Study On Fracture Behavior Of TRIP780 And Application Of Semi-coupled Ductile Fracture Criterion

With the rapid development of new energy vehicles,high strength steel has been widely used in the automobile industry.However,in the process of plastic deformation of some high strength steel,different degrees of softening appear,which leads to the loss of bearing capacity of high strength steel.As for the fracture prediction of high strength steel,the uncoupled ductile fracture criterion cannot accurately describe the softening phenomenon of high strength steel in the plastic deformation process because it does not have the influence of damage,while the coupled ductile fracture criterion is not widely used in industry because of its complex parameter calibration.Therefore,this paper intends to construct a semi-coupled ductile fracture criterion to describe the softening phenomenon caused by internal damage of metal materials and to predict the fracture of materials.In this paper,TRIP 780 was selected as the research object,six kinds of specimens were designed for different stress states and mechanical property tests were carried out.It can be seen from the experimental results of dog bone specimens that the yield strength and tensile strength anisotropy of TRIP780 are not obvious,but the r value,elongation and fracture strain show some anisotropy.The initial damage displacements of different samples were measured by the resistance measurement method.According to the DIC image processing technology,the strain concentration area of different specimens was analyzed.Based on the unidirectional tensile test results of dog bone specimen,the relevant parameters of unrelated Drucker yield function were determined as the yield function of TRIP780,and the plastic deformation process of TRIP780 was described by the Swift-Voce hardening model.The finite element models of different specimens were constructed by the finite element simulation software Abaqus,and the accuracy of the calibration yield function and hardening model was verified by the finite element simulation.A semi-coupled ductile fracture criterion was established: The initial damage of the material is predicted by the uncoupled ductile fracture criterion DF2012,and the softening phenomenon of the material is described by the damage evolution model.In order to express the nonlinear damage evolution of metal materials during plastic deformation,the plastic strain influence factor is added into the damage evolution model to improve the flexibility of the semicoupled ductile fracture criterion.The influence of each parameter on the damage evolution of metal materials were analyzed by using the control variable method.The parameters of the semi-coupling ductile fracture criterion were calibrated by using the finite element simulation results.The calibrated semi-coupled ductile fracture criterion was applied to the fracture prediction of other specimens.The results show that the semi-coupled ductile fracture criterion can effectively reflect the softening phenomenon of TRIP780.Among them,the shear specimen is no longer in the state of pure shear stress at the time of fracture,but the constructed semi-coupled ductile fracture criterion can still effectively predict the fracture displacement.