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Forming limit prediction of AA7075-T6 sheet based on ductile fracture criterion and the error analysis of parameters calibration

Abstract

It is worthy to investigate how it will affect the parameters calibration using an average stress state variable before the practical application of a ductile fracture criterion. In order to study this problem, ten notch specimens of AA7075-T6 sheet were designed to implement the tension tests and a parallel simulation of each test was run to obtain the variation of related variables such as stress triaxiality, Lode parameter and fracture strain. The Lou-Huh criterion was selected to research the prediction error through the difference between the damage value calculated by integral expression and that calculated by analytical expression. Based on the error analysis method, a clear answer was given on how to choose the tension tests of notch specimens in the calibrating process of fracture parameters. The studying results show that the stress state variation of notch specimens has a significant influence on the calibration result. It turns out that how to choose specimens from the ten notch specimens to calibrate the fracture parameters also has big influence on the result. Therefore, it is necessary to conduct an error analysis after the calibration of fracture parameters. Based on the error analysis results, the fracture parameters of AA7075-T6 sheet were optimized and its forming limit diagram (FLD) was deduced based on the optimized parameters. The predictive result of FLD is safe compared with the experimental forming limit results.

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Acknowledgements

The present work is financed by the National Natural Science Foundation of China (contract no. 51775481), the Key Project of Science and Technology Plan of Hebei Higher School of Education Department (grant number ZD2017078) and the Natural Science Foundation of Hebei Province (project number E2019203418). The authors would like express their sincere appreciation to the funds.

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Correspondence to Guojiang Dong.

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Appendix

Appendix

Table 10 The solving results of fracture parameters and the statistics of assessment error

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Yang, Z., Zhao, C., Dong, G. et al. Forming limit prediction of AA7075-T6 sheet based on ductile fracture criterion and the error analysis of parameters calibration. Int J Mater Form (2020). https://doi.org/10.1007/s12289-019-01528-w

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Keywords

  • Ductile fracture criterion
  • Error analysis
  • Forming limit diagram
  • AA7075-T6 sheet