THE RELATION BETWEEN FOREST DISLOCATIONS AND STRESS IN BCC METALS

During plastic deformation, the part of the applied stress related to dislocations is usually set proportional to the square root of their density. In bcc metals, screw dislocations experience a high lattice friction at temperatures below the transition temperature. Consequently, such a relation has no more any experimental and even no theoretical supports. A model to evaluate the forest dislocation contribution to the flow stress is proposed. The calculation is based on stored energy considerations. At low temperature, the resulting athermal part of the stress evolves linearly with the dislocation density, a proportionality which appears to be in good agreement with experimental evidences.