These surfaces are difcult to wet and are essentially

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: K. Chawla, Composites Material Science and Engineering, 1987, Springer-Verlag, New York. Reprinted with permission of SpringerVerlag, New York Publishers.) referred to as an interface region (or interphase region). Figure 14.3–5 shows the various regions of such an interface in a metal-matrix composite. Since the bonds are primary and a result of extensive chemical interactions between fiber and matrix, the interfacial strength is much greater than with wettability bonds alone. Coatings and coupling agents are frequently used to promote chemical reactions and increase the bond strength. ....................................................................................................................................... EXAMPLE 14.3–2 Many carbon fibers have an imperfect graphitic structure often with the basal planes forming the surface of the fiber. These surfaces are difficult to wet and are essentially incapable of forming primary bonds with epoxies or other matrices. Fibers may be treated with oxidizing reagents such as nitric acid to change the surface properties. The acid attacks the imperfections in the fiber surface. This results in blunting of surface cracks, an increase in surface area, and creation of a “rough” surface. In addition, the acid alters the fiber surface chemistry by creating hydroxyl ( @OH) and other reactive groups that are capable of forming primary bonds. Describe how the acid treatment changes the fiber and composite properties. Solution The blunting of surface cracks increases the strength of the fiber with a corresponding increase in the strength of the composite. The rough surface improves the mechanical bonding, the increased surface area permits a higher density of secondary bonds across the fiber-matrix interface, and the generation of reactive surface groups increases the density of primary bonds across the interface. Hence, the interfacial strength increases, with a corresponding improvement in composite properties. It is interesting to note that epoxy composites made using untreated carbon fibres are virtually useless. ....................................................................................................................................... 14.3.5 Fiber Architecture In previous sections we discussed how fiber, matrix, and interface characteristics influence the properties of composites. One additional factor in determining composite properties is the fiber arrangement, also known as the fiber architecture. | v v 590 iq 12.01.98 plm QC2 rps MP | e-Text Main Menu | Textbook Table of Contents pg591 [R] G1 7-27060 / IRWIN / Schaffer iq Chapter 14 12.01.98 plm QC1 rps MP Composite Materials rps 01-20-98 rps QC1 (a) Rectangular (b) Square (c) Hexagonal FIGURE 14.3–6 Rectangular, square, and hexagonal array of fiber arrangements in unidirectional composites. The 799 hexagonal array results in a transversely isotropic Glossary material. atom or ion ure under same or a in which d in the n in pure ere are zero y displacesence of an to remove an v of light de to impinge locity. The s. in...
View Full Document

This note was uploaded on 02/25/2013 for the course PHYS 2202 taught by Professor Sowell during the Spring '10 term at Georgia Institute of Technology.

Ask a homework question - tutors are online