. At sufficient bonding strengths, the mechanical properties are proportional to the volume fraction of the fibers. Filling levels of 30 to 60 % by volume and in extreme cases up to 80% can be attained, depending upon the location and mutual orientation of the fibers. The theoretical limit for unidirectional fibers is 90.7% by volume (by comparison... 

EUyin F, Martens M. Biaxial fatigue behavior of a multidirectional filament-wound glass-fiber/epoxy pipe. Compos Sci Technol 2001 61(4) 491—502. 

Trakas K, Kortschot MT. The relationship between critical strain energy release rate and fracture mode in multidirectional carbon-fiber/epoxy laminates. In Armanios EA, editor. Composite materials fatigue and fracture, vol. 1285. ASTM Special Technical Publication 1997. pp. 283—304. http //dx.doi.org/10.1520/ STP19933S. 

Choi NS, Kinloch AJ, Wilhams JG. Delamination fracture of multidirectional carbon fiber/epoxy composites under mode I, mode II and mixed-mode I/II loading. J Compos Mater 1999 99 73-100. http //dx.doi.org/10.1177/002199839903300105. 

Selcom SRL, Fregona (TV), Italy—produce UD and multidirectional carbon fiber fabrics. SGL Carbon Composites, Gardena, California, USA—formerly Hitco Technologies, acquired by SGL Carbon in 1997. Specialises in carbon-carbon composites and is the largest producer of carbon-carbon brakes. 

Woven roving Coarse fabric, bidirectional reinforcement, mostly plain weave, but some twill. Uni-and multidirectional nonwoven rovings are also produced. K to T fiber, fabric weights 10-48 oz/yd. HSB. Mostly wet lay-up, but some press molding. 

By means of the described technology properties, both processes are suitable for mass production. Nevertheless, there is a preferred field of application for both technologies. Unidirectional reinforcement fibers are best suited for the pultrusion process. In contrast, the CCM process is independent of the fiber orientation, thus it doesn t matter if unidirectional or multidirectional reinforcement materials are used. The assessment of the rates of production (= process speed) against the circumferences of the profiles, which are in contact with the tools surface (see Fig. 8.34), defines relevant process parameters and emphasizes the preferred field of application. Thus the circumference characterizes the profile shape. 

Fig. 6 Flow front sequence for matrix flow through nonwoven fabric (A) unidirectionally laid fiber mat of 4.4 dtex fibers, (B) unidirectionally laid fiber mat of I. I dtex fibers, and (C) multidirectionally laid 4.4 dtex fiber. Digits express flow time (sec).

Three-Dimensional Braid (3-D braid) A recent development in building reinforcement performs for complex shapes that permits the placing of reinforcing fibers in three orthogonal (or nonorthogonal) directions so as to best support multidirectional stresses expected to act on the finished part in service. 

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