In recent years, instability in the plastic deformation of metals and alloys has become the subject of intensive experimental and theoretical investigations [1-4]. An instability arises when the material is subjected to tensile loading at constant strain rate. Under normal conditions, one observes smooth stress-strain curves. However, under certain specific conditions of strain rate and temperature, one observes several yield drops. This is known as serrated yielding or repeated yielding or jerky flow, associated with Portevin Le-Chatelier (PLC) effect. Attempts have been made to construct appropriate mathematical models and simulate such instabilities [5, 6] in a finite domain of the control parameters. Occurrences of regular and chaotic behaviour of plastic flow have been found in a theoretical model [5,6]. However, so far, a dynamical analysis of the time series of serrated plastic flow obtained during an experiment has not been made.
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