Research On The Incremental Flanging Of AHSS Based On Numerical Simulation Of Microscopic Damage

There were various flangings in auto panels and with the industrialized application of advanced high strength steel(AHSS)in lightweight body structure,AHSS caused great challenges to the traditional flanging process: excessive high strength resulted in poor flanging formability;cracking failure behavior of AHSS was completely different from traditional sheet metals in forming process;complex flanging process made it difficult to estimate the deformation properties of blank intuitively and calculate the thinning accurately.Aiming at the above problems,this paper carried out an innovative design of die structure through a profound analysis of stress-strain state in flanging process in order to improve the forming performance of AHSS in stretch-flanging process.Meanwhile,plastic damage was introduced in order to predict and evaluate the formability of lightweight materials which could provide some technical guidance for complex flangings in auto panels through accurate material constitutive model and innovative process design.Therefore,the following research work was carried out in this paper based on theoretical analysis,numerical simulation and physical experiments:(1)Experiment was carried out by taking MC600 DP dual-phase high strength steel as research object.Numerical simulation model of uniaxial tension coupled with Gurson-Tvergaard-Needleman(GTN)mesoscopic damage model was established based on Abaqus.Aiming at the disadvantages of GTN damage parameter calibration by experiment design-agent model,a development of Abaqus with Python was presented and a fully automatic numerical simulation program based on genetic algorithm was established which achieved high-precision mapping and adaptive optimization between damage parameters and macro-mechanical properties.Finally,the constitutive model for accurately describing the actual flow behavior and damage evolution of AHSS is obtained.(2)Taking complex stretching flanging as the research object,mechanical analysis of flanging process was carried out in order to reveal the technological difficulties of flanging with AHSS.The stress-strain distribution of blank was studied and the ideal of incremental forming was put forward in order to design the die structure innovatively.The elastoplastic constitutive model coupled with mesoscopic damage mechanics was used to evaluate the formability of blank.Based on numerical simulation technology,the forming process,thinning,stress-strain state and damage evolution between traditional flanging and incremental flanging were compared and analyzed in order to reveal the mechanism and advantages of incremental flanging process.(3)The influence of related parameters on the stretch-flangeability with AHSS was investigated.The sensitivity of parameters was studied and the non-key factors were optimized based on the orthogonal experiment,while the neural network prediction model between key factors and objective functions(Minimum thickness and punch stroke)was established based on Matlab and optimized by multi-objective genetic algorithm.Referring to the results of parameters optimization and according to the requirements of press and process difficulties,this paper matched the relevant parameters reasonably and obtained the optimal parameters of die structure which could be used in actual production.The specifications of incremental flanging process established in this paper were not only applicable to AHSS,but also to complex flanging characteristics of lightweight materials such as magnesium alloys and aluminium alloys.