Study On Thermal Forming Fracture Characteristics Of Laser Tailored Welded High Strength Steel Blanks

Automobile lightweight is an important topic in the current automotive industry,and high-strength steel plates and their advanced manufacturing technologies are currently one of the main research directions for automobile body lightweight.The hot forming technology of high-strength steel welded blanks can reduce vehicle weight,save energy and reduce emissions,and significantly improve the forming accuracy and hard zone strength of high-strength steel welded blanks.However,due to the phenomena of rebound,wrinkling,fracture,and weld seam deviation during the hot forming of high-strength steel laser welded blanks,in order to improve the forming quality of the hot formed parts of high-strength steel laser welded blanks,this article takes high-strength steel laser welded blanks with substrates of Usibor1500P and Ductibor500 as the research object,and studies the damage evolution and formability during the hot forming process based on the GTN damage model.The specific research is as follows:Firstly,the thermal rheological behavior of the substrate was obtained through isothermal uniaxial tensile tests at 600℃,700℃,and 800℃for laser welded blanks of high-strength steel Usibor1500P and Ductibor500.The failure characteristics of the fracture location of the test specimen were analyzed using scanning electron microscopy.Then,using the GTN damage model combined with the central composite design method and genetic algorithm,the high temperature damage parameters of two substrates at 600℃,700℃,and800℃were obtained through finite element reverse calibration of GTN high temperature damage parameters.The influence of a single damage parameter on the simulation results of uniaxial tension and the damage evolution during uniaxial tension were analyzed,And the accuracy of the finite element simulation of the coupled GTN damage model was verified through uniaxial tensile tests of the welded joint.Secondly,the forming limit diagram of high-strength steel laser welded blanks under700℃thermal state was obtained through hot forming limit experiments.The experiments were analyzed by coupling the forming limit experiment finite element model with the GTN damage model.The load displacement and fracture location obtained from finite element simulation are consistent with actual experiments,and the critical hole volume fraction f _F in the GTN model is used as the basis for the hot forming limit of laser welded blanks.The simulation and actual test hot forming limit diagrams are compared,and the results show that the coupled GTN damage model hot forming limit simulation test can accurately simulate the actual hot forming test of high-strength steel laser welded blanks.Finally,a study was conducted on the thermal forming fracture characteristics of typical structural components of high-strength steel laser welded blanks.For the 180mm forming limit test piece of laser welded blanks,the influence of process parameters such as initial temperature of the sheet metal,blank holder force,and friction coefficient on the fracture failure mode during the hot forming process of high-strength steel laser welded blanks was explored.This article combines theory with finite element simulation to determine the high-temperature damage parameters that can be used for the hot forming of high-strength steel laser welded blanks,and verifies them.A coupled GTN damage model is used to simulate the hot forming of high-strength steel laser welded blanks,and its fracture characteristics are studied,providing certain theoretical support for the application of high-strength steel laser welded blanks hot forming.