Study On The Dislocation-based Physical Constitutive Relations Of Plastic Deformation Of Metals

This paper firstly introduces the past research works on metal material's plastic constitutive relations, and presents a specific description of main empirical and physical constitutive models which have been widely used by many researchers. Then, we have a discussion about the physical mechanisms of crystalline plastic deformation, and introduce the conception of dislocation kinetics to explain the plastic flow of metallic materials.Based on the thermally-activated dislocation mechanism of metallic plastic deformation, we propose a new constitutive model to describe the dynamic plasticity of FCC metals. In the establishment of this model, the constitutive parameters are directly linked with the microstructural characteristics of materials. As an example of its application, the model is used to describe the behavior of OFHC copper. To determine the constitutive parameters for OFHC copper, an improved multi-variable nonlinear optimization method is adopted based on the experimental data of flow stress. The reliability of the proposed model has been verified by the comparison of the model's predictions with experimental data. The new model for FCC medals is simple to apply and is better in terms of its prediction accuracy by comparison with MTS, Z-A and J-C models.Then, we propose a dynamic constitutive model for BBC medals based on the silimar physical mechanism of plastic deformation. The constitutive parameters are determined for an important military material, Tantalum, by using the multi-variable nonlinear programming. The comparisons with experimental data and some other models show that the new model for BBC metals is better to describe the plastic flow behavior of tantalum. Besides, the applicability of the model can be effectively extrapolated to a broad rang of strain rate and temperature.Finally, considering that the crystal structure of HCP has patial structural characteristics of FCC and BBC medals, we develop a new constitutive model for HCP metals by linearly adding the two constitutive models of FCC and BCC medals. The constitutive parameters of the titanium alloy Ti6A14V are determined by a new optimization method which is composed of a global genetic algorithm and a local penalty-function algorithm, and can guarantee that the constitutive parameters are a group of globally optimal solutions in their theoretically allowed ranges. The application of the model to Ti6A14V alloy shows that the model prediction can be more accurate than other models.