Characterizing the back stress of ultra-thin metallic sheet via pre-strain tension/bending process

Abstract

Abstract The buckling and instability of the ultra-thin sheet metal specimens subjected to compressive loading present an evident difficulty for the investigation of Bauschinger effect by using traditional tensile-compressive loading tests. In that regard, a pre-strain/bending method which is easier to implement was developed to characterize the back stress of ultra-thin metallic sheets. SS 316 L sheet specimens with the thickness of 0.1 mm were first subjected to uniaxial tension for a specific pre-strain. After that, they were bent at different radius levels to achieve different compression conditions. By calculating bending moments based on experiments and constitutive relationship respectively, the back stress which presented the offset stress between the stress-strain curves of loading and reverse loading, could be obtained through iteration according to the equivalence of above two moments. Experimental results indicated that the softening caused by Bauschinger effect led to evident increase of back stress when increasing the pre-strain. By utilizing the experiment and calculation method developed in this study, parameter identification of back stress evolution for ultra-thin metallic sheet can be realized practically and the relationship between the back stress, pre-strain along with reverse plastic strain could be established and analyzed. The presented method was thus proved to be an efficient solution for characterizing the back stress of ultra-thin metallic sheets.