Elastic and inelastic recovery after plastic deformation of DQSK steel sheet

Strain recovery after plastic prestrain and associated elastic and inelastic behavior during loading and unloading of DQSK steel sheet are measured. Average tangent modulus and Poisson's ratio during unloading and reloading are found to differ from their elastic values in the undeformed state, and they also vary as a function of stress. This modulus, often referred to as the springback modulus, decreases with plastic prestrain rapidly for prestrain values <2 percent and decays slowly for larger values of prestrain, while the average Poisson's ratio during unloading increases with plastic prestrain initially rapidly, and then remains almost unchanged at larger prestrain. Changes in the springback modulus and Poisson's ratio are shown to be due to recovery of microplastic strain and not due to viscoelastic effects. Springback modulus and Poisson's ratio are anisotropic, showing a maximum in modulus and a minimum in Poisson's ratio at 45 deg to rolling direction. To describe the combination of recoverable inelastic and elastic deformation as a,function of plastic prestrain, a set of equations has been developed based upon a previously developed constitutive model. Calculated results are capable of explaining experimental results on modulus and Poisson's ratio changes. Implication of the results on springback is illustrated and empirical relations are obtained.