Finite Element Analysis And Fracture Forecast Of Roll Forming

Roll Forming products have advantages of high dimensional accuracy, high surface quality, energy and material saving, and so on, which has been increasingly applied to manufacturing the structure of vehicles. Specifically, compared with traditional roll forming, advanced high-strength steel flexible roll forming can significantly improve load capacity of sheet and reduce structural weight, which can consequently further the objective of lightening the weight of vehicles. However, adoption of new techniques and new materials always accompany with new technical challenges. The most important one is the problem of fracture of advanced high-strength steel flexible roll forming. Ideally, it is desired to achieve a smaller bending radius. Unfortunately, at room temperature, advanced high-strength steel is easy to crack at the bending point due to its unsatisfactory toughness, plasticity, and deformability. Therefore, studying the fracture of advanced high-strength steel flexible roll forming is meaningful to enhance technical skill and product quality.This project has been conducted based on a series of researches such as experiment of material property, constitutive model research, ductile fracture mechanism analysis, building fracture criterion, finite element analysis, and then it has established a method to forecast the time and position of advanced high-strength steel ductile fracture in the process of flexible roll forming.According to metal material tensile test method, an experiment has been designed in order to test the performance of DP980. Specifically, based on the range of strain rate determined from roll forming finite element analysis and the analysis of stress state in deformation zone, three tensile experiments under various strain rates of uniaxial tension, plane strain and shear have been conducted. After a further analysis of the experimental data and cracked test specimen, the feasibility and reliability of established finite element model has been proved preliminarily.Via a study of metal elastic-plastic mechanics characterization method, a constitutive equations that is suitable for calculating the plasticity of DP980advanced high-strength steel has been established. Based on the data acquired from testing experiments of material performance, non-linear curve fitting has been conducted through MATLAB simulation, which provides the plastic constitutive model in relation to strain rate. Then, after loading the constitutive model, the feasibility and reliability can be proved by comparing the experimental data. Through the contrastive analysis, the simulation data and the experimental data are in good agreement, which proves that the feasibility and reliability of constitutive model is well established. Besides that, this project further proves the precision of material tensile test finite element model and provides an important experimental platform for the further study.Based on an in-depth research of the principle of metal ductile fracture and the criteria of common fracture criterion, the process of DP980fracture has been analyzed and tested combined with finite element analysis and fracture damage evolution methods. On this basis, a process planning for U channel flexible roll forming has been done in order to build finite element model and conduct simulation experiments. After thoroughly analyzing the stimulation results, the time and position of fracture can be forecasted during the process of U channel flexible roll forming, which consequently creates a theoretical basis for process optimization and engineering practices.