Study On The Simplified Schemes Of Thermal Elastoplastic

In the important industrial departments in the national economy, the effective analysis of high temperature structural responses is becoming a significent research topic which should be emphasised in order to ensure the safety and reliability of large complex high temperature systems. By the deep and detailed investigation and study of the elastic analysis, simplified inelastic analysis and detailed inelastic analysis in the engineering analysis / design, the following aspects are completed in this dissertation:1. The equivalent time method based on the equivalent time concept is proposed to calculate rapidly the transient temperature and thermal stress of the complex structures, which is a simplified analysis method for the preliminary elastic analysis of new designed equipment and the real-time analysis of on-line equipment.2. For the further analyses of those components which haven't passed the exact code rules according to elastic analysis, a series of simplified inelastic analysis methods are proposed. These simplified method are based on rather exact theoratical prooves, use the finite element method as an efficient tool, don't simplify the structural geometrical configurations and material properties, trace the loading histroy as much as possible and cost considerably little calculation to obtain the results which are almost as exact as those by the detailed inelastic analysis.(1). Based on the virtual work principle, an energy equation and the corresponding nonlinear algebraic equations respect to the deformation rate of steady creep are proposed. By the use of the equilibrium equation, the poisson equation of average stress is also formulated. The steady creep stress field can be obtained directly by solving these equations.(2). An exponent or power function is used to simulate the redistributed stresses of the structures subjected to sustained loads, which can give an effective estimation to the creep stress redistribution for materials exhibiting the secondary creep as well as the primary creep.(3). Based on the deformation theory of the linear hardening material, a simplified finite element method to calculate the elastoplastic responses of nonlinear hardening material is proposed. Combining it with the equivalent tracing method, we can give a simple and efficient estimation of the cyclic thermal elastoplastic responses.(4). By the comprehensive use of the conclusions above, the cyclicelastoplastic—creep responses in the structures subjected to cyclic mechanical loading including enduring time of load can be calculated rapidly.3. A half—analytical intergration scheme of the Kachanov—Robotonov isotropic creep damage equation coupled with stresses is develpoed and has incorperated into an inelastic finite element software.