Tensile deformation localized stress-whitening

Tensile deformation of the uncompatibilized blend with 50% PS was characterized by the appearance of several regions of localized stress-whitening in the gauge section without global necking. Fracture occurred at one of these regions at a relatively low strain, about 3.2%. This behavior is characterized as quasi-brittle rather than brittle, because some level of plastic deformation precedes fracture even though the fracture strain is low (Chapter 21). 

Under compression or shear most polymers show qualitatively similar behaviour. However, under the application of tensile stress, two different deformation processes after the yield point are known. Ductile polymers elongate in an irreversible process similar to flow, while brittle systems whiten due the formation of microvoids. These voids rapidly grow and lead to sample failure [50, 51]. The reason for these conspicuously different deformation mechanisms are thought to be related to the local dynamics of the polymer chains and to the entanglement network density. 

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