Quantification of large uniaxial Bauschinger effects in sheet metal from pure bending/unbending tests and interferometer techniques

This work presents an improved technique used to quantify uniaxial stress-strain reversals for sheet metal under pure bending tests. Data modeling on the lnσ-lnε scale resulted in simple and accurate descriptions ranging from small elastic strains to large strains typically represented by power fits. Pure bending-unbending strains of about 10% were measured by strain gages and interferometry. The reverse uniaxial stress-strain curves were determined from the optimal fit of the model. Bauschinger effects for two dual phase steels (DP590, DP780) and AA6022 aluminum alloy showed distinct features. For both DP steels the magnitudes of the reverse compressive σ-ε curves compared moderately higher, and merged to a power curve with parameters K, n previously defined by tension testing. Bauschinger effects at smaller reversed strains were less pronounced for the AA6022. However, at higher strains the reverse elasto-plastic response for AA6022 softened considerably. During the unbending span the magnitudes of the reverse compressive strains remained below the corresponding K, n tensile values.