Fiber-reinforced laminated composite materials applications

In this paper, the thermal and mechanical characteristics of balsa wood and balsa wood laminates are reviewed, and it is shown that "composite" mechanics that have been developed for the class of synthetic fiber-reinforced plastic (SFRP) materials may be useful for describing the density and direction—dependent mechanical properties of balsa wood in bulk or laminated form. It may be asked whether such advanced analytical methods, perhaps combined with specially developed methods of test, could be used effectively towards developing more applicable QA/QC procedures that will clearly qualify balsa wood as a structural material in applications where strictest code compliance is a necessity. This question has prompted the following review and discussion. 

For the remainder of this book, fiber-reinforced composite laminates will be emphasized. The fibers are long and continuous as opposed to whiskers. The concepts developed herein are applicable mainly to fiber-reinforced composite laminates, but are also valid for other laminates and whisker composites with some fairly obvious modifications. That is, fiber-reinforced composite laminates are used as a uniform example throughout this book, but concepts used to analyze their behavior are often applicable to other forms of composite materials. In many Instances, the applicability will be made clear as an example complementary to the principal example of fiber-reinforced composite laminates. 

Unlike ductile metals, composite laminates containing fiber-reinforced thermosetting polymers do not exhibit gross ductile yielding. However, they do not behave as classic brittle materials, either. Under a static tensile load, many of these laminates show nonlinear characteristics attributed to sequential ply failures. One of the difficulties, then, in designing with laminar composites is to determine whether the failure of the first ply constitutes material failure, termed first-ply failure (FPF), or if ultimate failure of the composite constitutes failure. In many laminar composites, ultimate failure occurs soon after first ply failure, so that an FPF design approach is justified, as illustrated for two common laminar composites in Table 8.9 (see Section 5.4.3 for information on the notations used for laminar composites). In fact, the FPF approach is used for many aerospace and aircraft applications. 

Photopolymerizable epoxies using onium salt photoinitiators also show considerable promise for use in high performance composite applications. Traditional thermally cured epoxy resins are already well entrenched in these applications however, the use of the recently developed photocurable epoxy materials offers considerable potential for rapid fabrication of fiber-reinforced composites without the need for cumbersome ovens and long cure times. Photopolymerized epoxy laminates and filament wound pipe have already been demonstrated in our laboratory. 

A fiber-reinforced composite part is generally a laminate composed of layers of stacked fiber-matrix material that are then bonded together. The fibers can either be continuous strands or chopped segments. The orientation of the fibers in each of the layers and the fiber volume ratio can be adjusted to tailor the composite for its final application. 

The laminate composites of Carbon Fibre Reinforced Plastic (CFRP) and Carbon Fiber Reinforced Carbon (CFRC) show a very high strength and a ductile behaviour compared to brittle materials and have a low density. CFRC composites are especially suitable for high temperature applications. Therefore they are very important to aerospace technology. A single lamina of CFRP or CFRC may be considered to be homogeneous and anisotropic. The composite consists of a stack of such plies. Since each ply may have a different orientation and/or elastic moduli, the composite as a whole must be treated as an inhomogeneous anisotropic material. 

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