Mechanical Behavior Modeling in the Presence of Strain Aging

In many fields some structural materials are subjected to strain aging, which gives rise to inhomogeneous yielding such as Piobert-Luders’ bands and Portevin — Le Chatelier instabilities. These phenomena occur in steels containing interstitial elements in solid solution such as carbon or nitrogen which segregate to dislocations during aging and pin them. Strain aging in ferritic steels induces a loss in ductility and fracture toughness at mild temperatures [1]. To study the influence of strain aging on ductile tearing, it is possible to simulate plastic strain instabilities using a local constitutive equation [2] taking into account the interaction between solute atoms and dislocations responsible for strain aging [3]. This study first requires the identification of the model parameters, which needs to correlate the experimental values obtained from tensile tests to the intrinsic behavior of the material and then requires a good interpretation of the upper and lower yield stresses in the presence of static strain aging. So we have performed a numerical study of the Luders’ plateau featuring the influence of several parameters such as meshing, boundary conditions or behavior law on the nucleation and growth of Luders’ bands. The influence of the local band development on the plateau has been investigated. Correlations between the plateau stress level and the local behavior will be discussed.