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Residual stresses due to roll bending of bi-layer Al-Cu sheet: Experimental and analytical investigations

Applications of bi-layer sheets are developing in different industries. In many cases, manufacturers need to form bi-layer sheets to a desired curve by roll bending process. This process can induce considerable residual stresses. In this article, the residual stress distribution due to bending to specified curvature radius is measured in an Al-Cu sample. The sample is bent by three roll bending process to curvature radius of 350 mm. The slitting method is extended to measure induced residual stresses in bi-layer sheets. Also, an analytical solution has been proposed for prediction of residual stresses in bi-layer sheet. The analytical solution has been derived for material with elastic-power law hardening plastic behavior as the actual behavior of aluminum and copper is. Also in the analytical solution, the neutral axis movement due to different elastic moduli of aluminum and copper layer is considered. A maximum and minimum of measured residual stresses equal to 35 and −28 MPa, respectively, showing a remarkable magnitude in comparison with 51 and 36 MPa yield strength of copper and aluminum layer, respectively. Comparing the results show good agreement between analytical solution and experimental results.