What is the phenomenon that occurs in some thermoplastic polymers in which very
localised plastic deformation leads to the formation of small and interconnected
microvoids called?
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A.
Devitrification
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B.
Crazing
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C.
Crystallisation
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D.
Annealing
Correct Answer:
B. Crazing
Explanation:
Crazing is a unique deformation process in thermoplastic polymers where mechanical stress causes highly localized plastic yielding. Unlike standard plastic deformation that occurs at a constant volume, crazing involves a cavitation process that increases the material's volume through the creation of a dense network of microscopic, interconnected voids. These microvoids are bridged by fine polymer fibrils that are capable of supporting loads, which distinguishes a craze from a physical crack. While crazing allows the polymer to absorb significant energy before failure, it often serves as a precursor to brittle fracture, as the voids can eventually coalesce into subcritical cracks. This phenomenon is frequently observed in glassy polymers like polystyrene or polycarbonate under tensile stress and is often identified by a stress-whitening effect caused by light scattering off the microvoid surfaces.
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