2002 Volume 88 Issue 6 Pages 334-339
A novel experimental method for precisely measuring the stress-strain relations of sheet metals subjected to plane-strain tension has been developed. A hydraulically servo-controlled biaxial tensile testing apparatus and newly-devised cruciform specimens have been used. The geometry of the cruciform specimen has been determined using FEM analysis so that the stress distribution in the gage section of the specimen becomes as uniform as possible. By measuring the principal strain components of the specimen by strain gages and controlling the nominal strain rates using an electrical feed-back circuit, we have been successful to realize plane-strain tension tests of sheet metals up to a tensile strain of 0.1. The minimum (width) strain has been confirmed to be almost zero within the resolution of strain measurement, ±22 με. The measurement error of the maximum principal flow stress has been estimated to be under 2% according the FEM analysis. Stress-strain curves for IF steel (SPCEN) and 370 MPa-level rephosphorized steel (SPFC370) under plane-strain tension have been measured and compared with those predicted by the Hill quadratic and Hosford yield criteria. It has been found that the stress-strain curves calculated by the Hosford yield criterion are generally in good agreement with the experimental ones during early work hardening stages (less than 0.02-0.03 tensile strains). However, the difference between the experimental and predicted flow stresses increases gradually with increasing the tensile strain. The plane-strain flow stresses predicted by the Hill quadratic yield criterion are tend to be larger than the observed ones for the whole strain range irrespective of materials.
