The Study On Flow Stress Model Based Dislocation Density

Micro-forming is a technology, with high efficiency, high precision, etc. It is very suitable for low-cost and mass manufacturing of micro-products. Due to the size effects, however, the know-how of conventional forming cannot be simply transferred to micro-forming. In the plastic deformation process, the storage and annihilation of dislocation density cause work-hardening and dynamic softening effect of material. Therefore, the study on flow stress model based on dislocation density will help to understand and grasp the nature of plastic deformation mechanism. In the past years, the models of flow stress were mainly focused on deformation temperature, deformation speed and deformation degree, but seldom on dislocation density.First of all, experiments were carried out on Gleeble-3500 Simulator and Instron machine. The flow stress-strain curves under various deformation conditions were obtained. Besides, micro-hardness experiments were conducted. Micro-hardness values of various samples under different deformation conditions were measured. The relationship between micro-hardness and dislocation density was researched.Secondly, according to the data of flow stress– strain curves, based on the Kocks-Mecking-Estrin model, the flow stress model of pure copper was established. Meanwhile, dislocation density evolution model and work-hardening rate - dislocation density model, work-hardening rate– stress model, work-hardening rate - strain model were established. Besides, the calculated results using these models are well consistent with the experimental results.Finally, through the finite element software ABAQUS / CAE for secondary development and the use of Fortran language, the program describing the performance of copper deformation process was written. The state of Mises stress and equivalent strain were simulated. Simulation results could describe the state of Mises stress and equivalent strain of pure copper accurately.