Chain Orientation During Fiber Alignment

Figure 11.6. Schematic illustrations of brittle fracture, (a) Idealized limiting case of perfectly uniaxially oriented polymer chains (horizontal lines), with a fracture surface (thick vertical line) resulting from the scission of the chain backbone bonds crossing these chains and perpendicular to them. This limit is approached, but not reached, in fracture transverse to the direction of orientation of highly oriented fibers, (b) Isotropic amorphous polymer with a typical random coil type of chain structure. Much fewer bonds cross the fracture surface (thick vertical line), and therefore much fewer bonds have to break, than for the brittle fracture of a polymer whose chains are perfectly aligned and perpendicular to the fracture surface, (c) Illustration of a defect, such as a tiny dust particle (shown as a filled circle), incorporated into the specimen during fabrication, which can act as a stress concentrator facilitating brittle fracture.

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