Whisker stress-strain curve

Fig. 8.8. Stress-strain curve for Cu whisker (adapted from Boyer (1987)).

A stress-strain curve for a Cu whisker is shown in fig. 8.8. It is seen that the stress scale associated with whiskers is in the gigapascal range in support of our hypothesis that in whiskers the ideal strength may be more approximately realized. It is not surprising that the ideal strength estimate is not reproduced exactly since our argument assumed a contrived sinusoidal dependence to the energy associated with uniform slip. 

Figure 23.3 Stress-strain curves of GSPI sheet and SPI/chitin whisker nanocomposites conditioned at 43 per cent RH. (Reprinted with permission from Reference [78].

Typical stress strain curves of chitin whisker/unvulcanized NR composites obtained by evaporation (T=25 °C, d /dt = 8.3 x 10 s ). The crab shell chitin whisker contents are indicated in the figure. (Reproduced from reference 107 with permission from the American Chemical Society.)... 

Since whiskers have high tensile strengths they are also capable of withstanding exceptionally large elastic strains. Metallic and even some oxide whiskers support strains of 2 to 5% before fracture or yield occurs. Towards the higher strains the stress-strain behavior is often nonlinear and substantial deviations from Hooke s law are observed. The stress-strain curves are similar to the one shown in Fig. 45 for the amorphous iron alloy fiber. At the highest strain some stress relaxation may also occur, giving rise to an irreversible residual deformation. 

The tensile stress-strain curves of pure PP and 10% whisker-filled composite material are shown in Figure 6.39. The tensile... 

Figure 6.39 Tensile stress-strain curves of composite materials prepared using extrusion and injection molding, (a) Pure PP. (b) 10% whisker content.

Dufresne et al. studied stress vs strain curves (nominal data) for the chitin whiskers/unvulcanized NR evaporated composites, shown in Figure 14.12."" The polymeric matrix is in the rubbery state and its elasticity from entropic origin is ascribed to the presence of numerous entanglements due to high molecular weight chains. They further observed that the incorporation of anhydride and isocyanate modified chitin whiskers into NR lead to composite materials with improved mechanical properties. The study of the morphology of these nanocomposites leads to the conclusion that the various chemical treatments improve the adhesion between the filler and the matrix (Figure 14.13). However in some cases there is loss of performance, which could be due to the partial or total destruction of the three-dimensional network of chitin whiskers assumed to be present in the unmodified composites. 

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