Research On The Constitutive Model Depending Upon Temperature & Strain Rate Of Carbon Constructional Quality Steels

Carbon constructional quality steels have been widely used in modern automobile and aeronautic industry. Huge investments are put to optimize their production. Recently, following the rapid development of computer technology and the gradual advancement of numerical method,semi-analytical numerical method, the finite element modeling technology has become the most practical and convenient way. In order to achieve the numerical simulation calculating of rheological forming process of materials, it is necessary to found the constitutive equations that the rheological properties of materials under hot-working condition are described more accurately.In this thesis, the basic factors relating to the rheological stress in the constitutive equations are introduced systematically. Carbon constructional quality steels are regarded as a kind of elastic-viscoplastic materials under high temperature. The elastic-viscoplastic constitutive models are summarized, meanwhile the parametric variational principle has been carried out.A series of tension experiments under the same temperature and different strain rates, under the same strain rate and different temperatures were done on 20 steel, 35 steel and 45 steel. We obtained 52 groups of rheological stress-strain curves. The experimental results were analyzed theoretically. Furthermore, take 20 steel as an example, the rheological stress constitutive models of carbon steels are built combining the strong points of the Perzyna model and Johnson-Cook model. Comparing the calculation results conducted from the model with the experiment results, it proves that the model can reflect the temperature effect and strain rate effect of Carbon constructional quality steels better. Besides, the creep experiments under high temperatures have been done on 35 steel. The integral creep constitutive equation and differential stress-strain constitutive relationship can be established according to relevant rheological model and the integral core of the creep has been achieved through the experiments. Moreover, the coefficient related with viscosity of 35 steel was obtained through creep experiments' datum. The viscosity coefficients of TC11 titanium alloy and Lc4 aluminum alloy were also compared and analyzed.