Nylon fracture

Fig. 5.45 SEM of a nylon fracture surface shows a brittle fracture that is consistent with poor mechanical properties of an unmodified polymer (A). A modified nylon has a significantly different morphology, although the modifier is not observed (B).

Injection moulding and extrusion may be carried out at temperatures in the range of 300-380°C. The polymer has a high melt viscosity and melt fracture occurs at a lower shear rate (about 10 s ) than with low-density polyethylene (about 10 s ) or nylon 66 (about 10 s ). Extruders should thus be designed to operate at low shear rates whilst large runners and gates are employed in injection moulds. 

The glass-fibre nylons have a resistance to creep at least three times as great as unfilled polymers. In the case of impact strength the situation is complex since unfilled nylons tend to break showing tough fracture whereas the filled polymers break with a brittle fracture. On the other hand the glass-filled polymers are less notch sensitive and in some tests and service conditions the glass-filled nylons may prove the more satisfactory. 

Figure 12 SEM photographs of fractured surfaces (X1000). (A) PBT-TLCP-elastomer blend. (B) Nylon 6-TLCP-elastomer blend. Source Ref. 56.

Figure 14 SEM photographs of fractured surfaces of non-elongated nylon 46-Vectra B (75 25 wt ratio) blend fibers. (A) 2.7 wt% SA-g-EPDM was added. (B) No compatibilizer was added. Source Ref. 57.

Figure 13.10 Schematic representation of the most general type of fatigue fracture of a nylon 6,6 fiber [26], From The fatigue of synthetic polymeric fibers, Brunsell, A. R. and Hearle, J. W. S., J. Appl. Polym. Sci., 18, 267 (1974), copyright (1974 John Wiley Sons, Inc.). Reprinted by permission of John Wiley Sons, Inc.

Fig, 7.16, Impact fracture toughness (O) and interlaminar shear strength (ILSS, ) of carbon fiber-epoxy matrix composites with varying number of nylon sheets as delamination promoters. After Havre (1977). 

Figure 4. Degradation in strength as a function of time for Nylon 6 samples in three different concentrations of NO, at 81° C. Final fracture was at room temperature. Concentrations are (a) 0.86% (b) 2.58% (c) 5.16%.

Figure 8. Fracture surface of a nylon filament exposed to an SO Sample was held at 90% strain for 4 d at room temperature.

Figure 11. Fracture surface of a nylon filament exposed to an NOt environment at a concentration of 2.58%. Sample was held at 90% strain for 2 h at room temperature. Magnification (a) ca. 1370yf (b) ca. 1370y (c) ca. JJ90X.

One surface preparation method that is unique for composites employs a peel or tear ply.77 Utilization of the peel ply is illustrated in Fig. 16.5. With this technique, a closely woven nylon or polyester cloth is incorporated as the outer layer of the composite during its production layup. This outer ply is then torn or peeled away just before bonding. The tearing or peeling process fractures the resin matrix coating and exposes a clean, fresh, roughened surface for the adhesive. This method is fast and eliminates the need for solvent cleaning and mechanical abrasion. 

Complex Formation and Fracture Surface Morphology of a Highly Doubly Oriented Nylon 66 Rod... 

Although much of the work referred to in this paper was done several years ago, it was not reported previously. The content and implications are sufficiently novel to merit mention even at this time. The fracture surface morphology of doubly oriented nylon 66 was studied in its untreated and I2-KI complexed state. All the work reported here was done on doubly oriented samples made from an unoriented nylon 66 rod according to the techniques outlined below. 

Figure 6. Electron micrograph illustrating V-shaped deformation bands within the hydrogen-bonded (010) planes of fractured nylon 66, Micron marker insert, an edge view of fracture surface running from (010) plane through the thin direction of the strip (Figure 2),...

Figure 8. Scanning electron micrograph of the unoriented nylon 66 rod fractured at 45° to the longitudinal axis...

Figure 11. Scanning electron micrograph of a freshly fractured sample of complexed nylon 66 showing the distorted layers corresponding to Figure 7. Sample was unshadowed and fractured at liquid nitrogen temperature.

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