Poly(ethylene terephthalate) fiber was continuously flow-drawn to a draw ratio of more than 20 with heating by laser irradiation. High-speed video imaging and drawing tension measurement observed a clear transition between the neck-drawing state and the flow-drawing state. A neck shape vanished at a draw ratio of about 3.2 and was accompanied by a step drop in drawing tension. Drawing stress during flow drawing is about 2 orders of magnitude smaller than the stress during neck drawing. THhe fiber broke at a draw ratio of about 25, immediately following instantaneous appearance of necking-like deformation. A critical drawing stress, about 6 MPa for post-drawn fiber, marks the transition between the neck drawing and the flow drawing.
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