Experimental Study On The Subsequent Yield And Anisotropic Hardening Of HRB400E Steel Under Tensile-Torsion Preloading

With the development of civil engineering towards super-tall building and large span structure,steel has been more widely used and the engineering structures and components has been subjected to more complex loads.In order to ensure the safety of the structure during service,it is quite essential to investigate the plastic hardening behaviors of steel with respect to different loading history.Considering the inadequate in study of the yield and hardening behaviors of steel under complex loading paths at present,a large number of experiments and theoretical studies needs to be done.The HRB400 E steel which is commonly used in civil engineering has been selected as the research object in this paper.The initial yield surface and the subsequent yield surface under uniaxial tension and compression and different combinations of pre-tension and pre-torsion paths and anisotropic hardening process has been studied by experiment.The law of plastic flow for subsequent yield surface has been analyzed.The main work and conclusions of this paper are as follows:1.The results of the initial yield surfaces show that the shape of the initial yield surface for the HRB400 E steel in (?) coordinate plane is in good agreement with the description of the Von-Mises criterion,which is a circle with the origin as the center and the yield stress as the radius.The material exhibits the property of initial isotropic.2.The results of the subsequent yield surfaces under uniaxial pre-tension and pre-compression show that the positions,shapes,and sizes of the subsequent yield surfaces are closely related to the preload history.The subsequent yield surfaces are close to the direction of preload in final stage.The greater the amplitude of preload,the further the position of the subsequent yield surface from the initial yield surface,and the larger the size of the subsequent yield surface.The shape of the subsequentyield surfaces under pre-tension and pre-compression are basically symmetric about the stress axis.3.The results of the subsequent yield surfaces tests under the combination of pre-tension and pre-torsion show that the shape of the subsequent yield surfaces are affected by the biaxial loading history of the tension and torsion,and the subsequent yield surfaces are not symmetric about the stress axis.The hardening in the preloading direction is extremely small.As the loading angle approaches the reverse direction of the preloading,the degree of hardening for yield point gradually becomes larger and the yield surfaces exhibit as irregular "scallops".4.HRB400 E steel has remarkable anisotropic hardening characteristics.The hardening of yield point near the preloading direction is small,and the hardening of yield point away from the preloading direction gradually increases.The offset strain method has been adopted to describe the anisotropic hardening behavior.The results show that the value of the offset strain has a significant effect on the size of the subsequent yield surface.With the increase of the offset strain,the size of the subsequent yield surface increases.The rate of subsequent yield surface hardening gets fast with a smaller offset strain(200??,500??),and the rate of subsequent yield surface hardening gets slows down with a larger offset strain(1000??,2000??).The anisotropic hardening behavior of HRB400 E steel presents the above trend.