Initial damage and its evolution with stretching of experimental microalloyed mild steel sheet

Abstract

An extensive study of damage developed in a stretched spheroidised carbon steel sheet has been made. Bulge and punch stretching tests were employed. Damage of the stretched specimens was measured using a SEM. Nucleation strains for the different particles present in the sheet were determined. When damage is heterogeneously distributed within the sheet, a set of magnifications (so as to scan a large area) is strongly recommended. Area density (and volumetric fraction) of voids close to the sheet surface is at least 10 times greater than in the sheet thickness and increases exponentially with void size. A small proportion of MnS stringers (V_f=0·0005) plays a relevant role in the overall sheet damage. Necking and subsequent fracture in this type of sheet can be explained by a progressive tearing mechanism originating in the free surface and progressing deeper into the thickness of the sheet.

MST/481

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