Study On Deformation Failure Mechanism Of Dual Phase Steel Laser Tailor Welded Blanks Based On GTN Damage Model

In order to meet the increasingly stringent requirements of automobile lightweight,advanced high-strength steel laser tailor welded blanks(LTWBs)are widely used in automobile body manufacturing.With the change of welding process parameters,LTWBs of advanced high-strength steel show different fracture modes and mechanical properties during the forming process.Therefore,it is of great significance to study the deformation and failure mechanism.However,the laser welded joint of advanced high-strength steel has a high degree of non-uniformity in microstructure and properties in narrow zone.At the same time,there are hardening zone and softening zone in heat affected zone,which brings a challenge to the study of its deformation failure mechanism.In this paper,aiming at the deformation and failure mechanism of advanced high-strength steel LTWBs.Taking DP780 high-strength dual phase steel laser tailor welded as the object,a fine finite element(FE)model of the joint is established based on the GTN damage model.Studying the failure behaviors of transverse joint tension and LTWBs stamping deformation by the FE simulation method.The main work of this paper is as follows:The mixure rule is used to refine the zone of the LTWBs joint,and the FE modeling of the base metal,welded,longitudinal joint and transverse joint is completed by combining the ABAQUS FE simulation software.The parameters of the GTN damage model in each zone of the joint are determined by using the FE inverse method.By comparing the tensile simulation results with the experimental results,the rationality of the mechanical model is verified.The unidirectional tensile FE simulation of the laser tailor welded transverse joint with different heat input is carried out.Besides,the necking deformation and fracture failure behavior of the transverse joint are analyzed.The results show that: there are non-uniform deformation zones near the softening zones of different heat input joints,and the volume fraction of holes can directly reflect the deformation failure process of the non-uniform joint compared with the equivalent plastic stress change.The failure modes of softened zone or base metal,which is depend on the sequence of plastic damage.Based on GTN damage model can reflect the plastic fracture trend of joint.The FE simulation of the limit dome height(LDH)test stamping formability with different heat input LTWBs were conducted to analyze its deformation and fracture failure behavior.The results show that: the joint FE simulation based on GTN damage model can obtain more accurate stamping formability of TWBs,and reflect the softening zone or welded two fracture failure modes of TWBs.Low heat input TWBs with the higher stress triaxiality in the initial stage of sheet metal stamping,which is helpful to slow down the deformation process of the softened zone and play a role of "restraining" the deformation of the softened zone.When the deformation of the weld zone develops to fracture,the weld first occurs fracture failure.