Chaboche Viscoplastic Law Based On The Polar Corotational Description And Its Numerical Implementation

Accompanying with the development of aerospace and nuclear energy engineering,the viscoplastic behaviors presented by the parts working at elevated temperature and multiaxial loading have been widely focused on by materials and mechanics scientists.In 1980s,Chabo-che established a representative unified viscoplastic law with an infinitesimal form.Thereafter,most investigations and improvements based on it were also limited to infinitesimal contexts.Although infinitesimal viscoplastic laws are usually of simple mathematical forms,they can not cover the viscoplastic engineering problems with large deformations.In the present work,the Chaboche viscoplastic law is extended under the local polar corotational coordinate syste-ms into the form with large deformation,the numerical algorithms related to the law are deri-ved and a user subroutine embedded in ABAQUS is coded.By comparing the numerical pre-dictions with two testing observations and simulating two types of metal forming,it can been drawn that the new viscoplastic model,the numerical algorithms and the subroutine are appli-cable and efficient.The major works and results in the thesis are summarized as follows:? On the basis of the Bingham unified viscoplastic phenomenological model,an infinitesi-mal Chaboche viscoplastic law is extended with the polar corotational description to the context of finite strain.? In the extension,the work-conjugate relation described under the polar corotational fram-eset is applied,the Clausius-Duhem inequality for the unified viscoplastic dissipation is derived under the same frameset.Based on the inequality and the standard normality rule of dissipation,the evolution equations for the strain-and stress-like internal variables are established,the finite strain Chaboche viscoplastic law is therefore coincident with the basic laws of thermodynamics.? From the finite strain viscoplastic law,the numerical algorithms for the finite element im-plementation are derived,including the algorithms for integrating the internal variables,updating stress and calculating the consistent tangent modulus,a finite element program is coded and embedded in the general program ABAQUS.? Under different strain rates,the uniaxial tensions of the nickel-base superalloy IN738 LC at 850? are numerically simulated.It can been seen that the numerical predictions are well consistent with the testing results.So,it can be drawn that the new law and the algo-rithms are reliable and efficient.? The testing on IN738 LC at 850? under uniaxial cyclic loading is simulated,the results show that the numerical prediction is also well consistent with the observation in the testing.? By modeling of a billet upsetting and a channel forming,the efficiencies of the new visc-oplastic law,the algorithms and the finite element code are verified under complex loading and boundary conditions.? The extension of the infinitesimal Chaboche viscoplastic law into the context of finite str-ain lays a foundation for more extensive engineering applications of the Chaboche models.