The plastic deformation of oriented polypropylene and polyethylene: deformation mechanisms
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Polypropylene and high-density polyethylene, oriented by hot drawing, have been tensile testedin situ in a low angle X-ray camera. Two orientations of polypropylene,Θ0=31° andΘ0=60°, and one orientation of polyethylene,Θ0=30°, were examined. (Θ0 is the initial angle between the tensile axis and the molecular axis.) Low-angle and wide-angle X-ray patterns were taken at successive stages of increasing strain up to approximately 100%. The rotations of the molecular axis and lamellar normal for both materials oriented nearΘ0=30° were quantitatively consistent with predominantly intermolecular shear, occurring within the lamellae. In the case of polypropylene, it is proposed that small amounts of interlamellar and interfibrillar shear were also present.
AtΘ0=60°, the polypropylene was shown to deform by void opening or fibril separation, followed by intermolecular shear. The behaviour of polypropylene was consistent with the yield criterion based on a fibre reinforced composite model which was presented in a previous paper .
KeywordsPolymer Polyethylene Plastic Deformation Polypropylene Fibril
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