Feasibility of estimation programs for hole expansion test on sheet steel
Shuai, Chufan (2016)
Shuai, Chufan
2016
Master's Degree Programme in Materials Science
Teknisten tieteiden tiedekunta - Faculty of Engineering Sciences
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Hyväksymispäivämäärä
2016-03-09
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201602193544
https://urn.fi/URN:NBN:fi:tty-201602193544
Tiivistelmä
Sheet steels are thin steels with excellent formability and good strength, which have various applications in industrial production. Hole expansion tests, which measure the hole expansion ratio (HER), can represent the formability of sheet steel, especially for highly advanced strength steel. Meanwhile, to increase the accuracy of the test, estimation program is an efficient method which used to predict or examine the test result. However, the feasibility of estimation programs always has fluctuation and due to some inherent defects of programing and training methods, the simulated results from estimation programs might have some extent of differences compared with the test results. Thus, thorough analysis of these differences and accuracy improvement of estimation programs are essential. In this master thesis, five different sheet steels and seven HER estimation programs are selected to analyze the feasibility of the estimation programs.
The thesis includes theoretical, experimental and discussion parts. Theoretical parts will introduce theoretical backgrounds which relate to the thesis topic. Experimental parts comprise tensile tests, hole expansion tests, HER program estimations and microscopy. Except hole expansion tests and part of tensile tests, which were conducted at SSAB Europe (Hämeenlinna), the other experiments were performed at material science department of Tampere University of Technology. The test materials were provided by SSAB.
According to the test results, none of the estimation programs are feasible for all steels. However, some certain programs can predict the HER for certain sheet steel with high accuracy, for example the program 6 for DX56D, which showed almost the same result as the test result. Based on the fracture and microstructure analysis, the ductility of sheet steels seems to be the main factor which affects the feasibility of an estimation program. Furthermore, the input selection of estimation program can also affect the estimation accuracy. According to the analysis, ultimate tensile strength (UTS) is a possible parameter which ensures the accuracy of estimation program.
The thesis includes theoretical, experimental and discussion parts. Theoretical parts will introduce theoretical backgrounds which relate to the thesis topic. Experimental parts comprise tensile tests, hole expansion tests, HER program estimations and microscopy. Except hole expansion tests and part of tensile tests, which were conducted at SSAB Europe (Hämeenlinna), the other experiments were performed at material science department of Tampere University of Technology. The test materials were provided by SSAB.
According to the test results, none of the estimation programs are feasible for all steels. However, some certain programs can predict the HER for certain sheet steel with high accuracy, for example the program 6 for DX56D, which showed almost the same result as the test result. Based on the fracture and microstructure analysis, the ductility of sheet steels seems to be the main factor which affects the feasibility of an estimation program. Furthermore, the input selection of estimation program can also affect the estimation accuracy. According to the analysis, ultimate tensile strength (UTS) is a possible parameter which ensures the accuracy of estimation program.