Partner: D. Banabic


Conference papers
1.Lumelskyj D., Lazarescu L., Banabic D., Rojek J., Comparison of two methods for detection of strain localization in sheet forming, ESAFORM 2018, 21ST INTERNATIONAL ESAFORM CONFERENCE ON MATERIAL FORMING , 2018-04-23/04-25, Palermo (IT), DOI: 10.1063/1.5035067, No.1960, pp.170010-1-6, 2018
Abstract:

This paper presents a comparison of two criteria of strain localization in experimental research and numerical simulation of sheet metal forming. The first criterion is based on the analysis of the through-thickness thinning (through thickness strain) and its first time derivative in the most strained zone. The limit strain in the second method is determined by the maximum of the strain acceleration. Experimental and numerical investigation have been carried out for the Nakajima test performed for different specimens of the DC04 grade steel sheet. The strain localization has been identified by analysis of experimental and numerical curves showing the evolution of strains and their derivatives in failure zones. The numerical and experimental limit strains calculated from both criteria have been compared with the experimental FLC evaluated according to the ISO 12004-2 norm. It has been shown that the first method predicts formability limits closer to the experimental FLC. The second criterion predicts values of strains higher than FLC determined according to ISO norm. These values are closer to the strains corresponding to the fracture limit. The results show that analysis of strain evolution allows us to determine strain localization in numerical simulation and experimental studies.

Keywords:

Sheet forming; Formability; Forming limit diagram; Strain localization; Numerical simulation

Affiliations:
Lumelskyj D.-IPPT PAN
Lazarescu L.-other affiliation
Banabic D.-other affiliation
Rojek J.-IPPT PAN
2.Lumelskyj D., Rojek J., Banabic D., Lazarescu L., Detection of Strain Localization in Nakazima Formability Test - Experimental Research and Numerical Simulation, SHEMET17, 17th International Conference on Sheet Metal, 2017-04-10/04-12, Palermo (IT), DOI: 10.1016/j.proeng.2017.04.016, No.183, pp.89-94, 2017
Abstract:

This paper presents the investigation on detection of strain localization in experimental research and numerical simulation of sheet metal forming. Experimental tests and numerical simulations of the Nakazima test have been performed for the DC04 grade steel sheet. The onset of localized necking has been determined using the criterion based on analysis of the major principal strain and its first and second time derivatives in the most strained zone. The strain localization has been evaluated by the maximum of strain acceleration which corresponds to the inflection point of the strain velocity vs. time. The limit strains have been calculated numerically and experimentally for specimens undergoing deformation at different strain paths. It has been shown that the numerical model predicts formability limits close to the experimental results. Analyzed criterion can be used as a potential alternative tool to determine formability in standard finite element simulations of sheet forming processes.

Keywords:

sheet forming, formability, forming limit curve, numerical simulation

Affiliations:
Lumelskyj D.-IPPT PAN
Rojek J.-IPPT PAN
Banabic D.-other affiliation
Lazarescu L.-other affiliation