Nucleation and growth of crazes in amorphous polychlorotrifluoroethylene in liquid nitrogen

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Abstract
The density of mature crazes initially increases linearly with stress and then more rapidly at higher stresses. Once the crazes become observable then density was independent of time. The lowest stress at which an appreciable density of crazes was produced corresponds to the proportional limit. The average velocity of mature crazes was constant for a given stress and varied exponentially with the stress. The velocity depended on stress in the same way that the post‐yield point stress depended on strain rate, whereas the yield point varied differently being a nonlinear function of the logarithm of the strain rate.The density of crazes was quantitatively related to the concentration of surface defects at which the crazes nucleate. The craze velocity was directly related to the diffusion coefficient of N2into the polymer. The analysis indicates that bulk diffusion of the N2governs the craze velocity and that plasticization of the tip of the craze is most important for the nucleation and growth of a craze in PCTFE.

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