Time-dependent methods for limit strains determination of sheet metal Métodos temporales para determinar deformaciones límite en chapas metálicas

SIGNORELLI, JAVIER WALTER; LEONARD, MARTÍN EDUARDO; ROATTA, ANALÍA; STOUT, MICHAEL GEORGE

REVISTA MATéRIA

UNIV FED RIO DE JANEIRO

Año: 2018 vol. 23

1517-7076

The forming limit diagram (FLD) ?broadly used to characterize sheet-metal formability? is made by means of strain measurement over the surface of stretched samples and the subsequent determination of limit-strain values associated with the onset of necking. Currently, researchers can make strain measurements with digital image-correlation analysis (DIC). Data measured by DIC easily adapt to the traditional position-dependent method for evaluating limit strains, but this method is not applicable to materials that exhibit inhomogeneous deformation, like multiple necking. DIC analysis allows for the application of time-dependent methods, which are based on analysis of the temporal evolution of strains to define the onset of necking. This article compares three recently proposed time-dependent techniques for determining limit strains: a thicknesscontrol method, the strain-control method and an acceleration-correlation method. For experimental purposes, duplex 2205 stainless-steel sheet, 0.92mm thick, was tested in uniaxial tension. The standard positiondependent method (ISO 12004-2) provides a reference for comparing results. We attribute differences in limit- strain values to the difficulty in objectively setting each method?s parameters. These differences show that there are still aspects of the temporal analyses that must be improved on before a precise and generalized methodology is available.