Multiscale modeling of the negative strain-rate sensitivity in solid solutions: A constitutive formulation

A physically based constitutive model capturing the reduced strain-rate sensitivity of dilute solid solutions is developed. The decrease of the strain-rate sensitivity parameter is associated with the variation of the strength of dislocation junctions with the size of solute clusters forming on forest dislocations. It is shown that the strength of junctions formed by unclustered mobile dislocations and clustered forests increases with the size of the cluster and, therefore, with the aging time of forests. The formulation is calibrated based on results obtained from mesoscopic models of dislocation interactions in the presence of solute clusters at forest dislocations. The strength of junctions is evaluated for most geometries and an averaging procedure is used to predict the strain-rate sensitivity. Several feat tires observed experimentally are reproduced by the model. Its limitations are discussed in closing. The data may also be used as input for discrete dislocation dynamics simulations.