A Non-classical Viscoplastic Constitutive Relationship For Single Crystal And Its Application Of Creep-Plasticity Interaction Behavior

The behavior of the materials subjected to complex loading has been increasingly attractive in recent years due to the needs of the quick development in many fields including chemistry, power generation, air crafts as well as aerospace systems, and new material, etc. . As pointed by Lekie that the new problems of loading-bearing system would mainly arise from the following motivation :to increase performance, to extend life and to avoid failure. For these purposes, materials will be suggested to work under more adverse operating conditions, so that on one hand high-performance materials are required and, on the other hand, more reliable estimation for operation life and failure analysis should be formulate. To be the premise, the research on more realistic constitutive models becomes more and more significant.In recent twenty years, a quick development of computer, advanced servo-hydraulic material testing system as well as powerful TEM and SEM provides powerful means in the study of constitutive behavior of materials subjected to complicated loading conditions. A lot of experimental and theoretical work shows that although classical theory of plasticity(CP)is of great theoretical significance and has been applied to a plenty of problems, it is reasonable to develop a new theory of plasticity beyond the framework of CP due to the recent by Drucker: "The more sensitive the measurements that are made, the smaller will be the diameter of cash yield surface. When a motion of a modest number of dislocations are detected as macroscopic plastic deformation the observed yield surface will shrink to zero size". With this concept, the work in this thiese was conducted on the basis of non-classical theory of viscoplasticity.Based on the energy storing characteristics of microscopic polycrystalline during irreversible deformation, a viscoplastic constitutive model with no yielding surface is developed by adopting a spring-dashpot mechanical system. Plastic dashpots reflecting the material transient response and Newton dashpots mirroring the material viscosity are introduced to describe the viscoplasticity of slip systems. The constitutive model is established based on the thermodynamics of internal variables and the theory of absolute reaction rate. By utilizing the KBW self-consistent theory, the numerical analysis is greatly simplified as no process searching for the activation of the slip system and slip direction is required. The creep-plasticity behavior described by this model was discussed. Simulation results show great agreement with the experimental data.