A Visco-elastic-Plastic Unified Constitutive Theory For Deformation

In this thesis, a Visco-elstic-plastic Unified Constitutive Model is founded. The comparison between this model and other unified constitutive shows that the new, model has many superiorities over other constitutive models.Unified constitutive theory, as a state-variable theory without yield surface, is a new constitutive theory that started to develop in the I 970s. The state variable can describe the inner change of material structure in loading and reloading process. All the deformations are combined up in a set of constitutive equations.In the first part of the paper, an out scope of the study of unified constitutive model is described. The thesis traced back of Miller抯 unified constitutive model. After the study of all kinds of constitutive models, a conclusion was coming that is all the constitutive were elastic visco-plastic constitutive model. A common backward of all these models was draw out. There is no transition between the elastic deformation and inelastic deformation.By studying the experiment information carefully, the visco-elastic deformations were pointed out. That means there is time dependent deformation during the elastic deformation stage. This kind of deformation is not included into the constitutive models before. So there is no transition between the elastic deformation and inelastic deformation.By introducing the visco-elastic deformation into the unified constitutive model, a new Visco-elastic-plastic Unified Constitutive Model is founded. The new model turns out to be better in simulating ajl kinds of material deformation. Excellent accuracy is obtained in simulation by the proposed model.Visco-elastic-plastic Unified constitutive theory becomes an access between macroscopic phenomenon and the inter change of material structures. Compared with classical macroscopic plastic theories, however, unified constitutive theory reduces the phenomenological description and increases influence of microscopic physical mechanisms by introducing two state variables. So the theory can encompass both microscopic and macroscopic research results, thereby presenting process of actual deformation more intrinsically. Moreover, Visco-elastic-plastic Unified constitutive theory also displays its unique advantages in application because it can describe various deformations by a set of unified equations. And thus makes it more suitable for structure analysis under sophisticated loading conditions at high temperature.A new kind of unified constitutive theory framework is developed in this paper. It concluded more kinds of deformations defined in classic strength theory. The new Viscoelastic-plastic Unified constitutive model can be used to simulate deformations of rnonotonic, creep, relaxation, cyclic hardening, Bauschinger effect, rate effect, andtemperature effect. This new constitutive theory framework shows more opportunities in the engineering applications.To make sure of the accuracy of the Visco-elastic-plastic Unified constitutive model, experiment information of several materials were used as samples. The materials are 304 stainless steel, Hastelloy-X, rock salt and concrete. The results of simulation are in strong agreement with those of the experiments in terms of accuracyFarther more the Visco-elastic-plastic Unified constitutive model is applied to concrete rate-related deformation prediction. The simulated curve is cooperated kindly with trend of the original deformation.Finally the parameters correlation evaluation method is draw out. The optimized parameters of the Visco-elastic-plastic Unified constitutive model can be obtained by the optimized progrem.