Measurement of the strength differential effect of DP980 steel sheet and experimental validation using pure bending test

The strength differential effect (SDE), i.e., the difference between the flow stress of uniaxial tension and compression, of a dual-phase steel sheet with a tensile strength of 980 MPa (DP980) was measured using an in-plane uniaxial tension-compression test apparatus for sheet metals. The SDE data were obtained for a logarithmic total strain range of 0 <= vertical bar epsilon vertical bar <= 0.086 in both the rolling (RD) and transverse (TD) directions of the test material. It was observed that the magnitude of the compressive flow stress, vertical bar sigma(C)vertical bar, was consistently higher than that of the tensile flow stress, sigma(T), for a strain range of vertical bar epsilon vertical bar>0.009 in both the RD and TD; the amount of SDE, defined as (vertical bar sigma(C)vertical bar - sigma(T))/sigma(T)x100 (%), at vertical bar epsilon vertical bar=0.086 was 5.2% in the RD and 6.2% in the TD. Moreover, in order to validate the SDE, a novel test apparatus for obtaining the pure bending moment M versus curvature kappa (i.e., M - kappa) diagram was designed and manufactured. The obtained M - kappa curves were consistent with those based on the elasto-plastic numerical analysis considering the SDE. Thus, the SDE of the test material is experimentally validated using the pure bending test.