Evaluation of ductile fracture in sheet metal forming using the ellipsoidal void model

•For an alloy, the void configuration and void shape calculated in my preceding paper are valid.•For a pure metal, the void configuration and void shape calculated in my previous paper are valid.•The prestrain in an as-rolled sheet is estimated.•The prestrain in an as-rolled sheet cannot be estimated using conventional criteria.

The ductile fracture in the simulation of sheet-metal-forming processes is evaluated by the ellipsoidal void model previously proposed by the author. In the present study, the simulation and experiment of the hole expansion test are performed using six types of metals. For an alloy, the relationship between prestrain and hole expansion ratio calculated using the ellipsoidal void configuration and ellipsoidal void shape and that calculated using the ellipsoidal void configuration and circular void shape agree with the relationship obtained experimentally. For a pure metal, the relationship between prestrain and hole expansion ratio calculated using the average void configuration and average void shape agrees with that obtained experimentally. Furthermore, the method of introducing prestrain to an as-rolled sheet is proposed, and the prestrain in this sheet is estimated.

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